Next Article in Journal
Heterogeneity and Actin Cytoskeleton in Osteoclast and Macrophage Multinucleation
Next Article in Special Issue
Polyamines Influence Mouse Sperm Channels Activity
Previous Article in Journal
Chitin Biosynthesis Inhibition of Meloidogyne incognita by RNAi-Mediated Gene Silencing Increases Resistance to Transgenic Tobacco Plants
Previous Article in Special Issue
HVCN1 Channels Are Relevant for the Maintenance of Sperm Motility During In Vitro Capacitation of Pig Spermatozoa
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
IJMS
Volume 21
Issue 18
10.3390/ijms21186628
ijms-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis

by
Hiroshi Yoshitake
1 and
Yoshihiko Araki
1,2,3,*
1
Institute for Environmental & Gender-specific Medicine, Juntendo University Graduate School of Medicine, Urayasu, Chiba 279-0021, Japan
2
Department of Obstetrics & Gynecology, Juntendo University Graduate School of Medicine, Bunkyo, Tokyo 113-8421, Japan
3
Division of Microbiology, Department of Pathology and Microbiology, Nihon University School of Medicine, Itabashi, Tokyo 173-8610, Japan
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2020, 21(18), 6628; https://doi.org/10.3390/ijms21186628
Submission received: 27 July 2020 / Revised: 6 September 2020 / Accepted: 8 September 2020 / Published: 10 September 2020
(This article belongs to the Special Issue Ion Channels of Spermatozoa: Structure, Function and Regulation Mechanisms)
Browse Figures
Review Reports Versions Notes

Abstract

:
Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) on the plasma membrane are involved in several cellular processes, including sperm functions. Thus far, several GPI-APs have been identified in the testicular germ cells, and there is increasing evidence of their biological significance during fertilization. Among GPI-APs identified in the testis, this review focuses on TEX101, a germ cell-specific GPI-AP that belongs to the lymphocyte antigen 6/urokinase-type plasminogen activator receptor superfamily. This molecule was originally identified as a glycoprotein that contained the antigen epitope for a specific monoclonal antibody; it was produced by immunizing female mice with an allogenic testicular homogenate. This review mainly describes the current understanding of the biochemical, morphological, and physiological characteristics of TEX101. Furthermore, future avenues for the investigation of testicular GPI-Aps, including their potential role as regulators of ion channels, are discussed.

1. Introduction

Mammalian spermatozoa acquire fertilizing capacity as they cross the epididymis in vivo [1,2,3]. However, spermatogenesis itself takes place in the testicular seminiferous tubules [4]. Spermatogenesis, i.e., testicular mitotic proliferation, meiosis, sperm cell division, and morphological changes from haploid sperm to mature spermatozoa, results in the generation of cells that are highly specialized in structure and function [4]. No other cell has undergone such extreme morphological changes while undergoing both genetic modification and reduced chromosomal pluripotency. It is generally believed that the testes have a unique mechanism to control spermatogenesis, where certain molecules are activated during germ cell production and others are repressed.
There is increasing evidence that glycosylphosphatidylinositol (GPI)-anchored proteins (APs) on the plasma membrane are involved in the function of a range of cell types [5], including gametes. For example, male infertility is caused by disruption of the testicular angiotensin-converting enzyme, which releases GPI-APs [6]. Thus, GPI-APs in the testis are quite important for proper sperm–plasma membrane structure formation, which influences normal fertilizing ability.
In the past two decades, we have studied the structure and function of testicular factors, especially the mechanism of germ cell production, starting with the discovery of a protein (TEX101). This protein is the core of our research, and we have accumulated a wealth of knowledge based on the functional relationship between TEX101, a GPI-AP, and other molecules.
In this review, we focus on TEX101, which belongs to the lymphocyte antigen 6 (Ly6)/urokinase-type plasminogen activator receptor (uPAR)-(LU) protein superfamily [7,8]; specifically, we discuss this as an important biomolecule for the production of normally functioning gametes. TEX101 was originally identified as a glycoprotein that contained the antigen epitope for a specific monoclonal antibody (mAb); it was produced by immunizing female mice with an allogenic testicular homogenate [9,10]. Using immunoprecipitation (IP)–liquid chromatography (LC)–tandem mass spectrometry (MS/MS) and immunofluorescence studies, we confirmed the association of TEX101 with at least two proteins in the plasma membranes of adult testicular seminiferous tubules: cellubrevin (a member of soluble N-ethylmaleimide-sensitive factor attachment protein receptor family) and Ly6k (a GPI-AP that was recently recognized as an LU protein) [11,12]. TEX101 is a unique germ cell marker that is expressed only during gametogenesis; its exhibits sexually dimorphic expression in developing gonadal tissues [13]. Before focusing on TEX101, we provide a brief explanation concerning the molecular nature of GPI-AP for understanding the scientific status of a class in membrane proteins.

2. GPI-APs

2.1. History of the Discovery

In 1960, Slein and Logan reported that the intravenous injection of purified components of Bacillus anthracis toxin into rabbits increased levels of alkaline phosphatase in their serum [14]. Moreover, phospholipase C (PLC) from Bacillus cereus culture medium induced the phosphatemia in those rabbits [15]. In 1976, Ikezawa and his colleagues purified phosphatidylinositol (PI)-specific PLC from B. cereus culture supernatant and found that the enzyme released alkaline phosphatase from plasma membranes of rat kidney cells [16]. Their research group also showed elevated alkaline phosphatase levels in rat serum following the intravenous injection of PI-PLC [17]. These results suggested that PI-PLC treatment removes alkaline phosphatase from cell plasma membranes. Subsequently, PI-PLC was found to induce the release of acetylcholinesterase, 5′-nucleotidase, and alkaline phosphodiesterase I from mammalian cell plasma membranes [18,19,20], indicating that these proteins are bound to the plasma membrane with phosphatidylinositol. Ferguson et al. discovered that variant surface glycoproteins of Trypanosoma brucei are anchored to the plasma membrane through C-terminus linkage with glycosyl-1,2-dimyristyl PI, which contains mannose, glucosamine, ethanolamine, and PI [21]. Several subsequent studies provided evidence that GPI-APs form a class of similar membrane proteins.

2.2. Basic Structure of GPI-APs

The plasma membrane contains many types of proteins, which are involved in cell functions and interactions with the cell environment. Membrane proteins are associated with the cell membrane lipid bilayer in various ways [22]. Many proteins on the cell surface exist as transmembrane proteins, which contain both intracellular and extracellular domains. However, some membrane proteins lack intracellular domains; they may be tethered to the outer leaflet of the plasma membrane by GPI, and these are called GPI-APs. The core structure of the GPI anchor consists of PI, glycans (glucosamine and three mannose residues), and phosphoethanolamine (Figure 1). Proteins bind to GPIs through an amino bond between the peptide C-terminus and the ethanolamine amino group (Figure 1).

2.3. General Characteristics and Potential Biological Significances of GPI-APs

GPI-APs are broadly conserved among eukariotes [23], comprising approximately 170 types of human and mouse proteins (UniProt, http://www.uniprot.org). GPI-APs are presumed to play pivotal roles in fertilization [6,24,25,26], the immune system [27,28,29], nerve formation [30,31,32], and embryonic development [33,34,35], where they function as enzymes (e.g., alkaline phosphatase, 5′-nucleotidase (CD73), and dipeptidase (DPEP)) [36], cell adhesion molecules (e.g., lymphocyte function-associated antigen 3 (CD58) and neural cell adhesion molecules) [37,38], component regulatory proteins (e.g., CD55 and CD59) [39,40], receptors (e.g., CD14, CD16b, and folate receptor) [41,42,43], mammalian antigens (e.g., Thy-1 (CD90), carcinoembryonic antigen (CD66e) [23,44], and ion channel or its modulator (e.g., α2δ subunit of voltage-gated calcium channel, prion protein, and Lynx1) [45,46,47].
Although GPI-APs lack an intracellular domain, a few hypotheses have been proposed to explain the mechanism by which they transduce extracellular signals into the cytoplasm. One tentative theory is that outside-in signaling mediated by GPI-APs passes through the plasma membrane by means of an associated transmembrane molecule. For example, uPAR (CD87), lipopolysaccharide (LPS)/LPS binding protein (LBP) receptor (CD14), Fcγ receptor IIIB (CD16b), and GPI-80 are associated with β2 integrin (CD11b/CD18) on the surfaces of polymorphonuclear leukocytes; these interactions regulate integrin-mediated cell adhesion [48].
A more likely theory is that lipid rafts are involved in signal transduction regulated by GPI-APs. Lipid rafts are membrane domains that contain many GPI-APs, Src family kinases, transmembrane proteins, cholesterol, and sphingolipids [49]; lipid rafts are presumed to play roles in signal transduction, cell adhesion, migration, and protein trafficking [50,51,52]. GPI-APs frequently cluster in lipid rafts and transiently recruit Lyn (a Src family member associated with lipid rafts) by means of both protein–protein and lipid–lipid (raft) interactions [53]. Indeed, GPI-AP clustering is known to induce cell activation via tyrosine phosphorylation [54,55,56,57]. Most GPI-APs are post-translationally modified by the addition of oligosaccharide (OS) chain(s) (UniProt, http://www.uniprot.org). Recently, Miyagawa-Yamaguchi et al. reported that GPI-APs with high-mannose or complex-type N-linked OS chains cluster on distinct lipid rafts under different physiological conditions [58]. This finding suggests that different GPI-AP types may form individual lipid rafts depending on the N-glycosylation pattern.
Many GPI-APs (e.g., CD14, CD16b, CD55, uPAR, and GPI-80) have been reported to exist on cell surfaces as membrane proteins and in extracellular fluid in soluble form [59,60,61,62,63]. Although some soluble GPI-APs are useful as biomarkers of cancers or inflammation diseases [64,65,66,67,68,69,70,71], the precise functions of soluble GPI-APs remain unclear. Further investigations are needed to understand the biological functions of these molecules.

2.4. GPI-APs in the Testis

Thus far, the UniProt database (http://www.uniprot.org) lists 29 GPI-APs that are expressed in the human and mouse testes (Table 1). Among these molecules, DPEP3, a glioma pathogenesis-related protein 1 (GLIPR1)-like protein 1, hyaluronidase PH-20, hyaluronidase-5, Ly6k, prion-like protein doppel, serine protease 41, sperm acrosome membrane-associated protein 4 (SPACA4), TEX101, and testisin are strongly expressed in the male gonad (i.e., testis, epididymis, or mature spermatozoa), but they are exhibited weakly or negligible in other tissues (e.g., female gonads and somatic organs) [9,25,72,73,74,75,76,77,78,79]. Among these, GLIPR1-like protein 1, PH-20, and SPACA4 are presumed to participate in the interaction between sperm and oocyte [73,79,80]. Although the other GPI-APs listed may be involved in male germ cell development and differentiation, the precise functions of most of these molecules remain unclear. As a hypothesis, the LU protein superfamily such as Ly6k and TEX101, which possesses three-fingered protein domain (TFPD) [81], may have a function as a regulator of ion channels. Indeed, Lynx1, a GPI-AP co-localized with α7 and α4β2-nicotinic acetylcholine receptors (nAChRs), is the first identified prototoxin having TFPD in the brain, which modulates the function of nAChRs [47]. In the testes, it has been well documented that ion channels, such as CatSpers, play an important role in sperm functions [82,83,84]. In fact, various ions are mediated with important functions of sperm, such as the acrosomal reaction and hyperactivation of the motility, so that ion channels are deeply involved in control. With respect to TEX101, recent crystal structure analysis provides direct evidence that this molecule actually has two LU domains, both of which have a TFPD [85]. It is striking that such structural analysis holds great promise for elucidating the actual interactions between this molecule and a group of molecules associated with the ion channels. However, the main points remain unclear, and the physiological functions of these molecules are far from completely understood. Accordingly, GPI-APs in the testis as these modulators could be a focus for further research, including studies of ion channels.

3. Significance of TEX101 in the Fertilization Process

3.1. Strategies for Identifying Testis-Specific Molecule(s)

Generally, researchers consider tissue-specific factors to be localized in tissues related to their specialized functions. Since the gonad is the sole organ of germ cell production, important factors for spermatogenesis are expected to be located in testicular germ cells (TGCs). In a previous study of the molecular mechanisms concerning gametogenesis and the fertilization process, we used mouse testes as an experimental material to identify such factors, because adult seminiferous tubules contain germ cells at all stages. To find out specific factor(s), we did not choose a genetic approach, because we know from our professional experience that the establishment of a specific molecular probe (such as Abs) is a key step for the further characterization of novel molecules. As producing mAbs with satisfactory performance for further molecular characterization was not always easy, we did not dare use a strategy that used a genetic approach. Using splenocytes from female mice immunized with syngenic male germ cells, we established several mAbs and first performed immunohistochemical staining (IHS) of the testis. Against the mAbs established, we did further Western blot (WB) and IP analyses, which was followed by micro-amino acid analysis (this process has now been effectively replaced by MS analysis) to find out unique factor(s). This procedure can be expected to find “novel” molecule(s) or molecular complexes, and the mAbs established can be expected to have almost perfect performances (compatible for IHS, WB, and IP) for further biochemical as well as morphological analyses.
We detected several hybrydoma clones that corresponded to an interesting IHS pattern within the testis. Among the hybridoma clones established, a protein detected by an mAb (IgG1, termed TES101) was produced from a hybridoma; this protein was tentatively named as TES101-reactive protein (RP); later, the nomenclature was changed to TEX101 [9,13].

3.2. Molecular Characteristics of TEX101, a Unique Glycoprotein Germ Cell Marker

TEX101 is composed of a signal peptide region of 25 amino acids and a mature protein region of 225 amino acids, thus forming a protein with a molecular weight of 24,093 in mice. TEX101 contains four potential N-glycosylation sites (Asn-Xaa-Ser/Thr) as well as many (>40) Ser/Thr residues, which could be possible O-glycosylation sites [9]. When we first described this molecule in 2001, the cDNA sequence revealed no homologous molecules in the DNA database; the molecule has since been classified as a member of the LU protein superfamily [7,8], based on the conserved position of cysteine residues within the molecule. The position of cysteine residues is highly conserved among major mammalian species including human, indicating similarity in the steric structure of these orthologues due to disulfide bonds (Table 2).
TEX101 contains strong hydrophobic portions [104] at both the N- and C-terminal ends of the molecule, which is typical of GPI-APs [105]. Morphological analysis of testicular tissues and molecular biological analysis of TEX101-expressing transfectants revealed that the enzyme PI-PLC, which removes surface GPI-APs, exhibited TEX101-releasing activity on the cell surface [10]. Although TEX101 is primarily detected on the TGC cell membrane [9,13], TEX101 appears to have at least two different forms in nature: GPI-AP and non-membrane-bound soluble forms—subcellular TEX101 was found in the Triton X-100-soluble fraction from the testicular membrane, as well as in water-soluble and extracellular fractions [9].
TEX101 has been known to be a glycoprotein since its identification [9,10] as described above. Various glycoproteins are generally presumed to be involved in mammalian physiological processes, from fertilization to implantation [106,107,108,109]. Glycosylation is among the most pivotal post-translational modifications; it is involved in biological processes including cell–cell interactions, as well as cell differentiation and proliferation [110].
During antigen-epitope analyses of an anti-sperm auto-Ab using spleen cells of aged mice (over one year) maintained under conventional conditions, we unexpectedly established a mAb, termed Ts4, which reacts with the OS moiety of TEX101 [111]. The Ts4 mAb serves as an auto-Ab against acrosomal regions of cauda epididymal spermatozoa [111]. At that time (two decades ago), quantitative molecular identification was quite poor; therefore, we attempted the molecular identification of a Ts4 target in testicular extract, rather than extracts of cauda epidydimal spermatozoa. In the male mouse gonad, Ts4 exhibits immunoreactivity against several types of glycoproteins in the acrosomal region of epididymal spermatozoa as well as against germ cells within seminiferous tubules by interacting with a common OS chain on the molecules [112,113]. The antigenic determinant for Ts4 was located on the fucosylated agalacto-biantennary complex-type N-glycan with bisecting N-acetylglucosamine (GlcNAc) of TEX101 [113]. Although TEX101 does not appear in mature epididymal spermatozoa [9,112,114] (Figure 2), we analyzed a Ts4-reactive glycoprotein in mouse cauda epididymal sperm. IP and LC-MS/MS analyses showed that alpha-N-acetylglucosaminidase (Naglu; a degradation enzyme of heparan sulfate) was among the glycoproteins recognized by Ts4 in epididymal spermatozoa. Using a similar strategy, we recently identified the direct target protein of Ts4 as NUP62; we also characterized GPI-AP molecular formation, including TEX101 and its related molecules, during testicular development [115].
Direct evidence of the biological significance of OS chain detected by Ts4 has not been reported. However, experimental observations increasingly suggest the potential importance of Ts4 target in the fertilization process; (1) this mAb affects fertilization in vitro [116]; (2) the molecular epitope for Ts4 showed unique structure [113]; and (3) its occurrence is limited to reproductive-related organs [112,113,115,116]. Indeed, the bisecting GlcNAc structures have been already reported to possess biological functions, such as cell growth and adhesion by modulating membrane glycoproteins [117,118,119]. Together, these findings suggest that TEX101, as the major testicular molecule possessing Ts4-reactive OS, is essential for elucidating its molecular function and mechanism.

3.3. Subcelllar Localization of TEX101 within Gonadal Organs

TEX101 was initially identified in the TGCs [9]; however, it is also expressed in other cells. During embryonic development, TEX101 appears in germ cells of both male and female gonads after the pregonadal period [13] (Figure 2). In the testis, TEX101 is constitutively expressed on surviving prospermatogonia during prespermatogenesis. Following the initiation of spermatogenesis, prospermatogonia differentiate into spermatogonia; TEX101 expression diminishes in spermatogonia, but it is enhanced in spermatocytes and spermatids. TEX101 is also expressed in female germ cells until the start of folliculogenesis (before birth), but it is not detected in oocytes surrounded by follicular cells within the ovary [13]. These findings imply that TEX101 exhibits sexually dimorphic expression in male and female germ cells during gonadal development. The gene name is currently registered as “Testis Expressed 101” in the Mouse Genome Informatics (MGI) database (The Jackson Laboratory, Bar Harbor, ME, USA), despite its expression in premature female germ cells. Thus, TEX101 should not be regarded as a specific marker for male germ cells. TEX101 (TES101RP) is a marker specific for both male and female germ cells during gonad development; however, in adult animals, it is found only in the testes [9,13].
In the testis, TEX101 has been detected in cells from seminiferous tubules, but not from interstitial tissues, including the Leydig cells [9,13]. The intensity of TEX101 immunofluorescence observed in seminiferous epithelium was nearly identical among various stages, but it is varied among cell types in seminiferous tubules. Spermatogonia attached to the basal lamina of the seminiferous tubules showed negative staining compared with more advanced cells (Stage V). However, TEX101-positive cells attached to the basal lamina were identified as leptotene or zygotene spermatocytes (Stage X). Sertoli cells were TEX101-negative at all stages [9,114].
When spermatogenesis in the testis is complete, the TEX101 protein remains on the cell surfaces of step 10–16 spermatids and testicular sperm, including the tail portion. However, TEX101 is shed from epididymal sperm in the caput epididymis [114]. In the cauda epididymis, TEX101 is no longer detectable on the male germ cells (Figure 2).

3.4. Molecules Associate with TEX101 in Male Germ Organ

In general, protein molecules perform their physiological actions via interactions with other proteins [120,121]. The elucidation of the functional and physical networks among proteins has fundamental importance for understanding their functions and their regulatory mechanisms [122]. Using IP followed by LC-MS/MS analyses, we identified several molecules associated directly or indirectly with TEX101 within testicular seminiferous tubules (Table 3).
Annexin A2 is a member of the annexin superfamily with Ca2+-dependent phospholipid-binding ability [123]. This molecule is widely expressed in many types of cells (e.g., epithelial, endothelial, trophoblast, immune, and tumor cells), and it is involved in a variety of biological functions, including membrane organization, membrane trafficking, and Ca2+ ion channels [123]. In the testis, Annexin A2 is found on Sertoli cells and elongated spermatids, and it is essential for the maintenance of the blood–testis barrier and the suitable release of spermatids [124].
Ly6k is a member of the LU protein superfamily, similar to TEX101. The relationship between TEX101 and Ly6k is described below.
Cellubrevin is a member of the soluble N-ethylmaleimide-sensitive factor attachment protein receptors family, which regulates membrane trafficking and fusion [125]. Our previous study using ultrahigh-resolution immunofluorescence microscopy revealed that cellubrevin plays a role in membrane trafficking of de novo TEX101 to the cell surface [11].
DPEP3 belongs to the membrane-bound DPEP family [92], which is a group of enzymes that converts leukotriene D4 to leukotriene E4 and dissolves cystinyl-bis-glycine [126]. This molecule is present only in the testis as a GPI-labeled protein [92]. Although its biological function in vivo remains to be clarified, Dpep3-deficient mice are fertile [127].
CD73 (the so-called ecto-5′-nucleotidase) is a GPI-anchored protein that has the enzymatic activity of the dephosphorylation of extracellular adenosine 5′-monophosphate to adenosine via the purinergic signaling pathway [128]. The expression of CD73 is broadly observed in various tissues (e.g., brain, heart, lung, liver, kidney, colon, and placenta) and some types of immune cells, such as T cells, neutrophils, monocytes, and dendritic cells [129,130]. Although CD73 and adenosine are believed to suppress the immune response in the tumor microenvironment [131], their precise function within the testis remains unclear.

3.5. TEX101 Function during Fertilization

Male and female mice with TEX101 gene disruption produce spermatozoa and oocytes with normal morphology, respectively [26], suggesting that TEX101 is not essential for the morphological formation of both male and female gametes. However, the TEX101-deficient male mice were infertile [26]. Although the in vitro fertilization ability of sperm from TEX101-null mouse seems normal, sterility is mainly caused by a defect in the migrating ability of sperm into the oviduct [26], as observed in ADAM3-null mice [132]. In the testis, TEX101 expression is restricted during prespermatogenesis and spermatocyte to testicular spermatozoa [9,13,96]; therefore, TEX101 may function as a molecular chaperone in the essential fertilization process. Thus far, TEX101 has been presumed to serve as a molecular chaperone solely for ADAM3, making it similar to CALMEGIN, CALRS, PDILT, or ADAM1a [26,133,134,135,136]. However, it should be noted that a defect in TEX101 expression also reduces the expression of Ly6k (a TEX101-associated GPI-AP) in TGCs [137] (Figure 3). The experimental evidence implies that TEX101 and Ly6k both contribute to the expression of post-translational counterpart proteins on the cell membrane.
To date, although several GPI-APs have been reported in TGCs as described above, TEX101 and Ly6k are known to be essential for the production of functionally intact sperm [26,138] among these proteins. These results are based on data in which both TEX101- and Ly6k-null mice showed phenotypes nearly identical to those of gene-disrupted mouse lines, such as Adam3−/− [132,139]. However, the precise molecular mechanisms that cause infertility among these spermatozoa remain unknown. Indeed, our polysome analysis results suggested that Adam3 signaling occurs in adult testes; however, translation activity was not detected [137]. In fact, almost no appropriate molecular probe for ADAM3 detection at the protein level exists, particularly with respect to morphological analyses; this limits our understanding of the molecular relationship between ADAM3 and its related molecules. In addition, the physiological role of TEX101 in female gametogenesis remains unclear. Therefore, we argue that researchers should be more cautious in asserting scientific conclusions regarding the molecular significance of ADAM3-related molecules at the protein level.

4. Conclusions and Future Aspects

In this review, we represented current knowledge of GPI-APs in the testis, mainly with respect to TEX101. Since GPI-APs do not possess an intracellular domain, the mechanism of GPI-AP cell–cell signal transduction, including its relation to ion channels, remains controversial. The specific roles of membrane-bound GPI-APs and their soluble form also remain unknown.
The functions of various biomolecules including GPI-APs have been elucidated since the development of gene-deficient model mice in the late 20th century. It is generally believed that biomolecule function can be fully explored only through gene-disruption model analysis; however, these techniques also have many limitations.
Biomolecules have existed “in vivo” for an extremely long time before scientists discovered them. Biomolecules also evolved “in vivo” for an extremely long time before scientists discovered them; therefore, their synthesis would be expected to be meaningful. However, “Does the existence of a molecule in an organism mean that it (its existence) is functional?”. Efforts to unravel this philosophical question continue for scientists, and it is easy to imagine that scientists will spend a large amount of time in this area, even in GPI-AP studies of testes.

Author Contributions

H.Y. and Y.A. conceived, designed, and directed the study, provided financial support, and wrote the article. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported in part by Grants-in Aid for Scientific Research Nos. 16591635/18591813/21592111/21592206/24592609/25462575/16K11111, for Challenging Research No. 17K19734, and for Fostering Joint International Research No. 18KK0256 from the Japan Society for the Promotion of Science (JSPS), grants Nos. 17gk0110024h0001/17cm0106XXXh0001 from the Japan Agency for Medical Research and Development (AMED), and “High-Tech Research Center” Project for Private Universities: matching fund subsidy from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Acknowledgments

We are indebted to all collaborators worked with us concerning TEX101 and related studies.

Conflicts of Interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References

  1. Orgebin-Crist, M.C.; Olson, G.E.; Danzo, B.J. Factor influencing maturation of spermatozoa in the epididymis. In Intragonadal Regulation of Reproduction; Franchimont, P., Channing, C.P., Eds.; Academic Press: London, UK, 1981; pp. 393–417. [Google Scholar]
  2. Orgebin-Crist, M.C. Androgens and epididymal function. In Pharmacology, Biology, and Clinical Application of Androgens; Bhasin, S., Gabeluick, H.L., Spieler, J.M., Swerdlott, R.S., Wang, C., Eds.; Wiley-Liss: New York, NY, USA, 1996; pp. 27–38. [Google Scholar]
  3. Orgebin-Crist, M.C. The epididymis across 24 centuries. J. Reprod. Fertil. Suppl. 1998, 53, 285–292. [Google Scholar]
  4. Russell, L.D.; Ettlin, R.A.; Shnha Hikim, A.P.; Clegg, E.D. Mammalian spermatogenesis. In Histological and Histopathological Evaluation of the Testis; Russell, L.D., Ed.; Cache River Press: Clearwater, FL, USA, 1990; pp. 1–40. [Google Scholar]
  5. Ferguson, M.A.J.; Hart, G.W.; Kinoshita, T. Glycosylphosphatidylinositol Anchors. In Essentials of Glycobiology, 3rd ed.; Varki, A., Cummings, R.D., Esko, J.D., Stanley, P., Hart, G.W., Aebi, M., Darvill, A.G., Kinoshita, T., Packer, N.H., Prestegard, J.H., et al., Eds.; Cold Spring Harbor Laboratory Press: Cold Spring Harbor, NY, USA, 2017; pp. 2015–2017. [Google Scholar]
  6. Kondoh, G.; Tojo, H.; Nakatani, Y.; Komazawa, N.; Murata, C.; Yamagata, K.; Maeda, Y.; Kinoshita, T.; Okabe, M.; Taguchi, R.; et al. Angiotensin-converting enzyme is a GPI-anchored protein releasing factor crucial for fertilization. Nat. Med. 2005, 11, 160–166. [Google Scholar] [CrossRef] [PubMed]
  7. Loughner, C.L.; Bruford, E.A.; McAndrews, M.S.; Delp, E.E.; Swamynathan, S.; Swamynathan, S.K. Organization, evolution and functions of the human and mouse Ly6/uPAR family genes. Hum. Genom. 2016, 10, 10. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  8. Vasilyeva, N.A.; Loktyushov, E.V.; Bychkov, M.L.; Shenkarev, Z.O.; Lyukmanova, E.N. Three-Finger Proteins from the Ly6/uPAR Family: Functional Diversity within One Structural Motif. Biochemistry 2017, 82, 1702–1715. [Google Scholar] [CrossRef] [PubMed]
  9. Kurita, A.; Takizawa, T.; Takayama, T.; Totsukawa, K.; Matsubara, S.; Shibahara, H.; Orgebin-Crist, M.C.; Sendo, F.; Shinkai, Y.; Araki, Y. Identification, cloning, and initial characterization of a novel mouse testicular germ cell-specific antigen. Biol. Reprod. 2001, 64, 935–945. [Google Scholar] [CrossRef] [Green Version]
  10. Jin, H.; Yoshitake, H.; Tsukamoto, H.; Takahashi, M.; Mori, M.; Takizawa, T.; Takamori, K.; Ogawa, H.; Kinoshita, K.; Araki, Y. Molecular characterization of a germ-cell-specific antigen, TEX101, from mouse testis. Zygote 2006, 14, 201–208. [Google Scholar] [CrossRef]
  11. Tsukamoto, H.; Yoshitake, H.; Mori, M.; Yanagida, M.; Takamori, K.; Ogawa, H.; Takizawa, T.; Araki, Y. Testicular proteins associated with the germ cell-marker, TEX101: Involvement of cellubrevin in TEX101-trafficking to the cell surface during spermatogenesis. Biochem. Biophys. Res. Commun. 2006, 345, 229–238. [Google Scholar] [CrossRef]
  12. Yoshitake, H.; Tsukamoto, H.; Maruyama-Fukushima, M.; Takamori, K.; Ogawa, H.; Araki, Y. TEX101, a germ cell-marker glycoprotein, is associated with lymphocyte antigen 6 complex locus k within the mouse testis. Biochem. Biophys. Res. Commun. 2008, 372, 277–282. [Google Scholar] [CrossRef]
  13. Takayama, T.; Mishima, T.; Mori, M.; Jin, H.; Tsukamoto, H.; Takahashi, K.; Takizawa, T.; Kinoshita, K.; Suzuki, M.; Sato, I.; et al. Sexually dimorphic expression of the novel germ cell antigen TEX101 during mouse gonad development. Biol. Reprod. 2005, 72, 1315–1323. [Google Scholar] [CrossRef] [Green Version]
  14. Slein, M.W.; Logan, G.F., Jr. Mechanism of action of the toxin of Bacillus anthracis. I. Effect in vivo on some blood serum components. J. Bacteriol. 1960, 80, 77–85. [Google Scholar] [CrossRef] [Green Version]
  15. Slein, M.W.; Logan, G.F., Jr. Partial purification and properties of two phospholipases of Bacillus cereus. J. Bacteriol. 1963, 85, 369–381. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  16. Ikezawa, H.; Yamanegi, M.; Taguchi, R.; Miyashita, T.; Ohyabu, T. Studies on phosphatidylinositol phosphodiesterase (phospholipase C type) of Bacillus cereus. I. purification, properties and phosphatase-releasing activity. Biochim. Biophys. Acta 1976, 450, 154–164. [Google Scholar] [PubMed]
  17. Ohyabu, T.; Taguchi, R.; Ikezawa, H. Studies on phosphatidylinositol phosphodiesterase (phospholipase C type) of Bacillus cereus. II. In vivo and immunochemical studies of phosphatase-releasing activity. Arch. Biochem. Biophys. 1978, 190, 1–7. [Google Scholar] [CrossRef]
  18. Low, M.G.; Finean, J.B. Non-lytic release of acetylcholinesterase from erythrocytes by a phosphatidylinositol-specific phospholipase C. FEBS Lett. 1977, 82, 143–146. [Google Scholar] [CrossRef] [Green Version]
  19. Low, M.G.; Finean, J.B. Specific release of plasma membrane enzymes by a phosphatidylinositol-specific phospholipase C. Biochim. Biophys. Acta 1978, 508, 565–570. [Google Scholar] [CrossRef]
  20. Nakabayashi, T.; Ikezawa, H. Release of alkaline phosphodiesterase I from rat kidney plasma membrane produced by the phosphatidylinositol-specific phospholipase C of Bacillus thuringiensis. Cell Struct. Funct. 1984, 9, 247–263. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  21. Ferguson, M.A.; Low, M.G.; Cross, G.A. Glycosyl-sn-1,2-dimyristylphosphatidylinositol is covalently linked to Trypanosoma brucei variant surface glycoprotein. J. Biol. Chem. 1985, 260, 14547–14555. [Google Scholar]
  22. Helenis, A.; Kuhlbrandt, W.; Lill, H.; Simons, K.; von Heijne, G.; Walther, T. Membrane structure. In Molecular Biology of the Cell, 6th ed.; Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., Walter, P., Eds.; Garland Science: New York, NY, USA, 2015; pp. 565–596. [Google Scholar]
  23. Kinoshita, T.; Fujita, M. Biosynthesis of GPI-anchored proteins: Special emphasis on GPI lipid remodeling. J. Lipid Res. 2016, 57, 6–24. [Google Scholar] [CrossRef] [Green Version]
  24. Baba, D.; Kashiwabara, S.; Honda, A.; Yamagata, K.; Wu, Q.; Ikawa, M.; Okabe, M.; Baba, T. Mouse sperm lacking cell surface hyaluronidase PH-20 can pass through the layer of cumulus cells and fertilize the egg. J. Biol. Chem. 2002, 277, 30310–30314. [Google Scholar] [CrossRef] [Green Version]
  25. Netzel-Arnett, S.; Bugge, T.H.; Hess, R.A.; Carnes, K.; Stringer, B.W.; Scarman, A.L.; Hooper, J.D.; Tonks, I.D.; Kay, G.F.; Antalis, T.M. The glycosylphosphatidylinositol-anchored serine protease PRSS21 (testisin) imparts murine epididymal sperm cell maturation and fertilizing ability. Biol. Reprod. 2009, 81, 921–932. [Google Scholar] [CrossRef] [Green Version]
  26. Fujihara, Y.; Tokuhiro, K.; Muro, Y.; Kondoh, G.; Araki, Y.; Ikawa, M.; Okabe, M. Expression of TEX101, regulated by ACE, is essential for the production of fertile mouse spermatozoa. Proc. Natl. Acad. Sci. USA 2013, 110, 8111–8116. [Google Scholar] [CrossRef] [Green Version]
  27. Gyetko, M.R.; Todd, R.F., 3rd; Wilkinson, C.C.; Sitrin, R.G. The urokinase receptor is required for human monocyte chemotaxis in vitro. J. Clin. Investig. 1994, 93, 1380–1387. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  28. Suzuki, K.; Watanabe, T.; Sakurai, S.; Ohtake, K.; Kinoshita, T.; Araki, A.; Fujita, T.; Takei, H.; Takeda, Y.; Sato, Y.; et al. A novel glycosylphosphatidyl inositol-anchored protein on human leukocytes: A possible role for regulation of neutrophil adherence and migration. J. Immunol. 1999, 162, 4277–4284. [Google Scholar]
  29. Lo Buono, N.; Parrotta, R.; Morone, S.; Bovino, P.; Nacci, G.; Ortolan, E.; Horenstein, A.L.; Inzhutova, A.; Ferrero, E.; Funaro, A. The CD157-integrin partnership controls transendothelial migration and adhesion of human monocytes. J. Biol. Chem. 2011, 286, 18681–18691. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  30. Paratcha, G.; Ledda, F.; Ibanez, C.F. The neural cell adhesion molecule NCAM is an alternative signaling receptor for GDNF family ligands. Cell 2003, 113, 867–879. [Google Scholar] [CrossRef] [Green Version]
  31. Jeong, S.Y.; David, S. Glycosylphosphatidylinositol-anchored ceruloplasmin is required for iron efflux from cells in the central nervous system. J. Biol. Chem. 2003, 278, 27144–27148. [Google Scholar] [CrossRef] [Green Version]
  32. Chen, C.H.; Wang, S.M.; Yang, S.H.; Jeng, C.J. Role of Thy-1 in in vivo and in vitro neural development and regeneration of dorsal root ganglionic neurons. J. Cell. Biochem. 2005, 94, 684–694. [Google Scholar] [CrossRef]
  33. Piedrahita, J.A.; Oetama, B.; Bennett, G.D.; van Waes, J.; Kamen, B.A.; Richardson, J.; Lacey, S.W.; Anderson, R.G.; Finnell, R.H. Mice lacking the folic acid-binding protein Folbp1 are defective in early embryonic development. Nat. Genet. 1999, 23, 228–232. [Google Scholar] [CrossRef]
  34. Spiegelstein, O.; Mitchell, L.E.; Merriweather, M.Y.; Wicker, N.J.; Zhang, Q.; Lammer, E.J.; Finnell, R.H. Embryonic development of folate binding protein-1 (Folbp1) knockout mice: Effects of the chemical form, dose, and timing of maternal folate supplementation. Dev. Dyn. 2004, 231, 221–231. [Google Scholar] [CrossRef]
  35. Lee, G.H.; Fujita, M.; Takaoka, K.; Murakami, Y.; Fujihara, Y.; Kanzawa, N.; Murakami, K.I.; Kajikawa, E.; Takada, Y.; Saito, K.; et al. A GPI processing phospholipase A2, PGAP6, modulates Nodal signaling in embryos by shedding CRIPTO. J. Cell Biol. 2016, 215, 705–718. [Google Scholar] [CrossRef]
  36. Hooper, N.M. Glycosyl-phosphatidylinositol anchored membrane enzymes. Clin. Chim. Acta 1997, 266, 3–12. [Google Scholar] [CrossRef]
  37. Dustin, M.L.; Selvaraj, P.; Mattaliano, R.J.; Springer, T.A. Anchoring mechanisms for LFA-3 cell adhesion glycoprotein at membrane surface. Nature 1987, 329, 846–848. [Google Scholar] [CrossRef] [PubMed]
  38. Powell, S.K.; Cunningham, B.A.; Edelman, G.M.; Rodriguez-Boulan, E. Targeting of transmembrane and GPI-anchored forms of N-CAM to opposite domains of a polarized epithelial cell. Nature 1991, 353, 76–77. [Google Scholar] [CrossRef] [PubMed]
  39. Davitz, M.A.; Low, M.G.; Nussenzweig, V. Release of decay-accelerating factor (DAF) from the cell membrane by phosphatidylinositol-specific phospholipase C (PIPLC). Selective modification of a complement regulatory protein. J. Exp. Med. 1986, 163, 1150–1161. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  40. Davies, A.; Simmons, D.L.; Hale, G.; Harrison, R.A.; Tighe, H.; Lachmann, P.J.; Waldmann, H. CD59, an LY-6-like protein expressed in human lymphoid cells, regulates the action of the complement membrane attack complex on homologous cells. J. Exp. Med. 1989, 170, 637–654. [Google Scholar] [CrossRef] [Green Version]
  41. Haziot, A.; Chen, S.; Ferrero, E.; Low, M.G.; Silber, R.; Goyert, S.M. The monocyte differentiation antigen, CD14, is anchored to the cell membrane by a phosphatidylinositol linkage. J. Immunol. 1988, 141, 547–552. [Google Scholar]
  42. Ravetch, J.V.; Perussia, B. Alternative membrane forms of Fc gamma RIII(CD16) on human natural killer cells and neutrophils. Cell type-specific expression of two genes that differ in single nucleotide substitutions. J. Exp. Med. 1989, 170, 481–497. [Google Scholar] [CrossRef]
  43. Verma, R.S.; Gullapalli, S.; Antony, A.C. Evidence that the hydrophobicity of isolated, in situ, and de novo-synthesized native human placental folate receptors is a function of glycosyl-phosphatidylinositol anchoring to membranes. J. Biol. Chem. 1992, 267, 4119–4127. [Google Scholar]
  44. Paulick, M.G.; Bertozzi, C.R. The glycosylphosphatidylinositol anchor: A complex membrane-anchoring structure for proteins. Biochemistry 2008, 47, 6991–7000. [Google Scholar] [CrossRef] [Green Version]
  45. Davies, A.; Kadurin, I.; Alvarez-Laviada, A.; Douglas, L.; Nieto-Rostro, M.; Bauer, C.S.; Pratt, W.S.; Dolphin, A.C. The alpha2delta subunits of voltage-gated calcium channels form GPI-anchored proteins, a posttranslational modification essential for function. Proc. Natl. Acad. Sci. USA 2010, 107, 1654–1659. [Google Scholar] [CrossRef] [Green Version]
  46. Solomon, I.H.; Biasini, E.; Harris, D.A. Ion channels induced by the prion protein: Mediators of neurotoxicity. Prion 2012, 6, 40–45. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  47. Miwa, J.M.; Ibanez-Tallon, I.; Crabtree, G.W.; Sánchez, R.; Sali, A.; Role, L.W.; Heintz, N. lynx1, an endogenous toxin-like modulator of nicotinic acetylcholine receptors in the mammalian CNS. Neuron 1999, 23, 105–114. [Google Scholar] [CrossRef] [Green Version]
  48. Sendo, F.; Araki, Y. Regulation of leukocyte adherence and migration by glycosylphosphatidyl-inositol-anchored proteins. J. Leukoc. Biol. 1999, 66, 369–374. [Google Scholar] [CrossRef] [PubMed]
  49. Lingwood, D.; Simons, K. Lipid rafts as a membrane-organizing principle. Science 2010, 327, 46–50. [Google Scholar] [CrossRef] [Green Version]
  50. Brown, D.A.; London, E. Functions of lipid rafts in biological membranes. Annu. Rev. Cell Dev. Biol. 1998, 14, 111–136. [Google Scholar] [CrossRef]
  51. Simons, K.; Toomre, D. Lipid rafts and signal transduction. Nat. Rev. Mol. Cell Biol. 2000, 1, 31–39. [Google Scholar] [CrossRef]
  52. Harris, T.J.; Siu, C.H. Reciprocal raft-receptor interactions and the assembly of adhesion complexes. Bioessays 2002, 24, 996–1003. [Google Scholar] [CrossRef]
  53. Suzuki, K.G.; Fujiwara, T.K.; Sanematsu, F.; Iino, R.; Edidin, M.; Kusumi, A. GPI-anchored receptor clusters transiently recruit Lyn and G alpha for temporary cluster immobilization and Lyn activation: Single-molecule tracking study 1. J. Cell Biol. 2007, 177, 717–730. [Google Scholar] [CrossRef] [Green Version]
  54. Morgan, B.P.; van den Berg, C.W.; Davies, E.V.; Hallett, M.B.; Horejsi, V. Cross-linking of CD59 and of other glycosyl phosphatidylinositol-anchored molecules on neutrophils triggers cell activation via tyrosine kinase. Eur. J. Immunol. 1993, 23, 2841–2850. [Google Scholar] [CrossRef]
  55. Harder, T.; Simons, K. Clusters of glycolipid and glycosylphosphatidylinositol-anchored proteins in lymphoid cells: Accumulation of actin regulated by local tyrosine phosphorylation. Eur. J. Immunol. 1999, 29, 556–562. [Google Scholar] [CrossRef]
  56. Sitrin, R.G.; Pan, P.M.; Harper, H.A.; Blackwood, R.A.; Todd, R.F., 3rd. Urokinase receptor (CD87) aggregation triggers phosphoinositide hydrolysis and intracellular calcium mobilization in mononuclear phagocytes. J. Immunol. 1999, 163, 6193–6200. [Google Scholar] [PubMed]
  57. Yoshitake, H.; Takeda, Y.; Nitto, T.; Sendo, F. Cross-linking of GPI-80, a possible regulatory molecule of cell adhesion, induces up-regulation of CD11b/CD18 expression on neutrophil surfaces and shedding of L-selectin. J. Leukoc. Biol. 2002, 71, 205–211. [Google Scholar] [PubMed]
  58. Miyagawa-Yamaguchi, A.; Kotani, N.; Honke, K. Each GPI-anchored protein species forms a specific lipid raft depending on its GPI attachment signal. Glycoconj. J. 2015, 32, 531–540. [Google Scholar] [CrossRef] [PubMed]
  59. Durieux, J.J.; Vita, N.; Popescu, O.; Guette, F.; Calzada-Wack, J.; Munker, R.; Schmidt, R.E.; Lupker, J.; Ferrara, P.; Ziegler-Heitbrock, H.W.; et al. The two soluble forms of the lipopolysaccharide receptor, CD14: Characterization and release by normal human monocytes. Eur. J. Immunol. 1994, 24, 2006–2012. [Google Scholar] [CrossRef] [PubMed]
  60. Huizinga, T.W.; de Haas, M.; Kleijer, M.; Nuijens, J.H.; Roos, D.; von dem Borne, A.E. Soluble Fc gamma receptor III in human plasma originates from release by neutrophils. J. Clin. Investig. 1990, 86, 416–423. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  61. Medof, M.E.; Walter, E.I.; Rutgers, J.L.; Knowles, D.M.; Nussenzweig, V. Identification of the complement decay-accelerating factor (DAF) on epithelium and glandular cells and in body fluids. J. Exp. Med. 1987, 165, 848–864. [Google Scholar] [CrossRef]
  62. Ploug, M.; Eriksen, J.; Plesner, T.; Hansen, N.E.; Dano, K. A soluble form of the glycolipid-anchored receptor for urokinase-type plasminogen activator is secreted from peripheral blood leukocytes from patients with paroxysmal nocturnal hemoglobinuria. Eur. J. Biochem. 1992, 208, 397–404. [Google Scholar] [CrossRef]
  63. Nitto, T.; Araki, Y.; Takeda, Y.; Sendo, F. Pharmacological analysis for mechanisms of GPI-80 release from tumour necrosis factor-alpha-stimulated human neutrophils. Br. J. Pharm. 2002, 137, 353–360. [Google Scholar] [CrossRef]
  64. Kurosaki, A.; Hasegawa, K.; Kato, T.; Abe, K.; Hanaoka, T.; Miyara, A.; O’Shannessy, D.J.; Somers, E.B.; Yasuda, M.; Sekino, T.; et al. Serum folate receptor alpha as a biomarker for ovarian cancer: Implications for diagnosis, prognosis and predicting its local tumor expression. Int. J. Cancer 2016, 138, 1994–2002. [Google Scholar] [CrossRef]
  65. Li, S.; Xie, L.; He, L.; Fan, Z.; Xu, J.; Xu, K.; Zhu, L.; Ma, G.; Du, M.; Chu, H.; et al. Plasma Mesothelin as a Novel Diagnostic and Prognostic Biomarker in Colorectal Cancer. J. Cancer 2017, 8, 1355–1361. [Google Scholar] [CrossRef] [Green Version]
  66. Liu, K.L.; Fan, J.H.; Wu, J. Prognostic Role of Circulating Soluble uPAR in Various Cancers: A Systematic Review and Meta-Analysis. Clin. Lab. 2017, 63, 871–880. [Google Scholar] [CrossRef]
  67. Ishikawa, N.; Takano, A.; Yasui, W.; Inai, K.; Nishimura, H.; Ito, H.; Miyagi, Y.; Nakayama, H.; Fujita, M.; Hosokawa, M.; et al. Cancer-testis antigen lymphocyte antigen 6 complex locus K is a serologic biomarker and a therapeutic target for lung and esophageal carcinomas. Cancer Res. 2007, 67, 11601–11611. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  68. Yoshitake, H.; Nitto, T.; Ohta, N.; Fukase, S.; Aoyagi, M.; Sendo, F.; Araki, Y. Elevation of the soluble form GPI-80, a β2 integrin-associated glycosylphosphatidylinositol anchored protein, in the serum of patients with Wegener’s granulomatosis. Allergol. Int. 2005, 54, 299–303. [Google Scholar] [CrossRef]
  69. Dong, F.; Lu, C.; Chen, X.; Guo, Y.; Liu, J. CD109 is a novel marker for squamous cell/adenosquamous carcinomas of the gallbladder. Diagn. Pathol. 2015, 10, 137. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  70. Demaret, J.; Venet, F.; Plassais, J.; Cazalis, M.A.; Vallin, H.; Friggeri, A.; Lepape, A.; Rimmele, T.; Textoris, J.; Monneret, G. Identification of CD177 as the most dysregulated parameter in a microarray study of purified neutrophils from septic shock patients. Immunol. Lett. 2016, 178, 122–130. [Google Scholar] [CrossRef]
  71. Xie, J.; Wang, H. Semaphorin 7A as a potential immune regulator and promising therapeutic target in rheumatoid arthritis. Arthritis Res. Ther. 2017, 19, 10. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  72. Yoshitake, H.; Yanagida, M.; Maruyama, M.; Takamori, K.; Hasegawa, A.; Araki, Y. Molecular characterization and expression of dipeptidase 3, a testis-specific membrane-bound dipeptidase: Complex formation with TEX101, a germ-cell-specific antigen in the mouse testis. J. Reprod. Immunol. 2011, 90, 202–213. [Google Scholar] [CrossRef]
  73. Gibbs, G.M.; Lo, J.C.; Nixon, B.; Jamsai, D.; O’Connor, A.E.; Rijal, S.; Sanchez-Partida, L.G.; Hearn, M.T.; Bianco, D.M.; O’Bryan, M.K. Glioma pathogenesis-related 1-like 1 is testis enriched, dynamically modified, and redistributed during male germ cell maturation and has a potential role in sperm-oocyte binding. Endocrinology 2010, 151, 2331–2342. [Google Scholar] [CrossRef] [Green Version]
  74. Lin, Y.; Kimmel, L.H.; Myles, D.G.; Primakoff, P. Molecular cloning of the human and monkey sperm surface protein PH-20. Proc. Natl. Acad. Sci. USA 1993, 90, 10071–10075. [Google Scholar] [CrossRef] [Green Version]
  75. Kim, E.; Baba, D.; Kimura, M.; Yamashita, M.; Kashiwabara, S.; Baba, T. Identification of a hyaluronidase, Hyal5, involved in penetration of mouse sperm through cumulus mass. Proc. Natl. Acad. Sci. USA 2005, 102, 18028–18033. [Google Scholar] [CrossRef] [Green Version]
  76. Maruyama, M.; Yoshitake, H.; Tsukamoto, H.; Takamori, K.; Araki, Y. Molecular expression of Ly6k, a putative glycosylphosphatidyl-inositol-anchored membrane protein on the mouse testicular germ cells. Biochem. Biophys. Res. Commun. 2010, 402, 75–81. [Google Scholar] [CrossRef] [PubMed]
  77. Peoc’h, K.; Serres, C.; Frobert, Y.; Martin, C.; Lehmann, S.; Chasseigneaux, S.; Sazdovitch, V.; Grassi, J.; Jouannet, P.; Launay, J.M.; et al. The human “prion-like” protein Doppel is expressed in both Sertoli cells and spermatozoa. J. Biol. Chem. 2002, 277, 43071–43078. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  78. Takano, N.; Matsui, H.; Takahashi, T. TESSP-1: A novel serine protease gene expressed in the spermatogonia and spermatocytes of adult mouse testes. Mol. Reprod. Dev. 2005, 70, 1–10. [Google Scholar] [CrossRef] [PubMed]
  79. Shetty, J.; Wolkowicz, M.J.; Digilio, L.C.; Klotz, K.L.; Jayes, F.L.; Diekman, A.B.; Westbrook, V.A.; Farris, E.M.; Hao, Z.; Coonrod, S.A.; et al. SAMP14, a novel, acrosomal membrane-associated, glycosylphosphatidylinositol-anchored member of the Ly-6/urokinase-type plasminogen activator receptor superfamily with a role in sperm-egg interaction. J. Biol. Chem. 2003, 278, 30506–30515. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  80. Hunnicutt, G.R.; Primakoff, P.; Myles, D.G. Sperm surface protein PH-20 is bifunctional: One activity is a hyaluronidase and a second, distinct activity is required in secondary sperm-zona binding. Biol. Reprod. 1996, 55, 80–86. [Google Scholar] [CrossRef] [Green Version]
  81. Galat, A. The three-fingered protein domain of the human genome. Cell Mol. Life Sci. 2008, 65, 3481–3493. [Google Scholar] [CrossRef]
  82. Kirichok, Y.; Navarro, B.; Clapham, D.E. Whole-cell patch-clamp measurements of spermatozoa reveal an alkaline-activated Ca2+ channel. Nature 2006, 439, 737–740. [Google Scholar] [CrossRef]
  83. Qi, H.; Moran, M.M.; Navarro, B.; Chong, J.A.; Krapivinsky, G.; Krapivinsky, L.; Kirichok, Y.; Ramsey, I.S.; Quill, T.A.; Clapham, D.E. All four CatSper ion channel proteins are required for male fertility and sperm cell hyperactivated motility. Proc. Natl. Acad. Sci. USA 2007, 104, 1219–1223. [Google Scholar] [CrossRef] [Green Version]
  84. Sun, X.H.; Zhu, Y.Y.; Wang, L.; Liu, H.L.; Ling, Y.; Li, Z.L.; Sun, L.B. The Catsper channel and its roles in male fertility: A systematic review. Reprod. Biol. Endocrinol. 2017, 15, 65. [Google Scholar] [CrossRef] [Green Version]
  85. Masutani, M.; Sakurai, S.; Shimizu, T.; Ohto, U. Crystal structure of TEX101, a glycoprotein essential for male fertility, reveals the presence of tandemly arranged Ly6/uPAR domains. FEBS Lett. 2020. [Google Scholar] [CrossRef]
  86. Martin-Satue, M.; Lavoie, E.G.; Fausther, M.; Lecka, J.; Aliagas, E.; Kukulski, F.; Sevigny, J. High expression and activity of ecto-5’-nucleotidase/CD73 in the male murine reproductive tract. Histochem. Cell Biol. 2010, 133, 659–668. [Google Scholar] [CrossRef] [PubMed]
  87. Egbunike, G.N. Changes in acetylcholinesterase activity of mammalian spermatozoa during maturation. Int. J. Androl. 1980, 3, 459–468. [Google Scholar] [CrossRef] [PubMed]
  88. Paiva, J.; Damjanov, I.; Lange, P.H.; Harris, H. Immunohistochemical localization of placental-like alkaline phosphatase in testis and germ-cell tumors using monoclonal antibodies. Am. J. Pathol. 1983, 111, 156–165. [Google Scholar] [PubMed]
  89. Koshida, K.; Stigbrand, T.; Hisazumi, H.; Wahren, B. Electrophoretic heterogeneity of alkaline phosphatase isozymes in seminoma and normal testis. Tumour Biol. 1989, 10, 181–189. [Google Scholar] [CrossRef] [PubMed]
  90. Mii, S.; Murakumo, Y.; Asai, N.; Jijiwa, M.; Hagiwara, S.; Kato, T.; Asai, M.; Enomoto, A.; Ushida, K.; Sobue, S.; et al. Epidermal hyperplasia and appendage abnormalities in mice lacking CD109. Am. J. Pathol. 2012, 181, 1180–1189. [Google Scholar] [CrossRef]
  91. Simpson, K.L.; Holmes, C.H. Differential expression of complement regulatory proteins decay-accelerating factor (CD55), membrane cofactor protein (CD46) and CD59 during human spermatogenesis. Immunology 1994, 81, 452–461. [Google Scholar]
  92. Habib, G.M.; Shi, Z.Z.; Cuevas, A.A.; Lieberman, M.W. Identification of two additional members of the membrane-bound dipeptidase family. FASEB J. 2003, 17, 1313–1315. [Google Scholar] [CrossRef]
  93. Davidoff, M.S.; Middendorff, R.; Koeva, Y.; Pusch, W.; Jezek, D.; Muller, D. Glial cell line-derived neurotrophic factor (GDNF) and its receptors GFRalpha-1 and GFRalpha-2 in the human testis. Ital. J. Anat. Embryol. 2001, 106 (Suppl. S2), 173–180. [Google Scholar]
  94. Thway, K.; Selfe, J.; Shipley, J. Immunohistochemical detection of glypican-5 in paraffin-embedded material: An optimized method for a novel research antibody. Appl. Immunohistochem. Mol. Morphol. 2012, 20, 189–195. [Google Scholar] [CrossRef]
  95. Nielsen, J.E.; Lindegaard, M.L.; Friis-Hansen, L.; Almstrup, K.; Leffers, H.; Nielsen, L.B.; Rajpert-De Meyts, E. Lipoprotein lipase and endothelial lipase in human testis and in germ cell neoplasms. Int. J. Androl. 2010, 33, 207–215. [Google Scholar] [CrossRef]
  96. Van Bragt, M.P.; Ciliberti, N.; Stanford, W.L.; de Rooij, D.G.; van Pelt, A.M. LY6A/E (SCA-1) expression in the mouse testis. Biol. Reprod. 2005, 73, 634–638. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  97. Trivedi, R.N.; Naz, R.K. Testis-specific antigen (TSA-1) is expressed in murine sperm and its antibodies inhibit fertilization. Am. J. Reprod. Immunol. 2002, 47, 38–45. [Google Scholar] [CrossRef]
  98. Zhang, Y.; Lang, Q.; Li, J.; Xie, F.; Wan, B.; Yu, L. Identification and characterization of human LYPD6, a new member of the Ly-6 superfamily. Mol. Biol. Rep. 2010, 37, 2055–2062. [Google Scholar] [CrossRef] [PubMed]
  99. Bera, T.K.; Pastan, I. Mesothelin is not required for normal mouse development or reproduction. Mol. Cell Biol. 2000, 20, 2902–2906. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  100. Meng, C.; Liu, W.; Huang, H.; Wang, Y.; Chen, B.; Freeman, G.J.; Schneyer, A.; Lin, H.Y.; Xia, Y. Repulsive Guidance Molecule b (RGMb) Is Dispensable for Normal Gonadal Function in Mice. Biol. Reprod. 2016, 94, 78. [Google Scholar] [CrossRef] [PubMed]
  101. Yoneda, R.; Kimura, A.P. A testis-specific serine protease, Prss41/Tessp-1, is necessary for the progression of meiosis during murine in vitro spermatogenesis. Biochem. Biophys. Res. Commun. 2013, 441, 120–125. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  102. Tepekoy, F.; Ozturk, S.; Sozen, B.; Ozay, R.S.; Akkoyunlu, G.; Demir, N. CD90 and CD105 expression in the mouse ovary and testis at different stages of postnatal development. Reprod. Biol. 2015, 15, 195–204. [Google Scholar] [CrossRef] [PubMed]
  103. Spierings, D.C.; de Vries, E.G.; Vellenga, E.; van den Heuvel, F.A.; Koornstra, J.J.; Wesseling, J.; Hollema, H.; de Jong, S. Tissue distribution of the death ligand TRAIL and its receptors. J. Histochem. Cytochem. 2004, 52, 821–831. [Google Scholar] [CrossRef] [Green Version]
  104. Kyte, J.; Doolittle, R.F. A simple method for displaying the hydropathic character of a protein. J. Mol. Biol. 1982, 157, 105–132. [Google Scholar] [CrossRef] [Green Version]
  105. Yeh, E.T.; Kamitani, T.; Chang, H.M. Biosynthesis and processing of the glycosylphosphatidylinositol anchor in mammalian cells. Semin. Immunol. 1994, 6, 73–80. [Google Scholar] [CrossRef]
  106. Tulsiani, D.R.; Yoshida-Komiya, H.; Araki, Y. Mammalian fertilization: A carbohydrate-mediated event. Biol. Reprod. 1997, 57, 487–494. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  107. Yonezawa, N. Posttranslational modifications of zona pellucida proteins. Adv. Exp. Med. Biol. 2014, 759, 111–140. [Google Scholar] [PubMed]
  108. Bianchi, E.; Wright, G.J. Sperm Meets Egg: The Genetics of Mammalian Fertilization. Annu. Rev. Genet. 2016, 50, 93–111. [Google Scholar] [CrossRef] [PubMed]
  109. Sun, T.C.; Wang, J.H.; Wang, X.X.; Liu, X.M.; Zhang, C.L.; Hao, C.F.; Ma, W.Z.; Deng, S.L.; Liu, Y.X. Effects of sperm proteins on fertilization in the female reproductive tract. Front. Biosci. 2019, 24, 735–749. [Google Scholar]
  110. Helenius, A.; Aebi, M. Intracellular functions of N-linked glycans. Science 2001, 291, 2364–2369. [Google Scholar] [CrossRef] [Green Version]
  111. Yoshitake, H.; Shirai, Y.; Mochizuki, Y.; Iwanari, H.; Tsubamoto, H.; Koyama, K.; Takamori, K.; Ogawa, H.; Hasegawa, A.; Kodama, T.; et al. Molecular diversity of TEX101, a marker glycoprotein for germ cells monitored with monoclonal antibodies: Variety of the molecular characteristics according to subcellular localization within the mouse testis. J. Reprod. Immunol. 2008, 79, 1–11. [Google Scholar] [CrossRef]
  112. Shirai, Y.; Yoshitake, H.; Maruyama, M.; Takamori, K.; Ogawa, H.; Hasegawa, A.; Araki, Y. Distribution of molecular epitope for Ts4, an anti-sperm auto-monoclonal antibody in the fertilization process. J. Reprod. Dev. 2009, 55, 240–246. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  113. Yoshitake, H.; Hashii, N.; Kawasaki, N.; Endo, S.; Takamori, K.; Hasegawa, A.; Fujiwara, H.; Araki, Y. Chemical Characterization of N-Linked Oligosaccharide As the Antigen Epitope Recognized by an Anti-Sperm Auto-Monoclonal Antibody, Ts4. PLoS ONE 2015, 10, e0133784. [Google Scholar] [CrossRef] [Green Version]
  114. Takayama, T.; Mishima, T.; Mori, M.; Ishikawa, T.; Takizawa, T.; Goto, T.; Suzuki, M.; Araki, Y.; Matsubara, S.; Takizawa, T. TEX101 is shed from the surface of sperm located in the caput epididymidis of the mouse. Zygote 2005, 13, 325–333. [Google Scholar] [CrossRef]
  115. Oda-Sakurai, R.; Yoshitake, H.; Miura, Y.; Kazuno, S.; Ueno, T.; Hasegawa, A.; Yamatoya, K.; Takamori, K.; Itakura, A.; Fujiwara, H.; et al. NUP62: The target of an anti-sperm auto-monoclonal antibody during testicular development. Reproduction 2019, 158, 503–516. [Google Scholar] [CrossRef]
  116. Yoshitake, H.; Oda, R.; Yanagida, M.; Kawasaki, Y.; Sakuraba, M.; Takamori, K.; Hasegawa, A.; Fujiwara, H.; Araki, Y. Identification of an anti-sperm auto-monoclonal antibody (Ts4)-recognized molecule in the mouse sperm acrosomal region and its inhibitory effect on fertilization in vitro. J. Reprod. Immunol. 2016, 115, 6–13. [Google Scholar] [CrossRef]
  117. Rebbaa, A.; Yamamoto, H.; Saito, T.; Meuillet, E.; Kim, P.; Kersey, D.S.; Bremer, E.G.; Taniguchi, N.; Moskal, J.R. Gene transfection-mediated overexpression of beta1,4-N-acetylglucosamine bisecting oligosaccharides in glioma cell line U373 MG inhibits epidermal growth factor receptor function. J. Biol. Chem. 1997, 272, 9275–9279. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  118. Kitada, T.; Miyoshi, E.; Noda, K.; Higashiyama, S.; Ihara, H.; Matsuura, N.; Hayashi, N.; Kawata, S.; Matsuzawa, Y.; Taniguchi, N. The addition of bisecting N-acetylglucosamine residues to E-cadherin down-regulates the tyrosine phosphorylation of beta-catenin. J. Biol. Chem. 2001, 276, 475–480. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  119. Isaji, T.; Gu, J.; Nishiuchi, R.; Zhao, Y.; Takahashi, M.; Miyoshi, E.; Honke, K.; Sekiguchi, K.; Taniguchi, N. Introduction of bisecting GlcNAc into integrin alpha5beta1 reduces ligand binding and down-regulates cell adhesion and cell migration. J. Biol. Chem. 2004, 279, 19747–19754. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  120. Pawson, T.; Nash, P. Assembly of cell regulatory systems through protein interaction domains. Science 2003, 300, 445–452. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  121. Seet, B.T.; Dikic, I.; Zhou, M.M.; Pawson, T. Reading protein modifications with interaction domains. Nat. Rev. Mol. Cell Biol. 2006, 7, 473–483. [Google Scholar] [CrossRef]
  122. Natsume, T.; Yamauchi, Y.; Nakayama, H.; Shinkawa, T.; Yanagida, M.; Takahashi, N.; Isobe, T. A direct nanoflow liquid chromatography-tandem mass spectrometry system for interaction proteomics. Anal. Chem. 2002, 74, 4725–4733. [Google Scholar] [CrossRef]
  123. Gerke, V.; Moss, S.E. Annexins: From structure to function. Physiol. Rev. 2002, 82, 331–371. [Google Scholar] [CrossRef]
  124. Chojnacka, K.; Bilinska, B.; Mruk, D.D. Annexin A2 is critical for blood-testis barrier integrity and spermatid disengagement in the mammalian testis. Biochim. Biophys. Acta Mol. Cell Res. 2017, 1864, 527–545. [Google Scholar] [CrossRef]
  125. Chen, Y.A.; Scheller, R.H. SNARE-mediated membrane fusion. Nat. Rev. Mol. Cell Biol. 2001, 2, 98–106. [Google Scholar] [CrossRef]
  126. Habib, G.M.; Shi, Z.Z.; Cuevas, A.A.; Guo, Q.; Matzuk, M.M.; Lieberman, M.W. Leukotriene D4 and cystinyl-bis-glycine metabolism in membrane-bound dipeptidase-deficient mice. Proc. Natl. Acad. Sci. USA 1998, 95, 4859–4863. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  127. Xie, Y.; Khan, R.; Wahab, F.; Hussain, H.M.J.; Ali, A.; Ma, H.; Jiang, H.; Xu, J.; Zaman, Q.; Khan, M.; et al. The testis-specifically expressed Dpep3 is not essential for male fertility in mice. Gene 2019, 711, 143925. [Google Scholar] [CrossRef] [PubMed]
  128. Zimmermann, H.; Zebisch, M.; Sträter, N. Cellular function and molecular structure of ecto-nucleotidases. Purinergic Signal 2012, 8, 437–502. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  129. Resta, R.; Hooker, S.W.; Hansen, K.R.; Laurent, A.B.; Park, J.L.; Blackburn, M.R.; Knudsen, T.B.; Thompson, L.F. Murine ecto-5’-nucleotidase (CD73): cDNA cloning and tissue distribution. Gene 1993, 133, 171–177. [Google Scholar] [CrossRef]
  130. Antonioli, L.; Pacher, P.; Vizi, E.S.; Haskó, G. CD39 and CD73 in immunity and inflammation. Trends Mol. Med. 2013, 19, 355–367. [Google Scholar] [CrossRef] [Green Version]
  131. Stagg, J.; Smyth, M.J. Extracellular adenosine triphosphate and adenosine in cancer. Oncogene 2010, 29, 5346–5358. [Google Scholar] [CrossRef] [Green Version]
  132. Yamaguchi, R.; Muro, Y.; Isotani, A.; Tokuhiro, K.; Takumi, K.; Adham, I.; Ikawa, M.; Okabe, M. Disruption of ADAM3 impairs the migration of sperm into oviduct in mouse. Biol. Reprod. 2009, 81, 142–146. [Google Scholar] [CrossRef] [Green Version]
  133. Ikawa, M.; Wada, I.; Kominami, K.; Watanabe, D.; Toshimori, K.; Nishimune, Y.; Okabe, M. The putative chaperone calmegin is required for sperm fertility. Nature 1997, 387, 607–611. [Google Scholar] [CrossRef]
  134. Ikawa, M.; Tokuhiro, K.; Yamaguchi, R.; Benham, A.M.; Tamura, T.; Wada, I.; Satouh, Y.; Inoue, N.; Okabe, M. Calsperin is a testis-specific chaperone required for sperm fertility. J. Biol. Chem. 2011, 286, 5639–5646. [Google Scholar] [CrossRef] [Green Version]
  135. Tokuhiro, K.; Ikawa, M.; Benham, A.M.; Okabe, M. Protein disulfide isomerase homolog PDILT is required for quality control of sperm membrane protein ADAM3 and male fertility [corrected]. Proc. Natl. Acad. Sci. USA 2012, 109, 3850–3855. [Google Scholar] [CrossRef] [Green Version]
  136. Nishimura, H.; Kim, E.; Nakanishi, T.; Baba, T. Possible function of the ADAM1a/ADAM2 Fertilin complex in the appearance of ADAM3 on the sperm surface. J. Biol. Chem. 2004, 279, 34957–34962. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  137. Endo, S.; Yoshitake, H.; Tsukamoto, H.; Matsuura, H.; Kato, K.; Sakuraba, M.; Takamori, K.; Fujiwara, H.; Takeda, S.; Araki, Y. TEX101, a glycoprotein essential for sperm fertility, is required for stable expression of Ly6k on testicular germ cells. Sci. Rep. 2016, 6, 23616. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  138. Fujihara, Y.; Okabe, M.; Ikawa, M. GPI-anchored protein complex, LY6K/TEX101, is required for sperm migration into the oviduct and male fertility in mice. Biol. Reprod. 2014, 90, 60–61. [Google Scholar] [CrossRef]
  139. Okabe, M. The cell biology of mammalian fertilization. Development 2013, 140, 4471–4479. [Google Scholar] [CrossRef] [PubMed] [Green Version]
Ijms 21 06628 g001 550
Figure 1. Schema of glycosylphosphatidylinositol-anchored protein (GPI-AP) structure. The C-terminus of core peptide binds to phosphoethanolamine followed by three mannose (Man) residues and glucosamine (GlcN). The glycan core further links to phosphatidylinositol.
Figure 1. Schema of glycosylphosphatidylinositol-anchored protein (GPI-AP) structure. The C-terminus of core peptide binds to phosphoethanolamine followed by three mannose (Man) residues and glucosamine (GlcN). The glycan core further links to phosphatidylinositol.
Ijms 21 06628 g001
Ijms 21 06628 g002 550
Figure 2. Molecular expression of TEX101 during gametogenesis. Germ cells that express TEX101 are indicated with bold lines. PGC, primordial germ cell; PSG, prospermatogonium or gonocyte; NSG, neonatal-type undifferentiated spermatogonium; SG, spermatogonium; SC, spermatocyte; ST, spermatid; SZ, spermatozoon, OG, oogonium; OC, oocyte; PF, primordial follicle; GF, glowing follicle (modified from [13]).
Figure 2. Molecular expression of TEX101 during gametogenesis. Germ cells that express TEX101 are indicated with bold lines. PGC, primordial germ cell; PSG, prospermatogonium or gonocyte; NSG, neonatal-type undifferentiated spermatogonium; SG, spermatogonium; SC, spermatocyte; ST, spermatid; SZ, spermatozoon, OG, oogonium; OC, oocyte; PF, primordial follicle; GF, glowing follicle (modified from [13]).
Ijms 21 06628 g002
Ijms 21 06628 g003 550
Figure 3. Molecular status of Ly6k with/without TEX101 in the testicular germ cells (TGCs). The left diagram indicates TEX101/Ly6k complex formation of wild-type (Tex101+/+) mouse. After translation, GPI remodeling of these molecules is completed from endoplasmic reticulum (ER) to Golgi apparatus; then, these molecules are expressed as a TEX101/Ly6k complex (represented by black square) on lipid bilayers including a transportation vesicle and plasma membrane. In addition, (a part of) both TEX101 and Ly6k are released into extracellular space. In TEX101-null TGCs (the right diagram), Ly6k expression is drastically decreased. Black cross marks indicate the disruption of the molecules. The potential status of Ly6k protein expression without TEX101 is boxed (originated from [137]).
Figure 3. Molecular status of Ly6k with/without TEX101 in the testicular germ cells (TGCs). The left diagram indicates TEX101/Ly6k complex formation of wild-type (Tex101+/+) mouse. After translation, GPI remodeling of these molecules is completed from endoplasmic reticulum (ER) to Golgi apparatus; then, these molecules are expressed as a TEX101/Ly6k complex (represented by black square) on lipid bilayers including a transportation vesicle and plasma membrane. In addition, (a part of) both TEX101 and Ly6k are released into extracellular space. In TEX101-null TGCs (the right diagram), Ly6k expression is drastically decreased. Black cross marks indicate the disruption of the molecules. The potential status of Ly6k protein expression without TEX101 is boxed (originated from [137]).
Ijms 21 06628 g003
Table
Table 1. GPI-APs expressed within the testis.
Table 1. GPI-APs expressed within the testis.
Protein NamePutative FunctionReference
5′-nucleotidase (CD73)Enzyme[86]
AcetylcholinesteraseEnzyme[87]
Alkaline phosphatase, placental-like Enzyme[88]
Alkaline phosphatase, tissue-nonspecific isozymeEnzyme[89]
CD109Receptor[90]
CD59Complement regulator[91]
Complement decay-accelerating factor (CD55)Complement regulator[91]
Dipeptidase 2 (DPEP2)Enzyme[92]
Dipeptidase 3 (DPEP3)Enzyme[72]
GDNF family receptor alpha-1Receptor[93]
GDNF family receptor alpha-2Receptor[93]
Glypican-5Receptor[94]
GLIPR1-like protein 1Others[73]
Hyaluronidase PH-20Enzyme[75]
Hyaluronidase-5Enzyme[75]
Lipoprotein lipaseEnzyme[95]
Lymphocyte antigen 6A-2/6E-1 (Ly6A/E)Others[96]
Lymphocyte antigen 6E (Ly6E)Receptor[97]
Lymphocyte antigen 6K (Ly6K)Others[12]
Ly6/PLAUR domain-containing protein 6 *Receptor[98]
Mesothelin *Others[99]
Prion-like protein doppelReceptor[77]
RGM domain family member BReceptor[100]
Serine protease 41Enzyme[101]
Sperm acrosome membrane-associated protein 4Enzyme[79]
Testis-expressed protein 101 (TEX101)Others[9]
TestisinEnzyme[25]
Thy-1 membrane glycoproteinOthers[102]
TNF receptor superfamily membrane 10C Receptor[103]
Bold type: highly specific expression in the gonad. *: Data from gene expression analysis only.
Table
Table 2. The primary structure of TEX101 in major mammalian species.
Table 2. The primary structure of TEX101 in major mammalian species.
Species Amino Acid #
Mousemgacriqyvl liflliasrw tlvqntycqv sqtlsleddp grtfnwtska50
Ratmgacriqyil lvflliashw tlvqniycev srtlslednp sgtfnwtska50
Humanmgtpriqhll illvlgasll tsglelycqk glsmtveadp anmfnwttee50
Bovinemgachfqgll llflvgaptl imaqklfcqk gtfmgiqeda tnmfnwtsek50
Mouse-eqcnpgelcq etvllikadg trtvvlasks cvsqggeavt fiqytappgl100
Rat-ekcnpgefcq etvllikaeg tktailasks cvpqgaetmt fvqytappgl100
Humanvetcdkgalcq etiliikag- tetailatkg cipegeeait ivqhssppgl100
Bovineveacdngtlcq etilliktag tktailatks csldgtpait fiqhtaapsl100
Mousevaisysnycn dslcnnkdsl asvwrvpett a-tsnmsgtr- hcptcvalgsc- 150
Ratvaisysnycn dslcnnrnnl asilqapept a-tsnmsgar- hcptclalepc-150
Humanivtsysnyce dsfcndkdsl sqfwefsett astvst--tl- hcptcvalgtcf150
Bovineaaisysnyce dpfcnnregl ydiwniqete eetkgt—tsl- hcptclalgsc150
Mousessapsmpcan gttqcyqgrl efsgggmdat vqvkgcttti gcrlmamids 200
Ratssapsmpcan gttqcyhgki elsgggmdsv vhvkgcttai gcrlmakmes200
Humansapslp-cpn gttrcyqgkl eitgggiess vevkgctami gcrlmsgila200
Bovinelnapsvacpn ntdrcyqgkl qvsegnvnsl leikgctsii gcklmsgvfk200
Mouse-vgpmtvketc syqsflqprk aeigasqmpt slwvlellfp- llllplth---fp250
Rat-vgpmtvketc syqsflhprm aeigaswmpt slwvlelllp- alslpliy---fp250
Human-vgpmfvreac phqlltqprk tengatclpi pvwglqlllp- ll-lpsfih--fp249
Bovinekigplwvketc psmsist-rk idngatwlht svwklklllm- llllilggsasgp253
Species Amino acid #
Conserved cysteine residues are indicated by black boxes, and possible N-glycosylation sites (n-x-s/t) are dark-gray shadows.
Table
Table 3. Possible proteins associated with TEX101 within the testis.
Table 3. Possible proteins associated with TEX101 within the testis.
Protein NameAntibody Used for the ExperimentsReference
Annexin A2TES101[11]
Ly6kTES101[11]
CellubrevinTES101[11]
DPEP3TES101, Ts4[72]
5′-nucleotidase (CD73)TES101, Ts4[115]

Share and Cite

MDPI and ACS Style

Yoshitake, H.; Araki, Y. Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis. Int. J. Mol. Sci. 2020, 21, 6628. https://doi.org/10.3390/ijms21186628

AMA Style

Yoshitake H, Araki Y. Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis. International Journal of Molecular Sciences. 2020; 21(18):6628. https://doi.org/10.3390/ijms21186628

Chicago/Turabian Style

Yoshitake, Hiroshi, and Yoshihiko Araki. 2020. "Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis" International Journal of Molecular Sciences 21, no. 18: 6628. https://doi.org/10.3390/ijms21186628

APA Style

Yoshitake, H., & Araki, Y. (2020). Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis. International Journal of Molecular Sciences, 21(18), 6628. https://doi.org/10.3390/ijms21186628

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop