Cloning and expression pattern of EPAS1 in the chicken embryo. Colocalization with tyrosine hydroxylase.

EPAS1 is a hypoxia-inducible transcription factor, highly expressed in vasculature and recently shown to be necessary for catecholamine production during embryogenesis. We report here the cloning and detailed expression pattern of this factor in the chicken embryo. We show that chicken EPAS1 presents an overall identity of 76% with the human sequence and that it is strongly expressed in the blood vessel wall, mostly in endothelial cells, but also in vascular smooth muscle cells. Moreover, we report non-vascular expression sites: liver, kidney, and, quite interestingly, cells of the sympathetic nervous system where EPAS1 is coexpressed with one of its putative target genes, the tyrosine hydroxylase. EPAS1 could therefore represent the link between the vascular system and the sympathetic nervous system, both sensitive to hypoxia.