Cytoplasmic competition between separate parental pronuclei in zygotes.

. Here, using a combination of mouse zygote manipulation, quantitative imaging and theoretical approaches, we show a cytoplasm-mediated competition mechanism between separate parental pronuclei that ensures developmental potential. This mechanism limits pronuclear volume and prevents epigenetic mark dysregulation, including loss of trimethylated histones. One-pronuclear biparental zygotes lack this mechanism, resulting in a reduced rate of development to term. This low developmental potential can be partially rescued by competition-based or drug-based restoration of epigenetic marks. This study provides a spatial mechanism linking fertilization to the establishment of the full developmental potential for the next generation, highlighting caveats in clinical use of one-pronuclear biparental zygotes.