Gap Junction-Mediated Communications Regulate Chromatin Remodeling During Bovine Oocyte Growth and Differentiation Through cAMP-Dependent Mechanism(s)

Oocyte development is characterized by impressive changes in chromatin structure and function in the germinal vesicle (GV) that are crucial in conferring to the oocyte meiotic and developmental competence. During oogenesis, oocyte and follicular cells communicate by paracrine and junctional mechanisms. In cow, cumulus-enclosed oocytes (CEOs) isolated from early antral follicles have uncondensed chromatin (GV0), functionally open gap junction (GJ)-mediated communications, and limited meiotic competence. The aim of the present study was to analyze the role of GJ communications on the chromatin remodeling process during the specific phase of folliculogenesis that coincides with the transcriptional silencing and the sequential acquisition of meiotic and developmental capability. CEOs were cultured in a follicle-stimulating hormone-based culture system that sustained GJ coupling and promoted oocyte growth and transition from GV0 to higher stages of condensation. When GJ functionality was experimentally interrupted, chromatin rapidly condensed, and RNA synthesis suddenly ceased. These effects were prevented by the addition of cilostamide, a phosphodiesterase 3 inhibitor, indicating that the action of GJ-mediated communication on chromatin structure and function is mediated by cAMP. Prolonging GJ coupling during oocyte culture before in vitro maturation enhanced the ability of early antral oocytes to undergo meiosis and early embryonic development. Altogether, the evidence suggests that GJ-mediated communication between germinal and somatic compartments plays a fundamental role in the regulation of chromatin remodeling and transcription, which in turn are related to competence acquisition.