Screening Whole-Genome Sequenced Strains to Investigate Genetic Determinants of Gentle Touch Sensitivity in Caenorhabditis elegans

Genetic screens have laid much of the groundwork for our current understanding of biology, and mutagenesis screens in Caenorhabditis elegans have proven to be a particularly useful tool in determining the molecular components of biological processes. The Million Mutation Project (MMP) is a collection of mutagenized C. elegans strains that have been clonally propagated and whole-genome sequenced. Utilizing the MMP, I have performed a screen for touch insensitive mutants to assess the phenotypic coverage of the set, to obtain new alleles of known genes, and to potentially identify touch phenotype-causing mutations in genes that have not yet been linked to the touch response. In this thesis I first present my rationale for screening the MMP set for touch phenotypes, then review what has already been learned about genes required for the function of the neurons that sense gentle touch in C. elegans. I describe my approach to phenotyping the MMP set and present statistics on response distributions. As expected, most of the MMP strains that I determined to have strong touch insensitive phenotypes had mutations in genes identified in previous touch phenotype mutageneses. However, some of the phenotype-causing MMP alleles cause protein-coding changes in regions that were not known to be affected by previously characterized alleles. The genomic data from the MMP also allowed me to consider protein-altering mutations in known touch genes that did not result in a detectable phenotype. Finally, I address the set of strains for which we have not identified candidate causative mutations. Although I have not discovered any previously unknown touch genes through my screen of the MMP, it is still quite possible that the touch insensitive mutants I have identified will lead us to identify additional genes needed for gentle touch sensation. Ultimately, my screen has successfully demonstrated the utility of the MMP set and provided new insights as to the structure and function of the genetic determinants of gentle touch sensation in C. elegans.