Regulation of DNA repair pathway choice during development

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The genetic code (DNA) contains a blueprint to produce all the machinery required for a cell to perform its various functions in a programmed manner. Preservation of this code is critical to maintain normal cellular functions. However, DNA is under continual attack from agents that cause changes in the genetic code. This can occur when cells copy their DNA (DNA replication), through changes in the sequence of DNA building blocks (mutation), or by creating breaks in the DNA molecule. Interestingly, DNA damage also occurs in a tightly regulated context during a number of normal cellular processes including development of the immune-system and transfer of genetic information as cells segregate their genomes in a process know as meiosis. Therefore, cells have developed a complex network of pathways to detect DNA damage when it occurs and correct these faults by DNA repair. The importance of DNA repair is underscored by the observations that defects in these pathways leads to a variety of debilitating clinical symptoms including premature ageing, immune-system failure, developmental abnormalities and increased cancer risk. Therefore, understanding DNA repair will provide insights into several fundamental biological processes in addition to clues regarding the molecular basis of a number of disease states. Breaks in both strands of the DNA double helix (double strand breaks; DSBs) are one of the most toxic varieties of DNA damage. These can be repaired by directly re-joining DNA breaks (non-homologous end-joining; NHEJ), or by using homologous DNA as a template to restore genome integrity (homology-directed repair; HDR). The components of these two pathways are well characterised. However, the factors that influence whether cells repair damage by NHEJ or HDR remains relatively ill defined. Defects in DNA repair lead to a variety of developmental abnormalities including defective antibody production, cranial-facial abnormalities and degeneration of the nervous system. Despite this, how these pathways are regulated as multi-cellular organisms develop into a variety of specialised tissues remains largely unexplored. DNA repair is achieved by similar mechanisms in all organisms from bacteria to humans. Therefore, studying these pathways in relatively simple model organisms has increased our understanding of how these processes work in humans. Unfortunately, certain commonly used model organisms lack key components of human DNA DSB repair pathways and do not undergo a developmental program into specialised cell types. In contrast, the soil dwelling amoeba Dictyostelium is an easily grown and manipulated organism that undergoes a relatively simple developmental program. As such, it is a commonly used model to study cell type specification and differentiation. In addition, our previous work has illustrated that DNA DSB repair pathways in this organism are more similar to humans than other commonly used model organisms. The aims of this research are to exploit these observations and use Dictyostelium as a model to study how DNA DSB repair pathway choice is regulated in the context of an organism's life cycle and developmental program. In addition to providing insights into how DNA repair pathways are regulated in Dictyostelium, these studies will likely be applicable to how these processes are achieved in other higher organisms including humans.