Endogenous circadian reporters reveal critical consequences of diverse novel mutations in clock genes

Adverse consequences from having a faulty circadian clock include compromised sleep quality and poor performance in the short-term, and metabolic diseases and cancer in the long-term. However, our understanding of circadian disorders is limited by the incompleteness of our molecular models and our dearth of defined mutant models. Because it would be prohibitively expensive to develop live animal models to study the full range of complicated clock mechanisms, we developed Per1-luc and Per2-luc endogenous circadian reporters in a validated clock cell model, U2OS, where the genome can be easily manipulated, and functional consequences of mutations can be accurately studied. Using these reporter cells, we uncovered critical differences between two paralogs of Per and Cry, as well as working principles of the circadian phosphotimer. Our system can be used as an efficient platform to study circadian sleep disorders such as Familial Advanced Sleep Phase Syndrome (FASPS) and their underlying molecular mechanisms.