Meiosis is essential for all sexually reproducing organisms. The production of haploid gametes with the correct chromosome complement ensures the restoration of diploidy at fertilization. The pairing and synapsis of homologous chromosomes and subsequent inter-homolog recombination, events that occur in meiotic prophase, are critical requirements for proper meiotic chromosome disjunction. Genetic studies of meiotic recombination in C. elegans have implicated specific chromosome regions as potential pairing centers (PCs): cis-acting sites that ensure appropriate homolog interactions. To gain additional insight into PC function, I am undertaking a RNAi based screen to identify trans-acting factors required for PC function. However, a standard RNAi Him screen will identify general meiotic and chromosome segregation factors in addition to any proteins involved with the PC. Therefore, to enrich for genes that specifically interact with the PC, I am using a mutant background in which one X chromosome lacks a PC as a sensitized genetic background already partially compromised for PC activity; these mutants produce 5-7% male progeny (hermaphrodites in which both X chromosomes lack a PC produce 35%). Animals heterozygous for the deficiency are fed E. coli expressing specific RNAi constructs to see if inactivation of any genes enhance the weak Him phenotype. Reconstruction experiments with RNAi constructs that inactivate him-3
and its homolog, F57C9.5, validate this approach to identifying genes required for pairing and synapsis. Employing cytology and genetics, candidate genes are currently being investigated for roles in PC function.