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STEM CELL GENOMICS AND PROTEOMICS

Mitochondrial DNA Transmission and Transcription After Somatic Cell Fusion to One or More Cytoplasts

^aMitochondrial and Reproductive Genetics Group, Medical School, University of Birmingham, Birmingham, United Kingdom;
^bMonash Immunology and Stem Cell Laboratories and
^dCentre for Reproduction and Development, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia;
^cStemagen Corporation, La Jolla, California, USA;
^eMitochondrial and Reproductive Genetics Group, Clinical Sciences Research Institute, Warwick Medical School, University of Warwick, Warwick, United Kingdom

Key Words. Cloning • Evolutionary distance • Heteroplasmy • Mitochondrial DNA • Replication • Transcription

Correspondence: Justin C. St. John, Ph.D., Mitochondrial and Reproductive Genetics Group, Clinical Sciences Research Institute, Warwick Medical School, University of Warwick, Warwick CV2 2DX, United Kingdom. Telephone: 44-2476-968701; Fax: 44-2476-968653; e-mail: J.C.St-John{at}Warwick.ac.uk

Received September 11, 2007; accepted for publication December 21, 2007.
First published online in STEM CELLS EXPRESS   January 10, 2008.



Following fertilization, mitochondrial DNA is inherited from the oocyte and transmitted homoplasmically. However, following nuclear transfer, mitochondrial DNA can be transmitted from both the donor cell and recipient oocyte, resulting in a state of heteroplasmy. To determine whether the genetic diversity between donor cell and recipient cytoplast mitochondrial DNA influences development, we generated bovine embryos by fusing a donor cell to one or more enucleated cytoplasts. Analysis of mitochondrial DNA from embryos, fetal tissues, and blood samples from offspring revealed that early preimplantation embryos from two or three cytoplasts had significantly more mitochondrial DNA variants than fetal tissues. Phylogenic analysis of embryos generated using single cytoplasts divided the mitochondrial DNA sequence variants into three separate groups with various amounts of genetic divergence from the donor cell line. In heteroplasmic tissue and blood samples, the predominant mitochondrial DNA population was significantly more divergent from the donor cell than the less frequent allele. Furthermore, analysis of the mitochondrially encoded cytochrome B gene showed that two heteroplasmic alleles encoded for different amino acids, and the ratios of mitochondrial DNA/mRNA for each allele differed significantly between tissues. The degree of evolutionary distance between the donor cell and the cytoplast and the variability in heteroplasmy between tissues may have an impact on more divergent intergeneric nuclear transfer and the use of this approach for the generation of embryonic stem cells.

Disclosure of potential conflicts of interest is found at the end of this article.