In mammals, the production of mature sperm relies on a complex multi-step process through the development.
Important nuclar rearrangements are occuring in order to obtain these highly specialised cells. Interestingly, one of the major remodeling event occuring during sperm formation if the eviction of histones from the DNA.
Histones are small basic proteins associating with the DNA and playing an important role in the expression of the genome in all cell types. However, at a late stage of spermatogenesis, the majority of those histones are evicted and replaced by small basic proteins called protamine that allow the compaction of the genome in the small head of the sperm cell. It is thought that the eviction of these histones might be important to prevent or minimise the transmission of information acquired during development or resulting from changes in the environment, thus minimising the transmission of acquired information, non carried by the DNA itself, that could be deleterious to the progeny. In the recent years, it has become clear that although the majority of histones are removed in the sperm, a small proportion, 1 to 10% in mice, are retained at specific loci and might carry information hat could affect the progeny.
In the recent years, it was shown that the environment (diet, stress, toxines..)that a father is subjected to can affect the fitness of his progeny. Some of these changes seem to be transmitted without any changes in the DNA sequence suggesting that other molecules might carry the information. It is therefore very important to understand how and to what extent this acquired information is transmitted to the next generation.
Since histones are able to carry information through cell division, we decided to investigate the role of the histones that are maintained in the mature sperm and whether these histones might transmit non-genetic information from one generation to the next.
The study of this process has been hindered until recently, since cells going through this histone to protamine exchnage are scarce and very difficult to isolate
Male gametogenesis has recently been successfully recapitulated in vitro leading to the production of embryonic stem cell (ESC)-derived SLCs (spermatid like cells) that display general hallmarks specific for in
vivo-spermatids and produce viable offspring when injected into mouse oocytes 8. We propose to use this
innovative in vitro system that uses ESCs that are amenable to genetic manipulation and reporter cell lines
facilitating the isolation of specific precursor germ cells to unravel the regulatory network involved in
histone/protamine exchange and to determine whether and how histones retained in sperm transmit epigenetic traits to the progeny.
