Gamete Biology

Meiotic Induction by Heat Stress in Mouse Oocytes: Involvement of AMP-Activated Protein Kinase and MAPK Family Members

Abstract
In the present study, we examined the effect of heat pulsing on oocyte maturation and assessed the possible role of stress-activated enzymes during heat stress-induced meiotic maturation. Denuded oocytes (DO) from immature, eCG-primed mice were pulsed for 30 minutes at increasing temperatures from 40°C to 43°C in dbcAMP-containing medium and subsequently cultured at 37°C for a total incubation time of 17-18 h. Oocytes exposed to 42°C showed the greatest stimulation of maturation, with no effect at 43°C. A heat pulse did not compromise progression to MII as observed by polar body formation. The PRKA inhibitors, compound C and araA, each blocked the meiosis-stimulating effects of heat. Western blots showed that ACACA, an important substrate of PRKA, was phosphorylated in heat-treated, GV-stage oocytes, indicating activation of PRKA prior to maturation. The MAP2K1 inhibitor, PD98059, also prevented heat-induced maturation, but this effect was unrelated to MAPK1/3 activation, which was not observed until after GVB, which was not observed until after germinal vesicle breakdown. Phosphorylated MAPK14 could not be detected in the oocyte under any experimental condition, and only high concentrations of the MAPK14 inhibitor, SB203580, could block heat-stimulated maturation, suggesting MAPK14 is not involved in the meiotic induction. MAPK8/9 was activated by heat, and the MAPK8/9 inhibitor, SP600125, but not JNK-I, blocked heat-induced maturation. Heat treatment transiently suppressed GVB and polar body formation in spontaneously maturing oocytes by a mechanism apparently different from its meiosis-inducing action. Collectively, these data show that an acute heat pulse stimulates GVB in meiotically-arrested oocytes and suggest this effect is mediated through the activation of PRKA.

Key words: Gamete Biology • Meiosis • Oocyte development • Stress