Description of the thesis topic

Targeting meiotic DNA breaks to the right place at the right time
Meiosis is the process through which diploid germ cells become haploid gametes (oocytes or spermatozoa), ready to transmit their genetic material to the next generation. In order to preserve the species, it is therefore crucial to faithfully preserve this heritage.
Surprisingly, during the first meiotic division, several hundred DNA double-strand breaks (DSBs) are formed and repaired. This step, called meiotic recombination, although extremely dangerous, is indispensable for the correct segregation of homologous chromosomes (of paternal and maternal origin). Indeed, the repair of those breaks will lead to the formation of chiasmas (or crossovers) that will allow the formation of a transient physical link between homologous chromosomes, which is a necessary condition for triggering the signal for their separation. Given what is at stake, these steps must be finely orchestrated in order to avoid errors that will lead to genetic diseases such as Down's syndrome. In our team, we are studying a crucial step in this process: the initiation of recombination in meiosis.
This initiation is not random in the genome. It occurs in small genomic regions of about 2kb, called hot spots. In mice and humans, their localization is determined by the zinc-finger histone methyl transferase PRDM9, which, upon binding to DNA, causes a series of chromatin modifications that are necessary for the recruitment of the double-strand break formation machinery (Grey, Baudat, de Massy 2018). Interestingly, in organisms, where PRDM9 is absent, or in mutant mice for PRDM9, DSBs still form, but they localize at functional genomic elements (FE) such as promoters and enhancers.
In this thesis we would like to address why, when PRDM9 is present, DSBs take place at hotspots rather than at FE. One factor that could be involved in this choice is MEI4, a protein expressed in many cancers, which is an indispensable element of the meiotic DSB formation machinery, but which exact function is not known. In order to learn more about MEI4 and its partners, we would like to study its localisation within the nucleus, its interaction with other proteins, and the pathways of its recruitment to hotspots and FE in different mutant contexts. The localisation of MEI4 will be studied by conventional and super-resolution microscopy combined with FISH. New interaction partners of MEI4 will be identified by rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME) in a context where PRDM9 is present or absent, and the genomic localization of its known co-factor REC114 will be studied by ChIP followed by NGS sequencing. For a better mechanistic insight of the recruitment of MEI4 to its target sites (hotspots or FE), its recruitment on genomic loci will be studied by ectopic expression of MEI4 and potential recruiters, such as the protein IHO1, in cellular systems.
The multiangle approach and the various experimental systems, combined with our preliminary data, should ensure the candidate to be able to rapidly yield interesting results that will be valuable for the fields of meiosis and cancer biology. The candidate will join a multinational team (France, Switzerland, India, Japan, Italy) of three researchers, two engineers, one doctoral student, one postdoc and one master student. The candidate should be able to communicate in English and have some training in molecular biology, cytology, basic bioinformatics.

Work Context

The PhD project will be carried out in the "Meiosis and Recombination" team at the Institut de Génétique Humaine (IGH) in Montpellier under the supervision of C. Grey (DR2, CNRS). The IGH is located on the Arnaud de Villeneuve campus, near the Faculty of Medicine. The Meiosis and Recombination team is multinational (France, Switzerland, Italy, India) and consists of three researchers, two engineers, one PhD student, and several master's students. The working language is English. The candidate will have access to all the team's equipment, the shared IGH facilities, and the Biocampus platforms.

Constraints and risks

Biological risk, work at a screen, and work outside regular hours.