Mitochondrial gene replacement in primate offspring and embryonic stem cells

Abstract

Mitochondria are found in all eukaryotic cells and contain their own genome (mtDNA). Unlike the nuclear genome which is derived from both the egg and sperm at fertilization, the mtDNA in the embryo are derived almost exclusively from the egg, i.e. is of maternal origin. Mutations in mtDNA contribute to a diverse range of still incurable human diseases and disorders. To establish preclinical models for new therapeutic approaches, we demonstrate here that the mitochondrial genome can be efficiently replaced in mature nonhuman primate oocytes by spindle-chromosomal complex transfer from one egg to an enucleated, mitochondrial-replete egg. The reconstructed oocytes with the mitochondrial replacement were capable of supporting normal fertilization, embryo development and produced healthy offspring. Genetic analysis confirmed that nuclear DNA in the three infants born so far originated from the spindle donors while mtDNA came from the cytoplast donors. No contribution of spindle donor mtDNA was detected in offspring. Spindle replacement is shown here as an efficient protocol replacing the full complement of mitochondria in newly generated embryonic stem cell lines. This approach may offer a reproductive option to prevent mtDNA disease transmission in affected families.

Functional Human Oocytes Generated by Transfer of Polar Body Genomes

“…Expanded use of PBNT, in addition to spindle transfer (ST), could provide an additional technique to support mitochondrial replacement therapy (MRT); a promising approach to avoid maternal transmission of mtDNA-based disease (Tachibana et al, 2013b;Tachibana et al, 2009). In mice, it has been demonstrated that a minimal mtDNA carryover can be achieved in offspring generated by polar body transfer (Wang et al, 2014;Yamada et al, 2016).…”

“…Next, we produced reconstructed PBNT oocytes by fusing intact, round PB1 with MII cytoplasts ( Figure 1A and 1C) (Tachibana et al, 2013b;Tachibana et al, 2009). Noninvasive imaging indicated that most PBNT oocytes (67%) formed visible spindles within 60 min of fusion ( Figure 1D).…”

The ups and downs of somatic cell nucleus transfer (SCNT) in humans

“…These approaches are now almost exclusively oriented on the elimination of mutated mitochondrial DNA (mtDNA), that can cause some devastating diseases [29]. It has been demonstrated quite recently in humans that the transfer of pronuclei or spindles, isolated from the cytoplasm containing mutated mtDNA, into healthy cytoplasts seems to be very promising and healthy looking blastocysts were obtained [30][31][32][33].…”

Reproductive medicine: The power of three

“…While Turnbull and his team were developing their pronuclear-transfer technique in human egg cells, a US team was testing a related method in monkeys. In 2009, reproductive biologist Shoukhrat Mitalipov at the Oregon Health and Science University in Beaverton and his colleagues reported the birth of two healthy rhesus macaques whose mitochondria and nuclei had come from different egg cells 5 . The monkey twins -named Mito and Tracker, after a reagent used to make mitochondria glow -were conceived through a method called maternal spindle transfer (see 'Genome transplant').…”