C. elegans molting requires rhythmic accumulation of the Grainyhead/LSF transcription factor GRH-1

C. elegans develops through four larval stages that are rhythmically terminated by molts, that is, the synthesis and shedding of a cuticular exoskeleton. Each larval cycle involves rhythmic accumulation of thousands of transcripts, which we show here relies on rhythmic transcription. To uncover the responsible gene regulatory networks (GRNs), we screened for transcription factors that promote progression through the larval stages and identified GRH-1, BLMP-1, NHR-23, NHR-25, MYRF-1, and BED-3. We further characterize GRH-1, a Grainyhead/LSF transcription factor, whose orthologues in other animals are key epithelial cell-fate regulators. We find that GRH-1 depletion extends molt durations, impairs cuticle integrity and shedding, and causes larval death. GRH-1 is required for, and accumulates prior to, each molt, and preferentially binds to the promoters of genes expressed during this time window. Binding to the promoters of additional genes identified in our screen furthermore suggests that we have identified components of a core molting-clock GRN. Since the mammalian orthologues of GRH-1, BLMP-1 and NHR-23, have been implicated in rhythmic homeostatic skin regeneration in mouse, the mechanisms underlying rhythmic C. elegans molting may apply beyond nematodes.

Automated summary

Development of C. elegans involves four larval stages terminated by molts, which are regulated by rhythmic transcription. Transcription factors GRH-1, BLMP-1, NHR-23, NHR-25, MYRF-1, and BED-3 were identified as components of the gene regulatory networks responsible for progression through larval stages. Depletion of GRH-1, a Grainyhead/LSF transcription factor, resulted in extended molt durations, impaired cuticle shedding, and larval death. GRH-1 is required for each molt and preferentially binds to promoters of genes expressed during this phase, suggesting it is part of a core molting-clock gene regulatory network. The findings may have implications beyond nematodes, as mammalian orthologues of GRH-1, BLMP-1, and NHR-23 are involved in rhythmic skin regeneration in mice.