Gene expression oscillators can coordinate developmental events in space and time. In C. elegans, a gene expression oscillator directs rhythmic accumulation of ~25% of the transcriptome, and thus thousands of transcripts, presumably to control molting, a process of rhythmic skin regeneration. The mechanism and organization of the oscillator are not known. Here, we report that rhythmic RNA polymerase II recruitment to promoters produces transcript level oscillations. We identify BLMP-1,

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... us to the mammalian transcription repressor PRDM1, as a rhythmically accumulating transcription factor that is required for timely molting, and oscillatory gene expression. We propose a dual function for BLMP-1 in shaping oscillatory gene expression and coupling it to a set of direct targets, which ensures cuticular integrity. With mammalian PRDM1/BLIMP1 promoting regular cycles of postnatal hair follicle regeneration, our findings point to the possible existence of a fundamentally conserved clock mechanism in control of rhythmic skin regeneration.