Expression of the Flk1 receptor and its ligand VEGF in the developing chick central nervous system.

The receptor tyrosine kinase Flk1 is known to mediate signals of vascular endothelial growth factor (VEGF) during vasculogenesis and hematopoiesis. We demonstrate by in situ hybridization that in addition to endothelial cells, chick Flk1 mRNA is also expressed in the notochord and in the neural epithelial cells of the ventral diencephalon, hindbrain, and spinal cord. During the development of the avascular chick retina, Flk1 mRNA is detected in the proliferative zone of the neural epithelium, whereas the VEGF ligand is expressed by differentiated retinal ganglion cells. Moreover, expression patterns of Flk1 in the retina are conserved among chick, quail and mouse, thus suggesting a distinct role of Flk1 and VEGF in the development of the vertebrate central nervous system. Copyright 2003 Elsevier Science B.V.