Pronounced Segregation of Donor Mitochondria Introduced by Bovine Ooplasmic Transfer to the Female Germ-Line1

Abstract

Ooplasmic transfer (OT) has been used in basic mouse research for studying the segregation of mtDNA, as well as in human assisted reproduction for improving embryo development in cases of persistent developmental failure. Using cattle as a large-animal model, we demonstrate that the moderate amount of mitochondria introduced by OT is transmitted to the offspring's oocytes; e.g., modifies the germ line. The donor mtDNA was detectable in 25% and 65% of oocytes collected from two females. Its high variation in heteroplasmic oocytes, ranging from 1.1% to 33.5% and from 0.4% to 15.5%, can be explained by random genetic drift in the female germ line. Centrifugation-mediated enrichment of mitochondria in the pole zone of the recipient zygote's ooplasm and its substitution by donor ooplasm led to elevated proportions of donor mtDNA in reconstructed zygotes compared with zygotes produced by standard OT (23.6% +/- 9.6% versus 12.1% +/- 4.5%; P < 0.0001). We also characterized the proliferation of mitochondria from the OT parents-the recipient zygote (Bos primigenius taurus type) and the donor ooplasm (B. primigenius indicus type). Regression analysis performed for 57 tissue samples collected from the seven OT fetuses at different points during fetal development found a decreasing proportion of donor mtDNA (r(2) = 0.78). This indicates a preferred proliferation of recipient taurine mitochondria in the context of the nuclear genotype of the OT recipient expressing a B. primigenius indicus phenotype.

Maternal control of oocyte quality in cattle “a review”

“…In addition, microinjection of mitochondria obtained from the same breed improved embryo quality during preimplantation development. There is a segregation of donor mitochondria by the oocyte after cytoplasmic transfer (Ferreira et al, 2010) supporting the hypothesis that mitochondrial homoplasmy is optimal.…”

Xenooplasmic Transfer between Buffalo and Bovine Enables Development of Homoplasmic Offspring

“…Moreover, detailed screening for buffalo mtDNA in offspring using a real-time protocol able to detect as little as 0.01% of buffalo mtDNA, was unsuccessful in identifying any vestige of buffalo mtDNA in somatic (blood, skin, muscle, and liver) and germline (oocytes) tissues of both calves born from XOT. Ferreira et al (2010), using a similar approach to that described in the present work, have performed ooplasmic transfer between B. indicus and B. taurus cows and found …”

Transmission of Mitochondrial DNA Diseases and Ways to Prevent Them

“…Mitochondrial DNA analysis of children born following the procedure demonstrated that the contribution of donor mtDNA is small [92], but, in some cases, the proportion of donor mtDNA far exceeded the expected 10–15% [93], based on the volume of cytoplasm derived from the donor. While genetic drift might occasionally underlie such a change, experiments on bovine zygotes suggest that mitochondrial replacement can be consistently improved by centrifugation and removal of the recipient mtDNA without apparent effects on development [94], [95]. Centrifugation causes mitochondria to concentrate in one of the zygote's poles [94], [95], allowing removal of mitochondrion-enriched cytoplasm by micromanipulation.…”