Immunocytochemistry of the placentas of giraffe (Giraffa cameleopardalis giraffa) and okapi (Okapi johnstoni): comparison with other ruminants.

Introduction: The trophoblast binucleate cell [BNC] is central to the structure and function of all ruminant placentas so far investigated. The Giraffidae are considered to form a separate family within the ruminant suborder.

Methods: The structure and function of two [mid and late pregnant] giraffe placentas and two term okapi placentas have been investigated immunocytochemically.

Results: Their major characteristics: polycotyledonary epitheliochorial structure, sequential glucose transport using two transporter isoforms, expression of water transporters in the interplacentomal [IP] and placentomal [P] trophoblast and restriction of calcium transport to the IP trophoblast are similar to those of the ruminant family Bovidae. . Giraffe and okapi also show characteristic ruminant trophoblast binucleate cells (BNC) which migrate and fuse with individual uterine epithelial cells as in the cow. However, there are many fewer BNC, of limited distribution, when compared with other ruminants so far investigated. The giraffe and okapi BNC also show a different range of proteins, Pregnancy Associated Glycoproteins (PAGs) and glycans which clearly distinguish the Giraffidae from the Bovidae.

Conclusions: The results support a separate giraffid family derived from a common ancestry, possessing subpopulations of BNC with potentially different functions.