The Use of Micromanipulation Methods as a Tool to Prevention of Transmission of Mutated Mitochondrial DNA

Reconstitution of the oocyte nucleolus in mice through a single nucleolar protein, NPM2

The mammalian oocyte nucleolus, the most prominent subcellular organelle in the oocyte, is vital in early development, yet its key functions and constituents remain unclear. We show here that the parthenotes/zygotes derived from enucleolated oocytes exhibited abnormal heterochromatin formation around parental pericentromeric DNAs, which led to a significant mitotic delay and frequent chromosome mis-segregation upon the first mitotic division. A proteomic analysis identified nucleoplasmin 2 (NPM2) as a dominant component of the oocyte nucleolus. Consistently, Npm2-deficient oocytes, which lack a normal nucleolar structure, showed chromosome segregation defects similar to those in enucleolated oocytes, suggesting that nucleolar loss, rather than micromanipulation-related damage to the genome, leads to a disorganization of higher-order chromatin structure in pronuclei and frequent chromosome mis-segregation during the first mitosis. Strikingly, expression of NPM2 alone sufficed to reconstitute the nucleolar structure in enucleolated embryos, and rescued their first mitotic division and full-term development. The nucleolus rescue through NPM2 required the pentamer formation and both the N- and C-terminal domains. Our findings demonstrate that the NPM2-based oocyte nucleolus is an essential platform for parental chromatin organization in early embryonic development.

Improvement of embryonic development and production of offspring by transferring meiosis-II chromosomes of senescent mouse oocytes into cytoplasts of young mouse oocytes

PURPOSE

The effects of reciprocal transplantation of meiosis-II chromosomes between senescent and young mouse oocytes were evaluated based on pre- and post-implantation development ability of resultant embryos.

METHODS

Karyoplasts including meiosis-II chromosomes of oocytes from senescent Rockefeller mouse/Ms-Rb(6, 15) females (10 to 12 months, age-related infertile mice) were transferred into cytoplasts of oocytes from young F(1) females (3 to 5 months). Reconstructed oocytes were fertilized in vitro, and then the resultant embryos were cultured in vitro and transferred to recipient mice.

RESULTS

The reconstructed oocytes that consisted of aged-karyoplasts and young-cytoplasts showed significantly improved embryonic development (from 23.2% to 30.0%) and development to term (from 6.3% to 27.1%, P < 0.05) as compared with the oocytes reconstructed from young-karyoplasts and aged-cytoplasts.

CONCLUSIONS

The present study showed successful rejuvenation for age-related infertility using transplantation of meiosis-II chromosomes in animal experimental models.

Transmission of Mitochondrial DNA Disorders: Possibilities for The Elimination of Mutated Mitochondria

The recent article by D.T. Brown et al. (2006) discusses the transmission of mitochondrial DNA disorders. In the second part, the authors describe certain techniques that can be potentially used to eliminate the transmission of mutated mtDNA from mother to offspring. It is our opinion that this brief account needs broader explanation. Moreover, some approaches mentioned are not always correctly interpreted.