Equine Placental Cup Cells show Glycan Expression Distinct from that of Both Chorionic Girdle Progenitor Cells and Early Allantochorionic Trophoblast of the Placenta

Abstract

Using lectin histochemistry on plastic-embedded material, the glycosylation patterns of equine girdle and cup cells, and associated endometrial glands, have been investigated from 37 to 67 days gestation. Results were compared with the glycosylation of the 50-day allantochorionic trophoblast of the established equine placenta that will later form the microcotyledons. The differentiated cup cells, which secrete equine chorionic gonadotropin (eCG), showed a pattern of glycosylation that was distinct both from the progenitor girdle cells and the allantochorionic trophoblast, with granules that bound lectins indicating high levels of α2,6 and α2,3-linked sialic acid, N-acetyllactosamine and bi/tri antennary non-bisected and bisected complex N-glycan. This is consistent with the known carbohydrate content of eCG. In contrast, the allantochorionic trophoblast at 50 days lacked detectable amounts of sialic acid and showed high levels of tri/tetra-antennary non-bisected complex N-glycan and N-acetyl galactosamine which was absent in the cup cells. During the process of girdle cell migration into maternal tissues, the uterine glands became greatly enlarged and dilated basally, with increased amounts of glycosylated secretory products revealed by lectins, which often seeped out into the extracellular space via ruptures in the apical regions of the gland wall.