N- and R-cadherin expression in the optic nerve of the chicken embryo.

Cadherins are a family of molecules mediating Ca(2+)-dependent cell-cell adhesion in various tissues. N- and R-cadherin are expressed in the chick embryonic CNS and differ in their expression pattern during development. Here we focus on the differential expression of N- and R-cadherin in the early optic nerve. N-cadherin is expressed by the retinal neurites growing through the optic nerve. R-cadherin is expressed by the early optic nerve glia, which derives from the optic stalk neuroepithelium and corresponds to an immature form of the type-1 astrocyte described in rat optic nerve. The close contact between the plasma membranes of the retinal neurites and the optic nerve glia is believed to be important in guiding retinal axons through the optic nerve. Using neuroblastoma cell lines transfected with R-cadherin, we demonstrate that the N-cadherin-positive retinal axons can use R-cadherin as a substrate for axon elongation. These results suggest that the R-cadherin expressed by the early optic nerve glia might provide a molecular substrate for the growth of N-cadherin-positive retinal axons through the optic nerve.