| TGFbeta and related signaling pathways have been shown to play important roles in many diverse biological processes in animals. In the nematode Caenorhabditis elegans (C. elegans), a TGFbeta-like pathway controls developmental programming of the dauer/reproductive decision in response to environmental inputs. Dauer larval development is programmed to allows animals to survive in and disperse from a challenging environment. Previous genetic epistasis analysis showed that the daf-5 gene, along with the daf-3 Smad gene, controls dauer formation; both daf-5 and daf-3 are antagonized by upstream TGFbeta ligand, receptors and receptor-regulated Smads. Preliminary genetic mapping data suggested that daf-5 might represent a new TGFbeta signaling component.; I cloned daf-5 by using single nucleotide polymorphism (SNP) mapping and cosmid transformation rescuing. An extensive phylogenetic analysis shows that DAF-5 is a novel member of the Sno/Ski superfamily. Sequencing daf-5 alleles and comparison to other Sno/Ski family members identified two important functional motifs in DAF-5: Dach box and SDS box. Yeast-two-hybrid experiments show that, like human Sno/Ski oncoproteins, DAF-5 can bind the DAF-3 Smad. Moreover, a DAF-5 gene tagged with GFP (Green Fluorescent Protein) is predominantly localized in the nucleus, suggesting that DAF-5, like Sno/Ski, is a regulator of transcription in a TGFbeta superfamily signaling pathway. This is the first genetic evidence that shows a Sno/Ski member functions in a TGFbeta pathway in vivo. However, DAF-5 is an unconventional Sno/Ski protein, because DAF-5 acts as a co-factor, rather than an antagonist, of a Smad protein.; I showed that expressing daf-5 in the nervous system rescues daf-5 mutants, whereas muscle or hypodermal expression does not. In addition, I also examined the role of daf-5 in other processes: egg-laying, regulation of cell cycle and pharyngeal muscle gene expression. I present a model in which DAF-5 and DAF-3 control the production or release of a hormone from the nervous system by either regulating the expression of biosynthetic genes or by altering the connectivity or the differentiated state of neurons in order to perfect reproductive timing. |
