Apoptosis in the human ovary.

Programmed cell death or apoptosis is an essential component of human ovarian function and development. During early fetal life approximately 7 x 10(6) oocytes are formed in the human ovary. However, the number of oocytes is dramatically reduced already before birth through apoptotic cell death. In reproductive life, a number of primordial follicles start growing during each menstrual cycle. Usually only one will ovulate and the fate of the rest of the follicles is atresia through the mechanism of apoptosis. Ultimately, only around 400 follicles will ovulate during a woman's reproductive life. After ovulation, the dominant follicle forms the corpus luteum, a novel endocrine gland that is responsible for the production of progesterone and maintenance of endometrium during early pregnancy. If pregnancy does not occur, corpus luteum action must cease so that new follicles can resume growing during the next menstrual cycle. Apoptosis is also responsible for corpus luteum regression in the human ovary. In recent years, new knowledge of the role and regulation of apoptosis in the ovary has been acquired through the use of knockout and transgenic animals. Apoptosis seems to be the mechanism that makes the female biological clock tick. The following review will discuss the role of apoptosis and its regulation of human ovarian function.