Samenvatting

It is estimated that over 30,000 lesions in the DNA are generated per cell per day. In S-phase, lesions in the DNA can stall replication, which can lead to secondary lesions such as DNA double- strand breaks. The DNA damage tolerance (DDT) network enables replication to be continued in the presence of replication-blocking DNA lesions and thereby prevents the formation of secondary lesions. DDT is activated by site-specific ubiquitination at the lysine residue 164 of PCNA, a homotrimeric DNA clamp. Alternatively, the damage tolerant translesion synthesis (TLS) polymerase Rev1. Prior work from our lab revealed that in unperturbed conditions, DDT deficiency causes severe hematopoietic stem cell (HSC) depletion, resulting in a severe embryonic lethal anemia (unpublished work). At present the relevance of DDT network in maintaining of HSCs as well as other tissue stem cells in adult mice is not known. Here, we make use of three unique mouse models carrying a Cre-deleteable wild-type allele Pcnafl/fl, a non-modifiable PcnaK164R knock-in allele, and a Rev1Ko allele. Combining these alleles, enabled us to study the impact of genetically defined, inducible DDT defects on maintaining HSCs and the overall tissue homeostasis in adult mice. We show that in adult mice, severe DDT-deficiency results in complete loss of the hematopoietic stem cell compartment, lethal anemia, and widespread systemic tissue damage. Additionally, we observed tumor development in DDT-deficient mice, suggesting that the DDT system functions to prevent tumor development. Our findings establish the necessity of the DDT network for hematopoietic stem cell maintenance, tissue homeostasis, prevention of tumor development, and mammalian life.