**2. Morphogenesis and Development**

GAGs, as essential constituents of the human glycome, play pivotal roles in a multitude of biological processes during embryonic development and in the maintenance of homeostasis. Such roles can be observed throughout the structural mold of aggregan and the diversity of its decoration by GAGs. The development of vertebrates from a single cell to the generation of various cell types and organs is carried out throughout a synchronized developmental program consisting of the spatial and temporal coordination of specific signaling molecules, including morphogens and growth factors. The importance of specific arrangements of GAG chains on aggrecan in all of its forms is also a primary morphogenetic functional determinant. It provides aggrecan with unique tissue-context-dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains [7].

The article by Colin-Pierre et al. [8] describes the evolution of heparan sulfate proteoglycans in hair follicles. The heparan sulfate proteoglycan distribution in hair follicles has traditionally been done by conventional histology, biochemical analysis, and immunohistochemistry. The authors use the absorption region that is relevant to sulfation as a spectral marker. This is performed using infrared spectral imaging (IRSI), which has been used intensively for cell (spectral cytology) and tissue (spectral histology) characterization. Supported by Western blot and immunohistochemistry analysis, infrared spectral imaging specifically shows the qualitative and/or quantitative evolution of the GAGs expression pattern between the anagen, catagen, and telogen phases. Moreover, this demonstrates that IRSI could be utilized for GAG cytology and tissue characterization.
