EXPRESSION OF C-ETS1 IN EARLY CHICK-EMBRYO MESODERM - RELATIONSHIP TOTHE 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 blastod isc. 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 a n intense signal was retained in the intermediate cell mass. When vasc ulogenesis started, c-ets1 transcripts labelled blood islands and endo thelial cells. Before the mesoderm split, transcripts were present ove r the whole layer, more abundant however on its ventral side in contac t with the endoderm. After the mesoderm split, silver grains became di stributed asymmetrically: splanchnopleural mesoderm expressed c-ets1 m essengers all over while expression in the somatopleural mesoderm was restricted to a few profiles corresponding to small endothelial cell g roups. This asymmetrical distribution of c-ets1 transcripts is in agre ement with our previous experimental findings establishing the differe nt potentialities of the two mesodermal layers regarding hemopoiesis, vasculogenesis and angiogenesis processes.