Selective expression of angiopoietin 1 and 2 in mesenchymal cells surrounding veins and arteries of the avian embryo.

The expression of angiopoietin1 and 2 (ang1 and 2) and their receptor tie-2 was studied in avian embryos using in situ hybridization. Ang1 was transcribed in the mesenchymal cells surrounding venous endothelium expressing tie-2. By contrast, ang2 was transcribed around arteries in which the endothelium down-regulated tie-2 mRNA. The aorta and large arteries of the heart outflow tract were never surrounded by ang2 positive cells and maintained tie-2 expression.