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

Using in situ hybridization, we have examined mRNA expression for five isoforms of protein kinase C (PKC alpha, beta1, beta2, gamma and epsilon) in the rat suprachiasmatic nuclei (SCN) and other central site 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 Ca2+-dependent (alpha, beta1, beta2 and gamma), but not for one of the Ca2+-independent PKCs (epsilon). PKC alpha 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 beta1, beta2 and gamma show a biphasic rhythm in the SCN with peaks at early subjective day, CT 0, and early subjective night, CT 14. The four Ca2+-dependent isoforms may therefore subserve phase-related functions within the SCN at the onset of subjective night and, in the case of beta1, beta2 and gamma, also at the onset of subjective day. Variation in the mRNAs for PKC beta1 and gamma (but not for alpha, beta2 or epsilon) 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 beta1 and gamma 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.