Departamento de Ciências Básicas, Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de São Paulo, Pirassununga, Brazil.
Biol Reprod. 2010 Jan;82(1):76-85. doi: 10.1095/biolreprod.109.077776. Epub 2009 Aug 19.
The extensive replication of mitochondria during oogenesis and the wide variability in mitochondrial DNA (mtDNA) copy numbers present in fully grown oocytes indicate that mtDNA amount may play an important role during early embryogenesis. Using bovine oocytes derived from follicles of different sizes to study the influence of mtDNA content on development, we showed that oocytes obtained from small follicles, known to be less competent in developing into blastocysts, contain less mtDNA than those originating from larger follicles. However, because of the high variability in copy number, a more accurate approach was examined in which parthenogenetic one-cell embryos were biopsied to measure their mtDNA content and then cultured to assess development capacity. Contrasting with previous findings, mtDNA copy number in biopsies was not different between competent and incompetent embryos, indicating that mtDNA content is not related to early developmental competence. To further examine the importance of mtDNA on development, one-cell embryos were partially depleted of their mtDNA (64% +/- 4.1% less) by centrifugation followed by the removal of the mitochondrial-enriched cytoplasmic fraction. Surprisingly, depleted embryos developed normally into blastocysts, which contained mtDNA copy numbers similar to nonmanipulated controls. Development in depleted embryos was accompanied by an increase in the expression of genes (TFAM and NRF1) controlling mtDNA replication and transcription, indicating an intrinsic ability to restore the content of mtDNA at the blastocyst stage. Therefore, we concluded that competent bovine embryos are able to regulate their mtDNA content at the blastocyst stage regardless of the copy numbers accumulated during oogenesis.
卵母细胞发生广泛的线粒体复制和成熟卵母细胞中线粒体 DNA(mtDNA)拷贝数的广泛变异性表明，mtDNA 含量可能在早期胚胎发生中发挥重要作用。使用来自不同大小卵泡的牛卵母细胞研究 mtDNA 含量对发育的影响，我们发现来自小卵泡的卵母细胞（已知在发育为囊胚方面能力较弱）比来自大卵泡的卵母细胞含有较少的 mtDNA。然而，由于拷贝数的高度变异性，我们检查了一种更准确的方法，即通过活检部分卵裂球胚胎来测量其 mtDNA 含量，然后培养以评估其发育能力。与之前的发现相反，在有能力和无能力的胚胎之间，活检中的 mtDNA 拷贝数没有差异，表明 mtDNA 含量与早期发育能力无关。为了进一步研究 mtDNA 对发育的重要性，通过离心使一细胞胚胎部分耗尽其 mtDNA（减少 64% +/- 4.1%），然后去除富含线粒体的细胞质部分。令人惊讶的是，耗尽 mtDNA 的胚胎正常发育成囊胚，其 mtDNA 拷贝数与未处理的对照相似。耗尽 mtDNA 的胚胎发育伴随着控制 mtDNA 复制和转录的基因（TFAM 和 NRF1）表达增加，表明在囊胚阶段具有内在的恢复 mtDNA 含量的能力。因此，我们得出结论，有能力的牛胚胎能够在囊胚阶段调节其 mtDNA 含量，而不论在卵母细胞发生过程中积累的拷贝数如何。
