Cadherin expression in the retina and retinofugal pathways of the chicken embryo.

The expression of two calcium-dependent adhesion molecules of the cadherin superfamily (cadherin-6B and cadherin-7) was mapped in the embryonic neural retina and retinofugal pathways of the chicken embryo and compared with the expression of R-cadherin, N-cadherin, and B-cadherin, studied previously. Whereas B-cadherin is only found in Miller glia, the other four cadherins are each expressed by specific subpopulations of retinal neurons. For example, different (but partly overlapping) populations of bipolar cells express R-cadherin, cadherin-6B, and cadherin-7. Cadherin-6B and cadherin-7 are also expressed by subsets of amacrine cells. In the inner plexiform layer, cadherin-6B and cadherin-7 immunoreactivities are restricted to specific sublaminae associated with synapsin-I-positive nerve terminals. In addition, cadherin-6B and cadherin-7 are expressed by a subset of ganglion cells that project to several retinorecipient nuclei forming part of the accessory optic system (e.g., nucleus of the basal optic root and external pretectal nucleus). Together with their connecting fiber tracts, these nuclei also express cadherin-6B and cadherin-7 in their neurons and neuropile. The expression patterns of the two cadherins overlap but show distinct differences. Some other visual nuclei express cadherin-7 but not cadherin-6B. The expression patterns differ from those previously described for N- and R-cadherin. Together, these results demonstrate that cadherins could provide a system of adhesive cues that specify developing retinal circuits and other functional connections and subsystems in the embryonic chicken visual system.