Activation of human ovarian follicles and derivation of competent oocytes

Women are born with a store of eggs that must last them throughout their reproductive life. These eggs are in the ovary at an immature stage within protective sac like structures (follicles) and held in a resting state until they are activated to grow. This process of activation is the most important factor that determines a womans reproductive lifespan and when she will enter menopause. However, almost nothing is known about how this process is regulated in humans although its disruption can lead to Premature Ovarian Failure (POF), infertility and associated female health problems.
This study is looking at how activation is regulated and how it can be manipulated to alter the number and quality of eggs that develop to the stage where they can be fertilised. We are now able to tackle this problem in human tissue by using a novel culture system that we have developed that supports activation of follicles outside the body. Using this we will investigate the role of two mechanisms (PTEN and mTORC1) that have been shown to affect the rate of follicle activation in mice by adding factors that disrupt (inhibit/stimulate) them. Oocyte development and function can then be tested after these manipulations. The results obtained could lead to improved treatments for POF, infertility as well as development of methods to regulate female fertility.

Women are born with a fixed population of germ cells that must last them throughout their reproductive lifespan. These germ cells are contained within resting primordial follicles that are activated to grow throughout life. The depletion of this population leads to reproductive ageing and this can occur prematurely leading to infertility. Some follicles from this quiescent population are being continuously activated whilst the rest remain dormant, indicating that quiescence is the default pathway. How this complex process of activation is regulated is unknown although it is a fundamental aspect of ovarian biology and has considerable practical importance as it underpins future improvements in the success of Assisted Reproductive Techniques (ART) i.e. the availability of high quality oocytes suitable for fertilisation as well as being a potential target for fertility regulation. Recent studies using tissue specific knock out mouse models have demonstrated the importance of the phosphatidylinositol-3?-kinase (PI3-K) signalling pathway in this process. PTEN (phosphatase and tensin homolog deleted on chromosome 10) has been shown to suppress whilst mTORC1 (mammalian target of rapamycin complex1) promotes follicle activation. In this proposal we will manipulate PTEN and mTORC1 signalling by using well defined inhibitors/activators in a continuum of in vitro methods to study human oocyte development from the most immature stage to fully grown oocytes. This model system represents a major advance in our ability to investigate the regulation of quiescence and activation of human primordial follicles and subsequent oocyte development. We will test the hypothesis that PTEN and mTORC1 regulate human primordial follicle quiescence/activation and demonstrate the efficacy and safety of this model for deriving mature oocytes capable of being fertilised. This proposal will significantly advance our knowledge of the initiation of follicle growth and how it underpins oocyte quality right through to fertilisation.