Reproduction Abstracts

There are several key stages in the development of a reproductively competent ovary. These include: i) successful migration of the primordial germ cells and associated precursor somatic cells to the genital ridge, ii) the entry and maintenance of the developing germ cells in meiotic arrest, iii) the accumulation of pre-granulosa cells by oocytes to form primordial follicles, and iv) the maintenance of the primordial follicles in a quiescent state. This population of inactive primordial follicles will then represent the female mammal’s, or woman’s, ovarian reserve and will be a key component of her lifetime reproductive potential.

This presentation will outline some of the key stages and controlling mechanisms in the formation of the primordial follicle. Some of the differences and similarities between key models, rodents, sheep and human fetus will be addressed. In doing this considerable focus will be placed on the human, partially informed by non-human primate studies, because of the emergence of a number of new studies over recent years. Primordial follicle formation and activation occur against a background of complex intra- and extra-ovarian signalling, including steroid hormones, gonadotrophins and local inhibin/activin signalling.

In addition, there is concern over the potential adverse effects of in-utero exposures to toxicants such as environmental chemicals, endocrine disrupting compounds and maternal cigarette use. The nature of adverse effects on the development of the ovary will be discussed and will include examples from electively terminated fetuses exposed to cigarette smoke during pregnancy. Animal models of chemical and cigarette exposure will also be outlined.

Finally, aspects of normal follicle activation will be put into perspective against the evidence for activation and progression of some primordial follicles even before birth. Transcription repressors such as PTEN and local AMH signalling have a key role to play in the regulation of primordial follicle activation.