Retinal vascular development is mediated by endothelial filopodia, a preexisting astrocytic template and specific R-cadherin adhesion.

A neonatal mouse retina developmental model was used to study endothelial cell guidance and subsequent formation of vascular patterns. Since most diseases that cause catastrophic loss of vision do so as a result of abnormal ocular angiogenesis, a better understanding of events regulating normal retinal vascular growth may provide insight into pathologic angiogenesis.Development of the retinal vasculature at various postnatal and embryonic time points was analyzed by collagen IV immunohistochemistry and staining with isolectin Griffonia simplicifolia. GFAP-GFP transgenic mice were used to evaluate the relationship between developing vessels and retinal glial cells. Immunolocalization of R-cadherin and intravitreous injection of R-cadherin-specific antibodies was performed to determine the role of R-cadherin during patterning of the superficial and deep retinal vascular plexuses.The characteristic honeycomb pattern of vessel formation observed in the superficial layer is a result of endothelial cell migration over a preexisting astrocytic template. Filopodial extensions associate with underlying astrocytes by protruding from the tips of endothelial cells at the migrating vascular front. Branching of vessels in the primary vascular plexus, as well as appropriate localization of the deep vascular network is mediated by R-cadherin, an adhesion molecule known to be involved in neuronal cell guidance. Injection of antibodies directed against R-cadherin prevents the normally extensive collateralization observed during formation of the superficial network. Injection of anti-R cadherin antibodies also dramatically affects vessels of the deep network. These vessels migrate beyond the normal turning point, penetrating into the deeper photoreceptor layer.. These studies suggest that angiogenesis and formation of vascular patterns in the retina may use many of the same developmental cues used by neurons in both the central and peripheral nervous systems. Furthermore, retinal vascular endothelial cell guidance mediated by filopodial extensions and neuronal guidance cues may represent a novel conceptual framework within which to study the establishment of vascular patterns in a variety of angiogenic systems.