Mitochondrial DNA heteroplasmy is modulated during oocyte development propagating mutation transmission

Area of Science:

• Genetics
• Molecular Biology
• Mitochondrial Diseases

Background:

• Heteroplasmic mitochondrial DNA (mtDNA) mutations are linked to inherited diseases.
• A small number of recurrent mutations cause most new familial cases, but the underlying reasons remain unclear.

Purpose of the Study:

• To investigate the transmission patterns of heteroplasmic mtDNA mutations.
• To understand the mechanisms driving the increase and regulation of pathogenic mtDNA mutations during inheritance.

Main Methods:

• Studied heteroplasmic mice transmitting the m.5024C>T mutation, analogous to a human pathogenic mutation.
• Analyzed 1167 mother-pup pairs for mtDNA transmission patterns.
• Utilized single-cell analysis of developing mouse oocytes to examine mtDNA dynamics.

Main Results:

• The m.5024C>T mutation preferentially increased from low to higher levels during maternal transmission but did not reach homoplasmy.
• Preferential propagation of mutant mtDNA over wild-type mtDNA was observed in oocytes, independent of cell division.
• Similar inheritance patterns were noted in human pedigrees with pathogenic mtDNA mutations.

Conclusions:

• Preferential mtDNA propagation during oocyte maturation drives the increase of pathogenic mutations.
• Purifying selection against high heteroplasmy levels counterbalances this propagation, preventing mutation fixation.
• This dynamic explains how disease-causing mtDNA mutations can increase to pathogenic levels across generations without becoming fixed in the population.