| dc.description.abstract | Nonsense-mediated decay (NMD) is an RNA processing pathway that helps maintain the quality of gene expression. It is best known as a surveillance system that detects aberrant mRNA molecules that result from mutations leading to premature stop codons. This pathway mainly operates in the cytoplasm and is linked to translation. Through cycles of phosphorylation and dephosphorylation of pathway proteins, mainly UPF1, a protein complex is assembled, which eventually degrades aberrant mRNAs. Thus, NMD prevents accumulation of truncated proteins. In the Ciosk lab, a forward genetic screen was performed to discover novel components of the NMD pathway using C. elegans as a model organism. In addition to known NMD factors such as smg proteins, the screen uncovered clk-2 as a novel NMD pathway component. clk-2 is an orthologue of human TELO2 (telomere maintenance 2) with functions in DNA damage response. Interestingly, the Gartner lab reported smg-1 (an NMD component) mutants to be hypersensitive to ionizing radiation (IR), which causes DNA double strand breaks. Therefore, there seems to be an interplay between the NMD and DNA damage response (DDR) pathways. DDR is a complex signaling network that mediates DNA repair while arresting the cell cycle. If the damage is extensive, DDR triggers apoptosis. Within this network, there are multiple overlapping pathways for repairing DNA double strand breaks. The two major pathways are homologous recombination (HR) and non-homologous end joining (NHEJ). In this work, we aim to delineate the interplay between the components of the NMD pathway and the DDR network. We did this by first assessing whether NMD mutants other than smg-1 and clk-2 are hypersensitive to IR. We further investigated whether the components of any specific pathway in the DDR network interact genetically with the NMD pathway. Using specific reporters to quantify DNA repair, we checked which pathway is affected upon knockdown of NMD components. We discovered that smg-2 mutants are also hypersensitive to IR, suggesting further involvement of NMD in DDR. The knockdown of NHEJ repair pathway proteins aggravated the phenotypes of smg-1 and smg-2 mutants, as opposed to HR pathway knockdowns which had no effect on phenotype. Additionally, we found that animals lacking smg-1 or smg-2 used homology dependent repair more, suggesting a decrease in NHEJ activity. In conclusion, considering the results of all the experiments, the NHEJ pathway is most likely linked with NMD. | eng |