Embryo, mouse embryonic induction

To establish more directly that visceral endoderm is required for induction of hematopoiesis in the gastrulating embryo, tissue recombination experiments were performed. A semi-quantitative RT-PCR protocol was used to assay for activation of the endogenous mouse embryonic p-like globin genes (15), Ectoderm and VE layers from individual embryos were cultured separately or in combination for two to four days. RNA was prepared from individual explants and analyzed for embryonic globin gene activation using the RT-PCR assay. 

In nearly all vertebrate animals, embryonic blood development begins during gastrulation and results from the induction of extraembryonic mesoderm to form hematopoietic tissue. In the mouse, these events are initiated at around 6.5 days post coitum (p.c.) and lead to the formation of the yolk sac, a bilaminar membrane composed of adjacent mesodermal and primitive endodermal cell layers (reviewed in ref. 3). The yolk sac is an extraembryonic tissue which surrounds the entire embryo. Though it will not contribute cells directly to the fully formed animal, its fimction is essential to normal development (reviewed in refs. 3,6). 

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