Bipolar Clark-Type Oxygen Electrode Arrays for Imaging and Multiplexed Measurements of the Respiratory Activity of Cells

Various miniature Clark-type oxygen electrodes (COEs), which are typically used to measure dissolved oxygen (DO) concentration in cellular respiration, have been developed since the 1980s. Arrays with individually addressable electrodes that constitute the sensor were used for various applications. However, the large number of leads and contact pads required for connecting the electrodes and the external instrument complicate the electrode layout and make the operation of integrated COE arrays challenging. Here, we fabricated closed bipolar electrochemical systems comprising 6 × 8 and 4 × 4 arrays of COEs for imaging and multiplexed detection. The cathodic compartment was sealed with a hydrophobic oxygen-permeable membrane to separate the internal electrolyte solution from the sample solutions. Using the bipolar Clark-type oxygen electrode (BCOE) arrays and electrochemiluminescence (ECL), we measured the DO concentration at each cathode. The results revealed that the ECL intensity changed linearly with the DO concentration. In addition, we used ECL imaging to investigate the respiratory activity of Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) in suspensions with different cell densities. The ECL images showed that the ECL intensity changed noticeably with the bacterial density. The bacterial respiratory activity was then qualitatively analyzed based on the ECL images acquired successively over a time duration. Further, we measured the antibiotic efficacy of piperacillin, oxacillin, gentamicin, and cefmetazole against E. coli and P. aeruginosa using the BCOE. We found that the ECL intensity increased with the antibiotic concentration, thus indicating the suppression of the bacterial respiratory activity.

Bipolar Electrode Arrays for Chemical Imaging and Multiplexed Sensing

Bipolar electrodes (BPEs) with arrays of cathodic and anodic poles were developed for use in closed bipolar systems. To increase the number of BPEs in the array, the anodic and cathodic poles were connected with each other using thin leads. A further increase in the number of BPEs was achieved by forming the cathodic and anodic poles of the BPEs and the leads in different layers. A device with 9 × 10 arrays of cathodes and anodes was thus realized. When using this device to sense hydrogen peroxide (H₂O₂), the sensitivity and linear range of calibration plots could be adjusted by changing the driving voltage and the area ratio between the cathodic and anodic poles. The devices were used to image H₂O₂ and obtain time-lapse images for the diffusion and dilution of H₂O₂. Furthermore, DNA detection was demonstrated using an electroactive intercalator. The sensitivity could be improved by making the anodic poles smaller with respect to the cathodic pole and concentrating the electrochemiluminescence (ECL) in a small area. The ECL intensity changed according to the target DNA concentration in the solution.

Wired Microfabricated Electrochemical Systems

Metal wires have been used as an alternative to liquid junctions for the connection of solutions in microfabricated electrochemical devices. They exhibit similar performance to liquid junctions, provided that the interfacial potentials at both ends of the wires were appropriately canceled. Cyclic voltammograms of devices with liquid junctions and metal wires were very similar when no current or a low current flowed through the metal wire between the working and reference electrodes. Iridium wires with iridium oxide at both ends facilitated canceling of the interfacial potentials at either end of the junction particularly well, and were used effectively for voltammetry, amperometry, and potentiometry by adjusting the pH of the solutions in the working and reference electrode compartments to be equal. This approach was used to effectively integrate a reliable common reference electrode between multiple working electrodes and to conduct automated electrochemical control of solution transport in microfluidic systems.

Microdevice with an Integrated Clark-Type Oxygen Electrode for the Measurement of the Respiratory Activity of Cells

A microdevice for the measurement of the respiratory activity of cells was fabricated using a microfabricated Clark-type oxygen electrode. The oxygen electrode was completed in a dry state and was activated by introducing water necessary for the reduction of oxygen in the form of water vapor through an oxygen-permeable membrane, which significantly facilitated handling of the device even by nonspecialists. The use of a thin paper layer stabilized the current response and enabled stable continuous operation of the oxygen electrode without current disturbance caused by the evaporation of water. The microdevice was tested in some model experiments including the measurement of the respiratory activity of Escherichia coli (E. coli), evaluation of the efficacy of antibiotics, and measurement of the antibacterial activity of neutrophils, all of which demonstrated that the consumption of dissolved oxygen by cells can be monitored clearly by following an easy procedure for the preparation of the measurements.

Growth differentiation factor-9 has divergent effects on proliferation and steroidogenesis of bovine granulosa cells

In addition to gonadotropins, steroidogenesis and proliferation of granulosa cells during follicular development are controlled by a number of intraovarian factors including growth differentiation factor-9 (GDF-9), bone morphogenetic protein-4 (BMP-4), and IGF-I. The objective of this study was to determine the effect of GDF-9 and BMP-4 and their interaction with IGF-I and FSH on ovarian granulosa cell function in cattle. Granulosa cells from small (1-5 mm) and large (8-22 mm) follicles were collected from bovine ovaries and cultured for 48 h in medium containing 10% fetal calf serum and then treated with various hormones in serum-free medium for an additional 48 h. We evaluated the effects of GDF-9 (150-600 ng/ml) and BMP-4 (30 ng/ml) during a 2-day exposure on hormone-induced steroidogenesis and cell proliferation. In FSH plus IGF-I-treated granulosa cells obtained from small follicles, 300 ng/ml GDF-9 reduced (P < 0.05) progesterone production by 15% and 600 ng/ml GDF-9 completely blocked (P < 0.01) the IGF-I-induced increase in progesterone production. In comparison, 300 and 600 ng/ml GDF-9 decreased (P < 0.05) estradiol production by 27% and 71% respectively, whereas 150 ng/ml GDF-9 was without effect (P > 0.10). Treatment with 600 ng/ml GDF-9 increased (P < 0.05) numbers (by 28%) of granulosa cells from small follicles. In the same cells treated with FSH but not IGF-I, co-treatment with 600 ng/ml GDF-9 decreased (P < 0.05) progesterone production (by 28%), increased (P < 0.05) cell numbers (by 60%), and had no effect (P > 0.10) on estradiol production. In FSH plus IGF-I-treated granulosa cells obtained from large follicles, GDF-9 caused a dose-dependent decrease (P<0.05) in IGF-I-induced progesterone (by 13-48%) and estradiol (by 20-51%) production. In contrast, GDF-9 increased basal and IGF-I-induced granulosa cell numbers by over 2-fold. Furthermore, treatment with BMP-4 also inhibited (P < 0.05) steroidogenesis by 27-42% but had no effect on cell numbers. To elucidate downstream signaling pathways, granulosa cells from small follicles were transfected with similar to mothers against decapentaplegics (Smad) binding element (CAGA)- or BMP response element (BRE)-promoter reporter constructs. Treatment with GDF-9 (but not BMP-4) activated the Smad3-induced CAGA promoter activity, whereas BMP-4 (but not GDF-9) activated the Smad1/5/8-induced BRE promoter activity. We have concluded that bovine granulosa cells are targets of both GDF-9 and BMP-4, and that oocyte-derived GDF-9 may simultaneously promote granulosa cell proliferation and prevent premature differentiation of the granulosa cells during growth of follicles, whereas theca-derived BMP-4 may also prevent premature follicular differentiation.

Impairment of spermatogenesis in transgenic mice with selective overexpression of Bcl-2 in the somatic cells of the testis

To explore the functional role of Bcl-2 in germ cell development, transgenic mice carrying 6 kilobases of the inhibin-alpha promoter were generated to express human bcl-2 gene product in the gonads. Although female transgenic mice demonstrated decreased follicle apoptosis, enhanced folliculogenesis, and increased germ cell tumorigenesis, the adult males exhibited variable impairment of spermatogenesis. The degree of damage ranged from tubules with intraepithelial vacuoles of varying sizes to near atrophied tubules consisting of Sertoli cells and a few spermatogonia. Although there was no significant change in body weight, an approximately 34% decrease in testicular weights was noted in transgenic animals compared with wild-type mice. Gamete maturation, assessed by determining the percentage of tubules with advanced (steps 13-16) spermatids, was decreased to 44.4% of the values measured in the wild-type animals. The incidence of germ cell apoptosis increased 3.8-fold in the transgenic animals and was associated with a marked loss of germ cells. Electron microscopy of the testes further revealed large vacuoles in the Sertoli cell cytoplasm and dilations of the intracellular spaces between adjacent Sertoli cells, spermatid malformations, and increased germ cell apoptosis in the transgenic animals. There was no evidence of Sertoli cell death either by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay or electron microscopy. Leydig cell ultrastructure, cell size and numbers, and plasma levels of testosterone were not different between normal and the transgenic animals. Collectively, these results support the critical role of Bcl-2 in male germ cell development and are consistent with the gender-specific role of the Bcl-2 family members in reproduction.

Stage-dependent role of growth differentiation factor-9 in ovarian follicle development

GDF-9 was shown to be essential for follicle progression and is the only factor secreted by the oocyte shown to increase the number of primordial and primary follicles in vivo. Furthermore, GDF-9 is a major growth factor involved in the oocyte control of granulosa cell differentiation. A concentration gradient of the paracrine factor GDF-9 established by the oocyte could provide the basis to explain the stratification of granulosa cells in antral and preovulatory follicles. The stimulatory effects of GDF-9 on early follicle development provide a basis for the use of GDF-9 in the treatment of infertility.

Underphosphorylated BAD interacts with diverse antiapoptotic Bcl-2 family proteins to regulate apoptosis

Survival factors activate kinases which, in turn, phosphorylate the proapoptotic Bcl-xl/Bcl-2-associated death promoter homolog (BAD) protein at key serine residues. Phosphorylated BAD interacts with 14-3-3 proteins, and overexpression of 14-3-3 attenuates BAD-mediated apoptosis. Although BAD is known to interact with Bcl-2, Bcl-w, and Bcl-xL, the exact relationship between BAD and anti- or proapoptotic Bcl-2 proteins has not been analyzed systematically. Using the yeast two-hybrid protein interaction assay, we found that BAD interacted negligibly with proapoptotic Bcl-2 proteins. Even though wild type BAD only interacted with selected numbers of antiapoptotic proteins, underphosphorylated mutant BAD interacted with all antiapoptotic Bcl-2 proteins tested (Bcl-2, Bcl-w, Bcl-xL, Bfl-1/A1, Mcl-1, Ced-9, and BHRF-1). Using nonphosphorylated recombinant BAD expressed in bacteria, direct interactions between BAD and diverse antiapoptotic Bcl-2 members were also observed. Furthermore, apoptosis induced by BAD was blocked by coexpression with Bcl-2, Bcl-w, and Bfl-1. Comparison of BAD orthologs from zebrafish to human indicated the conservation of a 14-3-3 binding site and the BH3 domain during evolution. Thus, highly conserved BAD interacts with diverse antiapoptotic Bcl-2 members to regulate apoptosis.

DNA array analysis of changes in preovulatory gene expression in the rat ovary

During the periovulatory period, the mammalian ovary is the site of dramatic functional and structural changes, leading to oocyte maturation, follicle rupture, and corpus luteum formation. To a large extent, these processes result from changes in the transcriptome of various ovarian cell types. To develop a broader view of periovulatory changes in gene expression in the ovary and to identify further genes involved in periovulatory events, we used the recently developed DNA array technology. Immature female eCG-primed rats were killed either immediately before or 6 h after ovulation induction with hCG. Total ovarian RNA was isolated and used to prepare radiolabeled cDNA probes, which were hybridized to DNA arrays representing approximately 600 rat genes. Quantitative analysis identified a multitude of regulated gene messages, including several genes involved in extracellular matrix degradation and lipid/steroid metabolism previously reported to be induced by hCG. This screening also identified a group of candidate genes whose ovarian expression and gonadotropin regulation was hitherto unknown. The induction of three of these genes, encoding cutaneous fatty acid-binding protein, the interleukin-4 receptor alpha chain, and prepronociceptin, was confirmed and further characterized by Northern blot analysis. In addition, in situ hybridization analysis showed that hCG administration resulted in exclusive or predominant expression of all three genes in theca cells. These results demonstrate that DNA arrays can be used to identify genes regulated during the periovulatory period, thus contributing to a more detailed understanding of the molecular mechanisms of ovulation.

Expression of messenger ribonucleic acid for the antiapoptosis gene P11 in the rat ovary: gonadotropin stimulation in granulosa cells of preovulatory follicles

P11, a member of the S100 family of calcium-binding proteins, has been shown to interact with BAD (Bcl-xL/Bcl-2-associated death promoter) in the yeast two-hybrid protein-protein interaction assay. Because overexpression of P11 dampens the proapoptotic activity of BAD in transfected cells, we tested the possibility that the expression of this antiapoptotic protein may be regulated by gonadotropins and other survival factors in the ovary. Northern blot analysis of ovaries obtained from prepubertal rats revealed an increased expression of P11 messenger RNA (mRNA) during prepubertal development in the theca cells of preantral and early antral follicles. Treatment of immature rats with PMSG did not affect P11 expression, whereas treatment of PMSG-primed rats with an ovulatory dose of human (h)CG stimulated ovarian P11 mRNA within 6-9 h in the granulosa cells of preovulatory follicles. Treatment of cultured preovulatory follicles in vitro with LH further confirmed the time-dependent stimulation of P11 by gonadotropins. In addition, treatment of cultured preovulatory follicles with MDL-12,330A, an inhibitor of adenylate cyclase, inhibited LH-stimulated P11 mRNA, whereas treatment with forskolin, an adenylate cyclase activator, but not the protein kinase C activator, 2-O-tetradecanol-phorbal-13-acetate, mimicked the LH action, suggesting the role of adenylate cyclase activation in P11 expression. Treatment with other follicle survival factors, including the epidermal growth factor, the basic fibroblast growth factor, and interleukin-1beta, could also stimulate P11 expression in cultured preovulatory follicles. These results demonstrate the expression of P11 mRNA in theca cells of different-sized follicles and in granulosa cells of preovulatory follicles following gonadotropin stimulation, and suggest that P11 may mediate, at least partially, the survival action of gonadotropins during the ovulatory process.

Evolution and classification of cystine knot-containing hormones and related extracellular signaling molecules

The cystine knot three-dimensional structure is found in many extracellular molecules and is conserved among divergent species. The identification of proteins with a cystine knot structure is difficult by commonly used pairwise alignments because the sequence homology among these proteins is low. Taking advantage of complete genome sequences in diverse organisms, we used a complementary approach of pattern searches and pairwise alignments to screen the predicted protein sequences of five model species (human, fly, worm, slime mold, and yeast) and retrieved proteins with low sequence homology but containing a typical cystine knot signature. Sequence comparison between proteins known to have a cystine knot three-dimensional structure (transforming growth factor-beta, glycoprotein hormone, and platelet-derived growth factor subfamily members) identified new crucial amino acid residues (two hydrophilic amino acid residues flanking cysteine 5 of the cystine knot). In addition to the well known members of the cystine knot superfamily, novel subfamilies of proteins (mucins, norrie disease protein, von Willebrand factor, bone morphogenetic protein antagonists, and slit-like proteins) were identified as putative cystine knot-containing proteins. Phylogenetic analysis revealed the ancient evolution of these proteins and the relationship between hormones [e.g. transforming growth factor-beta (TGFbeta)] and extracellular matrix proteins (e.g. mucins). They are absent in the unicellular yeast genome but present in nematode, fly, and higher species, indicating that the cystine knot structure evolved in extracellular signaling molecules of multicellular organisms. All data retrieved by this study can be viewed at http://hormone.stanford.edu/.

Human stresscopin and stresscopin-related peptide are selective ligands for the type 2 corticotropin-releasing hormone receptor

Adaptive stress responses mediated by the endocrine, autonomic, cardiovascular and immune systems are essential for the survival of the individual. Initial stress-induced responses provide a vital short-term metabolic lift, but prolonged or inappropriate exposure to stress can compromise homeostasis thereby leading to disease. This 'fight-or-flight' response is characterized by the activation of the corticotropin-releasing hormone (CRH)-adrenocorticotropin-glucocorticoid axis, mediated by the type 1 CRH receptor. In contrast, the type 2 CRH receptor mediates the stress-coping responses during the recovery phase of stress. We identified human stresscopin (SCP) and stresscopin-related peptide (SRP) as specific ligands for the type 2 CRH receptor. The genes encoding these peptides were expressed in diverse peripheral tissues as well as in the central nervous system. Treatment with SCP or SRP suppressed food intake, delayed gastric emptying and decreased heat-induced edema. Thus SCP and SRP might represent endogenous ligands for maintaining homeostasis after stress, and could allow the design of drugs to ameliorate stress-related diseases.

Mutations in the follicle-stimulating hormone receptor and familial dizygotic twinning

Concentrations of follicle-stimulating hormone (FSH) have an important role in multiple ovulation. An association has been reported between mutations in the FSH receptor (FSHR) in a family with increased twinning frequency. We sequenced the transmembrane region of FSHR (located on chromosome 2) in 21 unrelated mothers of dizygotic twins and found no differences to the published sequence. A linkage study of 183 sister pairs and trios, in which all sisters had given birth to spontaneous dizygotic twins, excluded linkage to this region of chromosome 2. We conclude that mutations in FSHR are not a common cause of familial dizygotic twinning.

Müllerian inhibitory substance induces growth of rat preantral ovarian follicles

Müllerian inhibitory substance (MIS), also known as anti-Müllerian hormone, is best known as the hormone that regulates the regression of the Müllerian duct in males. In females, MIS is expressed in granulosa cells of preantral and early antral follicles. The specific MIS type II receptor is present in granulosa and theca cells of these small, growing follicles. Because the role of MIS in preantral follicle development is unknown, we have evaluated the effect of MIS on the growth, differentiation, and apoptosis of intact preantral follicles in a serum-free culture system. In this system, treatment with FSH induces an increase in both follicle diameter, cell number, and follicle cell differentiation based on increased inhibin-alpha synthesis. Of interest, treatment with MIS enhances the effect of FSH both on follicle diameter and cell number. Although treatment with activin A also enhances FSH effects on follicle growth, treatment with transforming growth factor (TGF)-ss inhibits the FSH effects on follicle growth. Based on in situ staining of fragmented DNA, MIS was found to have no effect on follicle cell apoptosis, unlike its proapoptotic action on Müllerian ducts. In contrast to MIS and activin, TGF-ss was a potent proapoptotic factor for preantral follicles in culture. Analysis of inhibin-alpha expression of cultured preantral follicles further indicated that in contrast to activin, treatment with MIS did not enhance FSH-stimulated follicle differentiation. Thus, MIS is a unique factor that promotes preantral follicle growth but not preantral follicle cell differentiation and apoptosis.

Ovarian gene database

OBJECTIVE

The entire human genome will be sequenced in September 2000. Facing the exponential increase of data in the GenBank at the National Center for Biotechnology Information, reproductive biologists are being bombarded with massive amounts of information on diverse genes. It is becoming increasingly difficult for individual investigators to sort out the diverse genetic and physiologic information on the localization and function of different genes in the ovary. To alleviate the present situation, we have taken advantage of the accessibility of the Internet and initiated a project that serves the entire ovarian research community.

RESULTS AND DISCUSSION

The Ovarian Kaleidoscope database provides information regarding biologic function, expression pattern, and regulation of genes that are expressed in the ovary. In addition, it serves as a gateway to other online information resources relevant to ovarian research by offering results from original papers and data about nucleotide and amino acid sequences, and human and murine mutation phenotypes. All references are linked by hypertext to PubMed and additional links to sequence databases are also included. This information is accessible online and searchable not only by gene name but also by criteria such as the cellular and ovarian function of the gene product, the expression of genes in different ovarian cell types, or their association with specific ovarian phenotypes.

Characterization of two fly LGR (leucine-rich repeat-containing, G protein-coupled receptor) proteins homologous to vertebrate glycoprotein hormone receptors: constitutive activation of wild-type fly LGR1 but not LGR2 in transfected mammalian cells

The receptors for lutropin (LH), FSH, and TSH belong to the large G protein-coupled receptor (GPCR) superfamily and are unique in having a large N-terminal extracellular (ecto-) domain important for interactions with the large glycoprotein hormone ligands. Recent studies indicated the evolution of a large family of the leucine-rich repeat-containing, G protein-coupled receptors (LGRs) with at least seven members in mammals. Based on the sequences of mammalian glycoprotein hormone receptors, we have identified a new LGR in Drosophila melanogaster and named it as fly LGR2 to distinguish it from the previously reported fly LH/FSH/TSH receptor (renamed as fly LGR1). Genomic analysis indicated the presence of 10 exons in fly LGR2 as compared with 16 exons in fly LGR1. The deduced fly LGR2 complementary DNA (cDNA) showed 43 and 64% similarity to the fly LGR1 in the ectodomain and transmembrane region, respectively. Comparison of 12 LGRs from diverse species indicated that these proteins can be divided into three subfamilies and fly LGR1 and LGR2 belong to different subfamilies. Potential signaling mechanisms were tested in human 293T cells overexpressing the fly receptors. Of interest, fly LGR1, but not LGR2, showed constitutive activity as reflected by elevated basal cAMP production in transfected cells. The basal activity of fly LGR1 was further augmented following point mutations of key residues in the intracellular loop 3 or transmembrane VI, similar to those found in patients with familial male precocious puberty. The present study reports the cloning of fly LGR2 and indicates that the G protein-coupling mechanism is conserved in fly LGR1 as compared with the mammalian glycoprotein hormone receptors. The characterization of fly receptors with features similar to mammalian glycoprotein hormone receptors allows a better understanding of the evolution of this unique group of GPCRs and future elucidation of their ligand signaling mechanisms.

In vivo treatment with GDF-9 stimulates primordial and primary follicle progression and theca cell marker CYP17 in ovaries of immature rats

Growth differentiation factor (GDF)-9 is a cystine knot-containing hormone of the transforming growth factor-beta superfamily produced by the oocyte. In GDF-9 null mice, follicle development is arrested at the primary stage and GDF-9 treatment in vitro enhances preantral follicle growth. Immature female rats were treated with recombinant GDF-9 for 7 or 10 days. At 10 days, treatment with GDF-9 augmented ovarian weights, concomitant with an increase in the number of primary and small preantral follicles by 30 and 60%, respectively. Furthermore, the number of primordial follicles was decreased by 29%, but the number of large preantral follicles was not affected. In contrast, treatment with FSH increased the number of small and large preantral follicles by 36 and 177% but did not influence the number of primary and primordial follicles. Immunoblot analysis showed an increase of CYP17, a theca cell marker, in the ovarian homogenate after treatment with GDF-9 but not FSH. The present results indicate that in vivo treatment with GDF-9 enhances the progression of primordial and primary follicles into small preantral follicles. Thus, GDF-9 treatment could provide an alternative approach to stimulate early follicle development in addition to the widely used FSH that acts mainly on the development of more advanced follicles.

Growth differentiation factor-9 stimulates rat theca-interstitial cell androgen biosynthesis

Growth differentiation factor-9 (GDF-9) was shown recently to be essential for early follicular development, including the appearance of the theca layer. Theca cells provide the androgen substrate for aromatization and estrogen production by granulosa cells. Using biologically active recombinant GDF-9 (rGDF-9) and an androgen-producing immortalized theca-interstitial cell (TIC) line or primary TIC, we have examined the action of this paracrine hormone on theca cell steroidogenesis. The effect of GDF-9 on TIC progesterone synthesis was marginal and inconsistent in the primary cultures. In immortalized theca cells, GDF-9 attenuated the forskolin-stimulated progesterone accumulation. More significantly, this oocyte-derived growth factor enhanced both basal and stimulated androstenedione accumulation in the primary and transformed TIC cultures. The effects of GDF-9 on steroidogenesis by preovulatory follicles were relatively modest. Likewise, it did not affect the maturation of follicle-enclosed oocytes. The effect of GDF-9, an oocyte product, on TIC androgen production suggests a regulatory role of the oocyte on theca cell function and hence on follicle development and differentiation. This direct effect of GDF-9 on thecal steroidogenesis is consistent with its recently demonstrated actions on thecal cell recruitment and differentiation.

Activation of the luteinizing hormone receptor following substitution of Ser-277 with selective hydrophobic residues in the ectodomain hinge region

Glycoprotein hormone receptors are G protein-coupled receptors with ligand-binding ectodomains consisting of leucine-rich repeats. The ectodomain is connected by a conserved cysteine-rich hinge region to the seven transmembrane (TM) region. Gain-of-function mutants of luteinizing hormone (LH) and thyroid-stimulating hormone receptors found in patients allowed identification of residues important for receptor activation. Based on constitutively active mutations at Ser-281 in the hinge region of the thyroid-stimulating hormone receptor, we mutated the conserved serine in the LH (S277I) and follicle-stimulating hormone receptors (S273I) and observed increased basal cAMP production and ligand affinity by mutant receptors. For the LH receptor, conversion of Ser-277 to all natural amino acids led to varying degrees of receptor activation. Hydropathy index analysis indicated that substitution of neutral serine with selective nonpolar hydrophobic residues (Leu>Val>Met>Ile) confers constitutive receptor activation whereas serine deletion or substitution with charged Arg, Lys, or Asp led to defective receptor expression. Furthermore, mutation of the angular proline near Ser-273 to flexible Gly also led to receptor activation. The findings suggest the ectodomain of glycoprotein hormone receptors constrain the TM region. Point mutations in the hinge region of these proteins, or ligand binding to these receptors, could cause conformational changes in the TM region that result in G(s) activation.

Dizygotic twinning is not linked to variation at the alpha-inhibin locus on human chromosome 2

Natural multiple pregnancy in women leading to dizygotic (DZ) twins is familial and varies across racial groups, suggesting a genetic predisposition. Mothers of DZ twins have a higher incidence of spontaneous multiple ovulation and elevated FSH concentrations. FSH release is controlled by feedback of inhibin peptides from the ovary, and immunization against inhibin alpha-subunit results in an increased ovulation rate in animals. The inhibin alpha-subunit is therefore a candidate gene for mutations that may increase the frequency of DZ twinning. Restriction digests of a PCR product from exon 1 with the enzyme SpeI detects a C/T polymorphism at bp 128 with two alleles of 447 and 323/124 bp. The polymorphism was typed in 1,125 individuals from 326 pedigrees with 717 mothers of spontaneous DZ twins. The alpha-inhibin locus mapped within 3 centimorgans of D2S164, and linkage with DZ twinning was excluded [decimal log odds ratio (LOD) score, -2.81 at theta = 0]. There was complete exclusion of linkage (LOD, less than -2) of a gene conferring relative risk 1.8 (lambdas, >1.8) across the chromosome, except at the p-terminus region and a small peak (maximum LOD score, 0.6) in the region of D2S151-D2S326. Analysis using either recessive or dominant models excluded linkage with DZ twinning in this population (LOD score, less than -2.5) across chromosome 2. We conclude that dizygotic twinning is not linked to variation in the alpha-inhibin locus. The results also suggest that mutations in other candidates on chromosome 2, including the receptor for FSH and the betaB-inhibin subunit (INHBB) cannot be major contributors to risk for DZ twinning.

The Ovarian Kaleidoscope database: an online resource for the ovarian research community

The Ovarian Kaleidoscope database (OKdb) is a collaborative online resource for scientists investigating the ovary. It provides information regarding the biological function, expression pattern, and regulation of genes expressed in the ovary as well as for the phenotypes associated with their mutation. In addition, the records in the OKdb are linked to other sites offering online information about biomedical publications, nucleotide and amino acid sequences, and human genes and genetic disorders. A powerful search tool allows the retrieval of records for specific genes and gene products based on their properties at the molecular, cellular, ovarian, or organism level. Researchers working on particular aspects of ovarian physiology can submit information into the database through a simple web-based form and instantly update their records as additional data become available. Because of this approach, the OKdb website could serve as a tool with which to navigate through the rapidly expanding amount of information about the expression and function of individual genes in the ovary and could also enhance communication within the ovarian research community. Moreover, the design of the OKdb could serve as a model for the development of other online databases of tissue-specific gene expression and function. The OKdb can be accessed at http://ovary.stanford.edu/.

MCL-1S, a splicing variant of the antiapoptotic BCL-2 family member MCL-1, encodes a proapoptotic protein possessing only the BH3 domain

MCL-1 (myeloid cell leukemia-1) is an antiapoptotic BCL-2 family protein discovered as an early induction gene during myeloblastic leukemia cell differentiation. This survival protein has the BCL-2 homology (BH) domains 1, 2, and 3 and a C-terminal transmembrane region. We identified a short splicing variant of the MCL-1 mRNA in the human placenta encoding a protein, termed MCL-1 short (MCL-1S), with an altered C terminus as compared with the full-length MCL-1 long (MCL-1L), leading to the loss of BH1, BH2, and the transmembrane domains. Analysis of the human MCL-1 gene indicated that MCL-1S results from the splicing out of exon 2 during mRNA processing. MCL-1S, unlike MCL-1L, does not interact with diverse proapoptotic BCL-2-related proteins in the yeast two-hybrid system. In contrast, MCL-1S dimerizes with MCL-1L in the yeast assay and coprecipitates with MCL-1L in transfected mammalian cells. Overexpression of MCL-1S induces apoptosis in transfected Chinese hamster ovary cells, and the MCL-1S action was antagonized by the antiapoptotic MCL-1L. Thus, the naturally occurring MCL-1S variant represents a new proapoptotic BH3 domain-only protein capable of dimerizing with the antiapoptotic MCL-1L. The fate of MCL-1-expressing cells could be regulated through alternative splicing mechanisms and interactions of the resulting anti- and proapoptotic gene products.

The three subfamilies of leucine-rich repeat-containing G protein-coupled receptors (LGR): identification of LGR6 and LGR7 and the signaling mechanism for LGR7

Glycoprotein hormone receptors, including LH receptor, FSH receptor, and TSH receptor, belong to the large G protein-coupled receptor (GPCR) superfamily but are unique in having a large ectodomain important for ligand binding. In addition to two recently isolated mammalian LGRs (leucine-rich repeat-containing, G protein-coupled receptors), LGR4 and LGR5, we further identified two new paralogs, LGR6 and LGR7, for glycoprotein hormone receptors. Phylogenetic analysis showed that there are three LGR subgroups: the known glycoprotein hormone receptors; LGR4 to 6; and a third subgroup represented by LGR7. LGR6 has a subgroup-specific hinge region after leucine-rich repeats whereas LGR7, like snail LGR, contains a low density lipoprotein (LDL) receptor cysteine-rich motif at the N terminus. Similar to LGR4 and LGR5, LGR6 and LGR7 mRNAs are expressed in multiple tissues. Although the putative ligands for LGR6 and LGR7 are unknown, studies on single amino acid mutants of LGR7, with a design based on known LH and TSH receptor gain-of-function mutations, indicated that the action of LGR7 is likely mediated by the protein kinase A but not the phospholipase C pathway. Thus, mutagenesis of conserved residues to allow constitutive receptor activation is a novel approach for the characterization of signaling pathways of selective orphan GPCRs. The present study also defines the existence of three subclasses of leucine-rich repeat-containing, G protein-coupled receptors in the human genome and allows future studies on the physiological importance of this expanding subgroup of GPCR.

Hormonal regulation of early follicle development in the rat ovary

Although earlier studies focused on the hormonal regulation of antral and preovulatory follicles, recent studies indicate the importance of the hormonal control mechanism for preantral follicles. The endocrine hormone FSH is not only a survival factor for early antral follicles but also a potent growth and differentiation factor for preantral follicles. In addition, KGF secreted by theca cells and c-kit ligand secreted by granulosa cells play paracrine roles in the regulation of preantral follicle growth and development. Furthermore oocyte-derived GDF-9 promotes the growth and differentiation of early follicles by acting on somatic cells in the follicle. It is likely that the genetic makeup of an oocyte could determine the secretion of oocyte hormones which would, in turn, regulate the growth and differentiation of the surrounding somatic cells of that follicle. A better understanding of the hormonal mechanisms underlying early follicle development could provide a refined culture system for the in vitro maturation of fertilizable oocytes and future design of fertility and contraceptive agents.

Initial and cyclic recruitment of ovarian follicles

Mammalian ovaries consist of follicles as basic functional units. The total number of ovarian follicles is determined early in life, and the depletion of this pool leads to reproductive senescence. Each follicle develops to either ovulate or, more likely, to undergo degeneration. The dynamics of ovarian follicle development have interested endocrinologists and developmental biologists for many years. With the advent of assisted reproductive techniques in humans, the possibility of regulating follicle development in vivo and in vitro has gained clinical relevance. In this review, we focus upon key branching points during the development of ovarian follicles as well as factors involved in determining the eventual destiny of individual follicles. We discuss inconsistencies in the literature regarding the definitions of follicle recruitment and selection and propose to name the two major steps of follicle development as initial and cyclic recruitment, respectively. Because some of these disparities have arisen due to differences in the animal systems studied, we also compare the development of the ovarian follicles of both humans and rats. We also review the status of knowledge of several puzzling clinical issues that may provide important clues toward unlocking the mechanisms of follicle development.

Tissue-specific Bcl-2 protein partners in apoptosis: An ovarian paradigm

Apoptosis is an essential physiological process by which multicellular organisms eliminate superfluous cells. An expanding family of Bcl-2 proteins plays a pivotal role in the decision step of apoptosis, and the differential expression of Bcl-2 members and their binding proteins allows the regulation of apoptosis in a tissue-specific manner mediated by diverse extra- and intracellular signals. The Bcl-2 proteins can be divided into three subgroups: 1) antiapoptotic proteins with multiple Bcl-2 homology (BH) domains and a transmembrane region, 2) proapoptotic proteins with the same structure but missing the BH4 domain, and 3) proapoptotic ligands with only the BH3 domain. In the mammalian ovary, a high rate of follicular cell apoptosis continues during reproductive life. With the use of the yeast two-hybrid system, the characterization of ovarian Bcl-2 genes serves as a paradigm to understand apoptosis regulation in a tissue-specific manner. We identified Mcl-1 as the main ovarian antiapoptotic Bcl-2 protein, the novel Bok (Bcl-2-related ovarian killer) as the proapoptotic protein, as well as BOD (Bcl-2-related ovarian death agonist) and BAD as the proapoptotic ligands. The activity of the proapoptotic ligand BAD is regulated by upstream follicle survival factors through its binding to constitutively expressed 14-3-3 or hormone-induced P11. In contrast, the channel-forming Mcl-1 and Bok regulate cytochrome c release and, together with the recently discovered Diva/Boo, control downstream apoptosis-activating factor (Apaf)-1 homologs and caspases. Elucidation of the role of Bcl-2 members and their interacting proteins in the tissue-specific regulation of apoptosis could facilitate an understanding of normal physiology and allow the development of new therapeutic approaches for pathological states.

Growth differentiation factor-9 stimulates proliferation but suppresses the follicle-stimulating hormone-induced differentiation of cultured granulosa cells from small antral and preovulatory rat follicles

In addition to pituitary gonadotropins and paracrine factors, ovarian follicle development is also modulated by oocyte factors capable of stimulating granulosa cell proliferation but suppressing their differentiation. The nature of these oocyte factors is unclear. Because growth differentiation factor-9 (GDF-9) enhanced preantral follicle growth and was detected in the oocytes of early antral and preovulatory follicles, we hypothesized that this oocyte hormone could regulate the proliferation and differentiation of granulosa cells from these advanced follicles. Treatment with recombinant GDF-9, but not FSH, stimulated thymidine incorporation into cultured granulosa cells from both early antral and preovulatory follicles, accompanied by increases in granulosa cell number. Although GDF-9 treatment alone stimulated basal steroidogenesis in granulosa cells, cotreatment with GDF-9 suppressed FSH-stimulated progesterone and estradiol production. In addition, GDF-9 cotreatment attentuated FSH-induced LH receptor formation. The inhibitory effects of GDF-9 on FSH-induced granulosa cell differentiation were accompanied by decreases in the FSH-induced cAMP production. These data suggested that GDF-9 is a proliferation factor for granulosa cells from early antral and preovulatory follicles but suppresses FSH-induced differentiation of the same cells. Thus, oocyte-derived GDF-9 could account, at least partially, for the oocyte factor(s) previously reported to control cumulus and granulosa cell differentiation.

The nematode leucine-rich repeat-containing, G protein-coupled receptor (LGR) protein homologous to vertebrate gonadotropin and thyrotropin receptors is constitutively active in mammalian cells

The receptors for LH, FSH, and TSH belong to the large G protein-coupled, seven-transmembrane protein family and are unique in having a large N-terminal extracellular (ecto-) domain containing leucine-rich repeats important for interactions with the large glycoprotein hormone ligands. Recent studies indicated the evolution of an expanding family of homologous leucine-rich repeat-containing, G protein-coupled receptors (LGRs), including the three known glycoprotein hormone receptors; mammalian LGR4 and LGR5; and LGRs in sea anemone, fly, and snail. We isolated nematode LGR cDNA and characterized its gene from the Caenorhabditis elegans genome. This receptor cDNA encodes 929 amino acids consisting of a signal peptide for membrane insertion, an ectodomain with nine leucine-rich repeats, a seven-TM region, and a long C-terminal tail. The nematode LGR has five potential N-linked glycosylation sites in its ectodomain and multiple consensus phosphorylation sites for protein kinase A and C in the cytoplasmic loop and C tail. The nematode receptor gene has 13 exons; its TM region and C tail, unlike mammalian glycoprotein hormone receptors, are encoded by multiple exons. Sequence alignments showed that the TM region of the nematode receptor has 30% identity and 50% similarity to the same region in mammalian glycoprotein hormone receptors. Although human 293T cells expressing the nematode LGR protein do not respond to human glycoprotein hormones, these cells exhibited major increases in basal cAMP production in the absence of ligand stimulation, reaching levels comparable to those in cells expressing a constitutively activated mutant human LH receptor found in patients with familial male-limited precocious puberty. Analysis of cAMP production mediated by chimeric receptors further indicated that the ectodomain and TM region of the nematode LGR and human LH receptor are interchangeable and the TM region of the nematode LGR is responsible for constitutive receptor activation. Thus, the identification and characterization of the nematode receptor provides the basis for understanding the evolutionary relationship of diverse LGRs and for future analysis of mechanisms underlying the activation of glycoprotein hormone receptors and related LGRs.

The biological action of choriogonadotropin is not dependent on the complete native quaternary interactions between the subunits

Human CG (hCG) is a member of the glycoprotein hormone family characterized by a heterodimeric structure consisting of a common alpha-subunit noncovalently bound to a hormone-specific beta-subunit. The two subunits are highly intertwined and only the heterodimer is functional, implying that the quaternary structure is critical for biological activity. To assess the dependence of the bioactivity of hCG on the heterodimeric interactions, alpha- and beta-subunits bearing mutations that prevent assembly were covalently linked to form a single chain hCG. Receptor binding and signal transduction of these analogs were tested and their structural integrity analyzed using a panel of monoclonal antibodies (mAbs). These included dimer-specific mAbs, which react with at least four different epitope sites on the hormone, and some that react only with the free beta-subunit. We showed that there was significant loss of quaternary and tertiary structure in several regions of the molecule. This was most pronounced in single chains that had one of the disulfide bonds of the cystine knot disrupted in either the alpha- or beta-subunit. Despite these structural changes, the in vitro receptor binding and signal transduction of the single chain analogs were comparable to those of the nonmutated single chain, demonstrating that not all of the quaternary configuration of the hormone is necessary for biological activity.

Characterization of the antiapoptotic Bcl-2 family member myeloid cell leukemia-1 (Mcl-1) and the stimulation of its message by gonadotropins in the rat ovary

The majority of ovarian follicles undergo atresia mediated by apoptosis. Bcl-2-related proteins act as regulators of apoptosis via the formation of dimers with proteins inside and outside the Bcl-2 family. Previous studies have identified BAD as a proapoptotic Bcl-2 family member expressed in the ovary. It is known that BAD phosphorylation induced by survival factors leads to its preferential binding to 14-3-3 and suppression of the death-inducing function of BAD. To identify ovarian binding partners for hypophosphorylated BAD, we performed a yeast two-hybrid screening of a rat ovary complementary DNA library using as bait a mutant BAD incapable of binding to 14-3-3. Screening of yeast transformants yielded positive clones encoding the rat ortholog of Mcl-1 (myeloid cell leukemia-1), an antiapoptotic Bcl-2 protein. Amino acid sequence analysis revealed that rat and human Mcl-1 showed a complete conservation of the Bcl-2 homology domains BH1, BH2, and BH3. In the yeast two-hybrid system, Mcl-1 binds to the hypophosphorylated mutant of BAD and interacts preferentially with different proapoptotic (Bax, Bak, Bok, Bik, and BOD) compared with antiapoptotic Bcl-2 family members (Bcl-2, Bcl-xL, Bcl-w, Bfl-1, CED-9, and BHRF-1). Northern blot hybridization demonstrated expression of Mcl-1 transcripts of 2.3 and 3.7 kb in the ovary and diverse other rat tissues. In immature rats, PMSG treatment led to a transient increase in the 2.3-kb Mcl-1 transcript, peaking at 6 h after injection and returning to baseline levels after 24 h. Moreover, the same transcript was induced in the PMSG-primed preovulatory rat ovary 6 h after the administration of ovulatory doses of either hCG or FSH. In situ hybridization studies revealed that the gonadotropin stimulation of ovarian Mcl-1 message occurs in both granulosa and thecal cells. In conclusion, rat Mcl-1 was identified as an ovarian BAD-interacting protein and the message for the antiapoptotic Mcl-1 protein was induced after treatment with gonadotropins in granulosa and thecal cells of growing follicles.

Keratinocyte growth factor promotes the survival, growth, and differentiation of preantral ovarian follicles

OBJECTIVE

To determine the effect of treatment with keratinocyte growth factor (KGF) on the survival of cells in cultured preantral follicles and on the growth and differentiation of preantral follicles.

DESIGN

Preantral follicles (140-150 microm) were dissected mechanically from the ovaries of 14-day-old rats and cultured for 24 hours with and without KGF. Genomic DNA was extracted, labeled with [32P]-dideoxyadenosine triphosphate, and fractionated through agarose gels. For growth studies, the follicles were cultured individually in 96-well dishes. After 72 hours, the follicles were collected and their protein or DNA content was evaluated and their inhibin-alpha content was determined.

RESULT(S)

Keratinocyte growth factor suppressed apoptosis in cultured preantral follicles by 60%. Treatment with KGF or FSH increased follicle diameter by 8% and 16%, respectively, and combined treatment with KGF and FSH increased follicle diameter by 26%. Western blot analysis demonstrated increased expression of inhibin-alpha content after treatment with KGF (2-fold), treatment with FSH (4-fold), and combined treatment with FSH and KGF (12-fold), demonstrating the effect of KGF on preantral follicle differentiation.

CONCLUSION(S)

Treatment with KGF promotes the survival, growth, and differentiation of cultured preantral follicles. Keratinocyte growth factor produced by theca cells may play a role in the progression of early follicle development.

Recombinant growth differentiation factor-9 (GDF-9) enhances growth and differentiation of cultured early ovarian follicles

Transgenic mice with deletion of the GDF-9 (growth differentiation factor-9) gene are characterized by the arrest of ovarian follicle development at the primary stage. Based on the hypothesis that GDF-9 is important for early follicle development, we isolated rat GDF-9 complementary DNA (cDNA) and generated recombinant GDF-9 protein to study its physiological role. Using bacteria-derived GDF-9-glutathione S-transferase (GST) fusion protein, specific antibodies to the mature form of GDF-9 was generated. Immunohistochemical staining of ovarian sections indicated the localization of GDF-9 protein in the oocyte of primary, secondary and preantral follicles, whereas immunoblotting demonstrated the secretion of GDF-9 by mammalian cells transfected with GDF-9 cDNAs. Recombinant GDF-9 was shown to be an N-glycosylated protein capable of stimulating early follicle development. Growth of preantral follicles isolated from immature rats was enhanced by treatment with either GDF-9 or FSH whereas the combined treatment showed an additive effect. In addition, treatment with GDF-9, like forskolin, also stimulated inhibin-alpha content in explants of neonatal ovaries. In contrast, the stimulatory effects of GDF-9 were not mimicked by amino-terminal tagged GDF-9 that was apparently not bioactive. Thus, the present study demonstrates the important role of GDF-9 in early follicle growth and differentiation. The availability of recombinant bioactive GDF-9 allows future studies on the physiological role of GDF-9 in ovarian development in vivo.

Restricted expression of WT1 messenger ribonucleic acid in immature ovarian follicles: uniformity in mammalian and avian species and maintenance during reproductive senescence

WT1 is a zinc finger protein with transcriptional repressor activity on several growth factor and growth factor receptor genes. In the ovary, a potential role for WT1 in the suppression of the development of immature follicles has been demonstrated. Here, gel retardation assays further showed that recombinant WT1 protein interacted with consensus DNA sequences in the inhibin-alpha gene promoter. We investigated the pattern of WT1 expression in a wide variety of species and also over the reproductive life span in rats. In chicken ovaries, Northern blot analysis revealed the presence of WT1 transcript in small healthy white follicles (1-5 mm in diameter) and its absence in small yellow (6-12 mm in diameter) or larger follicles (F1-F5). In pig and monkey ovaries, WT1 expression was limited to granulosa cells of preantral follicles, as shown by in situ hybridization analysis. In rats, Northern blot analyses demonstrated the presence of WT1 transcript in the ovaries of young (3-mo-old) and middle-aged (9-mo-old) rats on the proestrous day, with a decrease in old (12-mo-old) rats in persistent estrus. In situ hybridization analysis further suggested that the decrease in WT1 expression in aging ovaries was associated with fewer immature follicles. Thus, WT1 expression is restricted to immature follicles in diverse avian and mammalian species and over the reproductive life span in rats. These data demonstrated that WT1 is a marker for immature follicles and suggested a potential role of this transcriptional repressor in the slow growth of early follicles.

DEFT, a novel death effector domain-containing molecule predominantly expressed in testicular germ cells

Apoptosis is a physiological process by which multicellular organisms eliminate unwanted cells. Death factors such as Fas ligand induce apoptosis by triggering a series of intracellular protein-protein interactions mediated by defined motifs found in the signaling molecules. One of these motifs is the death effector domain (DED), a stretch of about 80 amino acids that is shared by adaptors, regulators, and executors of the death factor pathway. We have identified the human and rat complementary DNAs encoding a novel protein termed DEFT (Death EFfector domain-containing Testicular molecule). The N-terminus of DEFT shows a high degree of homology to the DEDs found in FADD (an adaptor molecule) as well as procaspase-8/FLICE and procaspase-10/Mch4 (executors of the death program). Northern blot hybridization experiments have shown that the DEFT messenger RNA (mRNA) is expressed in a variety of human and rat tissues, with particularly abundant expression in the testis. In situ hybridization analysis further indicated the expression of DEFT mRNA in meiotic male germ cells. In a model of germ cell apoptosis induction, an increase in testis DEFT mRNA was found in immature rats after 2 days of treatment with a GnRH antagonist. Unlike FADD and procaspase-8/FLICE, overexpression of DEFT did not induce apoptosis in Chinese hamster ovary cells. Although cotransfection studies indicated that DEFT is incapable of modulating apoptosis effected by FADD and procaspase-8/FLICE, interactions between DEFT and uncharacterized DED-containing molecules in the testis remain to be studied in the future. In conclusion, we have identified a novel DED-containing protein with high expression in testis germ cells. This protein may be important in the regulation of death factor-induced apoptosis in the testis and other tissues.

Characterization of two LGR genes homologous to gonadotropin and thyrotropin receptors with extracellular leucine-rich repeats and a G protein-coupled, seven-transmembrane region

The receptors for LH, FSH, and TSH belong to the large G protein-coupled, seven-transmembrane (TM) protein family and are unique in having a large N-terminal extracellular (ecto-) domain containing leucine-rich repeats important for interaction with the glycoprotein ligands. We have identified two new leucine-rich repeat-containing, G protein-coupled receptors and named them as LGR4 and LGR5, respectively. The ectodomains of both receptors contain 17 leucine-rich repeats together with N- and C-terminal flanking cysteine-rich sequences, compared with 9 repeats found in known glycoprotein hormone receptors. The leucine-rich repeats in LGR4 and LGR5 are arrays of 24 amino acids showing similarity to repeats found in the acid labile subunit of the insulin-like growth factor (IGF)/IGF binding protein complexes as well as slit, decorin, and Toll proteins. The TM region and the junction between ectodomain and TM 1 are highly conserved in LGR4, LGR5, and seven other LGRs from sea anemone, fly, nematode, mollusk, and mammal, suggesting their common evolutionary origin. In contrast to the restricted tissue expression of gonadotropin and TSH receptors in gonads and thyroid, respectively, LGR4 is expressed in diverse tissues including ovary, testis, adrenal, placenta, thymus, spinal cord, and thyroid, whereas LGR5 is found in muscle, placenta, spinal cord, and brain. Hybridization analysis of genomic DNA indicated that LGR4 and LGR5 genes are conserved in mammals. Comparison of overall amino acid sequences indicated that LGR4 and LGR5 are closely related to each other but diverge, during evolution, from the homologous receptor found in snail and the mammalian glycoprotein hormone receptors. The identification and characterization of new members of the LGR subfamily of receptor genes not only allow future isolation of their ligands and understanding of their physiological roles but also reveal the evolutionary relationship of G protein-coupled receptors with leucine-rich repeats.

BOD (Bcl-2-related ovarian death gene) is an ovarian BH3 domain-containing proapoptotic Bcl-2 protein capable of dimerization with diverse antiapoptotic Bcl-2 members

Using the yeast two-hybrid protein-protein interaction system to search for genes capable of forming dimers with the antiapoptotic protein Mcl-1, we have isolated BOD (Bcl-2-related ovarian death agonist) from an ovarian fusion cDNA library. The three variants of BOD (long, medium, and short) have an open reading frame of 196, 110, and 93 amino acids, respectively; all of them contain a consensus Bcl-2 homology 3 (BH3) domain but lack other BH domains found in channel-forming Bcl-2 family proteins. In the yeast cell assay, BOD interacts with diverse antiapoptotic Bcl-2 proteins [Mcl-1, Bcl-2, Bcl-xL, Bcl-w, Bfl-1, and Epstein-Barr virus (EBV) BHRF-1] but not with different proapoptotic Bcl-2 proteins (BAD, Bak, Bok, and Bax). After overexpression in mammalian Chinese hamster ovary (CHO) cells, BOD induces apoptosis that can be prevented by the baculoviral caspase inhibitor P35. The cell-killing activity of BOD is also antagonized in cells cotransfected with the antiapoptotic Bcl-w protein, which showed high affinity for BOD in the two-hybrid assay. Furthermore, mutagenesis studies showed that BOD mutants with alterations in the BH3 domain lose cell-killing ability, suggesting that the BH3 domain is important for the mediation of cell killing by BOD. BOD mRNA is ubiquitously expressed in ovary and multiple other tissues. The BOD gene is also conserved in diverse mammalian species. Identification of BOD expands the group of proapoptotic Bcl-2 proteins that only contains the BH3 domain and allows future elucidation of the intracellular mechanism for apoptosis regulation in ovary and other tissues.

A splicing variant of the Bcl-2 member Bok with a truncated BH3 domain induces apoptosis but does not dimerize with antiapoptotic Bcl-2 proteins in vitro

Bok (Bcl-2-related ovarian killer) is a proapoptotic Bcl-2 family protein identified in the ovary based on its dimerization with the antiapoptotic protein Mcl-1. In addition to the Bcl-2 homology (BH) domains 1 and 2 and the transmembrane sequence, Bok also has a BH3 domain believed to be important for dimerization with selective antiapoptotic Bcl-2 proteins and cell killing. We identified a splicing variant of Bok mRNA with a deletion of 43 residues from the full-length protein (Bok-L), leading to the fusion of the N-terminal-half of its BH3 domain to the C-terminal-half of the BH1 domain. Genomic analysis indicated that the Bok has five exons, and the short form of Bok (Bok-S) represents the splicing out of exon three during transcription. Although Bok-S retains the apoptosis-inducing activity in transfected cells, it has lost the ability to dimerize with antiapoptotic proteins in vitro. Additional BH3 domain mutations of Bok-L also led to defective heterodimerization without affecting its proapoptotic action. Furthermore, similar deletions for the related channel-forming proapoptotic Bax and Bak did not impair their cell killing ability. Thus, the naturally occurring Bok-S variant represents a new form of proapoptotic protein that induces cell killing without heterodimerization with antiapoptotic Bcl-2 proteins. This variant appears to contain the minimal module spanning BH1 and BH2 domains and the transmembrane sequence for apoptosis induction by channel-forming Bcl-2 proteins.

Intracellular mechanisms of ovarian cell apoptosis

Apoptosis is an active cell 'suicide' essential for the elimination of superfluous cells during diverse physiological processes in essentially all animal species. Although regulation of apoptosis by extracellular mediators is cell type-specific, new insights based on characterization of conserved intracellular effectors have suggested that intracellular pathways leading to apoptosis in diverse organisms is regulated by a group of evolutionarily conserved genes including ced-9/Bcl-2, ced-4/Apaf-1 and ced3/caspases gene families. To study whether the Bcl-2 family proteins are important in the regulation of ovarian cell apoptosis, we have used transgenic mice and yeast 2-hybrid protein protein interaction assay to characterize the roles of Bcl-2 family proteins in ovarian atresia. The use of 2-hybrid analysis resulted in the isolation of a novel pro-apoptotic Bcl-2 protein, Bcl-2-related ovarian killer (Bok) and the identification of upstream mediators for ovarian cell apoptosis.

BOD (Bcl-2-related ovarian death gene) is an ovarian BH3 domain-containing proapoptotic Bcl-2 protein capable of dimerization with diverse antiapoptotic Bcl-2 members

Using the yeast two-hybrid protein-protein interaction system to search for genes capable of forming dimers with the antiapoptotic protein Mcl-1, we have isolated BOD (Bcl-2-related ovarian death agonist) from an ovarian fusion cDNA library. The three variants of BOD (long, medium, and short) have an open reading frame of 196, 110, and 93 amino acids, respectively; all of them contain a consensus Bcl-2 homology 3 (BH3) domain but lack other BH domains found in channel-forming Bcl-2 family proteins. In the yeast cell assay, BOD interacts with diverse antiapoptotic Bcl-2 proteins [Mcl-1, Bcl-2, Bcl-xL, Bcl-w, Bfl-1, and Epstein-Barr virus (EBV) BHRF-1] but not with different proapoptotic Bcl-2 proteins (BAD, Bak, Bok, and Bax). After overexpression in mammalian Chinese hamster ovary (CHO) cells, BOD induces apoptosis that can be prevented by the baculoviral caspase inhibitor P35. The cell-killing activity of BOD is also antagonized in cells cotransfected with the antiapoptotic Bcl-w protein, which showed high affinity for BOD in the two-hybrid assay. Furthermore, mutagenesis studies showed that BOD mutants with alterations in the BH3 domain lose cell-killing ability, suggesting that the BH3 domain is important for the mediation of cell killing by BOD. BOD mRNA is ubiquitously expressed in ovary and multiple other tissues. The BOD gene is also conserved in diverse mammalian species. Identification of BOD expands the group of proapoptotic Bcl-2 proteins that only contains the BH3 domain and allows future elucidation of the intracellular mechanism for apoptosis regulation in ovary and other tissues.

Paracrine mechanisms of ovarian follicle apoptosis

It has become evident that the physiological removal of cells through apoptosis during embryonic and postnatal development of multicellular organisms is a mandatory process to maintain a homeostatic state of the individual. In the ovary, massive cell death occurs during neonatal and postnatal life as an integral part of the normal ovarian development. At birth, mammalian ovaries are endowed with a fixed number of non-growing follicles that will be gradually recruited into a growing pool during reproductive life. Once follicles start growth they are either selected for ovulation or, for the majority of them, removed by apoptosis. Thus, removal of excess ovarian cells by apoptosis is necessary for normal development of the ovary. Despite the important role of follicle atresia in the maintenance of normal follicle development, studies on the hormonal control of follicle cell demise during follicle growth have not been possible until the recent development of apoptosis detection methods. Recent biochemical analysis has revealed the occurrence of internucleosomal DNA fragmentation, a hallmark of apoptosis, in atretic follicles and has facilitated the investigation into the intra-ovarian hormonal regulation of follicle atresia. This review summarizes the recent advances in the intra-ovarian hormonal mechanisms that control follicle apoptosis.

Phosphodiesterase 3 inhibitors suppress oocyte maturation and consequent pregnancy without affecting ovulation and cyclicity in rodents

During each reproductive cycle, a preovulatory surge of gonadotropins induces meiotic maturation of the oocyte in the preovulatory follicle followed by ovulation. Although gonadotropins stimulate cAMP production in somatic cells of the follicle, a decrease in intra-oocyte cAMP levels is required for resumption of meiosis in oocytes. Based on the observed compartmentalization of the cAMP-degrading enzyme, phosphodiesterase, in follicular somatic and germ cells, inhibitors of phosphodiesterase 3 were used to block meiosis in ovulating oocytes in rodents. By this strategy, we demonstrated that fertilization and pregnancy could be prevented without disturbing follicle rupture and normal estrous cyclicity. In contrast to conventional contraceptive pills that disrupt ovarian steroidogenesis and reproductive cycles, the present strategy achieves effective contraception by selective blockage of oocyte maturation and development without alterations in ovulation and reproductive cyclicity.

Cell death and survival during ovarian follicle development

Mammalian germ cells arise in the yolk sac endoderm at the caudal aspect of the embryo and migrate to the mesodermally-derived gonadal ridge early in development. After the oogonia reach the gonadal ridge, the process of meiosis begins which coincides with the first major wave of apoptosis of female germ cells (Coucouvanis et al., 1993). Subsequently, oocytes progress to the dictyate stage of prophase I where they remain arrested until ovulation.

Conversion of thyrotropin heterodimer to a biologically active single-chain

TSH and the gonadotropins, FSH, LH, and CG are a family of heterodimeric glycoprotein hormones composed of a common alpha-subunit noncovalently linked to a hormone specific beta-subunit. Assembly of alpha- and beta-subunits is essential for hormone-specific posttranslational modifications, receptor binding, and bioactivity. Structure-function studies of TSH and gonadotropins using site-directed mutagenesis can often affect folding, assembly, and secretion of the hormone. To circumvent these difficulties, recently, the gonadotropin heterodimers were converted to single chains. Here we converted the hTSH heterodimer to a biologically active single chain by genetically fusing the amino terminal end of the common alpha-subunit to the carboxyl terminal end of hTSHbeta in the presence or absence of hCGbeta carboxyl terminal peptide (CTP), which was used as a linker. Wild-type hTSH and the single chains were expressed in Chinese hamster ovary (CHO) cells, and they were efficiently secreted. Although the secretion rate of the single chain was 3-fold higher than that of hTSH wild-type. Moreover, the secretion of the single chain in the presence of the CTP linker was dramatically increased. On the other hand, receptor binding and in vitro bioactivity of the single chains were similar to that of hTSH wild-type. These data indicate the potential of the single chain approach to further investigate structure-function relationships of TSH.

Soluble ecto-domain mutant of thyrotropin (TSH) receptor incapable of binding TSH neutralizes the action of thyroid-stimulating antibodies from Graves' patients

A soluble form of the amino-terminal extracellular (ecto-) domain of the human TSH receptor was generated. This protein was capable of binding TSH and autoimmune antibodies found in Graves' patients. A deletion mutant of the ectodomain lacking nine amino acids in the C-terminal region lost its ability to interact with TSH but retained binding to Graves' IgGs. In cells expressing recombinant TSH receptors, cotreatment with the mutant protein blocked the cAMP production induced by stimulating antibodies from all Graves' patients tested but was without effect on TSH action. The ability to dissociate the actions of TSH and Graves' IgGs provides a tool with which to study the mechanisms underlying Graves' disease and the possibility of neutralizing the undesirable effects of thyroid-stimulating antibodies without altering the normal responses to TSH.

Expression and function of a proapoptotic Bcl-2 family member Bcl-XL/Bcl-2-associated death promoter (BAD) in rat ovary

Bcl-2-related anti- and proapoptotic proteins are important in the decision step of the intracellular death program upstream from the caspase proteases. Targeted overexpression of Bcl-2 in ovarian somatic cells of transgenic mice leads to decreased apoptosis of granulosa cells and is associated with higher ovulation rate, increased litter size, and ovarian teratoma formation. The ability of exogenous Bcl-2 proteins to promote follicle cell survival suggests that the transgene can bind to endogenous ovarian Bcl-2 family members and modulate the intracellular apoptosis process in favor of cell survival. We used the yeast two-hybrid system to search for ovarian Bcl-2 interacting proteins. The screening of an ovarian fusion complementary DNA library yielded several clones encoding for the death agonist Bcl-XL/Bcl-2-associated death promoter (BAD). Dimerization of Bcl-2-related proteins mediated by the consensus Bcl-2 homology (BH) domains is essential for their apoptosis-regulating function. Consistent with these observations, yeast two-hybrid assays indicated that the interaction of Bcl-2 with BAD is dependent on both BH4 and BH2 domains of Bcl-2. Northern blot analysis showed a wide distribution of BAD messenger RNA (mRNA) in diverse tissues with highest levels in the lung, ovary, uterus, and brain. In situ hybridization analysis indicated BAD mRNA expression in granulosa cells of different sizes of follicles and also in the theca and interstitial cells. BAD mRNA was expressed in the ovaries between postnatal 15-27 days and did not alter during the developmentally occurring apoptosis found about postnatal day 18 when the first group of early antral follicles were formed. Similarly, BAD mRNA levels did not change during follicle atresia induced by estrogen withdrawal in immature rats. To study the role of BAD in the ovary, BAD complementary DNA was transfected into primary cultures of granulosa cells and in a gonadal tumor cell line. Overexpression of BAD induced apoptosis in both cell types, and the effect of BAD was reversed by a membrane-permeable caspase inhibitor, indicating that BAD induces apoptosis via the activation of caspase cysteine proteases. In summary, the death agonist BAD was identified as a Bcl-2-interacting protein in the ovary, and BAD mRNA is constitutively expressed in granulosa cells, suggesting that BAD is an essential part of the ovarian cell death process. Because BAD overexpression in granulosa cells leads to apoptosis, future studies on ovarian BAD binding proteins and hormonal regulation of the interactions among different Bcl-2 family members could provide a better understanding of the cellular mechanism of ovarian follicle atresia.

Bok is a pro-apoptotic Bcl-2 protein with restricted expression in reproductive tissues and heterodimerizes with selective anti-apoptotic Bcl-2 family members

In the intracellular death program, hetero- and homodimerization of different anti- and pro-apoptotic Bcl-2-related proteins are critical in the determination of cell fate. From a rat ovarian fusion cDNA library, we isolated a new pro-apoptotic Bcl-2 gene, Bcl-2-related ovarian killer (Bok). Bok had conserved Bcl-2 homology (BH) domains 1, 2, and 3 and a C-terminal transmembrane region present in other Bcl-2 proteins, but lacked the BH4 domain found only in anti-apoptotic Bcl-2 proteins. In the yeast two-hybrid system, Bok interacted strongly with some (Mcl-1, BHRF1, and Bfl-1) but not other (Bcl-2, Bcl-xL, and Bcl-w) anti-apoptotic members. This finding is in direct contrast to the ability of other pro-apoptotic members (Bax, Bak, and Bik) to interact with all of the anti-apoptotic proteins. In addition, negligible interaction was found between Bok and different pro-apoptotic members. In mammalian cells, overexpression of Bok induced apoptosis that was blocked by the baculoviral-derived cysteine protease inhibitor P35. Cell killing induced by Bok was also suppressed following coexpression with Mcl-1 and BHRF1 but not with Bcl-2, further indicating that Bok heterodimerized only with selective anti-apoptotic Bcl-2 proteins. Northern blot analysis indicated that Bok was highly expressed in the ovary, testis and uterus. In situ hybridization analysis localized Bok mRNA in granulosa cells, the cell type that underwent apoptosis during follicle atresia. Identification of Bok as a new pro-apoptotic Bcl-2 protein with restricted tissue distribution and heterodimerization properties could facilitate elucidation of apoptosis mechanisms in reproductive tissues undergoing hormone-regulated cyclic cell turnover.

Interference of BAD (Bcl-xL/Bcl-2-associated death promoter)-induced apoptosis in mammalian cells by 14-3-3 isoforms and P11

Apoptosis and survival of diverse cell types are under hormonal control, but intracellular mechanisms regulating cell death are unclear. The Bcl-2/Ced-9 family of proteins contains conserved Bcl-2 homology regions that mediate the formation of homo- or heterodimers important for enhancing or suppressing apoptosis. Unlike most other members of the Bcl-2 family, BAD (Bcl-xL/Bcl-2 associated death promoter), a death enhancer, has no C-terminal transmembrane domain for targeting to the outer mitochondrial membrane and nuclear envelope. We hypothesized that BAD, in addition to binding Bcl-xL and Bcl-2, may interact with proteins outside the Bcl-2 family. Using the yeast two-hybrid system to search for BAD-binding proteins in an ovarian fusion cDNA library, we identified multiple cDNA clones encoding different isoforms of 14-3-3, a group of evolutionally conserved proteins essential for signal transduction and cell cycle progression. Point mutation of BAD in one (S137A), but not the other (S113A), putative binding site found in diverse 14-3-3 interacting proteins abolished the interaction between BAD and 14-3-3 without affecting interactions between BAD and Bcl-2. Because the S137A BAD mutant presumably resembles an underphosphorylated form of BAD, we used this mutant to screen for additional BAD-interacting proteins in the yeast two-hybrid system. P11, a nerve growth factor-induced neurite extension factor and member of the calcium-binding S-100 protein family, interacted strongly with the mutant BAD but less effectively with the wild type protein. In Chinese hamster ovary (CHO) cells, transient expression of wild type BAD or its mutants increased apoptotic cell death, which was blocked by cotransfection with the baculovirus-derived cysteine protease inhibitor, P35. Cotransfection with 14-3-3 suppressed apoptosis induced by wild type or the S113A mutant BAD but not by the S137A mutant incapable of binding 14-3-3. Furthermore, cotransfection with P11 attenuated the proapoptotic effect of both wild type BAD and the S137A mutant. For both 14-3-3 and P11, direct binding to BAD was also demonstrated in vitro. These results suggest that both 14-3-3 and P11 may function as BAD-binding proteins to dampen its apoptotic activity. Because the 14-3-3 family of proteins could interact with key signaling proteins including Raf-1 kinase, protein kinase C, and phosphatidyl inositol 3 kinase, whereas P11 is an early response gene induced by the neuronal survival factor, nerve growth factor, the present findings suggest that BAD plays an important role in mediating communication between different signal transduction pathways regulated by hormonal signals and the apoptotic mechanism controlled by Bcl-2 family members.

Follicle-stimulating hormone enhances the development of preantral follicles in juvenile rats

The stimulatory effects of gonadotropins on antral and preovulatory follicles are well known, but conflicting results have been reported regarding the gonadotropin responsiveness and dependency of preantral follicles. Taking advantage of the relatively uniform development of the first wave of follicles in the postnatal rat ovary, we evaluated the role of endogenous and exogenous gonadotropins on preantral follicle development. Reduction of the high levels of gonadotropins present in juvenile rats by either hypophysectomy (at Day 15) or GnRH antagonist treatment (starting from Day 11 of age) resulted in decreased ovarian weight at Day 19 of age that was associated with a reduced number of developing follicles and increased atresia of remaining follicles. In contrast, treatment with FSHctp (a long-acting FSH agonist) in intact (Days 5-19 of age), hypophysectomized (Days 15-19), or GnRH antagonist-treated (Days 11-19) animals resulted in increased ovarian weight and follicle development as determined histologically and by inhibin-alpha expression. A dose-dependent stimulatory effect of hCG on ovarian weight was seen when animals were cotreated with FSHctp and the GnRH antagonist. At low doses of hCG, augmentation of antral follicle formation occurred, whereas higher doses of hCG led to morphological signs of luteinization. These findings demonstrate the important role of endogenous gonadotropins in preantral follicle development and indicate that preantral follicles are highly responsive to exogenous gonadotropins.

Co-expression of defective luteinizing hormone receptor fragments partially reconstitutes ligand-induced signal generation

Gonadotropin receptors are unique members of the seven-transmembrane (TM), G protein-coupled receptor family with a large extracellular (EC) sequence forming the high-affinity ligand binding domain. In a patient with Leydig cell hypoplasia, we identified a mutant LH receptor that is truncated at TM5. This protein retains limited ligand binding ability but cannot mediate cAMP responses. To study interactions between receptor fragments defective in either ligand binding or signal transduction, we co-expressed this truncated receptor together with a chimeric receptor containing the EC region of the FSH receptor and the TM region of the LH receptor. Although the chimeric receptor could not respond to human chorionic gonadotropin in producing cAMP, co-expression with the truncated LH receptor allowed partial restoration of ligand signaling through intermolecular interactions. In addition, co-expression of the same truncated LH receptor with an N-terminally truncated LH receptor that lacked the EC ligand binding domain also partially restored ligand signaling. Further shortening of the TM region in the mutant receptor found in the patient indicated that the EC domain and TM1 were sufficient for interactions with the N terminally truncated receptor. In contrast, co-expression of the N terminally truncated receptor together with cell-associated or soluble EC region of the LH receptor did not allow ligand signaling. Unlike thrombin receptors, co-expression of the anchored EC region of the LH receptor together with the N-terminally truncated receptor did not allow ligand signaling despite moderate levels of human chorionic gonadotropin binding in transfected cells. These studies demonstrate that the co-expression of binding (+)/signaling (-) and binding (-)/signaling (+) receptor fragments partially restores ligand-induced signal generation and indicate the importance of TM1 of the LH receptor in the proper orientation of the EC ligand binding domain.