Identification and characterisation of determinants of genome stability in response to a double-strand break

Thesis

Chromosomal rearrangements can lead to loss of heterozygosity (LOH) and oncogene activation, both of which represent possible causative events in cancer development. Such outcomes can result from the misrepair of DNA damage arising from a variety of events including DNA double-strand breaks (DSBs), collapsed replication forks, and dysfunctional telomeres. In response to a DSB, chromosomal stability is principally maintained through the two major DNA repair pathways; non- homologous DNA end-joining (NHEJ) and homologous recombination (HR).

The objective of this thesis was to identify novel factors functioning in prevention of chromosomal instability in response to a DSB in Schizosaccharomyces pombe. To achieve this, a central aim was to identify the genes mutated in a number of radiation-sensitive mutants in fission yeast, previously isolated by the laboratory. These include the ‘loh’ mutants loh-2, loh-5, loh-6 and loh-7, which were found to harbour mutations in known DNA repair genes rad3, rad17, and rad57.

Further, a pan-genomic screen for novel HR repair factors was carried out. The Bioneer Version 2 deletion-library, consisting of 3308 haploid deletion strains, was screened for strains displaying hypersensitivity to the DNA damaging agents MMS, bleomycin and camptothecin. This screen yielded 209 hits which were further characterised, utilising a set of non-essential Ch¹⁶ minichromosomes . The minichromosome Ch¹⁶-LMYAU harbours an HO endonuclease recognition sequence and a centromere-distal ade6-M216 heteroallele. Following break-induction, failed repair of the DSB leads to loss of the ade6 allele, indicated by pink sectoring on low adenine plates. 39 sectoring hits were identified and further characterised to quantify levels of gene conversion via HR in response to a DSB, utilising Ch¹⁶-RMYAH. As a result of this study, a group of novel genes functioning in HR repair were identified.

Finally, one of these hits, putative RNA metabolism protein Nrl1, was subjected to further characterisation, associating this protein with DNA damage repair for the first time.

The work presented here, documents the approaches taken to successfully identify novel DNA repair factors in fission yeast.

Authors: Kasparek, TR

• Publication date: 2013
• DOI: 10.5287/ora-dxqqmvopy
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: oncology; DNA damage repair
• Subjects: Oncology