Follicle

Abstract: The mammalian hair follicle is a complex 'mini-organ' thought to form only during development; loss of an adult follicle is considered permanent However, the possibility that hair follicles develop de novo following wounding was raised in studies on rabbits, mice and even humans fifty years ago Subsequently, these observations were generally discounted because definitive evidence for follicular neogenesis was not presented Here we show that, after wounding, hair follicles form de novo in genetically normal adult mice The regenerated hair follicles establish a stem cell population, express known molecular markers of follicle differentiation, produce a hair shaft and progress through all stages of the hair follicle cycle Lineage analysis demonstrated that the nascent follicles arise from epithelial cells outside of the hair follicle stem cell niche, suggesting that epidermal cells in the wound assume a hair follicle stem cell phenotype Inhibition of Wnt signalling after re-epithelialization completely abrogates this wounding-induced folliculogenesis, whereas overexpression of Wnt ligand in the epidermis increases the number of regenerated hair follicles These remarkable regenerative capabilities of the adult support the notion that wounding induces an embryonic phenotype in skin, and that this provides a window for manipulation of hair follicle neogenesis by Wnt proteins These findings suggest treatments for wounds, hair loss and other degenerative skin disorders

Abstract: The maturation of ovarian follicles involves several sequential stages: initiation, growth, selection, ovulation, and luteinization (Fig. 1). Although the factor(s) that initiates the growth of “resting” primordial follicles remain elusive, the key endocrine events controlling follicular growth in mammals have been known for many years. For example, once follicles have begun to grow, basal concentrations of the gonadotropins, FSH and LH, maintain growth up until the small antral stage. Small antral follicles are selected to continue growth by subtle increases in basal concentrations of gonadotropins, such as those that occur at menses in primates (1) or at the end of pregnancy in rodents (2). Once selected, the growing dominant follicle(s) acquires specific functional characteristics that permit it to differentiate to the preovulatory stage and synthesize estradiol. Increased serum estradiol triggers the surge of gonadotropins that, in turn, stimulates the preovulatory follicle(s) to ovulate and luteinize...

Abstract: It isnot clearwhether the turnover of ovarianfollicles during the estrouscycle in cattleisContinuous and independent of thephase of the cycle,or whether waves of follicular growth occur at specifictimes of the cycle. To clarifythis controversy, the pattern of growth and regression of ovarian follicles was characterized during a complete estrous cycle in ten heifers by daily ultrasonographic examinations. Follicles � 5 mm were measured and theirrelativelocationswithin the ovary were determined in order tofollow the sequentialdevelopment of each individual follicle. Results indicated the presence of either two (n = 2 heifers), three (n = 7), or four (n = I) waves of follicular growth per cycle.Each wave was characterizedby the development of one large (dominant) follicle and a variable number of smaller (non-dominant) follicles. In the most common pattern observed (threewaves/cycle),thefirst, second, and third waves started on Days 1.9 ± 0.3, 9.4 ± 0.5, and 16.1 ± 0.7 (X ± SEM), respectively. The dominant follicle in the third wave was the ovulatory follicle. The maximal sizeand the growth rateof the dominant folliclein the second wave were significantlylower than inthe other waves, but no significant difference was observed between the first and third waves. For the two heifers that had two follicularwaves/cycle,the waves startedon Days 2 and 11, whereas in the remaining heifer (four waves/cycle), the waves began on Days 2, 8, 14, and 17, respectively. At 0, 1, 2, 3, and 4 days before estrus, the ovulatory follicle was the largest follicle in the ovaries in 100%, 95%, 74%, 35%, and25% offollicular phases monitored, respectively. The relative size of the preovulatory follicle at the completion of luteolysis (progesterone< I ng/ml) was negatively correlated (r = -0.90; p<0.0001) with the interval of time between the end of luteolysis and the luteinizinghormone surge,suggestingthat the length of proestrus isdetermined by the sizeof thepreovulatoryfollicleat the beginning ofproestrus.In conclusion,thisstudy shows thatthe development of ovarian follicles�5 mm in heifers occurs inwaves and thatthe most common pattern isthreewaves per estrouscycle.

Abstract: In the mammalian ovary, progressive activation of primordial follicles from the dormant pool serves as the source of fertilizable ova. Menopause, or the end of female reproductive life, occurs when the primordial follicle pool is exhausted. However, the molecular mechanisms underlying follicle activation are poorly understood. We provide genetic evidence that in mice lacking PTEN (phosphatase and tensin homolog deleted on chromosome 10) in oocytes, a major negative regulator of phosphatidylinositol 3-kinase (PI3K), the entire primordial follicle pool becomes activated. Subsequently, all primordial follicles become depleted in early adulthood, causing premature ovarian failure (POF). Our results show that the mammalian oocyte serves as the headquarters of programming of follicle activation and that the oocyte PTEN-PI3K pathway governs follicle activation through control of initiation of oocyte growth.