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Studies of rec-1 function in Caenorhabditis elegans Vijayaratnam, Vijeyakumary

Abstract

The faithful transmission of genetic information to succeeding generations relies on the accurate segregation of chromosomes during meiosis. Central to the meiotic process is recombination. Alteration of the pattern of crossing over can lead to improper chromosome segregation. A recessive mutation in the rec-1 gene in Caenorhabditis elegans eliminates the meiotic pattern of crossing over on the autosomes. Whether or not the rec-1 mutation also affects the X chromosome was investigated. Even though the amount of variation is less on the X chromosome, rec-1 randomized the distribution. Crossing over initiates as a result of double strand breaks. In C. elegans, mutations in the spo-11 gene, which is required for meiotic exchange, produce no viable progeny unless treated with ionizing radiation. In order to investigate the possibility that the Rec-1 mutant phenotype results from excess breaks in the DNA Rec-1; Spo-11 double mutant phenotype was determined. Rec-1 was not able to compensate for the spo-11 defect. Thus, DNA breakage is unlikely to be the basis of the altered crossover pattern observed in Rec-1. A recessive mutation in the him-1 gene reduces the total number of crossovers on the X chromosome. Whether or not rec-1 mutation can override the effect of him-1 mutation was investigated. In him-1 rec-1 double mutants, the total length of the X chromosome genetic map was further reduced. This indicated that wild type him-1 function is needed for rec-1 function on the X chromosome. In order to understand the molecular basis of rec-1, candidate genes were tested for allelism. The right end of eDf24 lies within the ribosomal gene cluster. There are 13 predicted protein encoding genes between the left breakpoint and the ribosomal gene cluster. These genes were tested using transgenic rescue, dsRNA inhibition of gene function and DNA sequencing. Deletions, which affect genes in the region of eDf24 where rec-1 is known to map, were generated. None of these deletions failed to complement the Rec-1 phenotype. Thus, considerably refining potential position of the rec-1 gene.

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