Seminar Nuclear dynamic series
12 April

Role of spatial chromatin (re)organization in recombinational DNA repair and genomic stability

Le 12 April - 09h-10h

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"Homologous recombination (HR) templates DNA double-strand break (DSB) repair off an intact homologous dsDNA “donor” molecule, which can exist in the form of a sister chromatid, a homologous chromosome, or dispersed repeats. HR fidelity partly depends on this competitive donor selection process, which embeds homology sampling by the RecA/Rad51-ssDNA nucleoprotein filament (NPF), DNA joint molecules reversal by ancillary HR factors and, presumably, regulation of the spatial collisions between the NPF and any given genomic loci (Savocco and Piazza, 2021). We developed various proximity ligation-based methodologies enabling detection of transient NPF-dsDNA interactions and early DNA joint molecules (as-of-yet recalcitrant to molecular detection), which granted direct study of these core HR steps and their regulation in S. cerevisiae (Piazza et al., 2017, 2018, 2019, 2021a). In collaboration with the Koszul lab, we recently identified two main ways by which cohesin bias ectopic donor identification: both promoting it in cis and inhibiting it in trans (Piazza et al., 2021b). We present here additional mechanistic insights into the promotion of cis-sampling by the NPF. Mutation accumulation experiments in genotoxic conditions reveals that perturbation of chromatin loop folding in hypomorph mutants of cohesin regulators leads to repeat-mediated genome instability. This preliminary work furthers the characterization of the cohesin-mediated regulation of homology search during HR and its role as a suppressor of genomic instability."

Hélène Bordelet1,2, Vinciane Piveteau1, Agnès Dumont1, Romain Koszul2, Aurèle Piazza1

1 Ecole Normale Supérieure de Lyon, CNRS UMR5239, 46 Allée d’Italie, 69007 Lyon, France

2 Institut Pasteur, CNRS UMR3525, Unité Régulation Spatiale des Génomes, 25-28 Rue du Docteur Roux, 75015, Paris, France


Piazza, A., Wright, W.D., and Heyer, W.-D. (2017). Multi-invasions are recombination byproducts that induce chromosomal rearrangements. Cell 170, 760-773.e15.

Piazza, A., Koszul, R., and Heyer, W.-D. (2018). A proximity ligation-based method for quantitative measurement of D-Loop extension in S. cerevisiae. In Methods in Enzymology, M. Spies, and A. Malkova, eds. (Academic Press), pp. 27–44.

Piazza, A., Shah, S.S., Wright, W.D., Gore, S.K., Koszul, R., and Heyer, W.-D. (2019). Dynamic processing of displacement loops during recombinational DNA repair. Mol. Cell 73, 1255-1266.e4.

Piazza, A., Rajput, P., and Heyer, W.-D. (2021a). Physical and genetic assays for the study of DNA joint molecules metabolism and multi-invasion-induced rearrangements in S. cerevisiae. In Homologous Recombination: Methods and Protocols, A. Aguilera, and A. Carreira, eds. (New York, NY: Springer US), pp. 535–554.

Piazza, A., Bordelet, H., Dumont, A., Thierry, A., Savocco, J., Girard, F., and Koszul, R. (2021b). Cohesin regulates homology search during recombinational DNA repair. Nat. Cell Biol. 23, 1176–1186.

Savocco, J., and Piazza, A. (2021). Recombination-mediated genome rearrangements. Curr. Opin. Genet. Dev. 71, 63–71.



Ecole Normale Supérieure de Lyon
Institut Curie
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Institut Curie
Institut Curie