We utilized the murine cerebellum to analyze the expression of G-proteins during vertebrate neural differentiation. Combining reverse transcription-polymerase chain reaction and immunocytochemistry, we monitored the expression and cellular localization, within the nascent cerebellar cortex, of G-proteins subunits known to mediate signal transduction in the adult cerebellum. The mRNAs encoding subunits Galphaq, Galphao, Galphai-2, and Galphaz are expressed in the cerebellar anlage at least from embryonic day 14 onward, and relative levels of these mRNAs do not change appreciably from E14 to adulthood. Galphao, Galphaz, and Galphai-2 could be localized to granule cell neuroblasts and postmigratory, mature granule cells, but not to early postmitotic, premigratory, and migrating granule neurons. All of the Galpha subunits analyzed could also be localized to the cell somata of postmitotic Purkinje neurons, irrespective of age. In contrast, Purkinje cell dendrites stained for Galphao only up to postnatal day 8, dendritic immunoreactivity for Galphaz increased during dendritogenesis, and appreciable levels of Galphai-2 and Galphaq were seen in Purkinje cell dendrites only transiently during the 2nd and 3rd postnatal week. Of the G-beta and -gamma subunits analyzed (beta1, beta2, gamma2, gamma3, gamma5, and gamma7), only expression of gamma3 varied with development. It could be localized to Purkinje cell somata and dendrites in early postnatal, but not in adult animals. These changes in the cellular distribution and subcellular segregation of G-proteins are correlated to tangible aspects of cerebellar cortical histogenesis and suggest a role for G-protein-mediated signaling in their mechanistic implementation.