Composition of parental mitochondrial DNA in cloned bovine embryos

We have investigated parental mitochondrial DNA (mtDNA) in cloned bovine embryos obtained by intraspecific cytoplast-blastomere fusion. Analysis of two-cell to blastocyst stage embryos revealed that in contrast to the exclusion of paternal (sperm) mtDNA during sexual inheritance in the cytoplast-blastomere fusion complexes, there was mixing and co-existence of parental mtDNA. The mixing of mtDNA was non-balanced with the minority deriving from the blastomere. The constant content of mtDNA during embryogenesis until the blastocyst stage suggesting an absence of mtDNA replication was shown for conventional 'in vitro fertilised' (IVF) embryos and for cloned embryos. The ratio of parental mtDNA was in accordance with the estimated quantitative participation of mtDNA from the fusion partners.