Dattani, A. | Search bioRxiv

bioRxiv2019

Ongoing repair of migration-coupled DNA damage allows stem cells to reach wound sites

The impact of mechanical stress during cell migration may be a previously unappreciated source of genome instability [1-3], but to what extent this happens in vivo remains unknown. Here we consider an in vivo system where the adult stem cells of planarian flatworms are required to migrate to a distal wound site [4]. We observe a relationship between adult stem cell migration and ongoing DNA damage and repair during tissue regeneration. Migrating planarian stem cells undergo changes in nuclear shape and increased levels of DNA damage. Increased DNA damage levels resolve once stem cells reach the wound site and stop migrating. Stem cells in which DNA damage is induced prior to wounding take longer to initiate migration suggesting migration activity is sensitive to DNA damage. Migrating stem cells populations are more sensitive to further DNA damage than stationary stem cells, providing evidence that levels of migration-coupled-DNA-damage (MCDD) are significant. RNAi mediated knockdown of DNA repair pathway components blocks normal stem cell migration, confirming that DNA repair pathways are required to allow successful migration to a distal wound site. Together these lines of evidence demonstrate that migration leans to DNA damage in vivo and requires DNA repair mechanisms. Our findings reveal that migration of stem cells represents an unappreciated source of damage, that could be a significant source of mutations in animals during development or during long term tissue homeostasis.

developmental biology↗

bioRxiv2019

Deciphering the interstrand crosslink DNA repair network expressed by Trypanosoma brucei

Interstrand crosslinks (ICLs) represent a highly toxic form of DNA damage that can block essential biological processes including DNA replication and transcription. To combat their deleterious effects all eukaryotes have developed cell cycle-dependent repair strategies that coopt various factors from classical DNA repair pathways to resolve such lesions. Here, we report that Trypanosoma brucei, the causative agent of African trypanosomiasis, possesses such systems that show some intriguing differences to those mechanisms expressed in other organisms. Following the identification of trypanosomal homologues encoding for CSB, EXO1, SNM1, MRE11, RAD51 and BRCA2, gene deletion coupled with phenotypic studies demonstrated that all the above factors contribute to this pathogens ICL REPAIRtoire with their activities split across two epistatic groups. We show that one network, which encompasses TbCSB, TbEXO1 and TbSNM1, may operate throughout the cell cycle to repair ICLs encountered by transcriptional detection mechanisms while the other relies on homologous recombination enzymes that together may resolve lesions responsible for the stalling of DNA replication forks. By unravelling and comparing the T. brucei ICL REPAIRtoire to those systems found in its host, targets amenable to inhibitor design may be identified and could be used alongside trypanocidal ICL-inducing agents to exacerbate their effects. Author summaryParasites belonging to the Trypanosoma brucei complex cause a human and animal infections collectively known as African trypanosomiasis. Drugs used against these diseases are problematic as medical supervision is required for administration, they are costly, have limited efficacy, may cause unwanted side effects while drug resistance is emerging. Against this backdrop, there is a need for new therapies targeting these neglected tropical diseases. Previous studies have shown compounds that induce DNA interstrand crosslinks (ICLs) formation are effective trypanocidal agents with the most potent invariably functioning as prodrugs. Despite the potential of ICL-inducing compounds to treat African trypanosomiasis little is known about the ICL repair mechanisms expressed by trypanosomes. Using a combination of gene deletion and epistatic analysis we report the first systematic dissection of how ICL repair might operate in T. brucei, a diverged eukaryote. It sheds light on the conservation and divergence of ICL repair in one of only a handful of protists that can be studied genetically, and offers the promise of developing or exploiting ICL-causing agents as new anti-parasite therapies. These findings emphasise the novelty and importance of understanding ICL repair in T. brucei and, more widely, in non-model eukaryotes.

microbiology↗