Maternal spindle transfer overcomes embryo developmental arrest caused by ooplasmic defects in mice

Abstract

The developmental potential of early embryos is mainly dictated by the quality of the oocyte. Here, we explore the utility of the maternal spindle transfer (MST) technique as a reproductive approach to enhance oocyte developmental competence. Our proof-of-concept experiments show that replacement of the entire cytoplasm of oocytes from a sensitive mouse strain overcomes massive embryo developmental arrest characteristic of non-manipulated oocytes. Genetic analysis confirmed minimal carryover of mtDNA following MST. Resulting mice showed low heteroplasmy levels in multiple organs at adult age, normal histology and fertility. Mice were followed for five generations (F5), revealing that heteroplasmy was reduced in F2 mice and was undetectable in the subsequent generations. This pre-clinical model demonstrates the high efficiency and potential of the MST technique, not only to prevent the transmission of mtDNA mutations, but also as a new potential treatment for patients with certain forms of infertility refractory to current clinical strategies.

Mitochondrial Genetic Drift after Nuclear Transfer in Oocytes

“…Similar results were reported by Kang et al [22]. In 2020, a mouse study showed that MST between B6CBAF1 and NZB lines resulted in healthy litters; mtDNA heteroplasmy was reduced in F2 mice and it was undetectable in subsequent generations [23].…”

Prospects of Germline Nuclear Transfer in Women With Diminished Ovarian Reserve

“…Nuclear transfer (both ST and PNT) between oocytes from NZB/OlaHsd mice that display a two-cell blockage and control B6D2 mice, rescued the embryonic development, resulting in high blastocyst rates ( 42 ). The use of ST by of Costas-Borges et al ( 43 ), using the same mouse model, demonstrated similar results but also low carry-over rates of maternal mitochondrial DNA and low heteroplasmy levels in the offspring for several generations, as well as normal fertility of the pups from the reconstructed embryos ( 43 ).…”

“…Two recent publications ( 42 , 43 ) investigated the use of NT technology to overcome embryo developmental arrest in a mouse model. Nuclear transfer (both ST and PNT) between oocytes from NZB/OlaHsd mice that display a two-cell blockage and control B6D2 mice, rescued the embryonic development, resulting in high blastocyst rates ( 42 ).…”

“…NT is currently clinically applied in a strict subset of patients suffering from mitochondrial DNA (mtDNA) disorders, aiming to overcome maternal mutant mtDNA transmission to the next generation. Besides, increasing interest has been shown in the application of NT to overcome certain types of female-related infertility ( 42 ), which is supported by some promising studies in animal models ( 42 , 43 ), but still, peer-reviewed reports in human patients remain scarce. The rationale of this treatment is that by transferring the nuclear DNA from an oocyte with inferior quality cytoplasm to an oocyte with more competent cytoplasm, like the ones of young, fertile women, could potentially improve embryo development.…”

Germ Cell Derivation from Pluripotent Stem Cells for Understanding In Vitro Gametogenesis

“…In addition, patient cell-derived oocytes can be used to rejuvenate or induce healthy oocytes and boost fertility by transferring ooplasm to old or low-quality oocytes [119]. For example, cytoplasts from hPSCs could be another therapeutic source for patients with mitochondrial DNA mutations, which is one of the causes of developmental arrest in embryos [120]. This approach is currently feasible because early germ cells, such as oogonia, can be used as ooplasm or mitochondrial donors [121].…”