Biology subjects

Giglia-Mari, G.

Publications and source records attributed to Giglia-Mari, G..

7 recordsLinked to original sources

bioRxiv2023

Decline of DNA damage response along with myogenic differentiation

DNA integrity is incessantly confronted to endogenous and exogenous agents inducing DNA lesions, which are harmful for cellular homeostasis. Luckily all organisms are equipped with a network of DNA damage response (DDR) mechanisms that will repair DNA lesions and restore the proper cellular activities. Despite DNA repair mechanisms have been revealed in vitro and in replicating cells, still little is known on how DNA lesions are repaired and consequently how cellular homeostasis is maintained in post-mitotic cells. Muscle fibers are highly specialised post-mitotic cells organized in syncytia and, they are vulnerable to age-related degeneration and atrophy following radiotherapy treatment. We have here studied in detail the DNA repair capacity of muscle fibers nuclei and compared it with the one measured in proliferative myoblasts. We focused on the DNA repair mechanisms that correct ionizing radiation (IR)-induced lesions, namely the base excision repair (BER), the non-homologous end joining (NHEJ) and the homologous recombination (HR). We found that in the most differentiated myogenic cells, myotubes, all of these DNA repair mechanisms present weakened kinetics of recruitment of DNA repair proteins to IR-damaged DNA. For BER and HR, this decline can be linked to reduced steady state levels of key proteins involved in these processes, probably since nuclei within muscle fibers no longer replicate their DNA. SIGNIFICANCEAlthough skeletal muscle tissue has been considered as resistant to injury caused by ionizing radiations (IR), in the long term, muscle surrounding irradiated regions of the body following radiotherapy has physiological consequences such as atrophy and muscle wasting. To prevent and/or counteract the harmful effects of IR in muscle fibers, it is essential, to evaluate the DNA repair capacity of post-mitotic myonuclei. By using fluorescently tagged DNA repair proteins expressed in myoblasts and myotubes, we were able to assess the kinetics of the DNA damage response in these cells and determine that DNA damage response is weakened during the process of myofibrillogenesis.

cell biology↗

bioRxiv2022

Nucleolar reorganization after cellular stress is orchestrated by SMN shuttling between nuclear compartments

SMA is an autosomal recessive neuromuscular disease caused by mutations in the multifunctional protein SMN. Within the nucleus, SMN localizes to Cajal bodies (CBs), which have been shown to be associated with nucleoli, nuclear organelles dedicated to the first steps of ribosome biogenesis. The highly organized structure of the nucleolus can be dynamically altered by genotoxic agents. After genotoxic stress, RNAP1, Fibrillarin (FBL) and nucleolar DNA are exported to the periphery of the nucleolus and once DNA repair is fully completed the organization of the nucleolus is restored. We found that SMN is required for the restoration of the nucleolar structure after genotoxic stress. Unexpectedly, during DNA repair, SMN shuttles from the CBs to the nucleolus. This shuttling is important for nucleolar homeostasis and relies on the presence of Coilin and the activity of PRMT1.

molecular biology↗

bioRxiv2022

Active mRNA degradation by EXD2 nuclease elicits recovery of transcription after genotoxic stress

The transcriptional response to genotoxic stress involves gene expression arrest, followed by recovery of mRNA synthesis (RRS) after DNA repair. Using a small-scale RNA interference screen, we found that the lack of the EXD2 nuclease impaired RRS and decreased cell survival after UV irradiation, without affecting DNA repair. Overexpression of wild-type, but not nuclease-dead EXD2, restored RRS and cell survival. We observed that UV irradiation triggered recruitment of EXD2 to chromatin where the nuclease transiently interacts with RNA Polymerase II (RNAPII) to promote the degradation of nascent mRNAs synthesized at the time of genotoxic attack. Reconstitution of the EXD2-RNAPII partnership on a transcribed DNA template in vitro showed that EXD2 primarily interacts with an elongation-blocked RNAPII and efficiently digest mRNA. Overall, our data highlight a crucial new step in the transcriptional response to genotoxic attack in which EXD2 interacts with elongation-stalled RNAPII on chromatin to degrade the associated nascent mRNA, allowing transcription restart after DNA repair.

molecular biology↗

bioRxiv2021

XAB2 Dynamics during DNA Damage-Dependent Transcription Inhibition

Xeroderma Pigmentosum group A (XPA)-binding protein 2 (XAB2) is a multi-functional protein that plays a critical role in distinct cellular processes including transcription, splicing, DNA repair and mRNA export. In this study, we detailed XAB2 involvement during Nucleotide Excision Repair (NER), a repair pathway that guarantees genome integrity against UV light-induced DNA damage and that specifically removes transcription-blocking damage in a dedicated process known as Transcription-Coupled repair (TC-NER). Here, we demonstrated that XAB2 is involved specifically and exclusively in TC-NER reaction and solely for RNA Polymerase 2 transcribed genes. Surprisingly, contrary to all the other NER proteins studied so far, XAB2 does not accumulate on the local UV-C damage but on the contrary is remobilized after damage induction. This fast change in mobility is restored when DNA repair reactions are completed. By scrutinizing from which cellular complex/partner/structure XAB2 is released, we have identified that XAB2 is detached after DNA damage induction from the DNA:RNA hybrids, commonly known as R-loops, and from the CSA and XPG protein and this release is thought to contribute to the DNA damage recognition step during TC-NER. Importantly, we have disclosed a role for XAB2 in retaining RNAP2 on its substrate.

molecular biology↗

bioRxiv2019

β-Actin and Nuclear Myosin I are responsible for nucleolar reorganization during DNA Repair.

During DNA Repair, ribosomal DNA and RNA polymerase I (rDNA/RNAP1) are reorganized within the nucleolus. Until now, the proteins and the molecular mechanism governing this reorganisation remained unknown.\n\nHere we show that Nuclear Myosin I (NMI) and Nuclear Beta Actin (ACT{beta}) are essential for the proper reorganisation of the nucleolus, after completion of the DNA Repair reaction.\n\nIn NMI and ACT{beta} depleted cells, the rDNA/RNAP1 complex can be displaced at the periphery of the nucleolus after DNA damage but cannot re-enter within the nucleolus after completion of the DNA Repair. Both proteins act concertedly in this process. NMI binds the damaged rDNA at the periphery of the nucleolus, while ACT{beta} brings the rDNA back within the nucleolus after DNA repair completion. Our results reveal a previously unidentified function for NMI and ACT{beta} and disclose how these two proteins work in coordination to re-establish the proper rDNA position after DNA repair.

molecular biology↗

bioRxiv2019

Cell-type specific concentration regulation of the basal transcription factor TFIIH

The basal transcription/repair factor TFIIH is a ten sub-unit complex essential for RNA polymerase II (RNAP2) transcription initiation and DNA repair. In both these processes TFIIH acts as a DNA helix opener (by the enzymatic activity of the XPB and XPD helicases), required for promoter escape of RNAP2 in transcription initiation, and to set the stage for strand incision within the Nucleotide Excision Repair (NER) pathway. We generated a knock-in mouse model that endogenously expresses a fluorescent version of XPB. Here we demonstrate, via confocal imaging of ex vivo tissues and cells derived from this mouse model, that TFIIH steady state levels are tightly regulated at the single cell level, thus keeping nuclear TFIIH concentrations remarkably constant in a cell type dependent manner. Moreover, we show that individual cellular TFIIH levels are proportional to the speed of mRNA production, hence to a cells transcriptional activity, which we can correlate to proliferation status. Importantly, cancer tissue presents a higher TFIIH than normal healthy tissues. Taken together, these results show that TFIIH cellular concentration might be used as a bona-fide marker of transcriptional activity and proliferation.\n\nSignificanceUsing a mouse model expressing a fluorescently version of TFIIH, we showed that TFIIH concentration is tightly controlled and that this concentration is proportional to the cellular transcriptional activity and proliferation capacity.

cell biology↗

bioRxiv2018

CSB-dependent CDK9 degradation and RNA Polymerase II phosphorylation during Transcription Coupled Repair

AUTHOR SUMMARYDNA lesions block cellular processes such as transcription, inducing apoptosis, tissue failures and premature ageing. To counteract the deleterious effects of DNA damage, cells are equipped with various DNA repair pathways. Transcription Coupled Repair specifically removes helix-distorting DNA adducts in a coordinated multi-step process. This process has been extensively studied, however once the repair reaction is accomplished, little is known about how transcription restarts. In this study, we show that, after UV irradiation, the CDK9/CyclinT1 kinase unit is specifically released from the HEXIM1 complex and that this released fraction is degraded in the absence of CSB. We determine that UV-irradiation induces a specific Ser2 phosphorylation of the RNA polymerase II and that this phosphorylation is CSB dependent. Surprisingly CDK9 is not responsible for this phosphorylation but instead plays a non-enzymatic role in transcription restart after DNA repair.

cell biology↗