Molecular basis of post-meiotic male genome reprogramming – EpiSperm2

This project is a direct continuation of our first ANR program EpiSperm1. It mainly involves the use of animal models we had generated in the previous phase. We have recently finalized one of these studies on the BET bromodomain member, Brdt, which involved the use of large-scale proteomic and genomic approaches. Important results have been obtained and the corresponding manuscript was submitted very recently. The same methodological approaches are underway for two other models on histone variants.
Additionally, our tripartite consortium involving two American laboratories (Chicago and San Diego) is now functioning in a very efficient way. Briefly, this consortium is constituted of a leader proteomic laboratory which has discovered a large number of new histone PTMs (Yingming Zhao, Chicago) a laboratory at the cutting edge of genome-wide approaches (Bing Ren, UCSD), and ourselves who applies these approaches to understand the programming of the male genome. After the publication of the first article end 2011 (Tan et al. Cell, 2011), we are now finalizing two other manuscripts, which will be submitted shortly.

The results obtained during these programs allow for the first time to propose a molecular model for an essential phasis of the life cycle of all eukaryotes : post-meiotic male/spore genome reorganization and the transmission of the corresponding epigenome.
The outputs of these results are of conceptual importance since they shed light on a yet obscure aspect of the biology of many organisms. Additionally, the knowledge generated here has implications in the understanding of some causes of male infertility and also give an insight into the relationship between environment and the male genome.
Finally, we are using these results to develop a cancer related project, since we have also shown that many of the factors we are studying become aberrantly activated in almost all cancers. This is poorly studied aspect of cancer biology with many applications in cancer management. With this respect we are in contact with several international pharmaceutical groups to inhibit the action of some of these factors in cancer.

Additional animal and cellular models will be generated to better define the molecular model of post-meiotic male genome reorganization. Application of this model on the transmission of the male epigenetic information, male infertility and cancer will be further developed.

Taking into account the complexity of the biological issue tackled and facing the scarcity of data on the biological issue investigated in this program, we are piloting this research on a highly collaborative basis. Since the beginning of the program in 2007, we have published 49 original and review in peer-reviewed journals. These publications involved 29 collaborations with national and international laboratories.
On the cancer aspect of this program we have already submitted 4 patents.

Post-meiotic differentiation of male germ cells is associated with one of the most spectacular genome reorganizations. Indeed, during this process the universal mode of genome packing in eukaryotes, based on nucleosomes, drastically changes towards a new form of DNA compaction using small basic proteins, called protamines. Although these post-meiotic changes are of high consequences for procreation and constitute an essential step in the life cycle, most of the mechanisms controlling the establishment of the male gamete genome remain obscure. For unknown reasons the understanding of the molecular basis of this essential biological process seems to have escaped the attention of the biologists. The extent of our ignorance is such that even in yeast, the genome reorganizations observed during the post-meiotic phases of sporulation, which show striking similarities with spermatogenesis, have remained unexplored. Indeed, it is still not known if histones are maintained or totally or partially replaced in the terminal phases of post-meiotic spore maturation and the mechanisms involved in directing this extreme genome compaction are unknown (please see our recent publication: Govin et al., Genes & Dev, 2010, PMID: 20713519).
Although very recent studies describing the existence and the nature of the male gamete epigenome have generated some excitement (see for example Hammoud et al Nature 2009 PMID: 19525931), no research group is currently developing a dedicated program focused on the understanding of the molecular basis of the mechanisms leading to the establishment of this specific epigenome.
During the last ten years, we have set up an ambitious research program, whose ultimate objective is the unravelling of the molecular mechanisms controlling haploid male genome reorganizations and the establishment of the associated epigenome. Due to the complexity of the question and to the extent of our ignorance, we are leading this project on a highly collaborative and multidisciplinary basis.
An “ANR Blanche” project, granted in 2007, was instrumental in lifting us to a leading position in this field. During the past few years, our structural and functional studies have uncovered some of the general traits of mechanisms controlling the haploid male germ cell differentiation. More specifically, we have unravelled the bases of the genome-wide histone removal by showing that it relies on the combined actions of histone variants and histone hyperacetylation. The structural functional investigation of a double bromodomain-containing factor characterized in our team, Brdt, was a key step (Morinière et al., 2009, Nature). The discovery and functional analyses of new histone variants as well as new post-translational histone modifications, revealed the occurrence of a region specific male genome reprogramming (Govin et al., J. Cell. Biol. 2007). Finally, a parallel study of yeast sporulation and mouse spermatogenesis appeared to be determinant in the understanding of post-meiotic genome compaction (Govin et al., Genes & Dev, 2010, PMID: 20713519). Additionally, the 2007 ANR grant allowed us to also generate the relevant animal models required to dissect the major molecular pathways controlling the histone-to-protamine transitions.
This proposal aims at supporting the important ongoing projects initiated thanks to the ANR EpiSperm (1) program. It should enable us to keep our leading position thanks to the unique tools, models and approaches we are developing, allow us to finalize our investigations and provide a comprehensive model for the establishment of the male genome and associated epigenome. Moreover, the planed development of ICSI in our laboratory will give us access to critical determinants in the male genome/epigenome, which are essential for early embryonic development after fertilization. These investigations are very rich in various types of applications, mainly in human male infertility, ART and also, unexpectedly, in somatic cancers.