Global gene expression analysis during bovine oocyte in vitro maturation

It is well known that factors such as nutrition, hormonal alterations and environmental compounds can have a profound effect on oocyte quality and subsequently embryo development. Global mRNA expression analysis of immature and mature bovine oocytes was carried out to identify key pathways associated with oocyte meiotic maturation and developmental potential. We have carried out a global mRNA gene expression analysis of bovine oocytes pre- and post-resumption of meiotic maturation using the Affymetrix GeneChip Bovine Genome Array. Approximately 54% of the probe sets representing 23,000 transcripts were detected in bovine oocytes. Of which, 821 transcripts were differentially expressed (>or=2-fold) between the two groups (p<0.05), corresponding to 209 upregulated and 612 down regulated transcripts in the in vitro matured oocytes compared to their immature counterparts. In addition, transcripts uniquely detected in germinal vesicle stage or metaphase II were identified. The gene expression data was classified according to gene ontology; in terms of biological processing, the majority of these genes were associated with regulation activities, including the regulation of: MAPK activity, translation initiation and transcription. Our findings are in agreement with similar data from both mouse and human oocytes. Taken together this data provides a molecular transcriptome blueprint of immature and mature mammalian oocytes. This resource will be invaluable to our long-term objective which is to target identified pathways to elucidate the sensitivity of key regulatory genes and checkpoints of oocyte maturation to internal and external environmental influences.