Abstract
In regular IVF, a portion of oocytes exhibit abnormal numbers of pronuclei (PN) that is considered as abnormal fertilization, and they are routinely discarded. However, it is known that abnormal ploidy still does not completely abandon embryo development and implantation. To explore the potential of cytoplasm from those abnormally fertilized oocytes, we developed a novel technique for the transfer of large cytoplasm between pronuclear-stage mouse embryos, and assessed its impact. A large volume of cytoplast could be efficiently transferred in the PN stage using a novel two-step method of pronuclear-stage cytoplasmic transfer (PNCT). PNCT revealed the difference in the cytoplasmic function among abnormally fertilized embryos where the cytoplasm of 3PN was developmentally more competent than 1PN, and the supplementing of fresh 3PN cytoplasm restored the impaired developmental potential of postovulatory “aged” oocytes. PNCT-derived embryos harbored significantly higher mitochondrial DNA copies, ATP content, oxygen consumption rate, and total cells. The difference in cytoplasmic function between 3PN and 1PN mouse oocytes probably attributed to the proper activation via sperm and may impact subsequent epigenetic events. These results imply that PNCT may serve as a potential alternative treatment to whole egg donation for patients with age-related recurrent IVF failure.
Highlights
The cytoplasm of oocytes or embryos is known to harbor cytoplasmic factors, including maternal messenger RNA, maternally stored proteins, energy substrates, and mitochondria that will impact the proper completion of meiosis, fertilization, and early preimplantation development of the embryo [1,2,3]
As we intended to explore the cytoplasmic function of abnormally fertilized embryos, it was necessary to develop a reliable technique to isolate and transfer the cytoplasm of PN-stage embryos instead of total replacement, i.e., Pronuclear transfer (PNT)
We initially developed and demonstrated a novel cytoplasmic transfer technique, termed pronuclear-stage cytoplasmic transfer (PNCT), which was shown to be feasible, yielding viable embryos in a two-step process
Summary
The cytoplasm of oocytes or embryos is known to harbor cytoplasmic factors, including maternal messenger RNA (mRNA), maternally stored proteins, energy substrates, and mitochondria that will impact the proper completion of meiosis, fertilization, and early preimplantation development of the embryo [1,2,3]. These factors are believed to be indispensable for enabling gamete genome reprogramming to an embryonic or totipotent state, important for the erasure of methylation marks on the entire genome by genome-wide demethylation [4]. We explored the cytoplasmic function of abnormally fertilized embryos
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