The effects of mitochondrial DNA supplementation at the time of fertilization on the gene expression profiles of porcine preimplantation embryos

Mitochondrial DNA (mtDNA) deficient metaphase II porcine oocytes are less likely to fertilize and more likely to arrest during preimplantation development. However, they can be supplemented with autologous populations of mitochondria at the time of fertilization, which significantly increases mtDNA copy number by the 2-cell stage due to the modulation of DNA methylation at a CpG island of the gene encoding the mtDNA-specific polymerase, POLG, and promotes preimplantation development. Although mitochondrial supplementation does not increase development rates or mtDNA copy number in oocytes with normal levels of mtDNA copy number, we tested whether this approach would also impact on chromosomal gene expression patterns in these oocytes at each stage of preimplantation development. Here, we have compared the gene expression profiles of embryos produced by mitochondrial supplementation at the time of fertilization with embryos produced by in vitro fertilization (IVF) using a panel of genes associated with different stages of preimplantation development. When compared to IVF-derived embryos, 27 (34%) genes were differentially expressed in supplemented embryos but this was restricted to one or two developmental stages. However, 53 (66%) genes were comparably expressed across all six stages and by the blastocyst stage 4 (5%) genes were differentially expressed. We conclude that additional copies of mtDNA can induce changes in gene expression at various stages of preimplantation development with the first changes occurring prior to maternal-to-zygotic transition (MZT). However, these changes appear to be transitory suggesting that some genomic resetting is taking place.