The role of mtDNAin oocyte quality and embryo development

The mitochondrial genome resides in the mitochondria present in nearly all cell types. The porcine (Sus scrofa) mitochondrial genome is circa 16.7 kb in size and exists in the multimeric format in cells. Individual cell types have different numbers of mitochondrial DNA (mtDNA) copy number based on their requirements for ATP produced by oxidative phosphorylation. The oocyte has the largest number of mtDNA of any cell type. During oogenesis, the oocyte sets mtDNA copy number in order that sufficient copies are available to support subsequent developmental events. It also initiates a program of epigenetic patterning that regulates, for example, DNA methylation levels of the nuclear genome. Once fertilized, the nuclear and mitochondrial genomes establish synchrony to ensure that the embryo and fetus can complete each developmental milestone. However, altering the oocyte's mtDNA copy number by mitochondrial supplementation can affect the programming and gene expression profiles of the developing embryo and, in oocytes deficient of mtDNA, it appears to have a positive impact on the embryo development rates and gene expression profiles. Furthermore, mtDNA haplotypes, which define common maternal origins, appear to affect developmental outcomes and certain reproductive traits. Nevertheless, the manipulation of the mitochondrial content of an oocyte might have a developmental advantage.

Automated summary

The mitochondrial genome resides in the mitochondria present in nearly all cell types. The porcine (Sus scrofa) mitochondrial genome is approximately 16.7 kb in size and exists in a multimeric format in cells. Different cell types have varying numbers of mitochondrial DNA (mtDNA) copy number based on their need for ATP, which is produced through oxidative phosphorylation. The oocyte, or egg cell, has the highest number of mtDNA copies among all cell types. During oogenesis, the oocyte determines the mtDNA copy number to ensure there are enough copies to support subsequent developmental events. Additionally, it initiates a program of epigenetic patterning that regulates DNA methylation levels of the nuclear genome. Once fertilized, the nuclear and mitochondrial genomes synchronize to ensure proper development of the embryo and fetus. However, altering the mtDNA copy number in the oocyte through mitochondrial supplementation can impact the programming and gene expression profiles of the developing embryo. Interestingly, oocytes that are deficient in mtDNA show improved embryo development rates and gene expression profiles. Furthermore, mtDNA haplotypes, which represent maternal origins, appear to influence developmental outcomes and certain reproductive traits. Overall, manipulating the mitochondrial content of oocytes can provide developmental advantages.