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In women, the non-growing population of follicles that comprise the ovarian reserve is determined at birth and serves as the reservoir for future fertility. This reserve of dormant, primordial follicles and the mechanisms controlling their selective activation which constitute the committing step into folliculogenesis are essential for determining fertility outcomes in women. Much of the available data on the mechanisms responsible for primordial follicle activation focuses on a selection of key molecular pathways, studied primarily in animal models, with findings often not synonymous in humans. The excessive induction of primordial follicle activation may cause the development of premature ovarian insufficiency (POI), a condition characterised by menopause before age 40 years. POI affects 1–2% of all women and is accompanied by additional health risks. Therefore, it is critical to further our understanding of primordial follicle activation in order to diagnose, treat and prevent premature infertility. Research in primordial follicle activation has focused on connecting new molecules to already established key signalling pathways, such as phosphatidylinositol 3-Kinase (PI3K) and mammalian target of rapamycin (mTOR). Additionally, other aspects of the ovarian environment, such as the function of the extracellular matrix, in contributing to primordial follicle activation have gained traction. Clinical applications are examining replication of this extracellular environment through the construction of biological matrices mimicking the 3D ovary, to support follicular growth through to ovulation. This review outlines the importance of the events leading to the establishment of the ovarian reserve and highlights the fundamental factors known to influence primordial follicle activation in humans presenting new horizons for female infertility treatment.

Germ cell proliferation, migration and survival during all stages of spermatogenesis are affected by stem cell factor signalling through the c-Kit receptor, the expression and function of which are vital for normal male reproductive function. The present study comprehensively describes the c-Kit mRNA and protein cellular expression profiles in germ cells of the postnatal and adult rodent testis, revealing their significant elevation in synthesis at the onset of spermatogenesis. Real-time PCR analysis for both mice and rats matched the cellular mRNA expression profile where examined. Localization studies in normal mouse testes indicated that both c-Kit mRNA and protein are first detectable in differentiating spermatogonia. In addition, all spermatogonia isolated from 8-day-old mice displayed detectable c-Kit mRNA, but 30–50% of these lacked protein expression. The c-Kit mRNA and protein profile in normal rat testes indicated expression in gonocytes, in addition to differentiating spermatogonia. However, in the irradiated adult rat testes, in which undifferentiated spermatogonia are the only germ cell type, mRNA was also detected in the absence of protein. This persisted at 3 days and 1 and 2 weeks following treatment with gonadotrophin-releasing hormone (GnRH) antagonist to stimulate spermatogenesis recovery. By 4 weeks of GnRH antagonist treatment, accompanying the emergence of differentiating spermatogonia, both mRNA and protein were detected. Based on these observations, we propose that c-Kit mRNA and protein synthesis are regulated separately, possibly by influences linked to testis maturation and circulating hormone levels.