Induction of erythropoiesis in the amphibian embryo

Germ-layer formation and differentiation of specialized tissues in vertebrate embryogenesis is a multistep mechanism that is mediated by different growth factors (or growth factor-related molecules). We have investigated various differentiation factors that contribute to mesoderm formation in amphibian embryos and analyzed the formation of blood islands during embryogenesis and in ectodermal explants that have been incubated with mesoderm inducing factors. Erythropoiesis in these explants is demonstrated by whole mount in situ hybridization using an embryonic alpha-globin probe. Furthermore, we have isolated several transcription factors of the fork head family and analyzed whether they are involved in the pathway leading to hematopoietic cells. One of these factors, termed Xenopus fork head (XFD)-2, is transcribed in blastula stage embryos for a limited time period in dorsal and ventral mesoderm. Moreover, the target sequence of this factor is found to be present within the upstream sequences of many genes that are expressed in mesoderm-derived tissues.