Structure and glycosylation of the term yolk sac placenta and uterine attachment site in the viviparous shark Mustelus canis

Abstract

The viviparous shark Mustelus canis nurtures its young within the uterus by means of a modified yolk sac which functions as a placenta. Two term specimens have been examined with a panel of 21 biotinylated lectins to assess whether glycans form a prominent interface between fetal and maternal tissues as in their therian counterparts. The yolk sac placenta was lined by a thin egg envelope which apposed though did not make contact with the uterine epithelium, and expressed fucosyl, N-acetyl glucosamine/lactosamine residues and some complex N-glycan, while the attached, thin ectoderm cells stained selectively with lectins from Anguilla anguilla and Arachis hypogaea indicating fucosyl and β-galactosyl residues; other lectins bound to a variable degree. Large yolk sac endoderm cells were heavily glycosylated and expressed a wide range of glycans. The apposing uterine epithelium had two epithelial layers with distinctive patterns of glycosylation, the apical layer stained strongly with Anguilla anguilla lectin and the basal cells with lectins from Wisteria floribunda and Helix pomatia, the latter indicating plentiful N-acetyl galactosamine though both layers stained variably with other lectins also. A population of sparse, large, globular cells expressed α2,3-linked sialic acid and N-acetyl glucosamine oligomers. Fetal and maternal vessels were heavily glycosylated as in their therian counterparts. These data indicate a prominent role for glycans at the fetomaternal interface of these chondrichthyan fishes.