Basement membrane-dependent survival of retinal ganglion cells

PURPOSE. The present study investigates the role of the inner limiting membrane (ILM) in the survival of ganglion cells (GCs) in embryonic chick and mouse retina. METHODS. In chick embryos, the ILM was enzymatically removed at embryonic day (E)5 and E7 in ovo, and GCs were counted over the following 7 days of incubation. In mice, the ILM ruptured early in development due to a targeted mutation of laminin-gamma1. The number of surviving GCs in late embryonic homozygous mutant mice was compared to GC counts in heterozygotic and nonmutant siblings. The survival of GCs was also assayed in vitro, using the ILM as a substrate. RESULTS. When the ILM was removed in E5 chick embryos, almost all GCs underwent apoptosis by E10. GC apoptosis was prevented by reconstituting the ILM shortly after its disruption. Apoptosis of retinal GCs also occurred in mouse embryos with a fragmented ILM. ILM disruption in both chick and mice not only affected GC survival but also led to the retraction of the end-feet processes of radial cells from the GC layer. In vitro, GCs thrived better on substrates of radial cell end feet than on plain ILM, indicating that the contact with the end feet is more important than the presence of the ILM for GC survival. CONCLUSIONS. The radial cell end feet are the natural substrate for GCs and are essential for their survival. The importance of the ILM lies in its function to anchor the radial end feet to the vitreal surface of the retina.