Novel spatiotemporal glycome changes in the murine placenta during placentation based on BS-I lectin binding patterns

Although spatiotemporal changes of the glycome (full set of glycans, otherwise known as saccharides or carbohydrates) during placenta formation (placentation) are functionally and clinically important, they are poorly defined. Here, we elucidated novel aspects of the glycome during mouse placentation, from embryonic day 6.5 (E6.5) to E12.5, by investigating the largely unexplored binding distribution of lectin I from Bandeiraea simplicifolia (BS-I lectin), a glycan-binding protein that recognizes the DGalNAc and DGal glycans found at the terminal ends of specific oligosaccharides attached to lipids or proteins. We show that BS-I lectin binding marks all trophoblast cells during early placentation (E7.5 and E8.5 stages), continues in labyrinthine and junctional zone trophoblast but is lost from parietal trophoblast giant cells by E10.5/E11.5 (definitive placenta stage) and is lost from all trophoblast types, but marks the fetal capillary endothelium of the labyrinth, by E12.5. In the decidua basalis (the maternal part of the placenta), BS-I lectin positivity mainly marks the decidual stroma cells of the venous sinusoid area (E7.5 and E8.5 stages) and the entire decidua basalis by E10.5, as well as the osteopontin-positive subset of uterine natural killer (uNK) cells from E7.5 onwards. This work provides the first comprehensive description of the hitherto ill-defined spatiotemporal binding distribution of BS-I lectin in the fetal and maternal placenta between E6.5 and E12.5, thereby contributing to glycome elucidation during placentation. It also establishes BS-I lectin positivity as a novel pan-trophoblast marker during early placentation and as a new marker for mature uNK cells from E7.5 onwards.