Expression of vascular endothelial growth factor receptors Flt-1 and Flk-1 in embryonic rat forebrain

To define better the putative targets of vascular endothelial growth factor (VEGF) in the developing brain we have examined the ontogeny of the two VEGF tyrosine kinase receptors, Flt-1 and Flk-1, in embryonic rat forebrain. Semiquantitative reverse transcriptase-polymerase chain reaction and immunoblot analysis showed expression of both receptors in the forebrain at all embryonic ages studied. Messenger RNAs for Flt-1 and Flk-1 appeared along most of the ventricular zone of the lateral ventricle as early as embryonic day (E) 13. Messages gradually became restricted to a limited ventricular zone at E20. Expression of VEGF receptors was also observed in the cerebral cortex, hippocampus and thalamic nuclei. In the cortex, expression of mRNA for both receptors was detected in the cortical plate around E15, and became relatively weak and restricted to the deeper layers of the cortical plate at E20. These data suggest that VEGF may contribute to early developmental processes including the proliferation, differentiation and maturation of specific neuronal populations via specific VEGF receptors in the developing rat forebrain.