New Research Confirms that Mitochondrial DNA is Exclusively Passed Down by the Mother
Scientists from Oregon Health & Science University and other institutions have made a breakthrough discovery regarding mitochondrial DNA (mtDNA) inheritance. The study, published in the journal Nature Genetics, sheds light on the longstanding scientific principle that only the mother contributes mtDNA to the offspring.
MtDNA is a distinct genetic code found in the organelle responsible for energy production in every cell of the body. It has long been known that mtDNA is passed down exclusively through egg cells in humans. However, it was previously believed that paternal mtDNA was eliminated after fertilization.
The recent study found that mature sperm cells do carry a small number of mitochondria but lack intact mtDNA. Shoukhrat Mitalipov, the Director of the Center for Embryonic Cell and Gene Therapy at Oregon Health & Science University, explained, “We found that each sperm cell does bring 100 or so mitochondria as organelles when it fertilizes an egg, but there is no mtDNA in them.”
Furthermore, the researchers discovered that sperm cells also lack a protein called mitochondrial transcription factor A (TFAM), which is essential for mtDNA maintenance. The reasons behind this exclusion of mtDNA from sperm cells remain unclear. Mitalipov suggests that it may be because sperm cells consume a significant amount of mitochondrial energy during fertilization, leading to an accumulation of mutations in mtDNA. In contrast, eggs, or oocytes, rely on energy from surrounding cells rather than their own mitochondria, resulting in relatively pristine mtDNA.
The study also highlights the significant impact mtDNA mutations can have on health. Mutations in mtDNA can cause various potentially fatal disorders affecting high-energy-demand organs like the heart, muscles, and brain.
To address the issue of passing on mtDNA disorders, Mitalipov pioneered a method called mitochondrial replacement therapy, which involves replacing mutant mtDNA with healthy mtDNA from donor eggs through in vitro fertilization. However, clinical trials for this procedure in the United States are currently prohibited by Congress, so trials are being conducted overseas.
The implications of this research extend beyond fertility and could have important applications in germ cell therapy. Understanding the role of TFAM during sperm maturation and fertilization may hold the key to treating certain infertility disorders and improving the efficacy of assisted reproductive technologies.
Overall, this study provides valuable insights into the intricacies of mtDNA inheritance and opens doors for further research in the field.