N-CADHERIN AND R-CADHERIN EXPRESSION IN THE OPTIC-NERVE OF THE CHICKEN-EMBRYO

Cadherins are a family of molecules mediating Ca2+-dependent cell-cell adhesion in various tissues. N- and R-cadherin are expressed in the c hick embryonic CNS and differ in their expression pattern during devel opment. Here we focus on the differential expression of N- and R-cadhe rin in the early optic nerve. N-cadherin is expressed by the retinal n eurites growing through the optic nerve. R-cadherin is expressed by th e early optic nerve glia, which derives from the optic stalk neuroepit helium and corresponds to an immature form of the type-1 astrocyte des cribed in rat optic nerve. The close contact between the plasma membra nes of the retinal neurites and the optic nerve glia is believed to be important in guiding retinal axons through the optic nerve. Using neu roblastoma cell lines transfected with R-cadherin, we demonstrate that the N-cadherin-positive retinal axons can use R-cadherin as a substra te for axon elongation. These results suggest that the R-cadherin expr essed by the early optic nerve glia might provide a molecular substrat e for the growth of N-cadherin-positive retinal axons through the opti c nerve.