Mutagenesis Screen in C. elegans Suggests Role of mor Genes in Pharyngeal Development

The study of organogenesis investigates the increasingly restrictive genetic programs that ultimately result in a single differentiated cell type. To study the genetic mechanisms orchestrating organ development, our lab chose the pharynx in Caenorhabditis elegans as a model system. The pharynx is a narrow tube composed of muscular epithelial tissue and is responsible for the grinding and ingestion of food in C. elegans. The pharynx has been so well studied that the complete lineage of cell divisions has been revealed. In addition, C. elegans possess a transparent body allowing researchers to track its development. To identify the genes responsible for the specification or differentiation of muscle cells in the pharynx, our lab used the specific pharynx muscle protein myosin-2, tagged with green fluorescent protein (myo-2::GFP) as a visual assay. Ethyl methane sulfonate (EMS), which yields random point mutations within DNA was used to perform a mutagenesis screen of ~10,000 haploid genomes. Administration of EMS resulted in over 200 mutant lines of worms. Of these mutants, we observed anatomical variations in the pharynx that could be attributed to cell adhesion, cell fate, cell morphology, and migration in both anterior and posterior pharynx regions. To locate the alleles responsible for disrupting myo2::GFP expression in the pharynx, our lab conducted single nucleotide polymorphism (SNP) mapping (Jorgensen et al., 2005). This mapping was carried out between the wild-type C. elegans strain (N2 Bristol) and the genetically similar strain (CD4856 Hawaiian). To acquire accurate mapping, chromosomal and interval mapping were performed. Thus far, our lab has successfully been able to establish a linkage for 10 different mutant phenotypes to various chromosomal regions. For instance, mor-1, which results in a shortened, rounded pharynx, was mapped to chromosome III. Furthermore, we found another 14 similar phenotypes, which may represent at least two other genes, mor-2 and mor-3. mor-2 has not been cloned, but is located on chromosome IV and has been shown to yield phenotypes very similar to mor-1 {{81 Lewis,J.A.1977;}}. The mor-3 gene, a calcium/calmodulin dependent protein kinase may also have a role in abnormal pharynx development. The human orthologue of mor-3—dapk-1 (death-associated protein kinase 1)— is known to play a role in cell death. We believe that these mor genes share the same molecular pathway during development in C. elegans and in humans. Therefore, studying the molecular pathways of mor-1, mor-2, and mor-3 will yield a greater comprehension of muscle cell fate in the pharynx and thereby grant insight ________________________________________________ *This author wrote the paper as a Senior thesis under the direction of Dr. Pliny Smith. into human development.