[SCAN] Gender inequality: The yeast perspective

Title: Gender inequality: The yeast perspective

Speaker: Celso Martins

From: Center for Integrative Genomics, University of Lausanne

Abstract: Anisogamous species, which produce gametes with significant morphological differences, are believed to have evolved from isogamous ancestors. The lack of evolutionary records and experimental evidence has made it difficult to understand how isogametes were selected for increased asymmetries. I will show how the morphologically indistinguishable fission yeast P- and M-gametes, which differentially express only a handful of genes, experience distinct mating type-specific selective pressures. We initially discovered that transcription of meiotic recombination genes, including the highly conserved meiotic cohesin rec8, occurs before fertilization. Surprisingly, only P-gametes produce Rec8 protein before gametes’ fusion, whereas Rec8 encoded by the M-gamete genome becomes detectable only when the two partners fuse. Here, we show that this asymmetry in Rec8 production is driven by distinct pheromone signalling between partners and that the P-gamete-produced Rec8 is critical for meiotic chromosome segregation. Strikingly, early expression of Rec8 also places a fitness cost on P-gametes; P-gametes that engage partners but fail to fuse exhibit increased genomic instability when allowed to proliferate asexually, which is prevented by removal of the rec8 gene. Finally, we show that P-gametes are at a competitive disadvantage to M-gametes in evolving populations that undergo cycles of mating and asexual reproduction and that the observed difference in fitness depends on the rec8 gene. Taken together, we demonstrate that distinct P- and M‑gametes investments in zygotic development impose different fitness costs. Our work provides the first example of how subtle molecular asymmetries can drive distinct selective pressures on isogametes during evolution.