Positional Syntenic Cloning and Functional Characterization of the Mammalian Circadian Mutation <i>tau</i>

TLDR

The tau mutation is a semidominant autosomal allele that dramatically shortens the period length of circadian rhythms in Syrian hamsters. The study aimed to identify the tau locus by applying genetically directed representational difference analysis to delineate a conserved syntenic region in hamsters, mice, and humans. Using representational difference analysis, the authors mapped the tau locus to the casein kinase I epsilon gene, a homolog of Drosophila double‑time, within a conserved syntenic block shared by hamster, mouse, and human genomes. In vitro assays revealed that the tau mutant CKIepsilon enzyme has markedly reduced maximal velocity and autophosphorylation, is deficient in phosphorylating PERIOD proteins, and thus supports that tau is an allele of CKIepsilon that disrupts circadian regulation.

Abstract

The tau mutation is a semidominant autosomal allele that dramatically shortens period length of circadian rhythms in Syrian hamsters. We report the molecular identification of the tau locus using genetically directed representational difference analysis to define a region of conserved synteny in hamsters with both the mouse and human genomes. The tau locus is encoded by casein kinase I epsilon (CKIepsilon), a homolog of the Drosophila circadian gene double-time. In vitro expression and functional studies of wild-type and tau mutant CKIepsilon enzyme reveal that the mutant enzyme has a markedly reduced maximal velocity and autophosphorylation state. In addition, in vitro CKIepsilon can interact with mammalian PERIOD proteins, and the mutant enzyme is deficient in its ability to phosphorylate PERIOD. We conclude that tau is an allele of hamster CKIepsilon and propose a mechanism by which the mutation leads to the observed aberrant circadian phenotype in mutant animals.