Mitochondrial DNA rearrangements in human oocytes and preimplantation embryos

Human cells contain mitochondria which provide energy for cellular functions through the biochemical process of oxidative phosphorylation (OXPHOS). Mitochondria contain mitochondrial DNA (mtDNA) which encodes for 13 proteins involved in OXPHOS. A variety of mtDNA rearrangements have been found to exist in association with degenerative diseases and shown to accumulate with age in tissues of normal individuals (1-10). The absence of these rearrangements from fetal tissues support the hypothesis that some mechanism exists that filters out rearrangements for the next generation to inherit only normal mtDNA (6, 11).;This dissertation was designed to test the following hypotheses: (1) That a variety of mtDNA rearrangements exist in human oocytes and preimplantation embryos, (2) That there is a decrease in the presence of rearrangements between the oocyte and the preimplantation embryo, (3) That these rearrangements accumulate with advancing maternal age, and (4) That the percentage of oocytes with these rearrangements decreases during oocyte development.;To investigate these hypotheses a nested PCR strategy was used to analyze mtDNA from oocytes and preimplantation embryos for a variety of rearrangements. The frequency of mtDNA rearrangements in 295 human oocytes was 50.5%, and the frequency of rearrangements in 197 human preimplantation embryos was 32.5%. The percentage of oocytes with mtDNA rearrangements was significantly higher than the percentage of preimplantation embryos with rearrangements (p ;These findings support the hypotheses that the human oocyte and preimplantation embryo do contain a variety of mtDNA rearrangements, that a decrease in the presence of rearrangements occurred during oocyte development, and that there is a significant decrease in the presence of mtDNA rearrangements between human oocytes and preimplantation embryos. The finding that there was not an age-related accumulation of mtDNA rearrangements in human oocytes did not support the hypothesis that rearrangements accumulate with age. In fact, since there was an age-related decrease in mtDNA rearrangements in the human oocyte, a direct contradiction to the hypothesis that age-related accumulations of rearrangements occur in the human oocyte was shown. The finding that mtDNA rearrangements decreased significantly after germinal vesicle breakdown occurred, supported the hypothesis that as oocyte development continues a decrease in the percentage of oocytes with rearrangements would be found.;The elimination of oocytes with mtDNA rearrangements during oocyte developmental will require further research, but may be related to energy requirements for germinal vesicle breakdown and the resumption of meiosis I. The significant decrease in the presence of mtDNA rearrangements between oocytes and preimplantation embryos will require further research to determine the cause of oocytes with rearrangements failing to fertilize, or preimplantation embryos failing to develop. The significant age-related decrease in mitochondrial DNA rearrangements seen in the human oocyte shows that the human oocyte is different from any other tissue studied. Why and how an age-related decrease in rearrangements occurs, and the role that mtDNA plays in fertility will require further investigation.