Hormone-Induced Proliferation and Differentiation of Granulosa Cells: A Coordinated Balance of the Cell Cycle Regulators Cyclin D2 and p27^Kip1

Abstract

The proliferation and terminal differentiation of granulosa cells are critical for normal follicular growth, ovulation, and luteinization. Therefore, the in situ localization and hormonal regulation of cell cycle activators (cyclin D1, D2, and D3) and cell cycle inhibitors (p27Kip1 and p21Cip1) were analyzed in ovaries of mice and rats at defined stages of follicular growth and differentiation. Cyclin D2 mRNA was specifically localized to granulosa cells of growing follicles, while cyclin D1 and cyclin D3 were restricted to theca cells. In hypophysectomized (H) rats, cyclin D2 mRNA and protein were increased in granulosa cells by treatment with estradiol or FSH and were increased maximally by treatment with both hormones. In serum-free cultures of rat granulosa cells, cyclin D2 mRNA was rapidly elevated in response to FSH, forskolin, and estradiol, indicating that estradiol as well as cAMP can act directly and independently to increase cyclin D2 expression. The levels of p27Kip1 protein were not increased in response to estradiol or FSH. In contrast, when ovulatory doses of human CG (LH) were administered to hormonally primed H rats to stimulate luteinization, cyclin D2 mRNA and protein were rapidly decreased and undetectable within 4 h, specifically in granulosa cells of large follicles. Also in response to LH, the expression of the cell cycle inhibitor p27Kip1 was induced between 12 and 24 h (p21Cip1 was induced within 4 h) and remained elevated specifically in luteal tissue. A critical role for cyclin D2 in the hormone-dependent phase of follicular growth is illustrated by the ovarian follicles of cyclin D2-/- mice, which do not undergo rapid growth in response to hormones, but do express markers of FSH/LH action, cell cycle exit, and terminal differentiation. Collectively, these data indicate that FSH and estradiol regulate granulosa cell proliferation during the development of preovulatory follicles by increasing levels of cyclin D2 relative to p27Kip1 and that LH terminates follicular growth by down-regulating cyclin D2 concurrent with up-regulation of p27Kip1 and p21Cip1.

Subfertility and defective folliculogenesis in female mice lacking androgen receptor

“…4). hCG, which mimics the function of LH, triggers the differentiation of granulosa cells into cumulus cells and luteal cells, which involves the transition from cell proliferation to growth arrest and is concurrent with down-regulation of cyclin D2 and up-regulation of p27 and p21 gene expression (20). The marked reduction of p21 expression in the AR Ϫ/Ϫ ovary at this stage (Fig.…”

“…It has been known that a certain number of granulosa cells must be present in the ovary for ovulation to occur (20). Therefore, the reduced number of CLs in the AR Ϫ/Ϫ ovaries could be in part due to the much lower number of granulosa cells in some of the POFs, which results in a reduction of ovulation events (Table 1) and a subsequent reduction in CL formation.…”

“…The expression level of insulin-like growth factor-I receptor is also reduced in the AR Ϫ/Ϫ ovaries, but to a lessened extent. When comparing 4.5-week-old ovaries treated with PMSG for 48 h with or without hCG for an additional 10 h, we found that the expression level of p21, which is known to be essential for granulosa luteinization (20), is very low in the AR Ϫ/Ϫ ovaries (Fig. 5B).…”

GSK3β mediates suppression of cyclin D2 expression by tumor suppressor PTEN

“…In the early stage of embryogenesis, cyclin D1 and cyclin D2 display opposite and specific expression patterns in the developing hindbrain (Wianny et al, 1998). Furthermore, this exclusive expression pattern of cyclin Ds is also preserved in some organs of adult animals (Ravnik et al, 1995;Robker and Richards, 1998). Thus, each of cyclin Ds may have distinct functions possibly by associating with tissue specific interactors (Ciemerych et al, 2002).…”

Aetiology and pathogenesis of cystic ovarian follicles in dairy cattle: a review

“…In rodents, the importance of this receptor in follicular growth and development has clearly been demonstrated 110 T. Vanholder et al [81,82] and its localisation in follicle cells throughout follicular development has been described in many mammals including cattle [83,84]. More specifically, in rat ovarian follicles ER-β mRNA expression precedes increased expression of mRNA for the LH receptor and specific steroidogenic enzymes [85].…”