Molecular aspects of follicular development
Huang Z., Wells D.
© Cambridge University Press 2011. Introduction The follicle has a fundamental reproductive role in the ovary. It consists of the oocyte (in various stages of growth and development) and its surrounding layers of supportive cells, the granulosa cells (GCs), cumulus cells (CCs) (during the antral phase of follicular development) and thecal cells (TCs). These somatic cells perform essential roles in ensuring optimal development and maturation of the oocyte. They receive signals from the external environment and pass them on to the oocyte to orchestrate its growth and development until ovulation. It is now widely recognized that there is bi-directional communication between the oocyte and surrounding somatic cells and that this is essential for the creation of a favorable follicular microenvironment in which the gamete can develop. Many complex and intricate molecular pathways are likely to be involved in the production of an optimal follicle and a viable gamete. This chapter aims to provide an insight into the molecular mechanisms likely to be involved in the various stages of follicular development, as determined from animal and human studies. The follicle develops in stages During fetal life, the human ovary is populated by ~7 × 10 < sup > 6 < /sup > oogonia as early as the 4th month of pregnancy with the highest mitotic activity seen just before meiosis commences . These oogonia, present during the early second trimester, ultimately give rise to approximately 1 million primordial follicles at birth. The number of follicles continues to decline during childhood reaching ~300 000 at menarche  .