PROLIFERATIVE ZONES OF POSTNATAL RAT-BRAIN EXPRESS EPIDERMAL GROWTH-FACTOR RECEPTOR MESSENGER-RNA

Two ligands for the epidermal growth factor receptor (EGF-R), EGF and transforming growth factor-alpha (TGF alpha), have recently been shown to influence the proliferation, differentiation or survival of divers e populations of fetal and neonatal neuronal and glial cells in cultur e. These findings suggest that EGF, TGF alpha, or another EGF-R ligand play a role in the regulation of similar cellular developmental event s in vivo. In the present study, in situ hybridization with an S-35-la beled cRNA probe was used to determine if mRNA for EGF-R is expressed in two principal germinal zones of the postnatal rat brain, the forebr ain ventricular/subventricular zone and the cerebellar external granul e layer. Cells labeled with the EGF-R cRNA were distributed throughout the subventricular zone, particularly in the dorsolateral aspect, fro m birth to adulthood, although the numbers of labeled cells as well as the density of hybridization diminished during development. In the de veloping cerebellum, virtually all cells in the external granule layer were densely labeled with the EGF-R cRNA, as were numerous perikarya throughout the molecular layer. EGF-R mRNA was also transiently expres sed at lower levels by neurons of the internal granule layer and deep cerebellar nuclei. By adulthood, cerebellar expression of EGF-R mRNA w as not detected. These results demonstrate prominent expression of EGF -R mRNA within germinal zones of the developing brain and indicate a r ole for EGF, TGF alpha, or another member of the EGF-related family in regulating the activities of neuronal and glial progenitor cells in v ivo.