Large Scale Rnai Screen To Identify Genes Involved In Axon Guidance In Caenorhabditis Elegans

This study was undertaken to identify genes involved in axon guidance in the nervous system of Caenorabditis elegans. Due to its unique physiological properties, the nematode worm C. elegans is a powerful genetic model system to study a variety of biological processes. The nervous system of C. elegans is a simple organ comprising 302 neurons. These neurons create stereotypic neuronal networks formed by their anterior-posterior and dorsal-ventral running axons. Here, we took advantage of the recently discovered phenomenon of RNA interference in the worm to identify axon guidance genes. However, the nervous system of C. elegans is refractory to the systemic RNA interference, and delivery of dsRNA molecules to the neighboring non-neuronal cells does not initiate RNAi in the neurons of the worm. Therefore, we started with the identification of mutants of C. elegans that are efficient for RNAi in the nervous system. A standard chemical mutagenesis screen was performed to identify mutants of the worm that showed enhanced RNAi efficiency in the nervous system. One of the mutants (nre-1, for neuronal RNAi efficient) showed marked suppression of gene expression in the nervous system by feeding RNAi approach. We used the nre-1 supersensitive strain as a tool in a reverse genetic screen to identify genes required for axon guidance in C. elegans. A transgenic strain was constructed in the nre-1 background, wherein a subset of interneurons and motor neurons were labeled with the yellow fluorescent protein to visualize axons of the neurons. We used this strain to screen 2416 gene of the worm located on chromosome I by feeding a library of bacterial clones expressing dsRNA fragments specific to the genes. This screen has identified 57 candidate genes that give rise to penetrant axon guidance defects in the commissural and ventral nerve cord axons in C. elegans. The genes identified include genes involved in various cellular processes such as DNA metabolism, translation, transcript.