LIN-42/PERIOD Controls Cyclical and Developmental Progression of C. elegans Molts

BACKGROUND Biological timing mechanisms that integrate cyclical and successive processes are not well understood. C. elegans molting cycles involve rhythmic cellular and animal behaviors linked to the periodic reconstruction of cuticles. Molts are coordinated with successive transitions in the temporal fates of epidermal blast cells, which are programmed by genes in the heterochronic regulatory network. It was known that juveniles molt at regular 8-10 hr intervals, but the anticipated pacemaker had not been characterized. RESULTS We find that inactivation of the heterochronic gene lin-42a, which is related to the core circadian clock gene PERIOD (PER), results in arrhythmic molts and continuously abnormal epidermal stem cell dynamics. The oscillatory expression of lin-42a in the epidermis peaks during the molts. Further, forced expression of lin-42a leads to anachronistic larval molts and lethargy in adults. CONCLUSIONS Our results suggest that rising and falling levels of LIN-42A allow the start and completion, respectively, of larval molts. We propose that LIN-42A and affiliated factors regulate molting cycles in much the same way that PER-based oscillators drive rhythmic behaviors and metabolic processes in mature mammals. Further, the combination of reiterative and stage-specific functions of LIN-42 may coordinate periodic molts with successive development of the epidermis.