Expression of C-ETS1 in early chick embryo mesoderm: relationship to the hemangioblastic lineage.

In situ hybridization was used to detect the expression of the c-ets1 protooncogene during formation of the germ layers in the chick blastodisc. c-ets1 transcripts were present during the gastrulation process, i.e. when the mesodermal cells invaginated. The expression became down-regulated in lateral plate and the dorsal part of the somites while an intense signal was retained in the intermediate cell mass. When vasculogenesis started, c-ets1 transcripts labelled blood islands and endothelial cells. Before the mesoderm split, transcripts were present over the whole layer, more abundant however on its ventral side in contact with the endoderm. After the mesoderm split, silver grains became distributed asymmetrically: splanchnopleural mesoderm expressed c-ets1 messengers all over while expression in the somatopleural mesoderm was restricted to a few profiles corresponding to small endothelial cell groups. This asymmetrical distribution of c-ets1 transcripts is in agreement with our previous experimental findings establishing the different potentialities of the two mesodermal layers regarding hemopoiesis, vasculogenesis and angiogenesis processes.