Self-diploidization of human haploid parthenogenetic embryos through the Rho pathway regulates endomitosis and failed cytokinesis

A diploid genome is necessary for normal mammalian development, thus haploid parthenogenetic embryos undergo frequent self-diploidization during preimplantation development; however, the underlying mechanism is unclear. In this study, time-lapse recording revealed that human haploid parthenotes (HPs) undergo self-diploidization via failed cytokinesis (FC) and endomitosis (EM). The frequencies of FC/EM were significantly higher in HPs than in normal fertilized embryos (26.3% vs. 1.6%, P   0.05). In 66.7% of the 1-cell stage HPs, furrow ingression was not observed during the time for normal cleavage, and both immunostaining and gene expression analysis of 1-cell stage HPs revealed the absence or down-regulation of several key genes of the Rho pathway, which regulates cytomitosis. Our results suggested that the major mechanism for self-diploidization is Rho pathway inhibition leading to FC/EM in the first cell cycle, and fine-tuning of this signalling pathway may help to generate stable haploid embryos for stem cell biology studies.