Activation of follicle development: The primordial follicle

Investigations of primordial follicle formation and growth are fundamental to our understanding of female gamete production. In all mammalian females the full complement of oocytes is established during fetal development. Thi s store of primordial follicles is not renewable and serves the entire repr oductive life span of the adult. The correct programming of fetal ovarian d evelopment and the number of primordial follicles formed will therefore lim it the fecundity of the ovary. Primordial follicles are characterized by th e presence of a single oocyte surrounded by a varying number of pregranulos a cells. The relatively small size, undifferentiated status and large numbe rs of primordial follicles make them prime candidates for use in basic and applied research in animal production, gene transfer and cloning. Furthermo re, the development of cell culture systems that use primordial follicles a s a source of oocytes for in vitro growth and maturation will enable us to maximize the potential of high genetic merit females and to shorten generat ion intervals. Despite these possibilities, primordial follicles are the le ast understood of all stages of follicle development. The factor(s) respons ible for maintaining the primordial pool or, conversely, for activating pri mordial follicle growth remain elusive. (C) 2001 by Elsevier Science Inc.