High expression of the gamma5 isoform of G protein in neuroepithelial cells and its replacement of the gamma2 isoform during neuronal differentiation in the rat brain.

High concentrations of G proteins, which include multiple isoforms of each subunit, alpha, beta, and gamma, are expressed in the adult brain. In this study, we concentrated attention on changes of these isoforms during embryonic development in the rat brain. Concentrations of gamma2 as well as GoAalpha, GoBalpha, and beta2 were low in early embryogenesis and then increased, whereas expression of gamma5, in contrast, was initially high followed by a drop, with only very low levels observed throughout postnatal development. Among the other isoforms, Gi1alpha, G(s)alpha-short, G12alpha, G13alpha, beta4, gamma3, gamma7, and gamma12 were present in the embryonic brain at low levels, but their levels markedly increased after birth. In contrast, the levels of Gi2alpha, G(s)alpha-long, Gq/11alpha, and beta1 were essentially constant throughout. Immunohistochemical staining of the brain vesicles in the embryos showed gamma5 to be specifically expressed in the proliferative region of the ventricular zone, whereas gamma2 was mainly present in differentiated neuronal cells of the marginal zone. Furthermore, differentiation of P19 mouse embryonal carcinoma cells to neuronal cells with retinoic acid induced the expression of gamma2 and a decrease of gamma5, the major isoform in the undifferentiated state. These results suggest that neuronal differentiation is responsible for the on/off switch of the expression of gamma2 and gamma5 subunits.