The D-type cyclins (D1, D2 and D3) are critical governors of the cell-cycle clock apparatus during the G1 phase of the mammalian cell cycle. These three D-type cyclins are expressed in overlapping, apparently redundant fashion in proliferating tissues. A human D-type cyclin gene (CCND1/cyclin D1/PRAD1) was isolated and identified as a candidate Bcl1 oncogene. Xiong et al. (1992) reported the molecular cloning of two additional human D-type cyclin genes, CCND2 (cyclin D2) and CCND3 (cyclin D3). All three human D-type cyclin genes encode small (33-34 kDa) proteins that share an average of 57% identity over the entire coding region and 78% in the cyclin box.
NCBI Summary:
The protein encoded by this gene belongs to the highly conserved cyclin family, whose members are characterized by a dramatic periodicity in protein abundance through the cell cycle. Cyclins function as regulators of CDK kinases. Different cyclins exhibit distinct expression and degradation patterns which contribute to the temporal coordination of each mitotic event. This cyclin forms a complex with and functions as a regulatory subunit of CDK4 or CDK6, whose activtiy is required for cell cycle G1/S transition. This protein has been shown to interact with and be involved in the phosphorylation of tumor suppressor protein Rb. Knockout studies of the homologous gene in mouse suggest the essential roles of this gene in ovarian granulosa and germ cell proliferation. High level expression of this gene was observed in ovarian and testicular tumors.
Robker et al. (1998) showed that cyclin D2 mRNA was specifically localized to granulosa cells of growing follicles. Furthermore, ovarian follicles of cyclin D2-/- mice do not undergo rapid growth in response to hormones.
Expression regulated by
FSH, LH, Steroids, Growth Factors/ cytokines
Comment
Regulation of Cyclin D2 Expression and Degradation by Follicle Stimulating Hormone During Rat Granulosa Cell Proliferation In Vitro. Han Y et al. Cyclin D2 (CCND2, encoded by Ccnd2) plays an important role in the induction of early-to-mid G1 phase transition and is required for granulose cell proliferation during ovarian folliculogenesis. In the present study, we investigated the role of follicle stimulating hormone (FSH) in the regulation of cyclin D2 expression and degradation during rat granulosa cell proliferation in vitro. FSH acutely increased granulosa cell Ccnd2 mRNA abundance and CCND2 protein content as well as proliferation. FSH-induced granulosa cell CCND2 protein content and proliferation were mimicked by forskolin and attenuated by inhibitors of protein kinase A (PKA; H89), phosphatidylinositol 3-kinase (PI3K; LY294002) but not mitogen-activated protein kinase kinase 1/2 (MEK1/2; U0126) as well as by PKA catalytic subunit (PRKACA) silencing (siRNA) and dominant-negative Akt (dn-Akt), suggesting that the PKA and PI3K, but not MEK signaling pathways are involved. Interestingly, FSH also enhanced CCND2 protein degradation in granulosa cells, a process involving a PKA-mediated ubiquitin-proteasome degradation pathway. Taken together, these results demonstrate that FSH acutely regulated CCND2 expression through both PKA and PI3K signaling pathways during granulosa cell proliferation and also accelerated its ubiquitination-proteasomal degradation which may prevent overstimulation of granulosa cell proliferation and follicular growth.
Robker et al. (1998) showed that , 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. 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.Talal El-Hefnawy et al 2001 reported the synergism Between FSH and Activin in the
Regulation of Proliferating Cell Nuclear Antigen (PCNA) and Cyclin D2
Expression in Rat Granulosa Cells .
Incubation of
undifferentiated rat granulosa cells with FSH, forskolin, activin-A, or T alone did not influence either the expression of
the proliferation-associated genes cyclin D2 and proliferating cell nuclear antigen or the differentiation-associated
genes P450 aromatase, LH receptor, P450 cholesterol side-chain cleavage enzyme, and 3?hydroxysteroid
dehydrogenase. However, when granulosa cells were stimulated with either FSH or forskolin in the presence of
activin-A, significant increases (P < 0.05) were observed for cyclin D2 and proliferating cell nuclear antigen at both
the mRNA and protein levels as well as mRNAs for P450 aromatase, LH receptor, P450 cholesterol side-chain
cleavage enzyme and 3?hydroxysteroid dehydrogenase.
Transcriptional Regulation of Cyclin D2 by the PKA Pathway and Inducible cAMP Early Repressor (ICER) in Granulosa Cells. Mu?LC et al. Cyclin D2 (Ccnd2) is an essential gene for folliculogenesis, as null mutation in mice impairs granulosa cell proliferation in response to FSH. Ccnd2 mRNA is induced during the estrus cycle by FSH and rapidly inhibited by LH. Yet, the responsive elements and transcription factors accounting for the gene expression of cyclin D2 in the ovary have not been fully characterized. In this report the presented data suggests a mechanism for the regulation of cyclin D2 at the level of transcription via a PKA dependent signaling mechanism using primary cultures of rat granulosa cells and immortalized mouse granulosa cells. The promoter activity of cyclin D2 was shown to be induced by FSH and the catalytic alpha subunit of PKA (PRKACA), and this activity was repressible by the CREM isoform ICER. In silico analysis of the mouse, rat and human cyclin D2 promoters identified two CREB binding sites, a conserved proximal element and a less conserved distal element relative to the translation start site. Mutational analysis on the proximal element drastically decreased the effects of PRKACA and ICER on the promoter activity, whereas the mutation on the distal element did not contribute to the decrease in promoter activity. EMSA and DNase Footprinting analysis confirmed ICER binding to the proximal element and ChIP analysis also demonstrated the occurrence of this binding in vivo. These results identified a CRE within the upstream region of cyclin D2 gene that is, at least partly, implicated in the stimulation and repression of cyclin D2 transcription. Finally, data presented suggests ICER involvement in the regulation of granulosa cell proliferation as over expression of ICER, resulted in the inhibition of PRKACA-induced DNA synthesis.
Gene expression increased. Luteinization of porcine preovulatory follicles leads to systematic changes in follicular gene expression. Agca C et al. The LH surge initiates the luteinization of preovulatory follicles and causes hormonal and structural changes that ultimately lead to ovulation and the formation of corpora lutea. The objective of the study was to examine gene expression in ovarian follicles (n = 11) collected from pigs (Sus scrofa domestica) approaching estrus (estrogenic preovulatory follicle; n = 6 follicles from two sows) and in ovarian follicles collected from pigs on the second day of estrus (preovulatory follicles that were luteinized but had not ovulated; n = 5 follicles from two sows). The follicular status within each follicle was confirmed by follicular fluid analyses of estradiol and progesterone ratios. Microarrays were made from expressed sequence tags that were isolated from cDNA libraries of porcine ovary. Gene expression was measured by hybridization of fluorescently labeled cDNA (preovulatory estrogenic or -luteinized) to the microarray. Microarray analyses detected 107 and 43 genes whose expression was decreased or increased (respectively) during the transition from preovulatory estrogenic to -luteinized (P<0.01). Cells within preovulatory estrogenic follicles had a gene-expression profile of proliferative and metabolically active cells that were responding to oxidative stress. Cells within preovulatory luteinized follicles had a gene-expression profile of nonproliferative and migratory cells with angiogenic properties. Approximately, 40% of the discovered genes had unknown function.
Ovarian localization
Cumulus, Granulosa, Luteal cells
Comment
Robker et al. (1998) indicated 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.
Differential gene expression in cumulus cells as a prognostic indicator of embryo viability: a microarray analysis. van Montfoort AP et al. Besides the established selection criteria based on embryo morphology and blastomere number, new parameters for embryo viability are needed to improve the clinical outcome of IVF and more particular of elective single embryo transfer (eSET). Genome-wide gene expression in cumulus cells was studied, since these cells surround the oocyte inside the follicle and therefore possibly reflect oocyte developmental potential. Early cleavage (EC) was chosen as a parameter for embryo viability. Gene expression in cumulus cells from eight oocytes resulting in an EC embryo (EC-CC; n=8) and from eight oocytes resulting in a non-EC (NEC) embryo (NEC-CC; n=8) was analysed using microarrays (n=16). A total of 611 genes were differentially expressed (P < 0.01), mainly involved in cell cycle, angiogenesis, apoptosis, epidermal growth factor, fibroblast growth factor and platelet-derived growth factor signalling, general vesicle transport and chemokine and cytokine signalling. Of the 25 selected differentially expressed genes analysed by quantitative real-time PCR (qRT-PCR) 15 (60%) genes could be validated in the original samples. Of these 8 (53%) could also be validated in 24 (12-EC-CC and 12 NEC-CC) extra independent samples. The most differentially expressed genes among these were CCND2, CXCR4 , GPX3 , CTNND1 DHCR7 , DVL3 , HSPB1 and TRIM28 , which probably point to hypoxic conditions or a delayed oocyte maturation in NEC-CC samples. This opens up perspectives for new molecular embryo or oocyte selection parameters which might also be useful in countries where the selection has to be made at the oocyte stage before fertilization instead of at the embryonic stage.
Follicle stages
Secondary, Antral, Preovulatory, Corpus luteum
Comment
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - ovarian defect Comment:Sicinski et al. (1996) generated mice bearing a disrupted cyclin D2 gene by using gene targeting in embryonic stem cells. Cyclin D2-deficient females are sterile owing to the inability of ovarian granulosa cells to proliferate normally in response to follicle-stimulating hormone (FSH), whereas mutant males display hypoplastic testes.