Maternal age effect on mouse oocytes: new biological insight from proteomic analysis. Mus musculus

The long-standing view of 'immortal germ line versus mortal soma' poses a fundamental question in biology concerning how oocytes age in molecular terms. A mainstream hypothesis is that maternal aging of oocytes has its roots in gene transcription. Investigating the proteins resulting from mRNA translation would reveal how far the levels of functionally available proteins correlate with mRNAs, and would offer novel insight into the changes oocytes undergo during maternal aging. Gene ontology semantic analysis reveals the high similarity of the detected proteome (2,324 proteins) to the transcriptome (22,334 mRNAs), though not all proteins have a cognate mRNA. Concerning their dynamics, 4-fold changes of abundance are more frequent in the proteome (3%) than the transcriptome (0.05%), with correlation. Whereas proteins associated with the nucleus (e.g. structural maintenance of chromosomes, spindle-assembly checkpoints) are largely represented among those that change in oocytes during maternal aging; proteins associated with oxidative stress/damage (e.g. superoxide dismutase) are infrequent. These quantitative alterations are either impoverishing or enriching. Using gene ontology analysis, these alterations do not relate in any simple way to the classic signature of aging known from somatic tissues. We conclude that proteome analysis of mouse oocytes may not be surrogated with transcriptome analysis, given the lack of correlation. Furthermore, we conclude that the classic features of aging may not be transposed from somatic tissues to oocytes in a one-to-one fashion. Overall, there is more to the maternal aging of oocytes than mere cellular deterioration exemplified by the notorious increase of meiotic aneuploidy. Overall design: Three pools of 20 zona-enclosed B6C3F1 oocytes from each age group were subjected for experiment.