Variation in the expression of the mRNA for protein kinase C isoforms in the rat suprachiasmatic nuclei, caudate putamen and cerebral cortex

Abstract

Using in situ hybridization, we have examined mRNA expression for five isoforms of protein kinase C (PKC α, β1, β2, γ and ε) in the rat suprachiasmatic nuclei (SCN) and other central sites during the 24 h cycle. The signal for each of these isoforms shows a marked local density within the SCN. In the absence of photic cues, there are changes in the expression of the mRNAs for the four isoforms that are Ca 2+-dependent ( α, β1, β2 and γ), but not for one of the Ca 2+-independent PKCs ( ε). PKC α mRNA exhibits a monophasic rhythm of expression in the SCN with a peak at early subjective night, circadian time (CT) 14. In contrast, the mRNAs for PKC β1, β2 and γ show a biphasic rhythm in the SCN with peaks at early subjective day, CT 0, and early subjective night, CT 14. The four Ca 2+-dependent isoforms may therefore subserve phase-related functions within the SCN at the onset of subjective night and, in the case of β1, β2 and γ, also at the onset of subjective day. Variation in the mRNAs for PKC β1 and γ (but not for α, β2 or ε) is also found in the caudate putamen and in the cingulate and parietal cortex; the biphasic pattern of expression for these mRNAs is precisely in phase with that observed in the SCN. The β1 and γ isoforms may therefore contribute to temporally regulated functions at sites outside the SCN. The present observations raise the possibility that receptor-mediated regulation of circadian functions is modulated or even gated by circadian changes in intracellular components that participate in distinct signal cascades.