Asymmetric Reprogramming Capacity of Parental Pronuclei in Mouse Zygote

It has been demonstrated previously that the reprogramming factors are sequestered in the pronuclei of zygote after fertilization, as the enucleated zygotes at interphase cannot support the development of cloned embryos whereas the enucleated zygotes at M-phase can reprogram somatic cells to full pluripotency. However, it remains unknown whether the parental pronucleus, derived either from the sperm or oocyte, possesses the similar reprogramming ability. Here, we provide evidence demonstrating that the parental pronuclei are asymmetric in reprogramming and the reprogramming factors reside mainly in the male pronucleus. As a result, only the female pronucleus-depleted mouse zygotes enucleated at M-phase of mitosis can support the somatic cell reprogramming, the derivation of chromosome transfer embryonic stem (ctES) cells with full pluripotency and the full term development of cloned embryos. In striking contrast, the male pronucleus-depleted zygotes enucleated at M-phase of mitosis fail to support the pre-implantation development of somatic cell cloned embryos. Furthermore, we demonstrated that the distinct epigenetic reprogramming ability of the parental pronucleus might contribute directly to the developmental difference of somatic cloned embryos. Our study highlights the developmental asymmetry of parental pronuclei in reprogramming. We compared the gene expression profile of ctES cells. Two biological repeats were included.