The expressions of epidermal growth factor receptor mRNA and protein gene product 9.5 in developing rat brain

To clarify the role of epidermal growth factor receptor (EGFR) in brain development, especially with regard to neuron differentiation, EGFR mRNA expression was studied by in situ hybridization in embryonic day (E)12, E16, postnatal day (P)1, P4, P15, P29 and adult rat, using protein gene product (PGP) 9.5 as a neuron marker. The primary germinal zone (neuroepithelium) expressed neither PGP 9.5 immunoreactivity (IR) nor EGFR mRNA. In the developing brain, cells expressing EGFR mRNA but not PGP 9.5 IR were found in the secondary germinal zone such as the subventricular zone and cerebellar external germinal layer, the cortical plate and, in later stage animals, the fiber tracts. Cells expressing both EGFR mRNA and PGP 9.5 IR appeared in a differentiating field. In the adult brain, strong EGFR mRNA expression was observed in Purkinje cells, Golgi cells, some hippocampal cells and neurons of the diencephalon, pontine and medullary nuclei, and weak expression was seen in neurons of the cerebral cortex. These results suggest that EGFR is related to the process of differentiation and maturation of neurons and the maintenance of some types of adult neurons.