Discussion

Genomes are constantly challenged by agents that promote DNA damage, with interstrand crosslinks (ICLs) representing a particularly dangerous lesion. Formed when the two complementary strands within the DNA double helix become covalently linked, ICLs block essential cellular processes that require strand separation and if left unchecked, can lead to chromosomal breakage, rearrangements, or cell death. In many organisms, zinc-dependent nucleases belonging to the SNM1/PSO2 family play a specific and key role in repair of these lesions, with the T. brucei homologue (TbSNM1) recently characterised. To further understand the complexity of ICL repair pathways within this parasite a series of cell lines lacking TbEXO1, TbCSB, TbMRE11, TbMPH1 or TbCHL1 were generated in wildtype or Tbsnm1-deficient genetic backgrounds: these repair enzymes are reported to function in ICL repair in other organisms. Phenotypic screens using a variety of DNA damaging agents were performed, revealing that TbSNM1, TbMRE11, TbEXO1 and TbCSB all help to fix ICLs. TbMPH1 and TbCHL1 played no role in repairing these lesions. In the case of TbCSB and TbEXO1, their activities are epistatic with TbSNM1. In contrast, the ICL repairing activity of TbMRE11 occurs independently of TbSNM1. By unravelling how T. brucei can repair ICLs, specific inhibitors against key components of these pathways could be developed and used to target trypanosomal and leishmanial infections.