Human ovarian follicular development: from activation of resting follicles to preovulatory maturation.

International audienceBy integrating morphometrical and endocrinological data, as well as biological effects of various molecules synthesized by the human follicle, we propose a dynamic view of the follicle growth within the human ovary. Folliculogenesis starts with entry of resting follicles into the growth phase, a process where the kit system plays a key role. Several months are required for a new growing follicle to reach the preantral stage (0.15mm), then 70 additional days to reach the size of 2mm. Early growing follicle growth is regulated by subtle interactions between follicle-stimulating hormone (FSH) and local factors produced by theca and granulosa cells (GCs), as well as the oocyte. From the time they enter the selectable stage during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of granulosa cell proliferation. During the early follicular phase, the early selected follicle grows very quickly and estradiol is present in the follicular fluid. However, the total steroid production remains moderate. From the mid-follicular phase, the preovulatory follicle synthesizes high quantities of estradiol, then after the mid-cycle gonadotropin surge, very large amounts of progesterone. At this stage of development, the responsiveness of the follicle to gonadotropins is maximum, especially to luteinizing hormone (LH) that triggers granulosa wall dissociation and cumulus expansion as well as oocyte nuclear maturation. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases under the control of local factors acting in an autocrine/paracrine fashion

[Is neo-oogenesis in the adult ovary, a realistic paradigm?]

International audienceIt is a central dogma of female reproductive biology that oogenesis ceases around the time of birth in mammalian species. In 2004 and 2005, two studies were published by Johnson et al., in which they claimed that in the adult mouse ovary, neo-oogenesis takes place and originates from female germline stem cells that are present in either the ovarian surface epithelium or bone marrow. Following these publications, experiments showed that non-germinal stem cells could generate oocytes. However, in the mouse, ability of extra-ovarian stem cells to refurbish the ovary in new oocytes competent to ovulate, and subsequent existence of a spontaneous neo-oogenesis in the adult ovary in normal physiologic conditions, have been disputed. Morphologic studies performed in the adult mouse ovary showed that atresia of the immature follicle pool was strongly overestimated by Johnson et al., and that no intermediary stages of meiosis were seen. These observations led to the conclusion that adult female mice do not need neo-oogenesis for maintaining a normal reproductive function. However, a recent study have shown that female germline stem cells might be present in the ovarian surface epithelium in mice and humans. When sampled in GFP transgenic mice, cultured for a long period and transplanted into ovaries of sterilized mice, these cells underwent oogenesis and the mice produced offsprings. These new data support the possibility to experimentally restore fertility in women suffering from a premature ovarian failure

Prise en charge globale de l'asthme (cas de la région d'Amiens)

ANGERS-BU Médecine-Pharmacie (490072105) / SudocSudocFranceF

Folliculogénèse

chap. 1National audienc

La fonction ovarienne

chap. 15National audienc

Ovarian function

chap. 15International audienc

La fonction ovarienne

chap. 15National audienc

Ovarian function

chap. 15International audienc