Analysis of clock proteins in mouse SCN demonstrates phylogenetic divergence of the circadian clockwork and resetting mechanisms

The circadian clock in the suprachiasmatic nuclei (SCN) is comprised of a c ell-autonomous, autoregulatory transcriptional/translational feedback loop. Its molecular components include three period and two cryptochrome genes. We describe circadian patterns of expression of mPER2 and mPER3 in the mous e SCN that are synchronous to those for mPER1, mCRY1, and mCRY2. Coimmunopr ecipitation experiments demonstrate in vivo associations of the SCN mPER pr oteins with each other and with the mCRY proteins, and of mCRY proteins wit h mTIM, but no mPER/mTIM interactions. Examination of the effects of weak a nd strong resetting light pulses on SCN clock proteins highlights a central role for mPER1 in photic entrainment, with no acute light effects on eithe r the mCRY or mTIM proteins. These crock protein interactions and photic re sponses in mice are divergent from those described in Drosophila.