Mitochondrial DNA transmission and confounding mitochondrial influences in cloned cattle and pigs

Abstract

Although somatic cell nuclear transfer (SCNT) is a powerful tool for production of cloned animals, SCNT embryos generally have low developmental competency and many abnormalities. The interaction between the donor nucleus and the enucleated ooplasm plays an important role in early embryonic development, but the underlying mechanisms that negatively impact developmental competency remain unclear. Mitochondria have a broad range of critical functions in cellular energy supply, cell signaling, and programmed cell death; thus, affect embryonic and fetal development. This review focuses on mitochondrial considerations influencing SCNT techniques in farm animals. Donor somatic cell mitochondrial DNA (mtDNA) can be transmitted through what has been considered a ''bottleneck'' in mitochondrial genetics via the SCNT maternal lineage. This indicates that donor somatic cell mitochondria have a role in the reconstructed cytoplasm. However, foreign somatic cell mitochondria may affect the early development of SCNT embryos. Nuclear-mitochondrial interactions in interspecies/intergeneric SCNT (iSCNT) result in severe problems. A major biological selective pressure exists against survival of exogenous mtDNA in iSCNT. Yet, mtDNA differences in SCNT animals did not reflect transfer of proteomic components following proteomic analysis. Further study of nuclear-cytoplasmic interactions is needed to illuminate key developmental characteristics of SCNT animals associated with mitochondrial biology.

Functional consequences of mitochondrial mismatch in reconstituted embryos and offspring

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Fig. 1.Mitochondrial DNA (mtDNA) bottleneck in an SCNT maternal lineage [3]. A) Schematic features of the mtDNA bottleneck associated with SCNT cattle and pigs.

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“…Maternal germline with mtDNA homoplasmy can result in the presence of mtDNA homoplasmy in G 1 embryos and animals. B) D-mtDNA transmission in SCNT heifers and their G 1 calves, as determined by PCR-mediated single-strand conformation polymorphism (PCR-SSCP) analysis based on the D-loop [2, 3]. The SCNT heifer (SCNT) and one of the G 1 offspring (G 1 -1) showed mtDNA heteroplasmy, with D-mtDNA contents of 8% and 51%, respectively.…”

“…In the case of cattle, base substitution frequently exists among each maternal line. Therefore, genetically different recipient oocytes are often used for nuclear transfer; hence, the probability that the mtDNA will be identical to that of the donor cells is extremely low [1,2,3].…”

“…However, during SCNT, small amounts of donor cell-derived mitochondria are mixed during nuclear transfer to the host ovum, resulting in a state where two types of mtDNAs are present (heteroplasmy). The proportion of heteroplasmy in SCNT animals fluctuates due to the random distribution or selective replication/degradation associated with cleavage or cell division [3]. Therefore, we investigated the influence of differences in mitochondrial and nuclear origins/mitochondrial heteroplasmy on embryonic development and individual production traits from a multifaceted perspective.…”

Modifying Mitochondrial Genetics

“…Indeed, depending on the specific methodology employed for nuclear transfer, additional models of heteroplasmy may or may not have been created. Lastly, over the last 12 years, specific culture-related conditions that may influence the prevalence or development of heteroplasmy in these techniques were described (see Takeda, 2013).…”