**2. The Placental Galectins**

A variety of galectins are expressed in the reproductive system. They are pleiotropic regulators of key functions in the reproductive tract. Gal-1 and Gal-3 are involved in regulating signaling pathways at the feto-maternal interface [31,32] and are expressed in the endometrium and the decidua. The tandem repeat of Gal-8 acts through spliced variants in various reproductive tissues [1–21]. Gal-9 is abundant via its three encoding genes [33]. In this respect, it is worth mentioning that the Gal 10 protein is also expressed by white blood cells (WBC), while its mRNA is exclusively expressed in bone marrow tissues. However, the WBC reach the reproductive system and influence this system during the process of pregnancy development, especially via generating an immune response against foreign (paternal) genes of the fetus and placenta [34,35]. Other galectins in the reproductive tract such as Gal-13 participate in trophoblast invasion into the decidua, spiral artery remodeling, and immune tolerance of maternal tissues to pregnancy [2].

Here we focus on a placental cluster of six galectins in anthropoid primates in the context of evolution of the highly invasive placentation and long gestation [31]. The expression of these galectins in the placental syncytiotrophoblast is altered in preeclampsia and early fetal growth restriction (FGR) [32]. Three of them, Gal-13, Gal-14, and Gal-16 are uniquely expressed in the placenta, indicating the massive differentiation effort dedicated by nature for assuring the establishment and maintenance of pregnancy in eutherian mammals [36].
