lin-42 and control of developmental timing in Caenorhabditis elegans

The heterochronic genes of C. elegans specify temporal information during post-embryonic development. Mutations in heterochronic genes alter the timing of terminal differentition of the lateral hypodermal seam cells. For example, seam cells in lin-42 mutants terminally differentiate and secrete a morphologically adult cuticle during the L3 molt, which is one stage earlier than in the wild type.; lin-42 encodes the C. elegans homologue of the PERIOD family of transcription factors from Drosophila and other organisms. LIN-42 contains a PAS domain, which is known to mediate protein interactions, as well as two previously undescribed motifs in the PER family of proteins. This similarity is especially interesting since PERIOD is involved in a second type of biological timing mechanism, the control of circadian rhythms.; I investigated the extent to which the sequence similarity between LIN-42 to Drosophila PER reflects a similarity in gene regulation. A hallmark of per in flies is that its mRNA and protein levels oscillate with a 24-hour periodicity. I found that, like per, lin-42 message levels also oscillate, but with a faster rhythm that is synchronized to the ∼6-hour molting cycles of post-embryonic development. LIN-42 accumulates in the nuclei of many cell types, and lin-42 protein levels mirror those of its message, suggesting that fluctuation of lin-42 activity during larval development is required for lin-42 function.; In flies, the PAS domain of PER mediates an interaction with a second circadian rhythm protein called TIMELESS. However, I did not detect an interaction between LIN-42 and the C. elegans TIMELESS homologue, TIM-1 using the yeast two hybrid system. I performed yeast two-hybrid screens and identified a C2H2 zinc-finger protein (ZNF) and a novel, proline-rich protein as potential LIN-42-interacting factors. Like mutations in many heterochronic genes, RNAi of znf suppresses the lethality of let-7, suggesting that it may have role in developmental timing.