New Histone Incorporation Marks Sites of UV Repair in Human Cells

SummaryChromatin organization is compromised during the repair of DNA damage. It remains unknown how and to what extent epigenetic information is preserved in vivo. A central question is whether chromatin reorganization involves recycling of parental histones or new histone incorporation. Here, we devise an approach to follow new histone deposition upon UV irradiation in human cells. We show that new H3.1 histones get incorporated in vivo at repair sites. Remarkably we find that H3.1, which is deposited during S phase, is also incorporated outside of S phase. Histone deposition is dependent on nucleotide excision repair (NER), indicating that it occurs at a postrepair stage. The histone chaperone chromatin assembly factor 1 (CAF-1) is directly involved in the histone deposition process in vivo. We conclude that chromatin restoration after damage cannot rely simply on histone recycling. New histone incorporation at repair sites both challenges epigenetic stability and possibly contributes to damage memory

Recruitment of Phosphorylated Chromatin Assembly Factor 1 to Chromatin after UV Irradiation of Human Cells

The subcellular distribution and posttranslational modification of human chromatin assembly factor 1 (CAF-1) have been investigated after UV irradiation of HeLa cells. In an asynchronous cell population only a subfraction of the two large CAF-1 subunits, p150 and p60, were found to exist in a chromatin-associated fraction. This fraction is most abundant during S phase in nonirradiated cells and is much reduced in G2 cells. After UV irradiation, the chromatin-associated form of CAF-1 dramatically increased in all cells irrespective of their position in the cell cycle. Such chromatin recruitment resembles that seen for PCNA, a DNA replication and repair factor. The chromatin-associated fraction of p60 was predominantly hypophosphorylated in nonirradiated G2 cells. UV irradiation resulted in the rapid recruitment to chromatin of phosphorylated forms of the p60 subunit. Furthermore, the amount of the p60 and p150 subunits of CAF-1 associated with chromatin was a function of the dose of UV irradiation. Consistent with these in vivo observations, we found that the amount of CAF-1 required to stimulate nucleosome assembly during the repair of UV photoproducts in vitro depended upon both the number of lesions and the phosphorylation state of CAF-1. The recruitment of CAF-1 to chromatin in response to UV irradiation of human cells described here supports a physiological role for CAF-1 in linking chromatin assembly to DNA repair

SUMOylation promotes de novo targeting of HP1α to pericentric heterochromatin.

International audienceHP1 enrichment at pericentric heterochromatin is considered important for centromere function. Although HP1 binding to H3K9me3 can explain its accumulation at pericentric heterochromatin, how it is initially targeted there remains unclear. Here, in mouse cells, we reveal the presence of long nuclear noncoding transcripts corresponding to major satellite repeats at the periphery of pericentric heterochromatin. Furthermore, we find that major transcripts in the forward orientation specifically associate with SUMO-modified HP1 proteins. We identified this modification as SUMO-1 and mapped it in the hinge domain of HP1α. Notably, the hinge domain and its SUMOylation proved critical to promote the initial targeting of HP1α to pericentric domains using de novo localization assays, whereas they are dispensable for maintenance of HP1 domains. We propose that SUMO-HP1, through a specific association with major forward transcript, is guided at the pericentric heterochromatin domain to seed further HP1 localization

HP1α recruitment to DNA damage by p150CAF-1 promotes homologous recombination repair

p150CAF-1-mediated recruitment of HP1α to DNA is essential for efficient assembly of DNA damage response complexes and subsequent homologous recombination repair

Comment permettre la mise place d’une dynamique d’alliance thérapeutique entre une famille et une équipe de soins lors d’une première hospitalisation pour un épisode psychotique

L’auteur décrit la réflexion du groupe pluridisciplinaire sur l’alliance thérapeutique entre équipes soignantes et familles lors d’une première hospitalisation pour un épisode psychotique. Cette alliance thérapeutique émerge et se développe dans le cadre du « système thérapeutique » constitué par la rencontre de deux groupes : le groupe famille et le groupe « équipe thérapeutique » regroupés autour de cette situation singulière et chargée émotionnellement d’une décompensation psychotique et de l’hospitalisation d’un(e) jeune. Dans cette optique, il s’agit donc de passer de la logique individuelle propre à la médecine pour passer à une logique groupale, d’une lecture purement médicale à une lecture plu- riaxiale. Alors, savoir médical et savoir profane de la famille peuvent s’énoncer et s’articuler au lieu de s’opposer. Enfin dans ce processus, la temporalité, les étapes et l’interactivité permet de gérer la part d’incertitude diagnostic et pronostic qui caractérise ces situations. Ce travail d’alliance permet d’éviter les ruptures de soins et optimise les capacités thérapeutiques des équipes et préserve l’avenir

Methods for Studying Chromatin Assembly Coupled to DNA Repair

International audienc