Increased supply from blood vessels promotes the activation of dormant primordial follicles in mouse ovaries

摘要

The controlled activation of dormant primordial follicles is important for the maintenance of periodic ovulation. Previous reports have clearly identified the signaling pathway in granulosacells and oocytes that controls the activation of primordial follicles; however, the exact cue for the activation of dormant primordial follicles is yet to beelucidated. In this study, we found that almost all activated primordial follicles made contact with blood vessels. Based on this result, we speculated that the contact between primordialfollicles and blood vessels may provide a cue for the activation of dormant primordial follicles. To confirm this hypothesis, we attempted to activate dormant primordial follicles within theovaries by inducing angiogenesis through the use of biodegradable gels containing recombinant vascular endothelial growth factor and in cultured ovarian tissues by increasing the serumconcentration within the culture medium. The activation of dormant primordial follicles was promoted in both experiments, and our results indicated that an increase in the supply of theserum component, from new blood vessels formed via angiogenesis, to the dormant primordial follicles is the cue for their activation. In the ovaries, angiogenesisoften occurs during every estrous cycle, and it is therefore likely that angiogenesis is the crucial event that influences the activation of primordial follicles.