Morphology of mouse egg cylinder development in vitro: A light and electron microscopic study

Abstract

Abstract Phase contrast, light, and electron microscopy showed that mouse egg cylinder development from the blastocyst stage in vitro closely resembled the egg cylinder stages of the fourth to seventh days of gestation in vivo. Primary endoderm and ectoderm formed on day 2 of culture, and on day 3 visceral and parietal endoderm could be distinguinshed. Mesoderm formed on days 6.5‐7 by delaminating from a thickened region of embryonic ectoderm. Extraembryonic ectoderm developed as single layer of cuboidal epithelial cells that appeared to originate from polar trophoblast cells. By day 8 of culture egg cylinders had an ectoplacental cavity, an exocoelom, a proamnionic cavity, a chorion, and an allantois and resembled egg cylinders in vivo after seven days' gestation. However, cultured blastocysts took longer to develop to these egg cylinder stages than embryos in vivo (8 days in vitro vs. 4 days in vivo) and were shorter (600 μm in vitro vs. 700 μm in vivo). The development of mural trophoblast, parietal endoderm, Reichert's membrane, and ectoplacental cone also differed from that of their counterparts in vivo. Nevertheless, because the egg cylinder itself, which produces the embryo proper, develops similarly in vitro as in vivo, we suggest that cultured mouse blastocysts provide an excellent model for studies on early postimplantation embryogenesis.