Deadline for full application: December 15th, 2013
Interviews: March, 2014
Start of the Ph.D.: October 1st, 2014
Department: Genomes and Genetics
Title of the PhD project: Mechanisms of nuclear and mitochondrial DNA maintenance in muscle adult stem cells and during regeneration
Name of the lab: Unité de Génétique Moléculaire des Levures
Head of the lab: Bernard Dujon
PhD advisor: Miria Ricchetti
Email address: firstname.lastname@example.org
Web site address of the lab:
Doctoral school affiliation and University: Complexité du Vivant (CdV), Université Pierre et Marie Curie (UPMC)
Presentation of the laboratory and its research topics:
The team works on the stability of nuclear and mitochondrial DNA in mammalian cells. The main aim is to understand how repair of DNA double-strand break (DSB) adapts and participates in different cellular states including differentiation, senescence, stress, and cancerogenesis. DSBs are possibly the most dangerous DNA lesion a cell can incur. We discovered a defect in DSB repair that accentuates cellular senescence and impacts on immortalisation of primary cells. We also also identified a novel repair mechanism in bacteria that affects survival and adaptation, and has links with a mechanism responsible for rearrangements in human malignancies. Ongoing work focuses on how adult muscle stem cells repair DSBs compared to their committed progeny, investigating cell differentiation versus efficiency and accuracy of DNA repair.
Linked to this topic, our previous work on the mechanism of integration of mitochondrial DNA (mtDNA) in the nuclear genome via DSB repair led us to study mtDNA dynamics. We developed a novel high-resolution quantitative imaging and 3D reconstruction tool (mTRIP), which allows the simultaneous detection of mitochondrial DNA and RNA, and proteins at the single-cell level. mTRIP reveals important alterations of mitochondrial DNA dynamics under physiological and pathological conditions. Largely based on this approach we showed that replication and transcription of mtDNA are correlated with the cell cycle. We previously showed that mitochondrial dynamics are associated with extraordinary survival capacity of adult muscle stem cells several days post-mortem. Ongoing investigations focus on the role of mtDNA dynamics in stem cell survival post-mortem, and during regeneration and ageing.
Description of the project:
Adult stem cells, which are responsible for homeostasis and tissue regeneration after injury, possess the combined capacity of proliferation, differentiation, and self-renewal. Genome integrity should be maintained during all these phases, which may also include long periods of quiescence. Failure to properly repair DNA damage results in the reduction of the adult stem cells pools, which in turn accelerates ageing, or might be at the origin of some cancers.
In collaboration with muscle stem (satellite) cells experts, we use skeletal muscle as a model system to study stem cells and their committed progeny. Results obtained in the lab (submitted manuscript) show that satellite cells repair DSBs more efficiently and accurately than their committed progeny. The main part of the PhD project is to decipher how satellite cells efficiently repair DNA damage, and which mechanistic changes occur during muscle differentiation to alter the repair potential. Transgenic mice are available to isolate homogeneous populations of rare satellite cells, as well within the native niche in the muscle fiber. Other studies are performed on satellite cells during a lineage progression in culture. We detect DSB repair in vivo and in vitro using DSB markers in wild type and mutant mice, and in the presence of specific inhibitors. The project includes analysis of chromatin remodelling during DSB repair and differentiation by specific immunomarkers. Moreover, it will be investigated whether alteration of the repair process functionally affects muscle regeneration, and whether repair mechanism(s) are impaired during ageing.
We recently analysed the dynamics of mitochondria in the resistance of satellite cells to stress, and we aim now to dissect the role of mitochondria and mtDNA processing (replication and transcription) therein. Largely based on the imaging approach that we developed, mTRIP, this part of the project concerns the stability and the processing of mtDNA in satellite cells during quiescence, activation, and differentiation, and the impact of these events in muscle regeneration.
This project focuses on assessing the mechanisms of nuclear and mitochondrial DNA maintenance in muscle adult stem cells versus their committed progeny.
Latil et al, 2012, Nature Commun. 3: 903, doi10.1038/ncomms1890. Skeletal muscle stem cells adopt a dormant cell state post mortem and retain regenerative capacity
Chatre and Ricchetti, 2013, Nucleic Acids Res 41:3068-3078. Prevalent coordination of mitochondrial DNA transcription and initiation of replication with the cell cycle.
Stem cells, DNA repair, chromatin, mitochondria, senescence, regeneration, cancer.
Expected profile of the candidate (optional):
Previous working experience with mammalian cells. Background in genetics and/or biochemistry appreciated.