Scott Everet Baird, Ph.D (Advisor); Quan Zhong, Ph.D. (Committee Member); Labib Rouhana, Ph.D. (Committee Member)
Master of Science (MS)
Two closely related Caenorhabditis species, C. briggsae and C. nigoni are cross fertile and produce viable adult progeny. From C. nigoni mothers, F1 adult females are viable and fertile, F1 males are viable but sterile. In crosses that utilize C. nigoni males and C. briggsae hermaphrodites produce viable adult F1 females but F1 males arrest during embryogenesis. A mutation in the Cbr-him-8 gene is a recessive maternal-effect suppressor of male-specific lethality. Hybrid crosses with cbr-him-8 mutant mothers produce viable adult male progeny. The HIM-8 protein in C. elegans is required for the pairing of X-chromosomes during meiosis. This function is likely conserved in C. briggsae. Unpaired chromosomes are transcriptionally silenced in a wide variety of taxa. Based on this information it’s been proposed that the meiotic silencing of unpaired chromosomes (MSUC) is suppressing an X-linked hybrid lethal gene responsible for male specific lethality. Multiple co-suppression assays identified two genes as candidate hybrid lethal genes, CBG30927 and CBG00239. These genes were knocked out with RNAi and CRISPR to evaluate if either of these genes were a hybrid lethal gene. sgRNA/Cas9 complexes and dsRNA of the candidate hybrid lethal genes was injected into C. briggsae hermaphrodites. Injections using CRISPR were able to disrupt expression of control targets but not the candidate hybrid lethal genes. Both RNAi and CRISPR injected nematodes were mated with C. nigoni males and the resulting progeny were scored for viable F1 males. From injections of dsRNA containing copies of CBG30927 or Cbr-hig-1, male progeny were derived. Cbr-hig-1 has a syntenic ortholog in C. nigoni that is not present in any other Caenorhabditis species. Several regions were identified in the C. briggsae and C. nigoni transcripts including an exon 5 extension that is responsible for a change in the predicted structure of the proteins that could be responsible for the dysgenic interactions.
Year Degree Awarded
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