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

The expression of angiopoietin I and 2 (ang I and 2) and their receptor tie -1 was studied in avian embryos using in situ hybridization, Ang I was tran scribed in the mesenchymal cells surrounding venous endothelium expressing tie-2. By contrast, ang2 was transcribed around arteries in which the endot helium 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. (C) 2001 Elsevier Science Ireland Ltd. All rights reserve d.