Biology subjects

Koundrioukoff, S.

Publications and source records attributed to Koundrioukoff, S..

3 recordsLinked to original sources

bioRxiv2023

The balance between ATR and DDK activities controls TopBP1-mediated locking of dormant origins at the pre-IC stage

Replication stress, a major hallmark of cancers, and ensuing genome instability source from impaired progression of replication forks. The first line of defense against fork slowing is compensation, a long-described process that elicits firing of otherwise dormant origins. It remains unclear whether compensation requires activation of the DNA replication checkpoint or passively results from lengthening of the window of time during which dormant origins can fire when fork progression slows, or both. Using molecular DNA combing we show here that a linear relationship ties inter-origin distances to fork speeds, independently of the checkpoint status. We called this line "stressline" and further show that its slope enables precise quantification of the compensation efficiency. Comparison of the slopes in different genetic backgrounds reveals that compensation requires ATR, not CHK1, while TopBP1 and CDC7/DBF4 repress dormant origin activation. These results strongly suggest that TopBP1 locks dormant origins at the pre-IC stage and that ATR and DDK oppose to control the conversion of dormant pre-ICs into functional salvage origins. Both passive and active processes thus contribute to compensation. Moreover, Repli-seq and OK-seq analyses confirm the activating role of ATR and permit development of ATRAP-seq, a new procedure allowing mapping of early constitutive origins.

genetics↗

bioRxiv2022

In vivo inactivation of RAD51-mediated homologous recombination leads to premature aging, but not to tumorigenesis

Genetic instability is a hallmark of both cancer and aging. Homologous recombination (HR) is a prominent DNA repair pathway maintaining genomic integrity. Mutations in many HR genes lead to cancer predisposition. Paradoxically, the consequences of mutations in the pivotal HR player, RAD51, on cancer development remain puzzling. Moreover, in contrast with other HR genes, RAD51 mouse models are not available to experimentally address the role of RAD51 on aging and carcinogenesis, in vivo. Here, we engineered a mouse model with an inducible dominant negative form of RAD51 (SMRad51) that suppresses RAD51-mediated HR without stimulating alternative non-conservative repair pathways. We found that, in vivo expression of SMRad51 did not trigger tumorigenesis, but instead induced premature aging. We propose that these in vivo phenotypes result from the exhaustion of proliferating progenitors submitted to chronic endogenous replication stress resulting from RAD51-mediated HR suppression. Our data underline the importance of the RAD51 activity for progenitors homeostasis, preventing aging, and more generally for the balance between cancer and aging.

cancer biology↗

bioRxiv2019

TRANSCRIPTION-MEDIATED ORGANIZATION OF THE REPLICATION INITIATION PROGRAM ACROSS LARGE GENES SETS UP COMMON FRAGILE SITES GENOME-WIDE

Common Fragile Sites (CFSs) are chromosome regions prone to breakage under replication stress, known to drive chromosome rearrangements during oncogenesis. Most CFSs nest in large expressed genes, suggesting that transcription elicits their instability but the underlying mechanisms remained elusive. Analyses of genome-wide replication timing of human lymphoblasts here show that stress-induced delayed/under-replication is the hallmark of CFSs. Extensive genome-wide analyses of nascent transcripts, replication origin positioning and fork directionality reveal that 80% of CFSs nest in large transcribed domains poor in initiation events, thus replicated by long-traveling forks. In contrast to formation of sequence-dependent fork barriers or head-on transcription-replication conflicts, traveling-long in late S phase explains CFS replication features. We further show that transcription inhibition during the S phase, which excludes the setting of new replication origins, fails to rescue CFS stability. Altogether, results show that transcription-dependent suppression of initiation events delays replication of large gene body, committing them to instability.

genomics↗