Reverse reconstitution of human zygotes reveals the competence of zygotic cytoplasts in women of advanced maternal age

Abstract

Introduction Embryo euploidy rates are dramatically decreasing with maternal age. It was shown that for women ≥42 years old less than 10% of embryos are euploid and the probability for them to have at least one euploid embryo per cycle is ∼25%; even if they have good ovarian reserve. It's known that the majority of aneuploidies is caused by failure of correct chromosome segregation during two consequential meiosis, but the reasons for this phenomenon for patients of advanced maternal age are still poorly understood. More than that, itwas remaining unclear; could zygotic cytoplast of women of advanced maternal age support normal embryo development if it would contain the set of chromosomes of a young donor? Material and methods Simultaneous intracytoplasmic sperm injection (ICSI) with patient's partner's sperm had been done for patient's (N = 14, mean age 42 years old) and donor (N = 20, mean age 28 years old) oocytes; pronuclear transplantation (1PNs and 3PNs included) at ∼12h after fertilization; culturing in time-lapse incubator up to 7 days; trophectoderm biopsy on Day 5-7; PGT-A (aCGH or NGS); data analysis. Results 71 zygotes were reconstituted in experimental group (donor cytoplasm, nuclear genetic material of the patient and her partner), 23 (32.4%) blastocysts from 28 were suitable for trophectoderm biopsy and only 2 (8.7%) of them were euploid.48 zygotes were reconstituted in reverse group (patient's cytoplasm, nuclear genetic material of the donor and the patient's partner), 19 (39.6%) blastocysts from 24 were suitable for trophectoderm biopsy; 13 (68.4%) of them were euploid. For the first time, we have shown that aged cytoplasm, in general, does not prevent blastulation, moreover, euploidy rates of reversely reconstituted embryos (68.4%) are similar to euploidy rates of embryos derived from the oocyte donation cycles (66.8%, P>0.05). Further investigations are needed to clarify the role of cytoplasm in early embryo development. Conclusions Zygotic cytoplast of women of advanced maternal age can support an effective development of euploid embryo to blastocyst stage if it contains donor nuclear genetic material.