Comparative analysis of oocyte transcript profiles reveals a high degree of conservation among species

Cross-species comparison of gene expression is a powerful approach for discovering genes that have been conserved throughout evolution. Conserved genes are presumably very important in the mechanisms related to the unique molecular functions in oocytes. The objective of this study was to identify genes expressed in the oocyte and conserved across three diverse vertebrate species. We report the global gene expression profiles of Bos taurus and Xenopus laevis oocytes on an NIA mouse development microarray that consists of 60-mer oligonucleotide probes representing more than 20,000 mouse transcripts derived from stem cell, oocyte, and early embryo cDNA libraries. Analysis based on intensity values revealed that 9853 and 10,046 genes are expressed in bovine and Xenopus oocytes respectively. Furthermore, previously published microarray data on preimplantation development in the mouse were used for a comparative analysis of global oocyte gene expression profiles. Interestingly, a substantial proportion of the genes expressed in mouse oocytes is conserved between the three species (74%, 7275 genes). Moreover, functional annotation of these conserved oocyte-expressed genes confirmed that certain functions are conserved among the three species. RNA metabolism and cell cycle were among the over-represented Gene Ontology terms in the biological process category. Finally, a pattern-matching analysis identified 208 conserved maternally expressed genes. Results from these cross-species hybridizations allowed numerous genes expressed in oocytes and conserved between Mus musculus, B. taurus, and X. laevis to be identified. This comparative analysis of oocyte transcript profiles revealed a high degree of conservation among species.