Multiple alternative splicings of the mammalian circadian clock gene period mRNAs

摘要

The molecular basis of the circadian clock indicates that the clock is an autoregulatory feedback loop in which the clock protein PERIOD periodically inhibits transcription of its own period gene. We have recently identified a distinct alternative splicing mechanism in several insect species and proposed that period splicing variants play an important role to drive circadian oscillation. In the present study, we attempted to identify the alternative splicing variants for each period among three different subtypes in mammalian species (human and mouse). A specific PCR-based cloning method was performed for cDNAs prepared from mRNAs isolated from mouse SCN and human brains. Eventually, we succeeded in identification of several alternative splicing sites: i.e., 5 sites in per1, 1 in per2, and 5 in per3. Except for 2 sites of per3 mRNA, all of these alternative splicing sites are found to be conserved between human and mouse per genes. These novel period isoforms were found to have a premature termination codon (PTC), which may bring about an immediate degradation of the particular mRNA. A high conservation of a PTC between human and mouse period mRNAs clearly indicates the importance of the NMD system as a posttranscriptional regulation of period mRNAs in these circadian systems.