CADHERIN EXPRESSION IN THE RETINA AND RETINOFUGAL PATHWAYS OF THE CHICKEN-EMBRYO

The expression of two calcium-dependent adhesion molecules of the cadh erin superfamily (cadherin-6B and cadherin-7) was mapped in the embryo nic neural retina and retinofugal pathways of the chicken embryo and c ompared with the expression of R-cadherin, N-cadherin, and B-cadherin, studied previously. Whereas B-cadherin is only found in Muller glia, the other four cadherins are each expressed by specific subpopulations of retinal neurons. For example, different (but partly overlapping) p opulations of bipolar cells express R-cadherin, cadherin-6B, and cadhe rin-7. Cadherin-6B and cadherin-7 are also expressed by subsets of ama crine cells. In the inner plexiform layer, cadherin-6B and cadherin-7 immunoreactivities are restricted to specific sublaminae associated wi th synapsin-I-positive nerve terminals. In addition, cadherin-6B and c adherin-7 are expressed by a subset of ganglion cells that project to several retinorecipient nuclei forming part of the accessory optic sys tem (e.g., nucleus of the basal optic root and external pretectal nucl eus). Together with their connecting fiber tracts, these nuclei also e xpress cadherin-6B and cadherin-7 in their neurons and neuropile. The expression patterns of the two cadherins overlap but show distinct dif ferences. Some other visual nuclei express cadherin-7 but not cadherin -6B. The expression patterns differ from those previously described fo r N- and R-cadherin. Together, these results demonstrate that cadherin s could provide a system of adhesive cues that specify developing reti nal circuits and other functional connections and subsystems in the em bryonic chicken visual system. (C) 1998 Wiley-Liss, Inc.