RESTRICTED EXPRESSION OF R-CADHERIN BY BRAIN NUCLEI AND NEURAL CIRCUITS OF THE DEVELOPING CHICKEN BRAIN

Cadherins are a family of Ca2+-dependent cell-cell adhesion molecules regulating morphogenesis by a preferentially hemophilic binding mechan ism. We have previously shown that the expression of R-cadherin in the early chicken forebrain (embryonic days E3-E6) is restricted to parti cular neuromeres or parts of neuromeres. R-cadherin-expressing neurobl asts born in these areas accumulate in the mantle zone and aggregate i n particular (pro-)nuclei (Ganzler and Redies [1995] J. Neurosci. 15:4 157-4172). In the present-study, these findings are extended to later developmental stages (embryonic days E8, Ell, and E15). By immunohisto chemical and in situ hybridization techniques, we show that, at these stages of development, R-cadherin expression remains restricted to par ticular developing gray matter regions and fiber tracts. The R-cadheri n-positive fiber tracts connect some of the R-cadherin-positive gray m atter areas to form parts of particular neural circuits in the visual, auditory, somatosensory, and motor systems. Moreover, R-cadherin expr ession reflects the morphologic differentiation of gray matter regions . As brain nuclei become morphologically more distinct, the expression of R-cadherin shows a clearer demarcation of the nuclear boundaries. In addition, R-cadherin expression in some nuclei becomes restricted t o particular subregions or to clusters of neurons. In the cerebellum, R-cadherin is expressed in parasagittal stripes. These results suggest that R-cadherin expression reflects the functional and morphologic ma turation of gray matter structures and of information processing circu its in the embryonic chicken brain. (C) 1996 Wiley-Liss, Inc.