Casein Kinase 1 Delta Regulates the Pace of the Mammalian Circadian Clock

Abstract

Both casein kinase 1 delta (CK1δ) and epsilon (CK1ε) phosphorylate core clock proteins of the mammalian circadian oscillator. To assess the roles of CK1δ and CK1ε in the circadian clock mechanism, we generated mice in which the genes encoding these proteins (Csnk1d and Csnk1e, respectively) could be disrupted using the Cre-loxP system. Cre-mediated excision of the floxed exon 2 from Csnk1d led to in-frame splicing and production of a deletion mutant protein (CK1δ^Δ2). This product is nonfunctional. Mice homozygous for the allele lacking exon 2 die in the perinatal period, so we generated mice with liver-specific disruption of CK1δ. In livers from these mice, daytime levels of nuclear PER proteins, and PER-CRY-CLOCK complexes were elevated. In vitro, the half-life of PER2 was increased by ∼20%, and the period of PER2::luciferase bioluminescence rhythms was 2 h longer than in controls. Fibroblast cultures from CK1δ-deficient embryos also had long-period rhythms. In contrast, disruption of the gene encoding CK1ε did not alter these circadian endpoints. These results reveal important functional differences between CK1δ and CK1ε: CK1δ plays an unexpectedly important role in maintaining the 24-h circadian cycle length.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/ .

ACKNOWLEDGMENTS

We thank Stephen N. Jones and the staff of the Transgenic Animal Modeling facility for assistance in generating the targeted mice and Haley Conde for assessing lethality in CK1δ^Δ2/Δ2 mice. The UMMS Transgenic Animal Modeling facility is supported in part by Diabetes and Endocrinology Research Center grant DK32520.

This study was supported by grants from the National Institute of Neurological Diseases and Stroke (R01 NS047141 to S.M.R. and R21 NS051458 and R01 NS056125 to D.R.W.). E.N. was supported by a long-term fellowship from the Human Frontier Science Program, R.D. was supported in part by DFG grant 525/2-1, and J.P.D. was supported in part by NIH NRSA F32 GM074277.

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