Fig. 6. Diagram showing interactions between different retinal cell types during retinal vasculature development. Hypoxic retinal astrocytes secrete VEGF and induce blood vessel growth. This leads to increased oxygen tension, which acts as a negative feedback on the hypoxia response in retinal astrocytes. Blood vessels also inhibit proliferation and stimulate maturation of retinal astrocytes. It is possible that these latter interactions are also mediated by oxygen.