Ferreira Roberta Machado, Chiaratti Marcos Roberto, Macabelli Carolina Habermann, Rodrigues Carlos Alberto, Ferraz Márcio Leão, Watanabe Yeda Fumie, Smith Lawrence Charles, Meirelles Flávio Vieira, Baruselli Pietro Sampaio
Departamento de Reprodução Animal, Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, São Paulo, São Paulo, Brazil Departamento de Medicina Veterinária, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil
Departamento de Ciências Básicas, Faculdade de Zootecnia e Engenharia de Alimentos da Universidade de São Paulo, Pirassununga, São Paulo, Brazil Departamento de Genética e Evolução, Centro de Ciências Biológicas e da Saúde, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil.
Biol Reprod. 2016 Mar;94(3):66. doi: 10.1095/biolreprod.115.133017. Epub 2016 Feb 3.
Oocyte quality is known to be a major cause of infertility in repeat-breeder (RB) and heat-stressed dairy cows. However, the mechanisms by which RB oocytes become less capable of supporting embryo development remain largely unknown. Thus, the aim of this study was to investigate whether the decreased oocyte competence of RB cows (RBs) during summer is associated with an altered gene expression profile and a decrease in mitochondrial DNA (mtDNA) copy number. Therefore, oocytes collected from heifers, non-RBs in peak lactation (PLs), and RBs were used to evaluate mtDNA amounts as well as the expression levels of genes associated with the mitochondria (MT-CO1, NRF1, POLG, POLG2, PPARGC1A, and TFAM), apoptosis (BAX, BCL2, and ITM2B), and oocyte maturation (BMP15, FGF8, FGF10, FGF16, FGF17, and GDF9). The oocytes retrieved from RBs during winter contained over eight times more mtDNA than those retrieved from RBs during summer. They also contained significantly less mtDNA than oocytes retrieved from heifers and PLs during summer. Moreover, the expression of mitochondria- (NRF1, POLG, POLG2, PPARGC1A, and TFAM) and apoptosis-related (BAX and ITM2B) genes, as well as of GDF9, in RB oocytes collected during summer was significantly greater than that in oocytes collected from heifers and PLs during the same season. In oocytes from heifers and PLs, the expression levels of these genes were lower in those collected during summer compared with winter, but this difference was not observed in oocytes collected from RBs. Altogether, these data provide evidence of altered gene expression and reduced mtDNA copy number in the oocytes collected from RBs during summer. This indicates a loss of fertility in RBs during summer, which might be caused by a possible mitochondrial dysfunction associated with a greater chance of oocytes to undergo apoptosis.
已知卵母细胞质量是屡配不孕（RB）奶牛和热应激奶牛不孕的主要原因。然而，RB卵母细胞支持胚胎发育能力下降的机制在很大程度上仍不清楚。因此，本研究的目的是调查夏季RB奶牛（RBs）卵母细胞能力下降是否与基因表达谱改变和线粒体DNA（mtDNA）拷贝数减少有关。因此，从后备母牛、泌乳高峰期的非RB奶牛（PLs）和RB奶牛收集的卵母细胞用于评估mtDNA含量以及与线粒体（MT-CO1、NRF1、POLG、POLG2、PPARGC1A和TFAM）、细胞凋亡（BAX、BCL2和ITM2B）和卵母细胞成熟（BMP15、FGF8、FGF10、FGF16、FGF17和GDF9）相关的基因表达水平。冬季从RB奶牛收集的卵母细胞所含的mtDNA比夏季从RB奶牛收集的卵母细胞多八倍以上。它们所含的mtDNA也明显少于夏季从后备母牛和PLs收集的卵母细胞。此外，夏季收集的RB卵母细胞中线粒体相关基因（NRF1、POLG、POLG2、PPARGC1A和TFAM）、细胞凋亡相关基因（BAX和ITM2B）以及GDF9的表达明显高于同一季节从后备母牛和PLs收集的卵母细胞。在后备母牛和PLs的卵母细胞中，与冬季相比，夏季收集的卵母细胞中这些基因的表达水平较低，但在从RB奶牛收集的卵母细胞中未观察到这种差异。总之，这些数据证明了夏季从RB奶牛收集的卵母细胞中基因表达改变和mtDNA拷贝数减少。这表明夏季RB奶牛生育力下降，这可能是由于与卵母细胞发生凋亡的更大可能性相关的线粒体功能障碍所致。
