Novel components of the dauer larva developmental signaling pathway in Caenorhabditis elegans

In harsh conditions Caenorhabditis elegans arrests development to enter a nonaging, resistant diapause state called the dauer larva. Olfactory sensation modulates the TGF-β and insulin-like signaling pathways to control this developmental decision. The dauer pheromone is required for formation of dauer larvae. This thesis shows that bacterial pathogenesis is an input into dauer formation in addition to the known inputs of starvation, overcrowding and high temperature. This was first suggested by the overabundance of innate immunity genes found in a screen for novel synthetic dauer formation mutants. A total of 21 genes were identified in this screen, only one of which, srh-100, was previously identified to influence dauer formation. This work also characterizes new genes and functions that define early, middle, and late steps in the dauer pathway. Epistasis analysis and a GFP-tagged reporter places DAF-25 (abnormal DAuer Formation) function in the sensory cilia. DAF-25 was shown to be required for DAF-11 cilia localization as well as proper olfaction to various cues. daf-25 and daf-11 mutants have similar phenotypes and epistatic order. Intraflagellar transport is not defective in daf-25 mutants although the ciliary localization of DAF-25 itself is altered in a mutant that is defective in retrograde IFT. A Daf-c enhancing mutant originally isolated as a double mutant with a novel daf-2 allele was also identified. m708 is allelic with sdf-9 (Synthetic Dauer Formation). Epistasis analysis and allele-specific interactions place it in the daf-2 pathway as a possible DAF-2 interactor. The molecular lesion in m708 was identified to be an insertion of the mariner transposon Cemar1. This is the first identified hopping event described for this transposon family, the largest in C. elegans. Finally, zip- 5 (initially identified as a candidate DAF-16/FOXO target by serial analysis of gene expression) was shown to be a basic-leucine zipper transcription factor (bZIP) that is down regulated in a daf-2 background. zip-5 mutants show an extension of life span that is dependent on SKN-1, a bZIP-like transcription factor. ZIP-5 expression is dependant on the longevity-associated DAF-16 transcription factor and the zip-5 GATA binding sites.Medicine, Faculty ofMedical Genetics, Department ofGraduat