Development of Larval Photobehaviour as a Paradigm to Indentify Mutations that Affect Nervous System Development and Function

Abstract

<p>In Drosophilia neurogenetics, one uses mutational approaches to dissect the function and development of the nervous system. This approach has been very successful in the isolation of many single gene mutations that affect adult fly behaviour. However, it has been estimated that 30-50% of all genes in Drosophilia mutate to result in adult inviability. This encouraged us to consider the larval stage as a platform for indentifying mutations that affect the nervous system through the use of larval behaviour assays.</p> <p>A part of this thesis describes the design, standardization and demonstration of behaviour assays. The assays employed both a population of animals and individual larva to study their response to light. Using these assays we screened a collection of mutagenized recessive lethal strains to identify new genes that affect nervous system function. The development of these assays enable the demonstration that larval visual system uses many of the same genes that participate in the transduction of light in the adults. Lack of response to light after genetic ablation of larval photoreceptors was also demonstrated.</p> <p>A partial automation of one of the individual larval assays was also established. Using this, an expeditious screening of 50 mutant lines was carried out. This pilot screen resulted in the isolation of candidate lines that show defects in larval photo-response and locomotion.</p> <p>This study also focused on a single behavioural mutant line and called tamas. Through genetic analysis and direct sequencing of pre-existing alleles that belong to this locus it was determined that the tamas gene codes for mitochondrial DNA polymerase catalytic subnit (tamas/pol γ-α/POLG). Mutations in this gene cause defects in nervous system development and locomotory behaviour. We also carried out phenotypic analysis of mutants with lesion in the gene that codes the accessory subunit of the mtDNA polymerase (pol γ-β). Pre-existing alleles in this gene were indentified first through genetic analysis, next, through direct sequencing the mutations in this gene were confirmed. These experiments consituted the first phenotypic analysis of mutants in the mitochondrial DNA polymerase for any metazoan.</p>