DISRUPTION OF THE PIAL BASAL LAMINA DURING EARLY AVIAN EMBRYONIC-DEVELOPMENT INHIBITS HISTOGENESIS AND AXONAL PATHFINDING IN THE OPTIC TECTUM

Bacterial collagenase was injected into the ventricular cavity of the optic tectum of chick and quail embryos. Histological examination up t o 6 days after enzyme injection revealed that the collagenase disrupte d the pial basal lamina, which was evident by the fragmented distribut ion of basal lamina proteins at the pial surface of the midbrain and t he brainstem. Although the disrupted basal lamina was not reestablishe d at later stages of development, the pial basal lamina of the newly d eveloping neuroepithelium in the caudal part of the tectum was continu ous and intact. Western blot analysis showed that the collagenase dige sted collagens but spared noncollagenous proteins. The disruption of t he pial basal lamina caused the neuroepithelial cells to retract their pial end feet and caused tectal axons to exit the brain tissue into t he adjacent mesenchyme. The vertical migration of neuroblasts to the p ial layers of the tectum was inhibited, leading to a disruption of the tectal histogenesis. In the developing optic pathways, retinal axons were misguided at the optic chiasma and terminated in the head mesench yme instead of the tectum. None of the abnormalities in histogenesis a nd axonal pathways were observed when the basal lamina was disrupted a t a later stage of embryonic development. The present experiments demo nstrate that the pial basal lamina has an important function during br ain morphogenesis in restricting axons to the brain, providing an anch oring of the neuroepithelial cells to the pial surface, and allowing t he formation of a defined cytoarchitecture of the brain. (C) 1998 Wile y-Liss, Inc.