High Expression of the γ5 Isoform of G Protein in Neuroepithelial Cells and Its Replacement of the γ2 Isoform During Neuronal Differentiation in the Rat Brain

Abstract

: High concentrations of G proteins, which include multiple isoforms of each subunit, α, β, and γ, 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 γ₂ as well as G_oAα, G_oBα, and β₂ were low in early embryogenesis and then increased, whereas expression of γ₅, in contrast, was initially high followed by a drop, with only very low levels observed throughout postnatal development. Among the other isoforms, G_i1α, G_sα-short, G₁₂α, G₁₃α, β₄, γ₃, γ₇, and γ₁₂ were present in the embryonic brain at low levels, but their levels markedly increased after birth. In contrast, the levels of G_i2α, G_sα-long, G_q/11α, and β₁ were essentially constant throughout. Immunohistochemical staining of the brain vesicles in the embryos showed γ₅ to be specifically expressed in the proliferative region of the ventricular zone, whereas γ₂ 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 γ₂ and a decrease of γ₅, the major isoform in the undifferentiated state. These results suggest that neuronal differentiation is responsible for the on/off switch of the expression of γ₂ and γ₅ subunits.