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

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.

Can Maternal Spindle Transfer and Pronuclear Transfer Be Prohibited under eu Legislation?

The question whether maternal spindle transfer (mst) and pronuclear transfer (pnt) can be prohibited under eu legislation was examined by the non-governmental organisation European Bioethics Research (ebr). It did so by submitting an official complaint to the eu Commission proposing that the uk Human Fertilisation and Embryology (Mitochondrial Donation) Regulations 2015 breached the prohibition on the modification of a person’s germ line genetic identity of the eu Clinical Trials Directive 2001/20/EC and the new Regulation eu 536/2014. A discussion then took place, during 2016, between ebr and the eu Commission whether mst and pnt principally involved a ‘medicinal product’ in which case the eu Clinical Trials Directive 2001/20/EC and Regulation eu 536/2014 would be applicable or whether the procedures just involved a medical procedure in which case the Tissue and Cells Directive 2004/23/EC was applicable which did not include any prohibition on the intentional modification of a person’s germline.

Advances in methods for reducing mitochondrial DNA disease by replacing or manipulating the mitochondrial genome

Mitochondrial DNA (mtDNA) is a multi-copy genome whose cell copy number varies depending on tissue type. Mutations in mtDNA can cause a wide spectrum of diseases. Mutated mtDNA is often found as a subset of the total mtDNA population in a cell or tissue, a situation known as heteroplasmy. As mitochondrial dysfunction only presents after a certain level of heteroplasmy has been acquired, ways to artificially reduce or replace the mutated species have been attempted. This review addresses recent approaches and advances in this field, focusing on the prevention of pathogenic mtDNA transfer via mitochondrial donation techniques such as maternal spindle transfer and pronuclear transfer in which mutated mtDNA in the oocyte or fertilized embryo is substituted with normal copies of the mitochondrial genome. This review also discusses the molecular targeting and cleavage of pathogenic mtDNA to shift heteroplasmy using antigenomic therapy and genome engineering techniques including Zinc-finger nucleases and transcription activator-like effector nucleases. Finally, it considers CRISPR technology and the unique difficulties that mitochondrial genome editing presents.