Annuaire
Unusual chromosome inheritance and asexual reproduction
Non-parasitic nematodes from the Rhabitidae family show a large diversity of reproductive modes. While male/female represent the ancestral state, alternative mode of reproductions have emerged several times independently in the phylogeny, such as 1) self-fertilizing hermaphrodites with facultative males, 2) strict parthenogenesis, 3) sperm-dependent parthenogenesis. These nematodes species can be bread in the laboratory following standard conditions used for the model species C. elegans.
We are exploring the cellular modifications that have allowed the emergence of new reproductive strategies. For instance, while the sperm centrosomes provide the first polarity cue of the C. elegans zygote, parthenogenetic species must polarize independently of this cue. In these species, centrosomes are not provided paternally, also raising the question of their origin. In parthenogenetic species, female produce diploid oocytes through modifications of meiosis, but the underlying molecular mechanisms of such changes are unknown.
We are currently studying the origin of asexuality within the Mesorhabditis genus.
In this group, females produce 90% of unreduced diploid oocytes. Although fertilization of these oocytes by a sperm is necessary for egg acitvation, the sperm DNA is not utilized. These embryos contain only the maternal DNA and develop as females. Females can also produce a small percentage of regular haploid oocytes. Here, after fertilization, the haploid sperm DNA fuses with the haploid female DNA and such diploid eggs develop as males.
We found that these sexual embryos produce only males because the sperm bearing the Y chromosomes are much more competent than the sperm bearing a X chromosome to fertilize the eggs.
In the population, we find 10% males because only 10% eggs develop from the two parental genomes. Overal, this species produces asexual females and sexual males, featuring a progressive loss of males and sexuality.
We are exploring the cellular basis of this innovation and the consequences on the population genetic structure of these species.
Recent publications:
