Chromatin remodelling and histone m RNA accumulation in bovine germinal vesicle oocytes

Major remodelling of the chromatin enclosed within the germinal vesicle occurs towards the end of oocyte growth in mammals, but the mechanisms involved in this process are not completely understood. In bovine, four distinct stages of chromatin compaction-ranging from a diffused state (GV0) to a fully compacted configuration (GV3)-are linked to the gradual acquisition of developmental potential. To better understand the molecular events and to identify mRNA modulations occurring in the oocyte during the GV0-to-GV3 transition, transcriptomic analysis was performed with the EmbryoGENE microarray platform. The mRNA abundance of several genes decreased as chromatin compaction increased, which correlates with progressive transcriptional silencing that is characteristic of the end of oocyte growth. On the other hand, the abundance of some transcripts increased during the same period, particularly several histone gene transcripts from the H2A, H2B, H3, H4, and linker H1 family. In silico analysis predicted RNA-protein interactions between specific histone transcripts and the bovine stem-loop binding protein 2 (SLBP2), which helps regulate the translation of histone mRNA during oogenesis. These results suggest that some histone-encoding transcripts are actively stored, possibly to sustain the needs of the embryo before genome activation. This dataset offers a unique opportunity to survey which histone mRNAs are needed to complete chromatin compaction during oocyte maturation and which are stockpiled for the first three cell cycles following fertilization.