| Summary: | <p>DNA double-strand breaks (DSBs) are toxic lesions that can be repaired by numerous mechanistically distinct pathways. However, regulation of DSB repair pathway utilisation is also essential for maintaining genomic integrity, and eukaryotes have evolved several mechanisms to achieve this. This includes post-translational modifications of DSB repair proteins to modulate their activity at DNA DSB ends. One example of a post-translational modification with a role in DNA repair is Poly-ADP ribosylation (PARylation), which in mammals is mediated by Poly-ADP ribose Polymerase 1 and 2 (PARP1 and 2). The best characterised roles of PARP1 and 2 is in single-strand break repair (SSBR) and base-excision repair (BER). However, their roles in DSB repair remain unclear, and to address this, the eukaryotic model Dictyostelium discoideum has been utilised. Several putative repair PARPs are conserved in the Dictyostelium genome, and the induction of PARylation following DNA SSBs and base-damage has been observed. Using a genetic approach, multiple Dictyostelium PARPs have been implicated in SSBR/BER, as is the case in mammals. PARylation is also induced following DNA DSBs, with the major contributor being Adprt1a. This work has demonstrated the regulatory role of Adprt1a in DSB repair by promoting non-homologous end joining (NHEJ), at the expense of homologous recombination (HR). This may be achieved by the enhanced association of the Ku70/Ku80 heterodimer, the DSB sensor that initiates NHEJ, with chromatin following DNA damage in a PAR-dependent manner. Consistent with this, a PAR binding zinc-finger, the PBZ domain, has been identified in Dictyostelium Ku70, which is involved in the enhanced chromatin-association of Ku post-DSB induction. This work therefore highlights a mechanism by which Adprt1a-induced PARylation post-DSBs promotes NHEJ via Ku recruitment. The enhanced Ku association at damaged chromatin reduces engagement of other DSB repair pathways, placing Adprt1a at the crossroads of DSB repair pathway choice.</p>
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