| There are many important aspects and emerging concepts of mitochondrial genetics involving studies of mtDNA heteroplasmy that need to be examined. To better understand these concepts, I tested several hypotheses. The first was the progression of age-related Alzheimer's Disease and Parkinson's Disease (ADPD) due to the accumulation of somatic mtDNA CR mutations in brain. I found, using sequencing analysis, that there are several somatic mtDNA CR mutations that do accumulate with age in ADPD. The second is that micro RNAs are involved in mitochondrial regulation. Using bioinformations, I found twelve putative pre-miRNAs that may result from degradation of the mtDNA during replication, as well as several nDNA encoded miRNAs that could possibly play a role in regulation of nuclear-encoded mitochondrial mRNAs or proteins. Specifically, mir-762, as it targets the most nuclear-encoded mitochondrially-related genes, and in general that miRNAs may regulate mtDNA mitochondrial gene expression. The third hypothesis is that recombination may be common in cells with heteroplasmic mtDNAs.;After cloning and sequencing mtDNA from heteroplasmic mice, I found recombination in up to 25% of the clones from some samples. The fourth is that heteroplasmic mtDNAs will be directionally segregated from the female germline in mice. Fragment analysis and SNaPshot genotyping of heteroplasmy levels of somatic tissues revealed that they are enriched as mice age. Specifically, NZB mtDNA is enriched in liver and kidney, and 129 mtDNA is enriched in spleen, pancreas, seminal vesicles and ovary. Additionally, it was revealed that the female germline does discriminate between different mtDNAs, as we saw a dramatic shift to 129 mtDNA homoplasmy within 1-2 generations nine times in our pedigree, while only after 15 generations of selective breeding did we acquire mice that were homoplasmic for NZB mtDNA. Additionally, we observed a selective loss of NZB mtDNA in individual oocytes, which implies that this shift occurs prior to oocyte ovulation. This changes how other studies, that assume neutral selection, have interpreted their results on random genetic drift of heteroplasmic mtDNAs. |
