Bovine Oocyte Transcriptome in Relation to Chromatin Configuration of the Germinal Vesicle

Various physiological contexts have been used to study the mRNA composition of bovine oocyte in relation with the potential to reach the blastocyst stage. The chromatin configuration of the oocyte at the germinal vesicle (GV) stage has been positively associated with developmental competence, where a more compacted chromatin is correlated with a better chance to get an embryo. Four distinct and progressive states of chromatin condensation can be observed and are linked with the sequential acquisition of the developmental potential in bovine species. Therefore, GV stage oocytes were collected and separated in four groups according to their degree of chromatin condensation. Transcriptomic analyses were performed with the EmbryoGENE microarray platform in order to identify transcripts modulations during the gradual chromatin remodeling. A reference design was used where GV0 stage (diffused chromatin state) was compared with the other three groups (GV1; GV2 and GV3, the latter refers to the condensed chromatin state). The number of transcripts significantly different was relatively similar between the three contrasts (an average of 300 genes, fold change > 2; p-value < 0.01) with the majority of them were presenting a reduced level in oocyte with more compacted chromatin. However, among the transcripts presenting an increased mRNA level in these contrasts, many of them are associated with histone genes, chromatin organization and transcriptional regulation. These results suggest that even in a context of transcriptional repression, there is still an accumulation of specific transcripts. Adequate storage of specific histone mRNAs could provide an optimal maternal accumulation in order to fulfill the requirement for the subsequent cell divisions until embryonic genome activation. This dataset will provide a more complete characterization of the oocyte transcriptome modulations and will help us to better understand the competence acquisition in the oocyte at the end of the follicular growth