Promoter Frame Position Affects Strength and Nature of Circadian Oscillations in hPER2 Luciferase Reporters

The PER2 gene is a crucial component responsible for the proper functioning of the mammalian core circadian clock. The circadian nature of the murine Per2 (mPer2) promoter's activity has been thoroughly investigated to identify important elements responsible for its oscillatory behavior; however, its human counterpart has not. While there are similarities between murine and human core clocks, there are differences and unconserved elements between their promoter sequences that may influence the nature of rhythms. Further, most studies to date have used murine-based sequences in human cell lines. To fully understand the role(s) of and factors involved in the human PER2 (hPER2) gene, human-derived sequences should be used. To this end, we developed two lentiviral luciferase reporters in well-established, circadian model U2OS cells using different hPER2 promoter regions. Their rhythmic nature was compared to that of the standard mPer2 promoter reporter. We found that hPER2 reporters exhibited stronger oscillations than the mPer2 reporter, and that the frame of the hPER2 promoter affected the period and phase. This work introduces a human sequence-based PER2 promoter in U2OS cells, which should be used for further in vitro tracking of hPER2 activity and to understand PER2 gene dynamics, in lieu of the murine iteration.