Bowles Emma J, Lee Joon-Hee, Alberio Ramiro, Lloyd Rhiannon E I, Stekel Dov, Campbell Keith H S, St John Justin C
The Mitochondrial and Reproductive Genetics Group, The Medical School, University of Birmingham, Birmingham B15 2TT, United Kingdom.
Genetics. 2007 Jul;176(3):1511-26. doi: 10.1534/genetics.106.070177. Epub 2007 May 16.
Mitochondrial DNA (mtDNA) is normally only inherited through the oocyte. However, nuclear transfer (NT), the fusion of a donor cell with an enucleated oocyte, can transmit both donor cell and recipient oocyte mtDNA. mtDNA replication is under the control of nuclear-encoded replication factors, such as polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). These are first expressed during late preimplantation embryo development. To account for the persistence of donor cell mtDNA, even when introduced at residual levels (mtDNA(R)), we hypothesized that POLG and TFAM would be upregulated in intra- and interspecific (ovine-ovine) and intergeneric (caprine-ovine) NT embryos when compared to in vitro fertilized (IVF) embryos. For the intra- and interspecific crosses, PolGA (catalytic subunit), PolGB (accessory subunit), and TFAM mRNA were expressed at the 2-cell stage in both nondepleted (mtDNA(+)) and mtDNA(R) embryos with protein being expressed up to the 16-cell stage for POLGA and TFAM. However, at the 16-cell stage, there was significantly more PolGA expression in the mtDNA(R) embryos compared to their mtDNA(+) counterparts. Expression for all three genes first matched IVF embryos at the blastocyst stage. In the intergeneric model, POLG was upregulated during preimplantation development. Although these embryos did not persist further than the 16+-cell stage, significantly more mtDNA(R) embryos reached this stage. However, the vast majority of these embryos were homoplasmic for recipient oocyte mtDNA. The upreglation in mtDNA replication factors was most likely due to the donor cells still expressing these factors prior to NT.
线粒体DNA（mtDNA）通常仅通过卵母细胞遗传。然而，核移植（NT），即将供体细胞与去核卵母细胞融合，可同时传递供体细胞和受体卵母细胞的mtDNA。mtDNA复制受核编码的复制因子控制，如聚合酶γ（POLG）和线粒体转录因子A（TFAM）。这些因子在植入前胚胎发育后期首次表达。为了解释供体细胞mtDNA即使在以残留水平（mtDNA(R)）引入时仍能持续存在的原因，我们推测与体外受精（IVF）胚胎相比，POLG和TFAM在种内和种间（绵羊-绵羊）以及属间（山羊-绵羊）NT胚胎中会被上调。对于种内和种间杂交，在未耗尽（mtDNA(+)）和mtDNA(R)胚胎的2细胞阶段均表达了PolGA（催化亚基）、PolGB（辅助亚基）和TFAM mRNA，POLGA和TFAM的蛋白质表达持续到16细胞阶段。然而，在16细胞阶段，与mtDNA(+)胚胎相比，mtDNA(R)胚胎中的PolGA表达显著更多。所有三个基因的表达在囊胚阶段首次与IVF胚胎匹配。在属间模型中，POLG在植入前发育过程中被上调。尽管这些胚胎在超过16+细胞阶段后无法继续发育，但达到该阶段的mtDNA(R)胚胎显著更多。然而，这些胚胎中的绝大多数对于受体卵母细胞mtDNA是同质性的。mtDNA复制因子的上调很可能是由于供体细胞在核移植前仍在表达这些因子。
