Asymmetric expression of proteins in the granules of the placentomal Binucleate cells in Giraffa camelopardalis†

Mature granulated trophoblast binucleate cells (BNC) have been found in all ruminant placentas examined histologically so far. BNC are normally fairly evenly distributed throughout the fetal villus and all their granules contain a similar variety of hormones and pregnancy associated glycoproteins (PAGs). Only the Giraffe is reported to show a different BNC protein expression, this paper is designed to investigate that. Gold labelled Lectin histochemistry and protein immunocytochemistry were used on deplasticised 1 μm sections of a wide variety of ruminant placentomes with a wide range of antibodies and lectins. In the Giraffe placentomes, even though the lectin histochemistry shows an even distribution of BNC throughout the trophoblast of the placental villi, the protein expression in the BNC granules is limited to the BNC either in the apex or the base of the villi. Placental lactogens and Prolactin (PRL) are present only in basally situated BNC: PAGs only in the apical BNC. PRL is only found in the Giraffe BNC which react with many fewer of the wide range of antibodies used here to investigate the uniformity of protein expression in ruminant BNC. The possible relevance of these differences to ruminant function and evolution is considered to provide a further example of the versatility of the BNC system.