Blood not only sustains and oxygenates organs--two reports show how blood vessel endothelium plays important roles in organ development. Lammert et al. found that the endothelium supplies signals that are necessary for pancreatic differentiation and insulin expression. Removal of the dorsal aorta in Xenopus embryos led to a failure in insulin expression, whereas vascularization in transgenic mice in the posterior foregut led to ectopic islet formation and insulin expression. Matsumoto et al. used flk-1 mutant mice, an embryo tissue explant system, and an angiogenesis inhibitor to show that endothelial cells promote liver development before vascular blood flow. Bahary and Zon provide a Perspective.
N. Bahary, L. I. Zon, Endothelium--Chicken soup for the endoderm. Science 294, 530-531 (2001). [Full Text]