A mammalian ortholog of Drosophila timeless, highly expressed in SCN and retina, forms a complex with mPER1

Background: It is now becoming clear that the circadian rhythm of behaviours and hormones arises from a rhythm at the level of gene expression, and that mammals and Drosophila essentially use homologous genes as molecular gears in the control of circadian oscillation. In Drosophila, the period and timeless genes form a functional unit of the clock and its autoregulatory feedback loop for circadian rhythm. However, in mammals, the counterpart of timeless has not been found. Results: We have isolated a mammalian homologue of timeclass, mTim, from the mouse brain. mTim is highly expressed, with a weak or absent rhythm in the suprachiasmatic nucleus, the mammalian circadian centre, In the retina, mTim mRNA was found to be expressed with a circadian rhythm, and a particularly robust cycle was observed in the presence of light/dark cycles. We demonstrated that mTIM physically associates with mPER1 in vitro and in the nuclei of cultured COS7 cells. Conclusions: We have reported the isolation of the mouse timeless cDNA, the expression of the mTim mRNA and an interaction of mTIM with mPER1, These results indicate that the autoregulatory feedback mechanism of circadian oscillation of the period gene may also be conserved in mammals.