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Departments of Pathology (S.A.P., M.T., J.A., X.L., M.M.M.), Molecular and Human Genetics (C.W.B.), Molecular and Cellular Biology (M.M.M.), and Program in Developmental Biology (C.J.J., M.M.M.), Baylor College of Medicine, Houston, Texas 77030; and Department of Molecular and Integrative Physiology (T.R.K.), The University of Kansas Medical Center, Kansas 66160
Address all correspondence and requests for reprints to: Martin M. Matzuk, M.D., Ph.D., The Stuart A. Wallace Chair and Professor, Department of Pathology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030. E-mail: mmatzuk{at}bcm.tmc.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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-subunit to produce inhibins [inhibin A (:ßA) and inhibin B (:ßB)] that negatively regulate FSH. The ßA- and ßB-subunits, encoded by the Inhba and Inhbb genes, respectively, are produced in multiple tissues during embryonic and postnatal development and have diverse physiological effects. Mice lacking activin ßA (homozygous Inhba null) die at birth secondary to craniofacial defects, whereas homozygous Inhbb null mice are viable but exhibit eyelid closure and nursing defects (4, 5, 6). Several studies indicate that activin signaling components, including the receptors ACVR1B (also known as ALK4) and ACVR2 (also known as ACTR2B), are critical for growth inhibition. For example, activins inhibit in vitro growth of both human breast cancer cells (7) and prostate cancer cells (8). Mutations in ACVR1B have been observed in human pituitary tumors (9) and pancreatic cancers (10). Likewise, ACVR2 mutations and loss of heterozygosity have been seen in pancreatic (11), colorectal (12), and prostate cancers (13). These studies suggest that the activin signaling pathway functions as a tumor suppressor pathway in some tissues to block cell growth and stimulate differentiation.
Inhba and Inhbb transcripts are prominently expressed by granulosa cells of large preantral and antral follicles (14). In vitro studies have identified multiple intraovarian roles for activins in granulosa cells including proliferation, potentiation of FSH action, and modulation of steroidogenesis (reviewed in Refs. 15 and 16). To study the in vivo roles of activins, we produced an ovarian Inhba conditional knockout (ßA cKO). We also generated the ßA cKO in the Inhbb null background mice to produce mice lacking all ovarian activins (double mutant mice; herein designated as ßB/ßA dKO). In contrast to extragonadal roles of these proteins as tumor suppressors, activins play redundant roles to block terminal differentiation of granulosa cells, leading to dosage-dependent fertility defects.
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). Exon 2 was floxed because it encodes the entire mature domain of the protein and a conditional exon 2 deletion would mimic the original null allele (Inhbatm1Zuk) (17). ßAflox/+ mice were intercrossed to produce ßAflox/flox homozygous mice, which were viable and fertile and obtained at the expected Mendelian frequency. To verify the presence of loxP sites and their ability to recombine in vivo, we crossed the ßAflox mice to EIIa-cre transgenic mice, which express cre recombinase in multiple tissues, including germ cells (18). Southern blot analysis using a 5' probe demonstrated the presence of the various Inhba alleles, including the recombined deleted (ßA
) (data not shown). Because ßAflox/–;EIIa-cre newborn mice demonstrate the neonatal lethality seen in the Inhba homozygous null mice (data not shown), recombination likely produced a null allele.
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). Recombination of the floxed allele in granulosa cells from female littermates varied from 60% to 99% (Fig. 1B). Variation in recombination and expression differences are likely the result of mosacism in recombination, as has been seen in other conditional knockout mice using Amhr2-cre mice (21, 22). Loss of the ßA transcript was confirmed by Northern blot analysis (Fig. 1C), and no compensatory up-regulation of the activin ßB-subunit was found in ßAflox/–;Amhr2cre/+ ovaries (Fig. 1D). Because the ß-subunit is also required for formation of inhibin, we measured serum inhibin levels in the ßAflox/–;Amhr2cre/+mice. The average serum inhibin A level in the ßA-deficient mice is significantly reduced from the control values, and six of nine females had undetectable levels. Loss of dimeric inhibin A was not due to reductions in inhibin -subunit mRNA expression because ovaries and granulosa cells of mutant mice demonstrated increased Inha mRNA levels over controls (Fig. 1E, inset, lane 4).
Redundant Roles of Activin ßA and ßB in Female Fertility
The fertility of control (ßAflox/–) mice was comparable with wild-type mice (data not shown). However, ßAflox/–;Amhr2cre/+ female mice demonstrated a statistically significant reduction (43%) in litters per month and pups per litter (33%) compared with controls (Table 1 and data not shown). Because subfertility could result from redundancy between the activin A and B isoforms (23), we generated ßA conditional knockouts in the activin ßB null (ßB–/–) background and additionally analyzed the following genotypes: ßB–/–;ßA+/–, ßB–/–; ßAflox/–, and ßB–/–; ßAflox/–;Amhr2cre/+ females. Neither ßA+/– nor ßB+/– heterozygous mice had fertility defects (5, 17). Double mutant females with only one remaining ßA-subunit allele (ßB–/–;ßA+/– or ßB–/–;ßAflox/–) had severe fertility defects (Table 1), indicating that activin dosage plays an important role in ovarian function. Of the 16 mice that were studied over 6 months, three of five ßB–/–;ßAflox/–, and three of 11 ßB–/–;ßA+/– female mice were infertile. In the mutant lines containing a single ß-subunit allele, the average number of litters per month was significantly reduced (89–91%), and the number of pups per litter was 87–90% lower than the controls (Table 1). Finally, female mice lacking all intraovarian activin ßA and ßB alleles (ßB–/–;ßAflox/–;Amhr2cre/+) were infertile (Table 1). Thus, although activin A appears to be functionally dominant [because activin A deficiency results in subfertility vs. normal fertility for activin ßB deficiency (5)], dosage of the activin ßA and ßB alleles is important for normal fertility.
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). Two of four female mice deficient for all activin alleles produced no oocytes.
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, A and B)]. However, at 8 months of age, ovaries from the ßAflox/–;Amhr2cre/+ mice contained a greater abundance of CLs (Fig. 2D) as compared with control ßAflox/– mice (Fig. 2C). Female mice with only one remaining activin ß allele (ßB–/–;ßA+/–) showed an earlier increase in the number of CLs (Fig. 2E) (i.e. the phenotype appears at 3 months of age instead of at 8 months of age for the single ßA conditional knockout). By 8 months of age, the ßB–/–;ßA+/– ovaries contained a readily identifiable abundance of CLs (Fig. 2F).
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). Abundant CLs were visible histologically at 6 wk (Fig. 3C) and 3 months of age (Fig. 3D). Also at 8–11 wk of age, there were statistically significant increases in the number of antral follicles (P < 0.05) (Fig. 4A) and in the number of CLs (P < 0.01) (Fig. 4B) only in ßB–/–; ßAflox/–;Amhr2cre/+ females, vs. all tested genotypes. No changes were found in the numbers of developing primordial, primary, or preantral follicles for any genotype at 6–11 wk of age (data not shown). At 8 months of age, ovaries of ßB–/–; ßAflox/–;Amhr2cre/+ mice had a 6-fold increase in mass [31.5 ± 2.9 mg (n = 8) vs. 5.2 ± 2.9 mg (n = 8) in the ßAflox/– cKO mice] (Fig. 3A). Also present were follicles with luteinizing granulosa cells (Fig. 3H), and multiple cysts that were either fluid-filled or hemorrhagic (Fig. 3, F and I). Cells lining cysts are immunopositive for the granulosa cell marker, inhibin (Fig. 3, J and K), and negative for epithelial markers (Fig. 3L and data not shown), and thus likely derive from ovarian follicles.
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). There were no significant differences in basal serum levels of LH (Fig. 5B), estradiol (Fig. 5D), or PRL (data not shown) in random cycling female mice for any genotype. However, a statistically significant increase (P < 0.01) was identified for FSH in mice lacking all activin subunits (Fig. 5A). In addition, there was a trend of increasing serum progesterone corresponding with the decreasing number of ß-subunit alleles, which reached statistical significance (P < 0.001) at 3 months of age for ßB–/–; ßAflox/–;Amhr2cre/+ females (Fig. 5C).
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), and expression of LH receptor was higher in those mice with increased numbers of CLs. To examine whether CLs in experimental mice could undergo functional regression, we examined expression of 20-hydroxysteroid dehydrogenase (20-HSD), which catalyzes the conversion of progesterone into 20-dihydroxyprogesterone, a biologically inactive form. Immunostaining for 20-HSD in the experimental and control mice identified functional regressing corpora even in mice with one or no remaining ß-alleles wild type (Fig. 6, F and I). These results suggest that part of the phenotype of the experimental mice may be that the rate of CL formation in activin-deficient mice might be greater than the rate of regression.
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), but this trend was not statistically significant when comparisons were made between all three genotypes (P = 0.08). These data suggest that in vivo, activin likely augments FSH-induced expression of Fshr, similar to its effects in vitro (28, 29), but is not necessary for basal FSH receptor expression. Unexpectedly, reduction of activin alleles had no effect on Ccnd2 expression (Fig. 7B). We also examined expression of Lhcgr and found that its expression was significantly up-regulated (P < 0.05) in granulosa cells of mutant mice (Fig. 7C). These gene expression results are similar to the previously reported gene expression pattern of Smad4 granulosa cell-specific knockout mice, which also show an increase in Lhcgr, but little effect on Ccnd2 (21). Misexpression of Lhcgr in activin-deficient granulosa cells is consistent with an inappropriate differentiation of granulosa cells (30).
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and 2, which are published as supplemental data on The Endocrine Society’s Journals Online web site at http://mend.endojournals.org. Because granulosa cells were collected from pregnant mare serum gonadotropin (PMSG)-stimulated females, differentially expressed genes represent genes expression changes induced in growing antral follicles by gonadotropin stimulation with or without endogenous activin. One hundred and eleven nonredundant genes showed statistically significant (P < 0.05) differences in the final analysis, whereas 14 genes were expected to change by chance alone. Eighty-one genes of these genes were down-regulated (Supplemental Table 1), whereas 30 genes were up-regulated (Supplemental Table 2). Pathway analysis demonstrated that three signaling pathways were significantly disrupted: the TGFß pathway (P = 0.005), as would be predicted by loss of activin alleles, the JAK-STAT pathway (P = 0.023), and the cytokine-cytokine receptor interaction pathway (P = 0.016). Genes differentially expressed in these pathways are highlighted in Supplemental Tables 1 and 2.
Expression of several differentially expressed genes with known ovarian roles were verified by qPCR on granulosa cells from individual mice collected independently from the samples used in the microarray analysis (Fig. 7, D–H, and Supplemental Table 1). In general, the fold changes found for qPCR verification in these experiments were larger than fold changes determined from microarray data. Likely, this results from the use in the microarray analysis of pooled RNA from samples that have variable recombination rates (Fig. 1B), leading to more conservative estimates of gene expression changes. We found that connective tissue growth factor (Ctgf) was significantly down-regulated in the microarray (4.7-fold) and by qPCR (1 ß-allele, 16-fold; 0 ß-alleles, 26-fold) in mutant mice (Fig. 7D). Importantly, Ctgf has been shown to be regulated by several members of the TGFß family, including activin (31). Other significantly down-regulated genes in mutant mice include GH receptor (Ghr) (1 ß-allele and 0 ß-alleles, 14-fold) (Fig. 7E), myelocytomatosis oncogene (Myc) (1 ß-allele, 13-fold; 0 ß-alleles, 15-fold) (Fig. 7F), and the TATA-binding factor-associated factor (Taf4b) (1 ß-allele, 3.9-fold; 0 ß-alleles, 4.4-fold) (Fig. 7G). It is unknown whether these genes are activin target genes. To determine whether Ghr, Myc, or Taf4b are regulated by activin, we treated wild-type granulosa cells with recombinant human activin A and measured changes in mRNA expression by qPCR (Fig. 8). Levels of Ghr and Myc were unchanged after 5 h, indicating that short-term activin treatment does not alter their transcription (Fig. 8, A and B). However, a statistically significant (P < 0.05), increase was seen for Taf4b (1.8-fold) (Fig. 8B) after 5 h.
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) and qPCR (1 ß-allele, 3-fold; 0 ß-alleles, 5-fold) (Fig. 7H). Kit ligand is a positive regulator of follicle growth (32) and has important growth stimulatory effects on granulosa cells (33). The expression of kit ligand has been shown to be increased by bone morphogenetic protein (BMP) 15 (33) and inhibited by GDF9 (34). To determine whether activin has any regulatory role on Kitl expression, Kitl transcript levels were measured in activin-treated wild-type granulosa cells by qPCR. Recombinant activin A significantly suppressed levels of Kitl in wild-type granulosa cells by approximately 7-fold (P < 0.05) (Fig. 8D). These data are consistent with the increase in Kitl expression detected in activin-deficient granulosa cells, and thus Kitl is a candidate gene for negative regulation by activin in granulosa cells. |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
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8-fold difference) (35).
A subfertility defect was uncovered when we generated a conditional knockout for the activin ßA-subunit. In addition, activin ßA-deficient females developed follicles with multiple oocytes (polyovular follicles; also called MOFs). The natural occurrence of polyovular follicles in mice have been reported since 1920 (36), and some mouse strains are more susceptible to polyovular follicle formation than others (e.g. C58/J vs. C57L/J) (37). Polyovular follicles are found in ovaries of some transgenic mice, including inhibin- overexpressing mice (38), germ cell nuclear factor conditional knockout mice (39), Bmp15 knockout mice (40) and FSH receptor haploinsufficient mice (41). Given the frequency of transgenic lines displaying this phenotype, it is likely that polyovular follicle formation occurs through multiple mechanisms; however, estrogen is one known mediator of polyovular follicle formation (42), likely caused by improper germ cell cyst breakdown (43, 44, 45, 46). An additional study has shown that neonatal estrogen exposure results in an increased incidence of polyovular follicles in conjunction with suppression of the activin ß-subunit (47). These data are consistent with polyovular formation in the ßA conditional knockout, because Amhr2-driven expression of cre recombinase is detectable in somatic cells of the developing embryonic gonad (19, 20), and could result in embryonic loss of the ßA-subunit in these cells. Our data further suggest a direct role of activin in normal follicle formation.
Mice lacking both activin ßA and ßB are sterile, with a complex ovarian phenotype, perhaps in part because activin has stage-specific functions during follicle development that also vary with age. In general, in vitro cultures demonstrate that activin induces small follicle growth and promotes granulosa cell proliferation alone and in combination with FSH (48, 49, 50). However, activins promote preantral follicle growth in isolated follicles derived from immature mice but prevent FSH-stimulated growth in isolated cultures of preantral follicles from adult mice (51). If growth induction is activin’s primary role at the preantral follicle stage, it would be predicted that loss of activin in granulosa cells could result in arrested granulosa cells growth, early differentiation of granulosa cells, or retarded follicle development. Indeed, follicles demonstrating luteinization of granulosa cells were apparent in the ovaries of activin-deficient mice. However, our data did not demonstrate any changes in numbers of primordial, primary, or secondary follicles in adult female mice that lacked all ß-subunits. Because activin is secreted and its actions are paracrine in nature, variations in timing of recombination between loxP sites in granulosa cells from different follicles may variably change local activin concentrations, which may be insufficient to cause complete intraovarian penetrance of the phenotype. Conditional mutations in activin receptors would thus contribute valuable information regarding activin function in granulosa cells.
Deletion of the activin ß-subunit genes in granulosa cells affects both activin and inhibin production. The gonad is the predominant source of circulating inhibin in rodents (52), and our data demonstrate that deletion of the ß-subunit genes in granulosa cells decreases serum inhibin to undetectable levels. Although previous in vitro studies show that recombinant activin increases inhibin -subunit expression in isolated granulosa cells (53), this does not appear to be a necessary physiological role for activin in vivo because there is an increase in Inha gene expression in activin-deficient ovaries. Because IGF-I is required for activin-induced Inha expression (54), compensation by IGF-I on Inha expression through an alternative pathway may occur in activin-deficient females.
Loss of dimeric serum inhibin likely favors FSH release due to loss of negative feedback by inhibin. The increased FSH may contribute to a number of defects, including a larger growing antral follicle pool present in the activin-deficient females, although not likely all. Female mice overexpressing FSH demonstrate hemorrhagic and cystic ovaries (55) but have a cystic phenotype much more severe than the phenotype that presents in activin-deficient females. Interestingly, even though the antral follicle pool is expanded, superovulation of immature female mice does not result in an increased ovulation rate. In fact, the ovulation rate in PMSG/human chorionic gonadotropin (hCG) stimulated activin-deficient females decreases approximately 60%. Gene expression analysis of granulosa cells from the preovulatory period indicates abnormal cell differentiation. Granulosa cells collected from PMSG-stimulated activin-deficient immature mice express more Kitl as measured by microarray and qPCR experiments, and kit ligand is a known mitogen for granulosa cells (33). Interestingly, the kit ligand-2 isoform is normally down-regulated during early antral follicle formation (56), and ovarian injection of antibody to the kit ligand receptor disrupts antral follicle granulosa cell proliferation (57). By in vitro experiments, we were able to show that activin is capable of suppressing Kitl expression. During the antral follicle period, activin may be partly responsible for the down-regulation of kit ligand, resulting in the transition from an FSH-driven growth phase, to a differentiation phase required for the preovulatory period. A role for activin in regulating the terminal differentiation of ovarian follicles has been proposed (58, 59).
We found that several other genes are down-regulated in preovulatory activin-deficient granulosa cells, including Ctgf, Ghr, Myc, and Taf4b. To date, only a few direct downstream targets of activin are known in granulosa cells. Ctgf is regulated by activin and other TGFß family members (31), but the consequence of loss-of-function of Ctgf in granulosa cells is unknown, and the contribution to the activin phenotype is unclear. In activin-deficient granulosa cells from immature mice, Myc and Taf4b are expressed less than in wild-type granulosa cells, and activin A up-regulates Taf4b in granulosa cells in culture. These experiments thus identify Taf4b as potential activin-response gene, although the activin pathway may not be the primary regulatory pathway because the expression changes are small, although significant. Taf4b homozygous null female mice are infertile, with defects in the inhibin/activin system and loss of expression of Inha, Inhba, Inhbb, and Ccnd2 (60). Thus, activin may be part of a positive regulatory loop involving TAF4B. However, Inha is expressed in activin-deficient ovaries as is Ccnd2. Differences in expression levels of Taf4b may explain the overall differences when comparing Taf4b knockout ovaries to activin-deficient ovaries (i.e. reduced levels of Taf4b in the activin-deficient mouse, compared with compete absence of Taf4b expression in Taf4b knockouts).
The most striking phenotype of ßB/ßA-deficient females is the progressive accumulation of CLs. Our data indicate a defect during structural regression because 20-ßHSD immunostaining is detectable in CLs of activin-deficient mice. Whereas no definitive data exist for activin in luteolysis, a number of studies suggest that activin plays an active role in regression of CLs. First, activin receptors localize to CLs in many species (61, 62, 63). And second, the activin antagonist follistatin is highly expressed in newly formed rodent CLs but undetectable during luteolysis (64), resulting in a permissive environment for activin signaling. Whereas the mechanism(s) by which activin could control structural regression of CLs is unknown, a recent study using a novel in vitro coculture system as a model for human luteolysis indicates that activin A from steroidogenic cells may directly induce matrix metalloproteinase 2 (Mmp2) expression through paracrine signaling to fibroblasts (62). MMPs are critical for tissue remodeling, and increased expression and activity of MMP2 is associated with luteolysis in women (65), and MMP2 levels also increase during the late luteal phase of monkeys (66). Whereas the hypothesis that activin-induced MMP2 expression is responsible for structural luteolysis remains to be tested in intact CLs, the activin-deficient dKO mouse model should provide a unique system to test the roles of various hormones and growth factors to examine CL physiology, and in particular luteal regression.
The activin-deficient mouse model has higher levels of serum progesterone at 3 months of age. Activin signaling requires the common SMAD transcription factor, SMAD4 and in granulosa cell-specific knockouts of Smad4, progesterone levels are also increased (21). However, this is due to premature luteinization of granulosa cells in preovulatory follicles. Unlike Smad4 cKO ovaries, activin-deficient preovulatory granulosa cells do not luteinize when immature mice are given supraphysiological injections of PMSG. And in contrast to the activin-deficient mouse model, luteinized follicles/structures do not accumulate in the Smad4 cKO ovary, even though progesterone levels remain increased. Therefore, both models have higher levels of progesterone, although it appears to be through different mechanisms. Studies of human and macaque luteal cells find that activin inhibits progesterone synthesis (67, 68). Therefore, it is possible that the increase in progesterone in the activin-deficient mice results from a lack of activin activity in CLs, which cannot be compensated for by another pathway. BMPs and GDF9 are known to inhibit FSH-induced progesterone production and have been hypothesized to be luteinization inhibitors in granulosa cells of antral follicles (69, 70). Our data from the activin-deficient mouse model support this hypothesis and suggest that the BMP and GDF9 pathways, and not the activin pathway, may be the primary luteinization inhibitors in preovulatory follicles because the BMP and GDF9 pathways are disrupted in Smad4 cKO, but not in the activin-deficient conditional knockout. An alternative hypothesis is that during the preovulatory period, activin, GDF9 and/or BMP pathways may be redundant with respect to luteinization inhibition, with the BMP and/or GDF9 pathways compensating for loss of activin in the activin-deficient mouse model and preventing premature luteinization.
The activin-deficient dKO ovary mouse model also highlights the widespread, cell-specific effects of activins in various cell types. In other tissues, activin signaling components act as tumor suppressors; for example, loss of activin receptors and SMAD signaling proteins, such as during the development of some pancreatic cancers, results in tumorigenesis. No tumor development was seen in the activin-deficient mouse models. Thus, in different cellular contexts, which may include expression of different transcription factors that interact with the downstream SMAD signaling proteins, the activins and their signaling components can either function as tumor suppressors to inhibit growth/stimulate differentiation, or as oncogenes to stimulate growth/inhibit differentiation. Thus, both loss-of-function and gain-of-function mutations in activin signaling pathway components may be observed to positively or negatively regulate cancer initiation and/or progression.
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MATERIALS AND METHODS |
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Morphological, Histological, and Immunohistochemical Analysis
All experimental animals were maintained in accordance with the National Institutes of Health (NIH) Guide for the Care and Use of Laboratory animals. Embedding and staining procedures were performed by standard protocols at the Baylor College of Medicine Pathology Core Services laboratory. 20-HSD staining (1:300 dilution) was performed as described (21). Rabbit polyclonal anti-inhibin antibody was used at a 1:500 dilution and was a gift from W. Vale (The Salk Institute, La Jolla, CA). TROMA-III (anti-cytokeratin 19) rat monoclonal antibody was used at 1:10 dilution and was obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the NICHD and maintained by the University of Iowa, Department of Biological Sciences. Immunohistochemistry was performed on at least four samples in duplicate. For follicle histomorphometric analysis, a minimum of three ovaries was counted for each genotype. Follicle classification was based on Pederson and Peters (73). For assessment of primordial, primary, and preantral follicles, follicle counts were carried out as described (74, 75). Briefly, ovaries of each genotype were serially sectioned at 5 µm, and every tenth section was kept. Follicles were counted from five of the largest sections, and normalized to the total area of the section. Counts and area were collected using the AxioVision 4.0 software (Carl Zeiss, Jena, Germany). For assessment of antral follicles and CLs, the total number of antral follicles and CLs in each ovary were counted. To avoid double counting antral follicles, only follicles with a visible oocyte nucleus were counted. For CL counts, images were taken of each section (every 50 µm), ordered sequentially, and each CL followed through the sections, comparing CLs with those on previous sections to avoid double counting.
Serum Analysis
Mice were anesthetized by isoflurane inhalation (Abbott Laboratories, North Chicago, IL), blood recovered by closed cardiac puncture, and serum separated by centrifugation in Microtainer tubes (Becton Dickinson, Franklin Lakes, NJ) and stored at –20 C. FSH, LH, estradiol, progesterone, and inhibin A measurements were made by the University of Virginia Ligand Core Facility (Specialized Cooperative Centers Program in Reproduction Research NICHD/NIH U54 HD28934). Assay information is available at (http://www.healthsystem.virginia.edu/internet/crr/ligand.cfm). The mouse FSH RIA has a sensitivity of 2.0 ng/ml, and an average intraassay coefficient of variation (CV) of 10.1 and interassay CV of 13.3%. The mouse LH Sandwich IRMA has a sensitivity of 0.07 ng/ml, and an average intraassay CV of 4.7% and interassay CV of 13.5%. The progesterone RIA has a sensitivity of 0.10 ng/ml and an average intraassay CV of 4.5% and interassay CV of 6.9%. The estradiol RIA has a sensitivity of 10 pg/ml, and an intraassay CV of 5.33%, and an interassay CV of 12.1%. The inhibin A ELISA has a sensitivity of assay 1 pg/ml and interassay variation of 6–7%. The percentage of cross reactivity of the inhibin A assay with other ligands was the following: inhibin B 0.012, activin A 0.002, activin B 0.001, and pro- C 0.01. Values that fell below the assay threshold were given the threshold value. Serum samples were diluted in PBS to fall within the detectable range, when necessary. National Hormone and Peptide Program (NHPP) made PRL measurements by using a highly sensitive double-antibody method with reagents provided by Dr. A. F. Parlow (NHPP, Torrance, CA). Mouse PRL (AFP10777D) was used for iodination, rabbit antimouse PRL (AFP131078) was used as antiserum, and mouse PRL (AFP6476C) was used as reference preparation.
Superovulation and Collection of Oocytes
Nineteen to 21-d-old and 6-month-old experimental and control female mice were injected with PMSG (ip, 5 IU/mouse), and given hCG (ip, 5 IU/mouse) 48 h later. Mice were bred to C57/129 hybrid known fertile males. The following morning oocytes were recovered from the ampulla of the oviduct in M2 medium and counted.
Granulosa Cell Preparation
For granulosa cell isolation, female mice 19–21 d of age were injected ip with 5 IU pregnant mare serum gonadotropins (Calbiochem, La Jolla, CA) for 44–46 h to stimulate follicle growth and granulosa cells collected by puncturing antral follicles with fine-gauge needles (72). RNA was extracted from mutant and control granulosa cells for microarray experiments and qPCR verification immediately upon harvest. For treatment of wild-type cells, 19–21 d CD1 female were used for granulosa cell collections and cells plated at a density of 5.5 x 105 cells/ml as described (76). Cells were incubated overnight in DMEM-F12 medium supplemented with 2% fetal calf serum, 1x insulin/transferring/selenite (Invitrogen Life Technologies, Carlsbad, CA), 10 U/ml penicillin and streptomycin and 250 ng/ml recombinant follistatin-288 to block endogenous activin signaling. After 18 h, cells were washed twice in PBS and incubated with medium only with 50 ng/ml recombinant human activin A (R&D Biosystems, Minneapolis, MN) in DMEM-F12 medium supplemented with 0.5% heat inactivated fetal bovine serum, 1x ITS, and 10 U/ml penicillin and streptomycin. Cells were treated for 5 h, then harvested for RNA. A minimum of four independent replicates was performed.
RNA Isolation and Northern Blot Analysis
For Northern blot analysis, total ovarian RNA was isolated from individual mice using RNA STAT-60 reagent (Leedo Medical Laboratories, Houston, TX). Twelve micrograms of each RNA sample were used for electrophoresis and transferred to nylon membranes as described previously (14) and probed with radioactive cDNA probe of 426 bp against activin ßA (1049–1474 of the clone X69619) generated using [32P]dATP and the Strip-EZ kit (Ambion, Inc., Austin, TX). Phosphorimaging plates were scanned and analyzed using Image Quant software (Molecular Dynamics, Inc., Sunnyvale, CA). A background level for each blot was determined and subtracted. Blots were stripped and reprobed for glyceraldehyde 3-phosphate dehydrogenase (Gapd) as a loading control.
Microarray Analysis and qPCR
RNA was isolated using the QIAGEN (Valencia, CA) RNeasy kit. RNA integrity, concentration, and quality were checked by the Baylor College of Medicine Microarray Core Facility. Labeling, hybridization, washing, scanning, and initial microarray analysis were performed by the Baylor College of Medicine Microarray Core Facility using standard Affymetrix protocols and the Affymetrix Mouse Genome 430 2.0 Array. Independent chips were analyzed from three independent wild-type and two independent activin-deficient (ßB–/–; ßAflox/–;Amhr2cre/+) granulosa cell samples. Each sample represented granulosa cells collected from a minimum of 2 immature mice stimulated for 44–46 h PMSG. Initial analysis was performed using the Microarray Analysis Suite 5.0 (Affymetrix) software to determine signal intensity and detection (absent, present, and marginal), and then data files were imported into GeneSpring GX for expression analysis. Data were filtered based on 1) MAS 5.0 call of "present" in a minimum of two samples; 2) a raw signal value of greater than 300 in a minimum of one of two conditions; 3) normalized expression change of 2-fold or greater. This resulted in a list of 280 genes, which were then analyzed for statistical significance at = 0.05 by one-way ANOVA; this should have resulted in 14 genes changes by chance alone. The final differentially expressed gene list contained 111 genes: 81 up- and 30 down-regulated. Genes lists of up-regulated and down-regulated were imported into DAVID Bioinformatic software (http://david.abcc.ncifcrf.gov/home.jsp) for pathway analysis (77). The complete microarray data set will be available at NCBI Gene Expression Omnibus (GEO) database (http://www.ncbi.nlm.nih.gov/geo) with the accession no. GSE7150.
qPCR
qPCR was performed as described (21). cDNA was prepared from 200 ng of total RNA using SuperScript III First Strand Synthesis Kit (Invitrogen) in a 50-µl reaction. Real-time qPCR was performed as previously described (21) using Applied Biosystems (ABI; Foster City, CA) Prism 7500 Sequence Detection System, Taqman Master Mix and Gene Expression Assays. Taqman (ABI) Assays used for qPCR: Ccnd2, Mm00438071; Ctgf, Mm00439093; Fshr, Mm00442819; Gapd, 4352339E; Ghr, Mm00439093; Inhbb, Mm03023992; Lhcgr, Mm00442931; Myc, Mm00487803. Primers to Kitl, Taf4b and Gapd were designed using the Primer Expression 2.0 Software (ABI) and amplified using Sybr Green Master Mix (ABI) with Gapd as a control. Primer sequences available upon request. The Kitl primer set recognizes both splice variants, Kl-1 and Kl-2. Dissociation curves were generated for Sybr Green qPCRs to verify amplification of a single PCR product. All qPCR data were analyzed by the cycle threshold method using the ABI 7500 System Software (version 1.2.3) as described by ABI and normalized to the endogenous reference (Gapd). One control sample was randomly as the calibrator sample. The mean and SEM were calculated, and the relative amount of target gene expression for each sample compared with the control was plotted in Excel (Microsoft, Redmond, WA).
Statistical Analysis
Statistical analysis was carried out using the JMP version 5.1 (SAS Institute Inc., Cary, NC) statistical package or in Excel (Microsoft). Statistical differences were tested using one-way ANOVA for multiple comparisons, followed by Tukey-Kramer honestly significant difference (HSD) or Dunnett’s post hoc tests as indicated in the text. Two-tailed Student’s t test was used for single comparisons at = 0.05. Statistics were performed on no less than three independent experiments.
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ACKNOWLEDGMENTS |
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-dihydroxyprogesterone antibody. We thank Dr. Alfred Parlow at National Hormone and Peptide Program (Torrance, CA) for PRL measurements. |
FOOTNOTES |
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Data Deposition: Affymetrix microarray data files (five files) have been deposited to the NIH Gene Expression Omnibus under the series accession no. GSE7150
Disclosure Statement: The authors have nothing to disclose.
First Published Online July 3, 2007
1 S.A.P. and C.J.J. contributed equally to this work. 
Abbreviations: BMP, Bone morphogenetic protein; cKO, conditional knockout; CL(s), corpus luteum/corpora lutea; Ctgf, connective tissue growth factor; CV, coefficient of variation; dKO, double mutant mice; Gapd, glyceraldehyde 3-phosphate dehydrogenase; Ghr, GH receptor; hCG, human chorionic gonadotropin; 20-HSD, 20-hydroxysteroid dehydrogenase; HSD, honestly significant difference; Lhcgr, LH receptor; Mmp2, matrix metalloproteinase 2; PMSG, pregnant mare serum gonadotropin; PRL, prolactin; qPCR, quantitative PCR.
Received for publication March 19, 2007. Accepted for publication June 28, 2007.
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