Presence of the Paternal Pronucleus Assists Embryo in Overcoming Cycloheximide Induced Abnormalities in Zygotic Mitosis

Abstract

After fertilization, the maternal and paternal chromosomes independently proceed through pronuclear formation. These chromatin reconfigurations occur within a shared cytoplasm thus exposing both gametes to the same factors. Here, we report that continuous cycloheximide [40 µg/mL] treatment of parthenogenotes, androgenotes, and ICSI embryos reveals ORC2 pronuclear instability in the maternal (MPN) but not the paternal pronucleus (PPN). When released from CHX after 8 hours, the MPN can recover ORC2 and proceed through replication, however, parthenogenotes encounter severe mitotic defects while both ICSI embryos and androgenotes are able to recover and develop at significantly higher rates. Taken together, these data suggest cycloheximide treatment promotes an environment that asymmetrically affects the stability of ORC2 on the MPN, and the ability of the MPN to develop. Furthermore, the presence of the PPN in the zygote can ameliorate both effects. These data suggest further evidence for crosstalk between the two pronuclei during the first cell cycle of the embryo.