Post-embryonic characterization of puf-9, a Caenorhabditis elegans Puf family protein

In C. elegans, genes in the heterochronic pathway direct the proper timing of organogenesis during development. Here I present the first comprehensive characterization of the C. elegans pumilio homolog, puf-9. I show that puf-9 interacts with multiple genes in the heterochronic pathway including the microRNA let-7, hbl-1, the C. elegans ortholog of hunchback, and lin-41, a homolog of Drosophila Brat, to control hypodermal seam cell development. My work demonstrates a role for puf-9 during C. elegans post-embryonic development and I show that loss-of-function mutations in puf-9 results in defective adult cuticle formation and a variety of gonad abnormalities. Consistent with this, puf-9 is expressed broadly throughout development and shows expression in multiple tissues known to be under heterochronic gene control, including the hypodermis, somatic gonad and neurons.; I present genetic data that puf-9(lf) enhances phenotypes caused by mutations in the microRNA let-7 and can be placed genetically between lin-41 and hbl-1. In C. elegans, heterochronic microRNAs of the let-7 family control epidermal stem cell fate and differentiation by repressing hbl-1. Here I show that puf-9 controls the differentiation of stem cells in the epidermis and may act coordinately with let-7 to mediate regulation of hbl-1 to direct the larval-to-adult switch.; Pumilio homologs act to regulate gene expression by binding to specific sites in the 3'UTR of their target RNAs. My work reveals that puf-9 is required for proper hbl-1 regulation in both the hypodermis and the ventral nerve cord. I show that this regulation is dependent on a region of the hbl-1 3'UTR, which contains potential Puf family binding sequences closely associated with let-7 family binding sites, thus suggesting that Puf family RNA binding proteins and microRNAs may interact to regulate target RNAs.; Additionally, I show that puf-9 interacts genetically and physically with lin-41, a known target of let-7 and a homolog of Drosophila Brat. My work could shed light on the unknown mechanism of lin-41 in the control of developmental timing.