FORMATION OF RETICULATED ENDODERM, REICHERTS MEMBRANE, AND AMNIOGENESIS IN BLASTOCYSTS OF CAPTIVE-BRED, SHORT-TAILED FRUIT BATS, CAROLLIA-PERSPICILLATA

Background and Methods: As part of an effort to develop the short-tail ed fruit bat (Carollia perspicillata) as a new animal model for the st udy of interstitial implantation and trophoblast-uterine interactions, early embryogenesis was examined histologically and ultrastructurally in captive-bred females at different intervals after the first appear ance of spermatozoa in daily vaginal smears (day 1 postcoitum [p.c.]), Results: In most of the early uterine embryos examined on days 16-18 p.c., much of the endoderm appeared as a reticulated meshwork; however , a unilocular yolk sac was formed prior to the development of any mes oderm, Early blastocysts of Carollia were also unusual in that endoder m surrounded much of the inner cell mass (ICM), Reichert's membrane co ntinued over the dorsal side of the ICM, and basal laminalike material was observed around many of the endoderm and epiblast cells. A primor dial amniotic cavity was formed between days 19 and 26 p.c. by cavitat ion, The first mesoderm appeared between days 23 and 26 p.c., concommi tant with the development of an embryonic shield. Conclusion: The unus ual reticulated appearance of early endoderm in Carollia, which is rem iniscent of that seen in early human blastocysts, may be attributable to constraints imposed on growth of the blastocyst by the site and mod e of implantation, temporary retardation of trophoblastic invasion by the basal laminae of endometrial epithelial elements, and endodermal p roliferation in anticipation of rapid yolk sec expansion, Reichert's m embrane appears to play an important role in this species in tethering the ICM and embryonic shield to the developing placenta prior to the formation of significant amounts of mesoderm. (C) 1997 Wiley-Liss, Inc .