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

Abstract

Mechanical stress during cell migration may be a previously unappreciated source of genome instability, but the extent to which this happens in any animal in vivo remains unknown. We consider an in vivo system where the adult stem cells of planarian flatworms are required to migrate to a distal wound site. 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 exhibit increased levels of DNA damage. Increased DNA damage levels reduce once stem cells reach the wound site. Stem cells in which DNA damage is induced prior to wounding take longer to initiate migration and migrating stem cell populations are more sensitive to further DNA damage than stationary stem cells. RNAi-mediated knockdown of DNA repair pathway components blocks normal stem cell migration, confirming that active DNA repair pathways are required to allow successful migration to a distal wound site. Together these findings provide evidence that levels of migration-coupled-DNA-damage are significant in adult stem cells and that ongoing migration requires DNA repair mechanisms. Our findings reveal that migration of normal stem cells in vivo represents an unappreciated source of damage, which could be a significant source of mutations in animals during development or during long-term tissue homeostasis.

High throughput expression-based phenotyping and RNAi screening reveals novel regulators of planarian stem cells

“…Neoblasts undergo migration to target locations in the animal, induced by injury and also in order to maintain particular differentiated tissues in the absence of injury (Guedelhoefer and Sanchez Alvarado, 2012). This process is dependent on integrins and also the EMT-regulating transcription factors snail-1/-2 and zeb-1 (Abnave et al, 2017;Bonar and Petersen, 2017;Seebeck et al, 2017) and is coupled to DNA damage repair processes (Sahu et al, 2021). Niche factors for neoblasts are not yet fully elucidated, but based on the phenotypes from disruption of intestine formation, this organ may be a source of signals important for neoblast maintenance (Forsthoefel et al, 2012).…”

Planarians as an In Vivo Experimental Model for the Study of New Radioprotective Substances

“…At lethal doses, the few surviving neoblasts completely lose their proliferation ability [ 43 , 44 ]. Note, radiation-induced death of planarian stem cells is probably due to the same mechanisms (DNA damage, repair, apoptosis) that have been described for mammalian stem cells [ 45 , 46 ]. At sublethal doses of radiation which were used in our study, the surviving neoblasts were still able to give rise to new clonal populations [ 47 ], but this process is quite slow.…”

Inhibition of the ATM kinase rescues planarian regeneration after lethal radiation

“…To test the dependence of surviving stem cells on these DNA repair pathways, we simultaneously knocked down components of HR or NHEJ in atm (RNAi) animals. We used the recombinase rad51 or its interacting partner brca2 as a proxy for HR (Peiris et al ., 2016; Sahu et al ., 2021), and dna-pk as a proxy for NHEJ. Knockdown of either rad51 or brca2 accelerated animal death after radiation (Fig.…”

“…Even at radiation doses of 2,000 rads, the fact that some stem cells survive while others perish within the same animal suggests that factors such as cell cycle state play an important role in driving radiation resistance. Despite conservation of key cell cycle regulators and components of the DDR pathway (Grohme et al ., 2018; Sahu et al ., 2021), molecular mechanisms that govern planarian stem cell responses to radiation are as yet unclear (Barghouth et al ., 2019). Here, we capitalize on the radiation sensitivity of planarian stem cells to understand how these cells decide whether to repair their DNA or undergo apoptosis.…”