INTRODUCTION: Little is known about the glycosylation of placental villi and areolae of cetaceans. Term tissue from the delivered placenta of an Indo-Pacific Bottlenose Dolphin (Tursiops aduncus) was examined using lectin histochemistry to compare trophoblast glycosylation in these two locations.
METHODS: Placental blocks fixed in 10% formalin were resin-embedded before semithin sections were stained with 24 biotinylated lectins and an avidin-biotin revealing system.
RESULTS: Areolar trophoblast was composed of large, bulbous cells packed with numerous granules compared to the smaller, cuboidal cells clothing the chorionic villi, which had a sparser, mainly subapical granule population. Both were richly glycosylated; generally areolar cells were more heavily stained apart from poor binding to some N-acetylgalactosamine and N-acetylglucosamine termini. Most striking was the distribution of α1,2-linked fucosyl residues, weakly expressed in villous trophoblast but intensely stained in some areolar cells, also terminal sialic acids. Some lectins bound in a variable fashion. Staining of terminal α-d-mannose, which locates mainly to lysosomes, was heavy in areolar cells compared to scattered irregular foci in villous cells.
DISCUSSION AND CONCLUSION: The many intracellular inclusions reflect ongoing lysosomal breakdown of histotroph in areolar cells which often show heterogeneous glycosylation staining unlike the uniformly stained villous cells, possibly reflecting partial breakdown of ingested sialoglycoprotein, cell turnover or regional variation in uptake of histotroph. Our results indicate that Dolphin areolae are functionally distinct from villous trophoblast, performing absorptive and phagocytic functions similar to other Artiodactyla.