PROJECT SUMMARY Proper timing of gene expression is essential for cellular and organismal development. The C. elegans heterochronic pathway, which regulates developmental timing, is thought to be an ancestral form of the circadian clock in other organisms. Within this pathway, multiple genes interact to mediate proper development. Misregulation of these genes causes inappropriate cell growth and ultimately death in C. elegans, and cancer and other developmental disorders in humans. An essential member of the circadian clock is the Period protein whose homolog, LIN- 42, is an important regulator of developmental timing in C. elegans. LIN-42 functions as a transcriptional repressor of multiple genes including the conserved lin-4 and let-7 microRNAs, which are also essential members of the heterochronic pathway. Like other Period proteins, levels of LIN-42 oscillate throughout development. In other organisms this cycling is controlled in part by phosphorylation and subsequent degradation. KIN-20 is the C. elegans homolog of the Drosophila Period protein kinase Doubletime. Worms containing a large deletion in kin-20 have a significantly smaller brood size, develop slower than wild type C. elegans, and display uncoordinated locomotion. We have previously shown that KIN-20 impacts lin-42 mutant phenotypes and LIN-42 protein levels, and that KIN-20 is important for post-transcriptional regulation of mature let-7 and lin-4 microRNA expression. However, the mechanisms by which KIN-20 regulates LIN-42, microRNA biogenesis, and development in C. elegans remain poorly understood. Accordingly, this proposal seeks to understand these mechanisms through three integrated specific aims. In Aim 1, we will characterize the relationship between KIN-20 and LIN-42 to better understand how KIN-20 regulates LIN-42. In Aim 2, we will determine the role of KIN-20 in microRNA production. In Aim 3, we will investigate the role of KIN-20 in development. Altogether our findings will enhance our understanding of the molecular mechanisms underlying developmental timing and thus elucidate new targets for diseases associated with cellular developmental defects including cancer. Importantly, the experiments described here will be performed by undergraduate students, which will significantly enhance the ability of Colgate University to provide undergraduate students with significant opportunities for independent research in preparation for careers in developmental biology and the biomedical sciences.