Fig. 3

The KEGG pathway of oxidative phosphorylation pathway responds to oocyte aging, and the genes highlighted in red are enriched and significantly down-regulated in oocytes from the old mice group. Most of these DEGs were encoded in the mitochondrial genome and participated in mitochondrial respiratory chain by encoding mitochondrially encoded nicotine-amide adenine dinucleotide (NADH) dehydrogenase (mt-Nd), the key protein subunits of Complex I. Those DEGs included mt-Nd2, mt-Nd3, mt-Nd4, mt-Nd4L and mt-Nd5. Also, the genes encoding the subunits Complex IV and Complex V of respiratory chain including mitochondrially encoded ATP synthase 6 (mt-ATP6), cytochrome c oxidase subunit II (COX2) and mitochondrial Cytochrome c oxidase subunit III (COX3) were found significant down-regulated in the GV oocytes of 32-week-old mice