The production of gametes involves a crossover exchange between chromosomes that is necessary to create diversity within sexual species and to promote their adaptation to the environment. This exchange is the result of meiosis, a particular type of cell division that is specific to the pool of germ cells [1] that ultimately become the spermatozoa or egg cells. Besides this crossover, meiosis allows halving the number of chromosomes (from 46 to 23 in humans) in the gametes, such that when they unite with their partners from the opposite sex, cells are formed that integrate the gene pool of both parents. If this reduction in genetic material goes bad, monosomy [2] or trisomy [3] abnormalities appear, notably trisomy 21. Infertility is also possible.

A team from the CEA-IRCM, specializing in the mechanisms of meiosis, has discovered a protein essential to its smooth execution. Named MEIOB [4], it is found in all vertebrates. The researchers tracked, using antibody staining, the movements of MEIOB to show that it intervenes during the mixing of chromosomes, specifically when strands of chromosomes randomly rearrange themselves together by a phenomenon known as “homologous recombination”. Additionally, studies on transgenic mice that lack the gene encoding the MEIOB protein demonstrated that its absence blocks meiosis. The male and female mice then turn out to be sterile.

​ Fluorescence imagery on a spread of male mice meiotic chromosomes (spermatocytes). MEIOB is marked green, and the chromosome axes are in blue (Sycp3). In red, the sex vesicle that contains non-paired X and Y chromosomes.

This discovery could have implications for the diagnosis of infertilities, through the search for mutations in the MEIOB gene. It will also undoubtedly advance the understanding of the DNA repair mechanisms in which MEIOB is involved and that we find altered in many diseases, including certain cancers.