Restarting life: fertilization and the transition from meiosis to mitosis

Fertilization triggers a complex cellular programme that leads to a totipotent mitotic embryo. The molecular mechanisms underlying the meiosis to mitosis transition include changes in sister chromatid linkages, the reintroduction of a centrosome, a shift to symmetric cell division and changes in genomic imprinting and protein expression control. Fertilization triggers a complex cellular programme that transforms two highly specialized meiotic germ cells, the oocyte and the sperm, into a totipotent mitotic embryo. Linkages between sister chromatids are remodelled to support the switch from reductional meiotic to equational mitotic divisions; the centrosome, which is absent from the egg, is reintroduced; cell division shifts from being extremely asymmetric to symmetric; genomic imprinting is selectively erased and re-established; and protein expression shifts from translational control to transcriptional control. Recent work has started to reveal how this remarkable transition from meiosis to mitosis is achieved.