Progesterone receptor activation mediates LH-induced type-I pituitary adenylate cyclase activating polypeptide receptor (PAC(1)) gene expression in rat granulosa cells

Signal pathway of LH-induced expression of nuclear progestin receptor in vertebrate ovulation

Nuclear progestin receptor (PGR), which is induced in the follicles destined to undergo ovulation, is believed to be obligatory for rupture of the follicles during ovulation in vertebrates. Studies in some mammals and teleost medaka have revealed the outline of the central signaling pathway that leads to the PGR expression in the preovulatory follicles at ovulation. In this review, we summarize the current knowledge on what signaling mediators are involved in the LH-induced follicular expression of PGR at ovulation in these animals. LH-inducibility of follicular PGR expression is conserved. In both group of animals, activation of the LH receptor on the granulosa cell surface with LH commonly results in the increase of intracellular cAMP levels, while the downstream signaling cascades activated by high level of cAMP are totally different between mice and medaka. PGR is currently presumed to be induced via PKA/CREB-mediated transactivation and ERK1/2-dependent signaling in mice, but the receptor is induced via EPAC/RAP and AKT/CREB pathways in the teleost medaka. The differences and similarities in the signaling pathways for PGR expression between them is discussed from comparative and evolutionary aspects. We also discussed questions concerning PGR expression and its regulation needed to be investigated in future.

Induction of tumor suppressor KCTD11 during periovulatory period in rat ovary

The tumor suppressor gene KCTD11 plays a critical role in cell proliferation, differentiation and invasion. The current study investigated the regulation and the spatiotemporal expression pattern of Kctd11 in the rat ovary during the periovulatory period. Ovaries, granulosa cells, or theca-interstitial cells were collected at various times after hCG administration using an established gonadotropin-primed immature rat model that induces follicular development and ovulation. Real-time quantitative PCR analysis revealed that mRNA for Kctd11 was significantly induced both in theca-intersititial and granulosa cells after hCG treatment although their temporal expression patterns differed. In situ hybridization analysis demonstrated that Kctd11 mRNA expression was induced in theca-intersititial cells at 6 h after hCG, and the expression remained elevated until 12 h after hCG. Kctd11 mRNA was stimulated in granulosa cells at 6 h and reached the highest expression at 12 h. There was negligible Kctd11 mRNA signal observed in newly forming corpora lutea. In addition, the data indicate that both the protein kinase A and the protein kinase C pathway regulate the expression of Kctd11 mRNA in granulosa cells. Either forskolin or phorbol 12 myristate 13-acetate can mimic hCG induction of Kctd11 expression. Furthermore, the stimulation of Kctd11 by hCG requires new protein synthesis. Inhibition of progesterone action and the EGF pathway blocked Kctd11 mRNA expression, whereas inhibition of prostaglandin synthesis had no effect. Our finding suggest that the induction of the Kctd11 may be important for theca and granulosa cell differentiation into luteal cells.

Synthesis and antiproliferative activity of conformationally restricted 1,2,3-triazole analogues of combretastatins in the sea urchin embryo model and against human cancer cell lines

A series of 1,5-diaryl- and 4,5-diaryl-1,2,3-triazole derivatives of combretastatin A4 were synthesized and evaluated as antimitotic microtubule destabilizing agents using the sea urchin embryo model. Structure-activity relationship studies identified compounds substituted with 3,4,5-trimethoxyphenyl and 3,4-methylenedioxy-5-methoxyphenyl ring A and 4-methoxyphenyl ring B as potent antiproliferative agents with high cytotoxicity against a panel of human cancer cell lines including multi-drug resistant cells. 4,5-Diaryl-1,2,3-triazoles (C-C geometry) were found to be considerably more active than the respective 1,5-diaryl-1,2,3-triazoles (N-C geometry). Compound 10ad' induced G2/M cell cycle arrest and apoptosis in human T-leukemia Jurkat cells via caspase 2/3/9 activation and downregulation of the antiapoptotic protein XIAP. A mitotic catastrophe has been evaluated as another possible cell death mode.

Role of PACAP in Female Fertility and Reproduction at Gonadal Level - Recent Advances

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide, first isolated from hypothalamic extracts, but later shown in peripheral organs, such as endocrine glands, gastrointestinal system, cardiovascular system, and reproductive organs. PACAP plays a role in fertility and reproduction. Numerous studies report on the gonadal regulatory effects of PACAP at hypothalamo-hypophyseal levels. However, the local effects of PACAP at gonadal levels are also important. The present review summarizes the effects of PACAP in the ovary. PACAP and its receptors are present in the ovary, and PACAP plays a role in germ cell migration, meiotic division, follicular development, and atresia. The autocrine-paracrine hormonal effects seem to play a regulatory role in ovulation, luteinization, and follicular atrophy. Altogether, PACAP belongs to the ovarian regulatory peptides.

Luteinizing hormone-stimulated pituitary adenylate cyclase-activating polypeptide system and its role in progesterone production in human luteinized granulosa cells

The present study examined the gonadotropin regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP type I receptor (PAC(1)-R) expression, and its role in progesterone production in the human luteinized granulosa cells. The stimulation of both PACAP and PAC(1)-R mRNA levels by LH was detected using a competitive reverse transcription-polymerase chain reaction (RT-PCR). PACAP transcript was stimulated by LH reaching maximum levels at 12 hours in a dose dependent manner. LH treatment also stimulated PAC(1)-R mRNA levels within 24 hours. Addition of PACAP-38 (10(-7) M) as well as LH significantly stimulated progesterone production during 48 hours culture. Furthermore, co-treatment with PACAP antagonist partially inhibited LH-stimulated progesterone production. Treatment with vasoactive intestinal peptide, however, did not affect progesterone production. Taken together, the present study demonstrates that LH causes a transient stimulation of PACAP and PAC(1)-R expression and that PACAP stimulates progesterone production in the human luteinized granulosa cells, suggesting a possible role of PACAP as a local ovarian regulator in luteinization.

Control of oocyte release by progesterone receptor-regulated gene expression

The progesterone receptor (PGR) is a nuclear receptor transcription factor that is essential for female fertility, in part due to its control of oocyte release from the ovary, or ovulation. In all mammals studied to date, ovarian expression of PGR is restricted primarily to granulosa cells of follicles destined to ovulate. Granulosa cell expression of PGR is induced by the pituitary Luteinizing Hormone (LH) surge via mechanisms that are not entirely understood, but which involve activation of Protein Kinase A and modification of Sp1/Sp3 transcription factors on the PGR promoter. Null mutations for PGR or treatment with PGR antagonists block ovulation in all species analyzed, including humans. The cellular mechanisms by which PGR regulates ovulation are currently under investigation, with several downstream pathways having been identified as PGR-regulated and potentially involved in follicular rupture. Interestingly, none of these PGR-regulated genes has been demonstrated to be a direct transcriptional target of PGR. Rather, in ovarian granulosa cells, PGR may act as an inducible coregulator for constitutively bound Sp1/Sp3 transcription factors, which are key regulators for a discrete cohort of ovulatory genes.

Regulation and function of tissue inhibitor of metalloproteinase (TIMP) 1 and TIMP3 in periovulatory rat granulosa cells

In the ovary, the matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinase (TIMPs) have been postulated to regulate extracellular matrix remodeling associated with ovulation. In the present study, we investigated the regulatory mechanisms controlling expression of Timp1 and Timp3 mRNA in periovulatory granulosa cells. Granulosa cells were isolated from immature pregnant mare serum gonadotropin-primed (10 IU) rat ovaries and treated with human chorionic gonadotropin (hCG; 1 IU/ml). At 4 h after hCG treatment, Timp1 expression was highest and then decreased gradually over the remaining 24 h of culture. In contrast, hCG induced a biphasic increase of Timp3 expression at 2 and 16 h. The hCG stimulated expression of Timp1 and Timp3 mRNA was blocked by inhibitors of the protein kinase A (H89), protein kinase C (GF109203), and MAPK (SB2035850) pathways. To further explore Timp1 and Timp3 regulation, cells were cultured with the progesterone receptor antagonist RU486, which blocked the hCG induction of Timp3 expression, whereas the epidermal growth factor receptor tyrosine kinase inhibitor AG1478 blocked the hCG stimulation of both Timp1 and Timp3 expression. The prostaglandin-endoperoxide synthase 2 inhibitor NS-398 had no effect. The potential function of TIMP3 was investigated with Timp3-specific small interfering RNA treatment. Timp3 small interfering RNA resulted in a 20% decrease in hCG-induced progesterone levels and microarray analysis revealed an increase in cytochrome P450 Cyp 17, ubiquitin conjugating enzyme E2T, and heat shock protein 70. IGF binding protein 5, stearyl-CoA desaturase, and annexin A1 were decreased. The differential regulation between Timp1 and Timp3 may correlate with their unique roles in the processes of ovulation and luteinization. For TIMP3, this may include regulating fatty acid synthesis, steroidogenesis, and protein turnover.

PACAP—A Multifacetted Neuropeptide

Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated from ovine hypothalamus based on its ability to stimulate cAMP production in pituitary cell cultures. The peptide exists in two forms, both of which are derived from the same precursor. PACAP38 and the C-terminal truncated PACAP27 can interact with three subtypes of receptors activating adenylate cyclase and/or phospholipase C. Since its discovery, numerous studies have provided evidence that PACAP is a pleiotropic substance having a broad spectrum of biological functions; the peptide can act as a hormone, neurohormone, autocrine/paracrine substance, neurotransmitter, neuromodulator, neurotrophic factor, and immunomodulator. Two examples of the functional role of PACAP on the biological timing system are presented: 1) the transient expression of PACAP during the periovulatory period in ovarian cells, in which PACAP functions as an autocrine/paracrine inducer of progesterone secretion and subsequent luteinization; and 2) the role of PACAP as a neurotransmitter in the retinohypothalamic tract mediating photic regulation of the brain's biological clock.

Expression and in vitro regulation of pituitary adenylate cyclase-activating polypeptide (pacap38) and its type I receptor (pac1-r) in the gonads of tilapia (Oreochromis mossambicus)

Pituitary adenylate cyclase-activating polypeptide (PACAP), a pleiotropic neuropeptide, has diverse functions in mammals. However, studies of the expression and function of PACAP and its receptor in fish, particularly in the reproductive system, are still limited. In this report, semi-quantitative RT-PCR and immunohistochemical staining were performed to identify expression domains of commercially important tilapia (Oreochromis mossambicus). PACAP (tpacap(38)) and its type I receptor (tpac(1)-r). Transcripts were detected in the brain, gallbladder, gill, heart, intestine, kidney, muscles, pancreas, spleen, stomach, testes, and ovaries, but not in the liver. Expression of tpacap(38) and tpac(1)-r mRNA in brain tissue was significantly higher in both sexes compared with other tissues. Addition of exogenous ovine PACAP(38) (0.25-5 nM), cAMP analog (dibutyryl-cAMP, 0.25-1.5 mM) or forskolin (adenylate cyclase activator, 1-10 microM) significantly upregulated tpacap(38) in the gonads via a dose- and time-dependent fashion. This effect reached a maximal level at 2 h after induction, and then decreased with prolonged culture for up to 4 or 8 h. Additionally, the expression levels of tpac(1)-r were not significantly affected by ovine PACAP(38) or dibutyryl-cAMP in either sex. Forskolin had a slightly inductive effect and its function could be suppressed with the addition of protein kinase A (PKA) inhibitor, H89 (10 microM), indicating involvement of the cAMP-PKA signaling pathway in the regulation of tpacap(38). Expression of tpacap(38) and tpac(1)-r in the gonads of tilapia suggests that PACAP may mediate gonadotropin action via paracrine/autocrine mechanisms in this bony fish.

Gonadotropin-dependent regulation of bovine pituitary adenylate cyclase-activating polypeptide in ovarian follicles prior to ovulation

To study the regulation of bovine pituitary adenylate cyclase-activating polypeptide (PACAP) in preovulatory follicles prior to ovulation, PACAP cDNA was isolated by RT-PCR. Its open reading frame (ORF) is composed of 531 bp, and encodes for a 176-amino acid protein that bears 76-90% identity with other PACAP homologs. Using bovine preovulatory follicles obtained between 0 and 24 h after human chorionic gonadotropin (hCG) and semiquantitative RT-PCR/Southern blot, we demonstrate that levels of PACAP mRNA were low at 0 h, markedly increased at 6 and 12 h (P<0.05), and declined 18 and 24 h after hCG. Levels of PACAP mRNA were high in the bovine pituitary, testis, intestine and uterus, but moderate to low in other tissues. Analyses performed on isolated preparations of granulosa and theca cells showed a significant increase of PACAP transcripts in both cell types after hCG, whereas primary granulosa cell cultures revealed high levels of PACAP as well as its receptors PAC-1 and VPAC-2 mRNA after forskolin treatment. Overexpression of the catalytic subunit of protein kinase A (PKA) in granulosa cells stimulated, but treatment with H89 or PKA inhibitor protein inhibited PACAP mRNA expression, whereas PACAP overexpression stimulated an increase in abundance of transcripts for PGHS-2, PGES, EP2 receptor, progesterone receptor, and ADAMTS-1, but not for P450-side chain cleavage and P450 aromatase. Thus, this study demonstrates the gonadotropin-dependent regulation of PACAP mRNA in bovine preovulatory follicles, the importance of PKA activation in the expression of PACAP in granulosa cells, and stimulating effect of PACAP on gene expression during the ovulatory process.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Cloning and characterization of a PAC1 receptor hop-1 splice variant in goldfish (Carassius auratus)

In several vertebrates, it has been demonstrated that alternative splicing of PAC1 receptor (PAC1-R) transcripts can generate a number of functional receptor variants which utilize different signal transduction pathways to mediate their activities. As PACAP is a physiological growth hormone-releasing factor in fish, and PACAP and the PAC1-R are highly conserved in vertebrate evolution, it would be of interest to investigate the structure and cellular distribution, particularly in the pituitary, of PAC1-R splice variants in a fish model. Our laboratory has previously cloned a receptor cDNA corresponding to the goldfish PAC1-R-s (goldfish PAC1-R-short). In the present study, a goldfish PAC1-R-hop1 variant was characterized. Functional expression of goldfish PAC1-R-s and PAC1-R-hop1 in Chinese Hamster Ovary cells revealed that, upon stimulation by ovine PACAP38, these receptor variants exhibited similar EC50 values (8.7+/-1.5 and 8.8+/-1.9 nM, respectively) and maximal responses in activating intracellular cAMP production. The presence and expression levels of these transcripts were measured by quantitative real-time PCR in the brain, heart, pituitary and male gonad, and goldfish PAC1-R-s were found to be the predominant form. In situ hybridization of goldfish PAC1-R in the pituitary revealed its prevalent presence in the pars distalis. In summary, the present study provides information to confirm the role of PACAP in the pituitary and to elucidate the pleiotropic effects of PACAP in fish.

Endogenous Ligands of PACAP/VIP Receptors in the Autocrine–Paracrine Regulation of the Adrenal Gland

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the main endogenous ligands of a class of G protein-coupled receptors (Rs). Three subtypes of PACAP/VIP Rs have been identified and named PAC(1)-Rs, VPAC(1)-Rs, and VPAC(2)-Rs. The PAC(1)-R almost exclusively binds PACAP, while the other two subtypes bind with about equal efficiency VIP and PACAP. VIP, PACAP, and their receptors are widely distributed in the body tissues, including the adrenal gland. VIP and PACAP are synthesized in adrenomedullary chromaffin cells, and are released in the adrenal cortex and medulla by VIPergic and PACAPergic nerve fibers. PAC(1)-Rs are almost exclusively present in the adrenal medulla, while VPAC(1)-Rs and VPAC(2)-Rs are expressed in both the adrenal cortex and medulla. Evidence indicates that VIP and PACAP, acting via VPAC(1)-Rs and VPAC(2)-Rs coupled to adenylate cyclase (AC)- and phospholipase C (PLC)-dependent cascades, stimulate aldosterone secretion from zona glomerulosa (ZG) cells. There is also proof that they can also enhance aldosterone secretion indirectly, by eliciting the release from medullary chromaffin cells of catecholamines and adrenocorticotropic hormone (ACTH), which in turn may act on the cortical cells in a paracrine manner. The involvement of VIP and PACAP in the regulation of glucocorticoid secretion from inner adrenocortical cells is doubtful and surely of minor relevance. VIP and PACAP stimulate the synthesis and release of adrenomedullary catecholamines, and all three subtypes of PACAP/VIP Rs mediate this effect, PAC(1)-Rs being coupled to AC, VPAC(1)-Rs to both AC and PLC, and VPAC(2)-Rs only to PLC. A privotal role in the catecholamine secretagogue action of VIP and PACAP is played by Ca(2+). VIP and PACAP may also modulate the growth of the adrenal cortex and medulla. The concentrations attained by VIP and PACAP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their adrenal content is consistent with a local autocrine-paracrine mechanism of action.

Role of pituitary adenylate cyclase-activating peptide (PACAP) in the cyclic recruitment of immature follicles in the rat ovary

Following the midcyclic gonadotropin surge, PACAP is transiently expressed for approximately 12 h in the cyclic adult rat ovary. PACAP is observed in granulosa/lutein cells of the large mature follicles destined to ovulate and is believed to be a regulator of acute progesterone production and luteinization in these follicles. PACAP is also observed in solitary theca cells of immature follicles and in interstitial glandular cells intimately surrounding immature follicles. To examine if PACAP could be involved in the process of cyclic recruitment of such immature follicles, we primed immature granulosa cells from prepubertal ovaries with PACAP (1 nM and 100 nM) for 12 h. The treatment significantly stimulated the subsequent 24 h FSH-induced estradiol production (2.2 and 2.4 fold, respectively). The response seemed to be caused by a stimulation of aromatase activity. Estradiol production induced by testosterone was increased 2.4 and 2.6 fold, respectively, whereas functional FSH-receptors (cAMP production following FSH stimulation) or spontaneous apoptosis (immunohistochemical detection of DNA fragments) was unaffected. We conclude that PACAP priming of immature rat granulosa cells for 12 h increases subsequent FSH induced estradiol production and that PACAP could be involved in the cyclic recruitment of immature follicles in the adult rat ovary.

Pituitary Adenylate Cyclase Activating Polypeptide Messenger RNA in the Paraventricular Nucleus and Anterior Pituitary During the Rat Estrous Cycle1

The neuropeptide pituitary adenylate cyclase activating polypeptide (ADCYAP 1, or PACAP) has been demonstrated to enhance gonadotropin-releasing hormone (GnRH)-induced gonadotropin secretion and regulate gonadotropin subunit gene expression in cultures of anterior pituitary cells. In the present study, we used in situ hybridization and real-time polymerase chain reaction to examine the expression of Pacap mRNA within the paraventricular nucleus (PVN) and anterior pituitary throughout the estrous cycle of the rat. Levels of luteinizing hormone in serum and pituitary gonadotropin subunit mRNAs were evaluated and displayed cyclic fluctuations similar to those reported previously. Pacap mRNA expression in the PVN and pituitary varied significantly during the estrous cycle, with the greatest changes occurring on the day of proestrus. Pacap mRNA levels in the PVN declined significantly on the morning of diestrus. During proestrus, PVN Pacap mRNA levels significantly increased 3 h before the gonadotropin surge and then declined. Pituitary expression of Pacap mRNA also varied on the afternoon of proestrus with a moderate decline at the time of the gonadotropin surge and a significant increase later in the evening. Expression of the mRNA species encoding the 288 amino acid form of follistatin increased significantly following the rise in pituitary Pacap mRNA, at the termination of the secondary surge in follicle-stimulating hormone beta (Fshb) gene expression. These results suggest that PACAP is involved in events before and following the gonadotropin surge, perhaps through increased gonadotroph sensitivity to GnRH and suppression of Fshb subunit expression through increased follistatin, as previously observed in vitro.

Progesterone-receptor antagonists and statins decrease de novo cholesterol synthesis and increase apoptosis in rat and human periovulatory granulosa cells in vitro

Progesterone-receptor (PR) stimulation promotes survival in rat and human periovulatory granulosa cells. To investigate the mechanisms involved, periovulatory rat granulosa cells were incubated in vitro with or without the PR-antagonist Org 31710. Org 31710 caused the expected increase in apoptosis, and expression profiling using cDNA microarray analysis revealed regulation of several groups of genes with functional and/or metabolic connections. This regulation included decreased expression of genes involved in follicular rupture, increased stress responses, decreased angiogenesis, and decreased cholesterol synthesis. A decreased cholesterol synthesis was verified in experiments with both rat and human periovulatory granulosa cells treated with the PR-antagonists Org 31710 or RU 486 by measuring incorporation of [14C]acetate into cholesterol, cholesterol ester, and progesterone. Correspondingly, specific inhibition of cholesterol synthesis in periovulatory rat granulosa cells using 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (lovastatin, mevastatin, or simvastatin) increased apoptosis, measured as DNA fragmentation and caspase-3/7 activity. The increase in apoptosis caused by simvastatin was reversed by addition of the cholesterol synthesis-intermediary mevalonic acid. These results show that PR antagonists reduce cholesterol synthesis in periovulatory granulosa cells and that cholesterol synthesis is important for granulosa cell survival.

Pituitary adenylate cyclase-activating peptide: a pivotal modulator of steroid-induced reproductive behavior in female rodents

Pituitary adenylate cyclase-activating polypeptide (PACAP) regulates the secretion of GnRH into the hypothalamic hypophysial portal system and sensitizes the pituitary for release of hormones that trigger ovulation. Because reproductive behavior is synchronized with GnRH release, the present study was undertaken to determine whether PACAP in the ventromedial nucleus (VMN) plays a role in receptivity. To this end, we used rat and mouse reproductive behavioral models to determine the biological relationship between PACAP and steroid receptor function in females. We provide evidence for the requirement of PACAP in the VMN for progesterone (P)-dependent sexual behavior in estrogen (E)-primed females. We clarify the biological and molecular mechanisms of PACAP activity by showing 1) that inhibition of endogenous PACAP suppresses P receptor (PR)-dependent sexual behavior facilitated by the steroid P or D1-like agonist SKF38393 and 2) that PR, steroid receptor coactivators-1 and -2, and new protein synthesis are essential for ligand independent PACAP-facilitated behavior. These findings are consistent with convergence of PACAP-mediated cellular signals on PR for genomic activation and subsequent behavioral changes. Further, we show that steroids regulate both endogenous PACAP mRNA in the VMN and immunoreactive PACAP in the medial basal hypothalamus and cerebral spinal fluid for ligand-dependent, steroid receptor-dependent receptivity. The present findings delineate a novel, steroid-dependent mechanism within the female hypothalamus by which the neuropeptide PACAP acts as a feed-forward, paracrine, and/or autocrine factor for synchronization of behavior coordinate with hypothalamic control of ovulation.

Intracellular mechanisms regulating cell survival in ovarian follicles

The vertebrate ovary represents a uniquely dynamic organ system charged with the responsibility to initially provide, and subsequently foster, optimal numbers of maturing, viable gametes that will insure the propagation of the species. Seemingly in spite of this charge, >99% of germ cells within the ovaries of mammalian and avian species present at the time of birth or hatch are lost via atresia at some point during the lifespan of the female. The consequence of this ongoing germ cell and ovarian follicle attrition in some species eventually leads to the natural termination of reproductive function (e.g. menopause in humans), while in all species an excessive loss of germ cells frequently results in diminished reproductive potential due to subclinical or clinical infertility. Apoptosis represents the primary pathway by which defective or excessive numbers of follicles are rapidly and effectively eliminated, and this process is actively opposed or entirely suppressed by a variety of cell survival signaling pathways and cellular anti-apoptotic proteins expressed within follicles destined for ovulation. Significantly, such survival mechanisms are regulated by many of the same endocrine-paracrine-autocrine factors that control follicle differentiation. This review will begin by briefly discussing the process of apoptosis, then focus on the varied and often redundant mechanisms that prevent apoptotic cell death in granulosa cells specifically during the late preantral (comparable to the prehierarchal stage of follicle development in avian species) and preovulatory stages of follicle development.

Delivery of the oocyte from the follicle to the oviduct: a time of vulnerability

The multiplicity of genes regulated by the actions of LH in specific granulosa cell and cumulus cell microenvironments of the follicle during ovulation has now revealed how complex and finely tuned the ovulation process is. Although many proteases are expressed in the ovary and are hormonally regulated, the novel proteases ADAMTS-1 and cathepsin L, rather than the MMPs, have gained particular recognition. These may play critical roles in the eventual rupture of the follicle at the ovarian surface. Rupture is only one part of ovulation. Another important aspect is the actual release of the oocyte from the ovulation pore. Several recent studies have shown that the production of the matrix that is evidenced by cumulus expansion is somehow critical for extrusion to occur and for the oocyte to travel into the oviduct. At any point the oocyte may be trapped within a non-ovulating structure. Lastly, if the events of ovulation fail to occur before the events of luteinization are complete, oocytes are destined to degenerate within the non-ovulating structures.

Growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide in the reproductive system

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are both members of the glucagon superfamily that, with gonadotropins, act at central and peripheral levels as paracrine and autocrine coregulators of reproductive function. GHRH and PACAP are ancient peptides. Their original forms (both 27 amino acids long) were encoded by a single ancestral gene, several duplications of which led to the genes that encode the neuropeptides of the glucagon superfamily. In the male and female reproductive tracts, GHRH and PACAP interact with a subset of G protein-coupled receptors that are structurally similar to the PACAP receptor and variants of the vasoactive intestinal peptide receptor, and share several biological actions. These are related mainly to the modulation of cAMP-dependent and other signal transduction pathways in several cells of the pituitary-gonadal axis. The recent discovery that antagonists of GHRH and PACAP suppress the growth of human cancer cell lines that are derived from reproductive tissues indicates the potential importance of these peptides as local regulators of cell division, cell cycle arrest, differentiation and cell death.

Transcription of the mouse PAC1 receptor gene: cell-specific expression and regulation by Zac1

Regulations of the PACAP type 1 (PAC1) receptor expression have been described in the brain and the anterior pituitary. To understand the molecular mechanisms underlying mouse PAC1 gene regulation, we first mapped its transcription start sites (tss). PAC1 receptor RNA initiates from two major sites in embryos and adult tissues. Functional analysis revealed a basal promoter within the first 180 bp upstream of transcription start. Negative regulatory sequences upstream of this minimal promoter control the cell type-specific transcription of a luciferase reporter gene. Zac1, a zinc finger protein mainly expressed in the brain and the pituitary gland, binds to a GC-rich motif of the promoter regulatory elements. The Zac1 DNA binding site is required to positive and negative regulations of the promoter. Our findings provide bases for future studies on the regulatory elements controlling PAC1 gene transcription and demonstrate the PAC1 receptor promoter as a target of Zac1.

Progesterone and progesterone receptors in reptiles

The role of progesterone (P) has been most extensively studied in the female reproductive tissues (ovary, reproductive tract, mammary gland) and in the brain, in which it is an important regulator and modulator in conjunction with estradiol (E). In nonmammalian vertebrate species, less work has been done on P metabolites involved in ovulation. In addition, P induces the expression of egg-white proteins, decreases myometrial contractility, and facilitates processing of eggs, formation of eggshell, and deposition of egg-white proteins. Actions of P may be synergistic with, or antagonist to, the actions of E, depending on hormone ratios, timing of exposure, and physiological state. These effects of P are mediated through progesterone receptor isoform A (PRA), a general transcription inhibitor of P target genes, and isoform B (PRB), a specific transcriptional stimulator of some reproductive tract genes. In this review, we focus on P action and PR expression in the liver and reproductive tissues of several reptilian species, especially Chelonia, since most of the data obtained are from this group. We also present novel data showing the expression of PR in nonreproductive tissues (such as kidney, spleen, gastrointestinal tract) in the painted turtle, Chrysemys picta.

Ovulation: new dimensions and new regulators of the inflammatory-like response

Ovulation is a complex process that is initiated by the lutenizing hormone surge and is controlled by the temporal and spatial expression of specific genes. This review focuses on recent endocrine, biochemical, and genetic information that has been derived largely from the identification of new genes that are expressed in the ovary, and from knowledge gained by the targeted deletion of genes that appear to impact the ovulation process. Two main areas are described in most detail. First, because mutant mouse models indicate that appropriate formation of the cumulus matrix is essential for successful ovulation, genes expressed in the cumulus cells and those that control cumulus expansion are discussed. Second, because mice null for the progesterone receptor fail to ovulate and are ideal models for dissecting the critical events downstream of progesterone receptor, genes expressed in mural granulosa cells that regulate the expression of novel proteases are described.

Pituitary adenylate cyclase-activating polypeptide modulates plasminogen activator expression in rat granulosa cell

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a bioactive peptide isolated from ovine hypothalamus. It has been demonstrated to be transiently expressed in preovulatory follicles and to positively affect several parameters correlated with the ovulatory process. The aim of the present study was to investigate whether PACAP influences the plasminogen/plasmin system in rat ovary. Plasminogen activators (PAs) are serine proteases, modulated by gonadotropins and several peptides in preovulatory follicles, that appear to be involved in ovulation. Granulosa cells obtained from immature eCG-treated rats were cultured for 24 h in the presence of increasing concentrations of PACAP and vasoactive intestinal peptide (VIP). A significant, dose-dependent increase in tissue-type PA (tPA) activity and decrease in urokinase-type (uPA) PA activity were observed in PACAP-treated cells. These effects were exerted at the mRNA level. The use of cycloheximide, a protein synthesis inhibitor, suggested that PACAP requires an intermediary protein to decrease uPA-mRNA, but not to induce tPA-mRNA. However, no significant modulation of PAs was observed in the presence of VIP. When granulosa cells were stimulated within the intact follicle (i.e., maintaining the three-dimensional structure and in the presence of the theca cell layers), both PACAP and VIP dose-dependently stimulated tPA. These data suggest that, in addition to the PACAP type I receptor present on granulosa cells, different subtypes of PACAP receptors are present in the different ovarian compartments.

Characterization of a putative membrane receptor for progesterone in rat granulosa cells

Progesterone (P(4)) inhibits granulosa cell apoptosis in a steroid-specific, dose-dependent manner, but these cells do not express the classic nuclear P(4) receptor. It has been proposed that P(4) mediates its action through a 60-kDa protein that functions as a membrane receptor. The present studies were designed to determine the P(4) binding characteristics of this protein. Western blot analysis using an antibody that recognizes the P(4) binding site of the nuclear P(4) receptor (C-262) confirmed that the 60-kDa protein was localized to the plasma membrane of both granulosa cells and spontaneously immortalized granulosa cells (SIGCs). To determine whether this protein binds P(4), proteins were immunoprecipitated with the C-262 antibody, electrophoresed, transferred to nitrocellulose, and probed with a horseradish peroxidase-labeled P(4) in the presence or absence of nonlabeled P(4). This study demonstrated that the 60-kDa protein specifically binds P(4). Scatchard plot analysis revealed that (3)H-P(4) binds to a single site (i.e., single protein), which is relatively abundant (200 pmol/mg) with a K(d) of 360 nM. (3)H-P(4) binding was not reduced by dexamethasone, mifepristone (RU 486), or onapristone (ZK98299). Further studies with SIGCs showed that P(4) inhibited apoptosis and mitogen-activated protein kinase kinase (MEK) activity, and maintained calcium homeostasis. These studies taken together support the concept that the 60-kDa P(4) binding protein functions as a low-affinity, high-capacity membrane receptor for P(4).

Differential Display and Suppressive Subtractive Hybridization Used to Identify Granulosa Cell Messenger RNA Associated with Bovine Oocyte Developmental Competence1

The main objective of this study was to identify mRNA expressed in the granulosa cells characterizing differentiated follicles bearing developmentally competent bovine oocytes. Analytical comparisons were made on mRNA pools of granulosa cells using differential display reverse transcription polymerase chain reaction (DDRT) analysis and suppressive subtractive hybridization (SSH). With DDRT, mRNA patterns of granulosa cells from small (< 4 mm) and large (> 8 mm) follicles cultured in the presence or absence of LH were compared to identify mRNA associated with follicular size or with the LH response. Nine clones were sequenced, and two were identified. One of the clones, DRAK 1, was associated with the presence of LH in the medium. Other comparisons directed toward the identification of mRNA associated with the presence of a competent oocyte were done on granulosa cells collected in vivo from superstimulated heifers. With the DDRT analysis, four clones associated with the oocyte developmental competence status were identified. With the SSH analysis, four clones specific to the presence of an incompetent oocyte were sequenced and none were identified, whereas 49 clones specific to the presence of a competent oocyte were sequenced and 18 were identified. Among these clones, early growth response 1, sprouty 2, cytochrome C oxidase, matrix metalloproteinase inducer, matrix metalloproteinase, epiregulin, prostaglandin receptor, and progesterone receptor were the most relevant to the ovarian physiology being examined.