부산대학교 도서관

Oogenesis already begins in the embryo with the formation and migration of primordial germ cells (PGC) and their sexual differentiation into mitotically dividing oogonia and primary oocytes. The latter initiate the early steps of meiosis in which pairing and recombination between homologous chromosomes take place before there is a meiotic arrest in the dictyate stage that can last for decades before follicle and oocyte maturation and ovulation. By the breakdown of nests of oocytes and the coating of oocytes by pregranulosa cells in the fetal ovary, all primordial follicles that are available for reproduction until the end of the reproductive life span are formed. The pool becomes deleted by atresia and the irreversible transition from the primordial to primary follicle stages. The further development of secondary to the large antrum folliculi up to ovulation of an euploid, developmentally competent oocyte depends on complex paracrine, neuroendocrine and hormonal regulation. Oocyte quality relates to maternal age and efficient bidirectional signaling between the somatic compartment and oocyte secreted factors (OSFs). Factors secreted by secondary and antral follicles restrict the number of recruited primordial follicles, whereas gonadotropins, steroids and their receptors are important for follicle survival and differentiation. Disturbances in the germ cell formation prior to birth and the dynamics of folliculogenesis before and after puberty can cause premature ovarian insufficiency (POI). Identifying the origin (e. g. genetic, immunologic, ovotoxic) of POI as early as possible can help when counselling patients for targeted family planning, cryopreservation, oocyte donation or prevention of disorders (e. g. by life style alterations or treatment of malignant or chronic diseases).