Delay in Feedback Repression by Cryptochrome 1 Is Required for Circadian Clock Function

SummaryDirect evidence for the requirement of delay in feedback repression in the mammalian circadian clock has been elusive. Cryptochrome 1 (Cry1), an essential clock component, displays evening-time expression and serves as a strong repressor at morning-time elements (E box/E′ box). In this study, we reveal that a combination of day-time elements (D box) within the Cry1-proximal promoter and night-time elements (RREs) within its intronic enhancer gives rise to evening-time expression. A synthetic composite promoter produced evening-time expression, which was further recapitulated by a simple phase-vector model. Of note, coordination of day-time with night-time elements can modulate the extent of phase delay. A genetic complementation assay in Cry1−/−:Cry2−/− cells revealed that substantial delay of Cry1 expression is required to restore circadian rhythmicity, and its prolonged delay slows circadian oscillation. Taken together, our data suggest that phase delay in Cry1 transcription is required for mammalian clock function.

Graphical AbstractFigure optionsDownload high-quality image (186 K)Download as PowerPoint slideHighlights
► A combination of day-time and night-time produces delayed evening-time expression
► A simple phase-vector model can be used to design an array of delayed expressions
► Substantial delay in feedback repression is required for mammalian clock function
► Prolonged delay in feedback repression slows circadian oscillation