BLOCKING N-CADHERIN FUNCTION DISRUPTS THE EPITHELIAL STRUCTURE OF DIFFERENTIATING NEURAL TISSUE IN THE EMBRYONIC CHICKEN BRAIN

The cell adhesion molecule N-cadherin is ubiquitously expressed in the early neuroepithelium, with strongest expression in the ependymal lin ing. We blocked the function of N-cadherin during early chicken brain development by injecting antibodies against N-cadherin into the tectal ventricle of embryos at 4-5 d of incubation [embryonic day 4 (E4)-E5] . N-cadherin blockage results in massive morphological changes in rest ricted brain regions. At approximately E6, these changes consist of in vaginations of pieces of the ependymal lining and the formation of neu roepithelial rosettes. The rosettes are composed of central fragments of ependymal lining, surrounded by an inner ventricular layer and an o uter mantle layer. Radial glia processes are radially arranged around the ependymal centers of the rosettes. The normal layering of the neur al tissue is thus preserved, but its coherent epithelial structure is disrupted. The observed morphological changes are restricted to specif ic brain regions such as the tectum and the dorsal thalamus, whereas t he Ventral thalamus and the pretectum are almost undisturbed. At E10-E 11, analysis of late effects of N-cadherin blockage reveals that in th e dorsal thalamus, gray matter is fragmented and disorganized; in the tectum, additional layers have formed at the ventricular surface. Toge ther, these results indicate that N-cadherin function is required for the maintenance of a coherent sheet of neuroepithelium in specific bra in regions. Disruption of this sheet results in an abnormal morphogene sis of brain gray matter.