Histone acetylation during the in vitro maturation of bovine oocytes with different levels of competence

Abstract

We aimed to analyse the histone acetylation status and expression profile of genes involved in histone acetylation (histone acetyltransferase 1 (HAT1), lysine acetyltransferase 2A (KAT2A), histone deacetylase 1 (HDAC1), HDAC2 and HDAC3) in bovine oocytes of different competences during in vitro maturation (IVM). Cumulus–oocyte complexes were recovered from two groups of follicles: minor follicles (1.0–3.0 mm in diameter), classified as low competence (LC) and large follicles (6.0–8.0 mm in diameter) classified as high competence (HC). Oocytes were submitted to IVM for 0, 8 and 24 h and stored for analysis. Acetylation status of histone H4 on lysine K5, K6, K12 and K16 was assessed by immunohistochemistry. For gene expression, mRNA levels were determined by real-time quantitative polymerase chain reaction. All oocytes, regardless of their competence, showed a gradual decrease (P < 0.05) in acetylation signals during IVM. From 0 to 8 h of maturation, an increase (P < 0.05) in the relative abundance of HAT1 mRNA was observed only in the HC oocytes. In this group, higher (P < 0.05) mRNA levels of HDAC1 at 8 h of maturation were also observed. In conclusion, in the present study, LC oocytes were shown to have adequate acetylation levels for the resumption and progression of meiosis; however, these oocytes do not have the capacity to synthesise RNA during IVM as the HC oocytes do.