Blood vessels are an essential, but largely passive infrastructure for organ development, supplying metabolic provisions to the dividing cells. But, in September 28 on line Science, Eckhard Lammert and colleagues from Howard Hughes Medical Institute, Harvard University, show that during pancreatic organogenesis blood vessels not only provide metabolic provisions but also offer inductive signals for organ development.

Lammert et al. performed cell culture experiments with embryonic mouse tissue and found that endothelium from blood vessels induced insulin expression in isolated endoderm. They then removed the dorsal aorta in Xenopus embryos and recorded a failure of insulin expression in vivo. In addition, transgenic mice overexpressing vascular endothelial growth factor showed ectopic vascularization in the posterior foregut, resulting in ectopic insulin expression and islet hyperplasia (Science 2001, 10.1126/science.1064344).

This mechanism may prevent the pancreas, and possibly other organs, from developing until an adequate blood-supply system is in...

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