Constitutive expression and delayed light response of casein kinase Iε and Iδ mRNAs in the mouse suprachiasmatic nucleus

Casein kinase I epsilon (CKI epsilon) and casein kinase I delta (CKI delta) phosphorylate clock oscillating mPER proteins, and play a key role in the transcription (post)translation feedback loop that generates circadian rhythm. In the present study, the expression profiles of CKI epsilon of and CKI delta mRNAs were examined in the mice clock center, suprachiasmatic nucleus (SCN), Moderate levels of CKI epsilon and CKI delta mRNAs were constantly expressed in the SCN in both light, dark and constant dark conditions. This finding supports the hypothesis that CKI may form a constant threshold to the nuclear entry of mPER proteins as in the Drosophila homologue, double-time. Further, we demonstrated that the light exposure at subjective night induced a delayed increase in CKI epsilon and CKI delta mRNAs in the SCN, CKI epsilon and CKI delta proteins may play a role on light-induced phase-shift. (C) 2001 Wiley-Liss, Inc.