Oocyte Developmental Competence: Insights from Cross-Species Differential Gene Expression and Human Oocyte-Specific Functional Gene Networks.

Understanding oocyte developmental competence remains a key challenge for reproductive biology and systems sciences. The transcriptome of oocytes in eutherians is highly complex and is associated with the success of embryo development. Due to sample limitations from humans, animal models are used for investigation of the oocyte transcriptome. Nonetheless, little is known about the diversity of the oocyte transcriptome across eutherians. In this report, comprehensive investigation of 7 public data sets in 4 species, human, macaque, mice, and cattle, shows that 16,572 genes are expressed in oocytes. Approximately 26% of the genes were expressed in all four species. There were 1390, 489, and 187 genes specifically expressed in human, mice, and cattle oocytes, respectively. Coexpression clustering of the genes specifically expressed in human oocytes revealed functional enrichment (FDR <0.05) of Gene Ontology (GO) terms important for oocyte physiology (i.e., "cellular response to metal ion," "negative regulation of growth," "hormone activity," and "receptor activity"). Interrogation of 4 data sets revealed 26 genes whose expressions were significantly (FDR ≤0.1) associated with oocyte developmental competence and concordant fold change in 2 studies. The genes AK2, AKAP1, ECHS1, MRPL10, MRPL24, PTRH2, STX17, SUCLG1, SUOX, and TOMM34 were associated with the GO term "mitochondrion" (FDR <0.01). Collectively, the results offer new insights on gene transcript levels associated with oocyte developmental competence and the central role of mitochondrion for oocyte's health among eutherians. Caution should be exercised, however, when extending the inferences related to gene expression associated with oocyte quality across eutherians.