Cadherin expression by embryonic divisions and derived gray matter structures in the telencephalon of the chicken

The expression of three cadherins (cadherin-6B, cadherin-7, and R-cadherin) was studied by immunohistochemistry in the telencephalon of chicken embryo s at intermediate stages of development (11 and 15 days of incubation). Exp ression patterns were related to cytoarchitecture and to previously publish ed data on functional connections and on the expression of gene regulatory proteins. Our results indicate that, like in other regions of the embryonic chicken brain, the expression of each cadherin is restricted to parts of e mbryonic divisions as well as to particular nuclei, areas or their subdivis ions. The expression patterns are largely complementary with partial overla p. The regional expression of the cadherins respects the boundary between t he pallium and the subpallium as well as between various pallial and subpal lial subdivisions. Novel subdivisions were found in several telencephalic a reas. For example, subjacent to the hyperstriatum, the neostriatum contains multiple islands of cells with a profile of cadherin expression that diffe rs from the surrounding matrix ("island fields"). Moreover, the expression of each cadherin is apparently associated with parts of intratelencephalic neural circuits and of thalamopallial and basal ganglia pathways. These res ults support a role for cadherins in the aggregation and differentiation of gray matter structures within embryonic brain divisions. The cadherin immu nostaining patterns are interpreted in the context of a recently proposed d ivisional scheme of the avian pallium that postulates medial, dorsal, later al, and ventral divisions as complete radial histogenetic units (Puelles et al. [2000]). J. Comp. Neurol. 438:253-285, 2001. (C) 2001 Wiley-Liss, Inc.