The gene encoding the beta-subunit of rat luteinizing hormone. Analysis of gene structure and evolution of nucleotide sequence

Molecular Characterization and Expression Profiles of the Ovine LHβ Gene and Its Association with Litter Size in Chinese Indigenous Small-Tailed Han Sheep

Simple Summary

Litter size is one of the most important reproductive traits in sheep, and the luteinizing hormone beta polypeptide (LHβ) plays an important role in mammalian follicular development. In this study, we cloned and analyzed the cDNA sequence of the ovine LHβ gene, and the expression patterns of LHβ were determined. Furthermore, the synonymous mutation g.727C > T detected in the LHβ gene was confirmed to be significantly associated with litter size (p < 0.01). These findings support LHβ g.727C > T as a genetic marker for litter size in sheep.

Abstract

The luteinizing hormone beta polypeptide (LHβ) is a glycoprotein hormone secreted by basophilic granular cells of the adenohypophysis, and plays an important role in mammalian follicular development. In this study, we cloned and analyzed the cDNA sequence of the ovine LHβ gene. RT-qPCR analysis showed that ovine LHβ was widely expressed in tissues, with significantly higher expression in the hypophysis than that in other tissues (heart, liver, spleen, lung, kidney, rumen, duodenum, muscle, fat, hypothalamus, and sex glands) (p < 0.01). Hypophyseal expression of LHβ mRNA in lamb increased with age and reached a peak at 70 days, although a slight decrease was observed at 84 days of age. In addition, the synonymous mutation g.727C > T detected in the LHβ gene was confirmed to be significantly associated with the litter size (p < 0.01). Ewes carrying the TT genotype produced more lambs than those carrying the TC and CC genotypes (0.42 and 0.39 per delivery, respectively; p < 0.05). Our results confirm the association of ovine LHβ with litter size in Small-Tailed Han Sheep and implicate LHβ as a candidate for improving reproductive traits in agricultural sheep breeding programs.

A novel two-promoter-one-gene system of the chorionic gonadotropin β gene enables tissue-specific expression

The New World monkey (NWM), Callithrix jacchus, a preferred model in medical research, displays an interesting endocrine regulation of reproduction: LH, the heterodimeric glycoprotein hormone, is functionally replaced by the chorionic gonadotropin (CG), a hormone indispensable for establishment of pregnancy in humans and normally expressed in the placenta. In the marmoset pituitary, the expression of the β-subunit (CGB) gene is regulated similar to human LH β-subunit, but its placental regulation is unknown. This study intended to decipher the underlying mechanism of tissue-specific expression of CGB in the marmoset placenta. We identified a new placental transcriptional start site, described a new, previously undiscovered exon, and define a novel placental core promoter in the marmoset CGB gene. This promoter contains a TATA box and binding sites for activating protein 2 and selective promoter factor 1, the latter acting synergistically by forming a regulation cassette. Differential first exon usage directed the tissue-specific expression. Methylation analyses revealed a tissue-specific pattern in the placental promoter indicating additional epigenetic regulation of gene expression. Our findings point toward a hitherto unknown evolutionary plasticity in the LH/CG hormonal system in NWM, which could be used as a model to study human CGB regulation in clinical pathologies.

PPARγ co-activator-1α co-activates steroidogenic factor 1 to stimulate the synthesis of luteinizing hormone and aldosterone

The orphan nuclear receptor SF-1 (steroidogenic factor 1) is highly expressed in the pituitary, gonad and adrenal glands and plays key roles at all levels of the hypothalamic-pituitary-steroidogenic tissue axis. In the present study, we show that PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator 1α] interacts with and co-activates SF-1 to induce LHβ (luteinizing hormone β) and αGSU (α-glycoprotein subunit) gene expression, subsequently leading to the increased secretion of LH in pituitary gonadotrope-derived αT3-1 cells. PGC-1α co-activation of LHβ expression requires an SF-1-binding element [GSE (gonadotrope-specific element)] mapped to the promoter region of LHβ. Mammalian two-hybrid and co-immunoprecipitation assays, as well as GST (glutathione transferase) pull-down experiments demonstrated that PGC-1α interacts with SF-1 in vivo and in vitro. Additionally, PGC-1α stimulates the expression of Cyp11b2 (aldosterone synthase gene), Cyp11b1 (steroid 11β-hydroxylase gene) and P450scc (cholesterol side-chain cleavage enzyme), and the synthesis of aldosterone in adrenal-cortex-derived Y-1 cells. Chromatin immunoprecipitation assays confirmed that endogenous PGC-1α co-localizes with SF-1 in the LHβ and Cyp11b2 promoter region. Knockdown of endogenous SF-1 by siRNA (small interfering RNA) abolished the PGC-1α induction of LHβ and Cyp11b2 gene expression in αT3-1 and Y-1 cells respectively. Finally, we demonstrated that PGC-1α induces SF-1 gene expression in both αT3-1 and Y-1 cells. Taken together, our findings reveal the potential role of PGC-1α and suggest that it may play important roles in steroidogenesis, gonad development and sex differentiation through SF-1.

Chorionic gonadotropin beta-subunit gene expression in the marmoset pituitary is controlled by steroidogenic factor 1, early growth response protein 1, and pituitary homeobox factor 1

In most mammals, the gonads are under the control of the pituitary gonadotropins LH and FSH. However, in the common marmoset monkey Callithrix jacchus, no LH is detectable in the pituitary but chorionic gonadotropin (CG) instead, normally produced in the placenta. This study investigated the mechanism of CGbeta subunit activation in the pituitary and why humans do not express CG in the pituitary. 5'-Rapid amplification of cDNA ends, EMSA, and promoter-driven luciferase assays performed with the gonadotropic LbetaT2 cells showed that marmoset monkey CGbeta is GnRH responsive and activated similar to human LHbeta by the transcription factors steroidogenic factor 1 (SF1), early growth response protein 1 (Egr1), and pituitary homeobox factor 1 (Pitx1) and displayed a transcriptional start site 7 bp upstream of exon 1. In contrast, the human CGbeta promoter displayed in the binding elements for pituitary homeobox factor 1 and early growth response protein 1 three consensus sequence mismatches, leading to very low activity that could be drastically increased by mutation to the consensus sequences. Vice versa, marmoset CGbeta promoter activity was reduced after introduction of the human CGbeta mismatches. An in vivo study in pregnant marmoset monkeys showed that during pregnancy, there is no significant decrease of pituitary CG production, contrasting human LH down-regulation. In conclusion, pituitary CG production is lacking in humans due to the absence of appropriate DNA-binding elements, which are present in marmosets, thereby enabling GnRH activation of expression. However, during pregnancy of marmosets, pituitary CG expression is not inhibited.

Molecular cloning and histological localization of LH-like substances in a bottlenose dolphin (Tursiops truncatus) placenta

All mammals exhibit pituitary-specific expression of LH and FSH, whereas placental expression of gonadotropins has been reported only in primates and equids. Some cetaceans, such as dolphins, have a long gestational period and a sexual cycle of about 27 days almost comparable with that of humans. Histologically, dolphins have an epitheliochorial placentae that resembles placentas of Perissodactyla including horses. In the present study, we cloned cDNAs encoding gonadotropins and observed their immunohistochemical localization in the placenta of bottlenose dolphin. The cDNAs obtained encoded 120 amino acids for the alpha-subunit (including 96 amino acids of mature proteins), and 141 amino acids for the beta-subunit (including 121 amino acids of mature proteins). The sequence of the alpha-subunit was similar to that in the pig (Artiodactyla) pituitary glycoprotein hormone [96.7% homology at amino acids (aa) level], and the sequence of the beta-subunit was similar to that of luteinizing hormone (LH) in the pig [94.3% homology at aa level] and white rhinoceros (Perissodactyla) [93.3% homology at aa level]. Of interest, dolphin LHbeta lacks carboxyl-terminal-peptides (CTP). This fact suggests that CTP are not essential for placental expression of gonadotropin in dolphins. Immunohistochemical observations employing anti-ovine LHbeta antibody revealed positive staining in the villositycal tissue. Our observations suggest placental expression of gonadotropin homologues in cetaceans and possible evolutionary conservation of placentae-derived hormonal control of ovarian functions during pregnancy.

The LHbeta gene of several mammals embeds a carboxyl-terminal peptide-like sequence revealing a critical role for mucin oligosaccharides in the evolution of lutropin to chorionic gonadotropin in the animal phyla

The expression of a previously untranslated carboxylterminal sequence is associated with the ancestral lutropin (LH) beta to the beta-subunit gene evolution of choriogonadotropins (CG). The peptide extension (denoted as CTP) is rich in mucin-type O-glycans and confers new hormonal properties on CG relative to the LH. Although the LHbeta gene is conserved among mammals and only a few frameshift mutations account for the extension, it is merely seen in primates and equids. Bioinformatics identified a CTP-like sequence that is encrypted in the LHbeta gene of several mammalian species but not in birds, amphibians, or fish. We then examined whether or not decoding of the cryptic CTP in the bovine LHbeta gene (boCTP) would be sufficient to generate the LHbeta species of a ruminant with properties typical to the CGbeta subunit. The mutated bovine LHbeta-boCTP subunit was expressed and N-glycosylated in transfected Chinese hamster ovary cells. However, unlike human (h) CGbeta CTP, the cryptic boCTP was devoid of mucin O-glycans. This deficiency was further confirmed when the boCTP domain was substituted for the natural CTP in the human CGbeta subunit. Moreover, when expressed in polarized Madin-Darby canine kidney cells, this hCGbeta-boCTP chimera was secreted basolaterally rather than from the apical compartment, which is the route of the wild type hCGbeta subunit, a sorting function attributed to the O-glycans attached to the CTP. This result shows that the cryptic peptide does not orientate CG to the apical face of the placenta, to the maternal circulation as seen in primates. The absence of this function, which distinguishes CG from LH, provides an explanation as to why the LHbeta to CGbeta evolution did not occur in ruminants. We propose that in primates and equids, further natural mutations in the progenitor LHbeta gene resulted in the efficient O-glycosylation of the CTP, thus favoring the retention of an elongated reading frame.

Acute regulation of translation initiation by gonadotropin-releasing hormone in the gonadotrope cell line LbetaT2

The hypothalamic neuropeptide hormone GnRH is the central regulator of reproductive function. GnRH stimulates the synthesis and release of the gonadotropins LH and FSH by the gonadotropes of the anterior pituitary through activation of the G-protein-coupled GnRH receptor. In this study, we investigated the role of translational control of hormone synthesis by the GnRH receptor in the novel gonadotrope cell line LbetaT2. Using immunohistochemical and RIA studies with this model, we show that acute GnRH-induced synthesis and secretion of LH are dependent upon new protein synthesis but not new mRNA synthesis. We examined the response to GnRH and found that activation of cap-dependent translation occurs within 4 h. LHbeta promoter activity was also examined, and we found no increases in LHbeta promoter activity after 6 h of GnRH stimulation. Additionally, we show that increased phosphorylation of translation initiation proteins, 4E-binding protein 1, eukaryotic initiation factor 4E, and eukaryotic initiation factor 4G, occur in a dose- and time-dependent manner in response to GnRH stimulation. Quantitative luminescent image analysis of Western blots shows that 10 nm GnRH is sufficient to cause a maximal increase in factor phosphorylation, and maximal responses occur within 30 min of stimulation. Further, we demonstrate that the MAPK kinase inhibitor, PD 98059, abolishes the GnRH-mediated stimulation of a cap-dependent translation reporter. More specifically, we demonstrate that PD 98059 abolishes the GnRH-mediated stimulation of a downstream target of the ERK pathway, MAPK-interacting kinase. Based on these findings, we conclude that acute GnRH stimulation of LbetaT2 cells increases translation initiation through ERK signaling. This may contribute to the acute increases in LHbeta subunit production.

Cloning of cDNAs encoding the three pituitary glycoprotein hormone beta subunit precursor molecules in the Japanese toad, Bufo japonicus

Complementary DNAs encoding precursor molecules of the beta subunits of three pituitary glycoprotein hormones (LH, FSH, and TSH) of the Japanese toad (Bufo japonicus) were isolated and sequenced. Unexpectedly large numbers of single nucleotide substitutions were found in all three beta subunit cDNAs. The eight isolated LH beta precursor cDNA clones were classified into six forms of nucleotide sequence, with four nucleotide substitutions each in the apoprotein coding region and in the 3' untranslated region (UTR). In the deduced amino acid sequence, the LH beta subunit showed two forms with a single amino acid substitution. The seven isolated FSH beta subunit cDNAs were classified into two forms, which differed from each other at 11 positions in the 3' UTR. The six isolated TSH beta subunit clones were classified into four forms with 2 and 5 nucleotide substitutions in the signal peptide and apoprotein coding regions, respectively. However, all the substitutions in the apoprotein coding region were silent. The substitution in the signal peptide coding region could produce three forms of signal peptide. Amino acid sequence comparison revealed that the toad LH beta subunit is more similar to the fish GTH II beta subunit than to mammalian and avian LH beta subunits. We found that the toad LH beta subunit molecule is a partial chimera of LH and FSH; amino acid residues located in 36th to 42nd and 96th to 99th are identical or similar to those of not LH- but FSH-beta subunit in mammalian, whereas it is more similar to LH- than FSH-beta subunit in total. We also found that the toad FSH beta subunit is more similar to the fish GTH II beta subunit than to the fish GTH I beta subunit and that the toad TSH beta subunit is more similar to tetrapod TSH beta subunits than to fish TSH beta subunits.

Species differences in GnRH activation of the LHbeta promoter: role of Egr1 and Sp1

Activation of the luteinizing hormone beta (LHbeta) promoter by gonadotropin-releasing hormone (GnRH) via the transcription factor early growth response protein-1 (Egr1) has been well characterized. To determine the mechanisms affecting Egr1 regulation of LHbeta, we analyzed five different species of LHbeta promoters (equine, mouse, rat, bovine and human). Electrophoretic mobility shift assays (EMSAs) identified multiple transcription factors binding to the Egr regions on the LHbeta promoter. Species-specific differences existed in the binding affinity for Sp1, Sp3, steroidogenic factor-1 (SF-1) and Egr1. Upon mutation of the Egr elements, competition for the binding of all zinc finger proteins was lost, suggesting that the Sp proteins compete for binding to the same site that Egr1 occupies. In addition, the promoters from species that had the highest affinity for Sp1 also had the lowest activation by Egr1 and GnRH. Thus we hypothesize that Sp1 competes for Egr1 binding to the Egr elements on the LHbeta promoter and thus inhibits the ability of GnRH and Egr1 to activate the LHbeta promoter.

Chorionic gonadotropin has a recent origin within primates and an evolutionary history of selection

Chorionic gonadotropin (CG) is a critical signal in establishing pregnancy in humans and some other primates, but this placentally expressed hormone has not been found in other mammalian orders. The gene for one of its two subunits (CG beta subunit [CGbeta]) arose by duplication from the luteinizing hormone beta subunit gene (LHbeta), present in all mammals tested. In this study, 14 primate and related mammalian species were examined by Southern blotting and DNA sequencing to determine where in mammalian phylogeny the CGbeta gene originated. Bats (order Chiroptera), flying lemur (order Dermoptera), strepsirrhine primates, and tarsiers do not have a CGbeta gene, although they possess one copy of the LHbeta gene. The CGbeta gene first arose in the common ancestor of the anthropoid primates (New World monkeys, Old World monkeys, apes, and humans), after the anthropoids diverged from tarsiers. At least two subsequent duplication events occurred in the catarrhine primates, all of which possess multiple CGbeta copies. The LHbeta-CGbeta family of genes has undergone frequent gene conversion among the catarrhines, as well as periods of strong positive selection in the New World monkeys (platyrrhines). In addition, newly generated DNA sequences from the promoter of the CG alpha subunit gene indicate that platyrrhine monkeys use a different mechanism of alpha gene expression control than that found in catarrhines.

Molecular characterization of LH-beta and FSH-beta subunits and their regulation by estrogen in the goldfish pituitary

The gonadal steroids, along with gonadotropin-releasing hormone (GnRH) are involved in the regulation of gonadotropin (GtH) production in vertebrates. Goldfish have an annual reproductive cycle, characterized by seasonal fluctuations in the circulating levels of the reproductive hormones, including 17beta-estradiol (E2). The purpose of the present study was to investigate the effect of E2 on basal and GnRH-induced GtH subunit (alpha, FSH-beta and LH-beta) gene expression in the goldfish pituitary. Northern analyses were performed to determine changes in steady state mRNA levels. Both in vivo and in vitro treatment with E2 resulted in a stimulation of all three GtH subunit mRNA levels, although a higher concentration was required for the stimulation of the FSH-beta subunit mRNA levels. The effect of E2 on GnRH-induced GtH mRNA level was also investigated and demonstrated that E2 influences the GnRH-induced GtH subunit mRNA levels in a seasonally dependent manner. Overall, the present results indicate that E2 stimulates GtH subunit mRNA levels directly at the level of the pituitary in a seasonally dependent manner in goldfish.

Regulation of gonadotropin subunit gene transcription by gonadotropin-releasing hormone: measurement of primary transcript ribonucleic acids by quantitative reverse transcription-polymerase chain reaction assays

GnRH regulates the synthesis and secretion of the pituitary gonadotropins LH and FSH. One of the actions of GnRH on the gonadotropin subunit genes (alpha, LHbeta, and FSHbeta) is the regulation of transcription [messenger RNA (mRNA) synthesis]. Gonadotropin subunit transcription rates increase after gonadectomy and following exogenous GnRH pulses. However, prior studies of subunit mRNA synthesis were limited by the available methodology that did not allow simultaneous measurement of gene transcription and mature mRNA concentrations. The purpose of the current studies was to: 1) develop a reliable and sensitive method for assessing transcription rates by measuring gonadotropin subunit primary transcript RNAs (PT, RNA before intron splicing); 2) investigate the PT responses to GnRH following castration or exogenous GnRH pulses; 3) characterize the half-disappearance time for the three PT species after GnRH withdrawal; and 4) correlate changes in PT concentration with steady-state gonadotropin subunit mRNA levels measured in the same pituitary RNA samples. Using oligonucleotide primers that flanked intron-exon boundaries, quantitative RT-PCR assays for each subunit PT species were developed. These assays require only ng amounts of RNA to measure each gonadotropin subunit PT and allow us to measure both PTs and steady-state mRNAs in a single pituitary RNA sample. Primary transcript concentrations in intact male rats showed a relative abundance of alpha > LHbeta congruent with FSHbeta, similar to the relationship found previously for mRNA levels. Additionally, each PT species was only 1-2% as abundant as the corresponding mRNA. One week after castration, gonadotropin subunit PT levels were increased (alpha: 3-fold, LHbeta: 6-fold, and FSHbeta: 3-fold) in a pattern similar to subunit mRNAs. Administration of GnRH antagonist to 7-day castrate male rats resulted in a rapid decline in PT concentrations with a half-disappearance time of 2.7 h for LHbeta and 0.8 h for FSHbeta, significantly faster than earlier measurements of the half-disappearance time for mature mRNA. Finally, in a GnRH-deficient male rat model, LHbeta and FSHbeta PT concentrations increased 4- to 6-fold 5 min after a GnRH pulse and then declined toward levels seen in control animals. These data indicate that the effects of GnRH on subunit gene transcription are an important determinant of gonadotropin regulation. The appearance and disappearance of PT RNA occurs more rapidly than changes in mature mRNA. Additionally, concentrations are elevated in long term castrates, and following an exogenous GnRH pulse the transcriptional burst is rapid and brief.

Salmon gonadotropin IIbeta subunit promoter contains multiple DNA elements responsible for stimulation by gonadotropin-releasing hormone through protein kinase C-dependent and -independent pathways

Gonadotropin-releasing hormone (GnRH) stimulates gonadotropin (GTH) production by activating GTH subunit gene transcription. In salmonid fish, the expression of the beta subunit gene of GTH II (sGTH IIbeta) is stimulated by GnRH at the final stages of reproduction. DNA elements required for the GnRH stimulation were examined by analyzing sGTH IIbeta promoter activity by transfection studies in a gonadotrope-derived cell line, alphaT3-1. A GnRH analog (GnRHa) specifically stimulated the sGTH IIbeta promoter (3358 bp) expression 3.6-fold, while phorbol myristate acid (PMA) stimulated it 6.2-9-fold. Analysis of a series of 5'-deletion mutants has revealed that a proximal region (-258 to -199) was important in GnRHa stimulation through protein kinase C (PKC)-independent signal transduction pathways, because an internal deletion mutant (delta(246 - 217)/3358) showed a significant decrease in the level of GnRHa stimulation, but showed no change in stimulation by PMA. A large upstream region (-3358 to -1260) showed an enhancing activity of the GnRHa stimulation, and a far upstream 530 bp segment in this region (-3358 to -2829) may be responsible for this activity. The present results suggest that sGTH IIbeta gene may be controlled by GnRH through multiple DNA elements including those responsive to PKC-dependent and -independent signal transduction pathways.

Isolation and characterization of the goldfish thyrotropin beta subunit gene including the 5'-flanking region

The complete gene encoding the beta subunit of thyrotropin (thyroid-stimulating hormone, TSH) was isolated from a goldfish genomic library. The goldfish TSHbeta subunit gene, which is approximately 2.0 kilobase pairs (kb) in length, consisted of three exons and two introns. The first intron was much longer (0.89 kb) than the second intron (0.3 kb) as are TSHbeta genes in mammalian species. On the basis of the location of the first intron, the goldfish TSHbeta gene belongs to the mammalian TSHbeta/FSHbeta gene group, which is distinct from the LHbeta group. Inspection of the 5'-flanking and exon 1 regions of the goldfish TSHbeta gene (1.2 kb) revealed the presence of several putative cis-acting elements, including the negative triiodothyronine (T(3))-responsive element (nTRE), Pit-1 element, and GATA-2 element. Comparison of the goldfish sequence with mammalian TSHbeta promoter sequences showed an identical region, nTRE, in the first exon-intron junction region. An in vitro study using dispersed goldfish pituitary cells showed that T(3) treatment (20 ng/ml) suppressed the TSHbeta mRNA level in the cells. These data indicate that (1) the basic structure of TSHbeta genes is highly conserved in vertebrates and that (2) T(3) acts directly on the pituitary and inhibits TSHbeta gene expression in goldfish, probably via the nTRE in the TSHbeta gene.

The equine luteinizing hormone beta-subunit promoter contains two functional steroidogenic factor-1 response elements

The requirements for basal expression of the LH beta-subunit promoter in pituitary gonadotropes are largely unknown. We have used the equine (e) LHbeta subunit promoter as a model to unravel the combinatorial code required for gonadotrope expression. Through the use of 5'-deletion mutagenesis, a region between -185 and -100 of the eLHbeta promoter was shown to play a critical role in maintaining basal promoter activity in alphaT3-1 and LbetaT2 cells. This region encompasses the steroidogenic factor-1 (SF-1) binding site that has been reported to have a functional role in expression of the LHbeta promoter in other species. We have also identified an additional SF-1 site at -55 to -48. Binding of SF-1 to both sites was confirmed by electrophoretic mobility shift assays. Mutations within these sites, either individually or in combination, did not attenuate basal activity of the eLHbeta promoter in alphaT3-1 cells, but did diminish promoter activity in LbetaT2 cells. Interestingly, cotransfection with an expression vector encoding SF-1 induced eLHbeta promoter activity, and this induction was abrogated by mutations within the SF-1 sites in alphaT3-1 cells. Block replacement mutagenesis was performed on the -185/-100 region of the eLHbeta promoter to identify DNA response elements responsible for maintaining basal promoter activity. From this analysis, two regions emerged as being important: a distal 31-bp segment (-181 to -150) and an element located immediately 3' to the distal SF-1 site (-119 to -106). It is hypothesized that these two regions as well as the SF-1 sites represent regulatory elements that contribute to a combinatorial code involved in targeting expression of the eLHbeta promoter to gonadotropes.

Steroidogenic factor-1 interacts with a gonadotrope-specific element within the first exon of the human gonadotropin-releasing hormone receptor gene to mediate gonadotrope-specific expression

GnRH plays a pivotal role in regulating human reproductive functions. This hypothalamic peptide interacts with its receptor (GnRHR) on the pituitary gonadotropes to trigger the secretion of gonadotropins, which, in turn, regulates the release of sex steroids from the gonads. In light of the importance of GnRHR, the molecular mechanisms underlying the transcriptional regulation of the human GnRHR (hGnRHR) gene become a key issue in understanding human reproduction. In this report, the possible involvement of steriodogenic factor-1 (SF-1) as a key cell-specific regulator for hGnRHR gene expression was examined. By the transient luciferase reporter gene assays, the wild-type promoter, containing 2.3 kb ofthe hGnRHR gene 5'-flanking region relative to the ATG codon, was able to drive a 3.6 +/- 0.2-fold (P < 0.05) increase in luciferase activity in the mouse alphaT3-1 gonadotropes. Subsequent deletion analysis indicated that the most proximal 173 bp within the first exon of the gene, although not a promoter itself, contains a critical regulatory element(s) essential for the basal expression of the hGnRHR gene. The functional roles of the putative gonadotrope-specific elements (GSE; consensus 5'-CTG(A)/(T)CCTTG-3') residing at positions -5, -134, and -396 were studied by site-directed mutagenesis, and it was found that only the mutation at position -134 significantly reduced the promoter activity (80% reduction; P < 0.05). The attenuation effect of this GSE mutant was cell specific, as it was restricted to alphaT3-1 cells, but not to COS-7 and human ovarian adenocarcinoma (SKOV-3) cells. Competitive mobility shift assays using either alphaT3-1 nuclear extract or recombinant SF-1 protein clearly indicated that SF-1 is able to interact specifically with this GSE element positioned at -134. Using a SF-1 antibody that completely abrogated complex formation in the gel shift assays, the involvement of endogenous nuclear SF-1 was further evidenced. By competitive gel shift assays using oligoprimers with 2-bp scanning mutations, the sequences essential for the interaction with SF-1 were identified (5'-TTG(A)/(T)CCCTG-3', underlined sequences were important). To study the in vivo function of SF-1, vector directing expression of sense or antisense SF-1 messenger RNA (mRNA) was cotransfected with the hGnRHR promoter-luciferase construct into alphaT3-1, SKOV-3, and COS-7 cells. Overexpression of the SF-1 mRNA was able to enhance promoter activities in all of the cells tested. On the contrary, expression of the antisense SF-1 mRNA reduced the hGnRHR promoter activity only in alphaT3-1 cells, not in COS-7 or SKOV-3 cells. In summary, the data reported here provide conclusive evidence that SF-1 interacts with the GSE motif at position -134 within the first exon of the hGnRHR gene to mediate its cell-specific expression.

Early growth response protein 1 binds to the luteinizing hormone-beta promoter and mediates gonadotropin-releasing hormone-stimulated gene expression

The hypothalamic neuropeptide, GnRH, regulates the synthesis and secretion of LH from pituitary gonadotropes. Furthermore, it has been shown that the LH beta-subunit gene is regulated by the transcription factors steroidogenic factor-1 (SF-1) and early growth response protein 1 (Egr1) in vitro and in vivo. The present study investigated the roles played by Egr1 and SF-1 in regulating activity of the equine LH beta-subunit promoter in the gonadotrope cell line, alpha T3-1, and the importance of these factors and cis-acting elements in regulation of the promoter by GnRH. All four members of the Egr family were found to induce activity of the equine promoter. The region responsible for induction by Egr was localized to the proximal 185 bp of the promoter, which contained two Egr response elements. Coexpression of Egr1 and SF-1 led to a synergistic activation of the equine (e)LH beta promoter. Mutation of any of the Egr or SF-1 response elements attenuated this synergism. Endogenous expression of Egr1 in alpha T3-1 cells was not detectable under basal conditions, but was rapidly induced after GnRH stimulation. Reexamination of the promoter constructs harboring mutant Egr or SF-1 sites indicated that these sites were required for GnRH induction. In fact, mutation of both Egr sites within the eLH beta promoter completely attenuated its induction by GnRH. Thus, GnRH induces expression of Egr1, which subsequently activates the eLH beta promoter. Finally, GnRH not only induced expression of Egr1, but also its corepressor, NGFI-A (Egr1) binding protein (Nab1), which can repress Egr1- induced transcription of the eLH beta promoter.

Egr-1 is a downstream effector of GnRH and synergizes by direct interaction with Ptx1 and SF-1 to enhance luteinizing hormone beta gene transcription

Pituitary gonadotropins are critical regulators of gonadal development and function. Expression and secretion of the mature hormones are regulated by gonadotropin-releasing hormone (GnRH), which is itself secreted from the hypothalamus. GnRH stimulation of gonadotropin expression and secretion occurs through the G-protein-linked phospholipase C/inositol triphosphate intracellular signaling pathway, which ultimately leads to protein kinase C (PKC) activation and increased intracellular calcium levels. Transcription factors mediating the effects of GnRH-induced signals on transcription of gonadotropin genes have not yet been identified. Recent studies have identified key factors involved in luteinizing hormone beta (LHbeta) gonadotropin gene transcription: the nuclear receptor SF-1, the bicoid-related homeoprotein Ptx1 (Pitx1), and the immediate-early Egr-1 gene. We now show that GnRH is a potent stimulator of Egr-1, but not Ptx1 or SF-1, expression. Further, Egr-1 activation of the LHbeta promoter is specifically enhanced by PKC, in agreement with a role for Egr-1 in mediating a GnRH effect on transcription. Egr-1 interacts directly with Ptx1 and with SF-1, leading to an enhancement of Ptx1- and SF-1-induced LHbeta transcription. Thus, Egr-1 is a likely transcriptional mediator of GnRH-induced signals for activation of the LHbeta gene.

The protein kinase C system acts through the early growth response protein 1 to increase LHbeta gene expression in synergy with steroidogenic factor-1

Expression of the LHbeta gene has been shown to be modulated by both the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1, Egr-1. It is also well known that LHbeta mRNA levels are increased after hormonal activation of the protein kinase C (PKC) signaling system, for example by GnRH; however, the mechanisms by which the PKC system exerts this effect has not been fully characterized. By transient transfection of the GH3 cell line, we demonstrate that activation of the PKC system with the phorbol ester, phorbol 12-myristate 13-acetate (PMA), increases activity of region -207/+5 of the rat LHbeta gene promoter (approximately 2-fold) and markedly augments SF-1-induced stimulation (95-fold in the presence of both factors vs. 13-fold for SF-1 alone). Mutation of the two previously identified Egr-1 sites not only prevents Egr-1 effects on the LHbeta gene promoter, but also eliminates the synergistic response to PMA and SF-1 together, findings that were confirmed in a longer construct spanning region -797/+5. In the gonadotrope-derived cell line, alphaT3-1, these mutations eliminate the GnRH responsiveness of the -207/+5 LHbeta promoter construct. We next show that PMA treatment (GH3 and alphaT3-1 cells) or GnRH treatment (alphaT3-1 cells) induces expression of Egr-1, as detected by Egr-1 interaction with Egr-1 DNA-binding sites in the rat LHbeta gene promoter sequence. Furthermore, we demonstrate that PMA increases steady-state Egr-1 mRNA levels via increased Egr-1 transcription. We conclude that PMA-induced stimulation of LHbeta gene expression is achieved, at least in part, by induction of Egr-1 expression.

Structural and expression analyses of gonadotropin Ibeta subunit genes in goldfish (Carassius auratus)

Gonadotropin (GTH) is a pituitary glycoprotein hormone that regulates gonadal development in vertebrates. In teleosts, it is considered that two types of GTH, GTH I (follicle-stimulating hormone-like GTH) and GTH II (luteinizing hormone-like GTH), are produced in the pituitary, and their molecules are comprised of common alpha and distinct beta subunits. In this study, we describe the complete structure and 5'-flanking regulatory region of two distinct genes encoding GTH Ibeta in goldfish, Carassius auratus. The two goldfish GTH Ibeta genes, gfGTHIbeta-1 and gfGTHIbeta-2, span 1719 and 1545 base pairs (bp) nucleotides, respectively, and there is a high sequence identity (92.1%) between the coding regions. Both genes consist of three exons separated by two introns as in mammalian FSH beta genes. The locations of the first intron and second intron showed a well-conserved pattern similar to those of mammalian FSH beta genes. Inspection of the 5'-flanking region of the gfGTHIbeta-1 and gfGTHIbeta-2 (approximately 1.4 and 1.1kb, respectively) revealed the presence of several putative cis-acting elements, including the gonadotrope-specific element, gonadotropin-releasing hormone responsive element, and half steroid hormone responsive elements. Interestingly, some of their elements were located contiguously between -187 and -124bp upstream from a TATAA sequence. Reverse transcription polymerase chain reaction confirmed that these two genes are expressed in the pituitary of individual fish. These results, taken together, demonstrate that there are at least two functional genes encoding GTH Ibeta, probably due to the tetraploidy of goldfish. The unique locations of the cis-acting elements in the GTH Ibeta genes suggest they may be involved in the expression of the goldfish GTH Ibeta gene.

Steroidogenic factor-1 and early growth response protein 1 act through two composite DNA binding sites to regulate luteinizing hormone beta-subunit gene expression

Recent in vivo and in vitro studies have implicated the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1 (Egr-1) in the transcriptional regulation of the luteinizing hormone beta-subunit (LHbeta) gene. We have previously demonstrated the ability of SF-1 to bind to and transactivate the rat LHbeta gene promoter acting at a consensus gonadotrope-specific element (GSE) located at position -127. We have now identified a second functional GSE site at position -59. In addition, based on electrophoretic mobility shift assay, in vitro translated Egr-1 is shown to bind to two putative Egr-1 binding sites (positions -112 and -50), which appear to be paired with the identified GSE sites. By transient transfection assay in pituitary-derived GH3 cells, it was seen that Egr-1 increases promoter activity of region -207/+5 of the rat LHbeta gene promoter through action at both Egr-1 sites. Furthermore, LHbeta gene promoter activity is markedly augmented in the presence of both factors together relative to activity in the presence of SF-1 or Egr-1 alone (150-fold versus 14-fold and 12-fold, respectively). These data define two composite SF-1-Egr-1 response-elements in the proximal LHbeta gene promoter and suggest that SF-1 and Egr-1 act synergistically to increase expression of the LHbeta gene in the gonadotrope.

Presence of distinct cis-acting elements on gonadotropin gene promoters in diverse species dictates the selective recruitment of different transcription factors by steroidogenic factor-1

The nuclear receptor steroidogenic factor-1 (SF-1) regulates the cell-specific expression of the pituitary gonadotropin subunit genes. Several potential DNA-binding sites for SF-1, estrogen receptor (ER) and the immediate-early transcription factor NGFI-A are found in LHbeta genes from many species. In this study, we have examined the action and interaction of these transcription factors on LHbeta gene promoters from two representative vertebrate species, i.e. rat and salmon. Cotransfection studies in COS-1 cells have shown that the action of SF-1 on salmon gonadotropin IIbeta (sGTHIIbeta) gene promoter was dramatically enhanced when combined with ER. The rat LHbeta promoter was activated by SF-I or ER individually, but these two factors, however, were unable to act in synergism on this promoter. In contrast, NGFI-A, specifically in cooperation with SF-1, transactivated the rat LHbeta gene expression but was ineffective on the sGTHIIbeta gene. Gel shift experiments showed that this lack of activation was due to the low affinity of the salmon NGFI-A-responsive element for its binding protein. In conclusion, our studies demonstrate that differential recruitment of distinct transcription factors by SF-1 might be a common mechanism to activate the cell-specific gonadotropin gene expression in different species.

Characterization and phylogenetic significance of rhinoceros luteinizing hormone beta (LHbeta) subunit messenger RNA structure, complementary DNA sequence and gene copy number

The luteinizing hormone (LH) beta subunit gene is expressed in the pituitary glands of all mammals, whereas the closely related chorionic gonadotropin (CG) beta subunit genes have been identified only in primates and equids, and are expressed in placenta. In the case of horses, there is a single-copy equine (e) luteinizing hormone/chorionic gonadotropin hormone beta subunit gene (eLH/CGbeta) that (1) is expressed in both pituitary gland and placenta, (2) encodes a characteristic carboxyl terminal peptide (CTP) extension, and (3) transcribes an atypically elongated 5'-untranslated region (UTR) in both pituitary and placenta. However, it is not known whether similar expression patterns and gene locus characteristics may be exhibited by other members of the order Perissodactyla (equid, rhinoceros and tapir species). To begin to investigate these possibilities, we undertook analysis of the rhinoceros (rn or rhino) LH/(CG?)beta gene locus and the rnLHbeta cDNA. Total RNA isolated from the pituitary gland of a female white rhino was used as template for amplifying rnLHbeta cDNA by reverse transcription-polymerase chain reaction. Following cloning of the amplified cDNA, nucleotide (nt) and deduced amino acid sequences were determined. The first in-frame stop codon occurred at codon position +122, suggesting that the rnLHbeta subunit does not contain a CTP. To assess gene copy number, Southern blot analysis of Indian rhino genomic DNA was performed. The resulting simple hybridization pattern indicated that, as in the horse and donkey, there is a single-copy gene at the rnLH/(CG?)beta gene locus. Primer extension mapping of the pituitary transcriptional start site of the rnLHbeta subunit gene revealed an 8 nt 5'-UTR which is similar to that reported for the majority of mammalian LHbeta transcripts. Northern analysis was consistent with the transcriptional start site findings. We postulate from these data that rhinos diverged from equids prior to the occurrence of the mutations causing CTP expression and adoption of a non-consensus 5'-UTR/proximal promoter region. However, these findings do not rule out the possibility of expression of a placental CGbeta subunit lacking a CTP in rhinos.

Mapping and expression of southern bean mosaic virus genomic and subgenomic RNAs

The coat protein of the cowpea strain of southern bean mosaic sobemovirus (SBMV-C) is translated from a subgenomic RNA (sgRNA) that is synthesized in the virus-infected cell. Like the SBMV-C genomic RNA, the sgRNA has a viral protein (VPg) covalently bound to its 5' end. The mechanism(s) by which ribosomes initiate translation on the SBMV-C RNAs is not known. To begin to characterize the translation of the sgRNA it was first necessary to precisely map its 5' end. Primer extension was used to identify SBMV-C nucleotide (nt) 3241 as the transcription start site. As a control, the 5' end of the genomic RNA was also mapped. Surprisingly, the 5' terminal nt of this RNA was identified as SBMV-C nt 2. The primary structure of the 5' ends of these two RNAs is therefore expected to be VPg-ACAAAA. Precise mapping of the 5' end of the sgRNA of the bean strain of SBMV (SBMV-B) demonstrated that it has these same elements. Translation of coat protein from the SBMV-C sgRNA and p21 from the SBMV-C genomic RNA was compared using a cell-free system. The results of these experiments were consistent with translation of these proteins by a 5' end-dependent scanning mechanism rather than by internal ribosome binding.

Luteinizing hormone deficiency and female infertility in mice lacking the transcription factor NGFI-A (Egr-1)

The immediate-early transcription factor NGFI-A (also called Egr-1, zif/268, or Krox-24) is thought to couple extracellular signals to changes in gene expression. Although activins and inhibins regulate follicle-stimulating hormone (FSH) synthesis, no factor has been identified that exclusively regulates luteinizing hormone (LH) synthesis. An analysis of NGFI-A-deficient mice derived from embryonic stem cells demonstrated female infertility that was secondary to LH-beta deficiency. Ovariectomy led to increased amounts of FSH-beta but not LH-beta messenger RNA, which suggested a pituitary defect. A conserved, canonical NGFI-A site in the LH-beta promoter was required for synergistic activation by NGFI-A and steroidogenic factor-1 (SF-1). NGFI-A apparently influences female reproductive capacity through its regulation of LH-beta transcription.

A steroidogenic factor-1 binding site is required for activity of the luteinizing hormone beta subunit promoter in gonadotropes of transgenic mice

Analysis of luteinizing hormone (LH) beta subunit promoters from a broad range of species including teleosts and humans revealed strict conservation of a sequence homologous to the steroidogenic factor-1 (SF-1) regulatory element of cytochrome P-450 steroid hydroxylase genes. Interaction between SF-1 and this putative response element in the bovine LH beta promoter was confirmed by electrophoretic mobility shift assays. Furthermore, cotransfection of alpha T3-1 cells with an expression vector encoding SF-1 induced binding site-dependent transcription from the bovine LH beta promoter. Physiological significance of the LH beta SF-1 consensus sequence was established using transgenic mice containing either the wild type bovine promoter or a promoter with a site-specific mutation of this site. Mutation of the SF-1 binding site nearly eliminated promoter activity, and the mutant transgene remained inactive following induction of gonadotropin-releasing hormone accomplished by castrating male and female mice. Thus, increases of gonadotropin-releasing hormone within a physiological range did not compensate for the loss of the SF-1 binding site. Together, these findings indicate that the SF-1 binding site is a key regulator of LH beta promoter activity in vivo and implicate SF-1 as at least one of the transcription factors that acts through this site.

Stimulation of luteinizing hormone beta gene promoter activity by the orphan nuclear receptor, steroidogenic factor-1

The orphan nuclear receptor, steroidogenic factor-1 (SF-1), is expressed in the pituitary and in the gonadotrope precursor cell line, alphaT3-1, where it is believed to enhance expression of the common gonadotropin alpha-subunit gene through transactivation of the gonadotrope-specific element (GSE). Sequence analysis of the rat luteinizing hormone beta-subunit (LH beta) gene promoter revealed the presence of a consensus GSE at -127 to -119 (TGACCTTGT). We have demonstrated the ability of SF-1 to bind specifically to this putative GSE sequence by electrophoretic mobility shift assay, utilizing both alphaT3-1 nuclear extracts and in vitro translated SF-1. In addition, mutation of the putative LHbeta-GSE (TGAAATTGT) eliminated specific DNA binding. To examine the ability of SF-1 to enhance LHbeta promoter activity, CV-1 cells, which lack endogenous SF-1, were cotransfected with an SF-1-containing expression vector and an LHbeta-luciferase reporter construct. When cotransfected with -209/+5 of the LHbeta promoter, SF-1 increased luciferase activity by 56-fold. SF-1 responsiveness was markedly diminished with loss of the putative GSE region in deletion constructs and in the presence of a two base pair mutation, analogous to the mutation which eliminated DNA binding. Finally, the LHbeta-GSE was able to confer SF-1 responsiveness on a heterologous minimal growth hormone promoter, GH50 (57-fold). We conclude that SF-1 both binds to and transactivates the rat LHbeta promoter. These data suggest that SF-1 may participate in the expression of the LHbeta gene by the gonadotrope.

Cloning of the mouse gonadotropin beta-subunit-encoding genes, II. Structure of the luteinizing hormone beta-subunit-encoding genes

A genomic clone encoding the mouse luteinizing hormone (LH) beta-subunit was isolated. The nucleotide and the deduced amino-acid sequences show high identity to the rat, bovine and human homologues. This confirms an important role of LH, together with follicle-stimulating hormone (FSH), in regulating several aspects of reproduction.

The groove between the alpha- and beta-subunits of hormones with lutropin (LH) activity appears to contact the LH receptor, and its conformation is changed during hormone binding

Gonadotropins are heterodimeric glycoprotein hormones that control vertebrate fertility through their actions on gonadal lutropin (luteinizing hormone, LH) and follitropin (follicle-stimulating hormone, FSH) receptors. The beta-subunits of these hormones control receptor binding specificity; however, the region of the beta-subunit that contacts the receptor has not been identified. By a process of elimination we show this contact to be the portions of beta-subunit loops one and three found in a hormone groove created by the juxtaposition of the alpha- and beta-subunits. Most other regions of the beta-subunit can be recognized by antibodies that bind to human chorionic hormone (hCG)-receptor complexes or replaced without disrupting hormone function. Using a series of bovine LH/hCG and human FSH/hCG beta-subunit chimeras we identified key hCG beta-subunit residues in the epitopes of two antibodies that bind to hCG-receptor complexes. These epitopes include the surfaces of beta-subunit loops one and three near residue 74 on the outside of the hormone groove and parts of the C-terminal end of the "seat belt" that holds the two subunits together. The antibody that recognized residue 74 bound to receptor complexes containing most mammalian lutropins better than to the free hormones, an indication that the outside surface of the beta-subunit groove is altered during hormone binding. This region of the beta-subunit is furthest from the alpha-subunit and is recognized equally well in the free beta-subunit and in the heterodimer. Thus, the receptor associated increase in antibody binding appears due to an interaction of this portion of the beta-subunit with the receptor and not to an effect of the receptor on the relative positions of the alpha- and beta-subunits. Unlike most previous studies designed to identify portions of the beta-subunit likely to contact the LH receptor, this indirect approach provides data that are more easily interpreted because it does not rely on the use of mutations that disrupt hormone function. The approach described here should be valuable for studying the receptor interactions of other complex ligands.

Further characterization of the impact of ethanol on βLH: alterations in polyribosome association of βLH mRNA

We have previously reported a decrease in Luteinizing Hormone (LH) levels in serum afterin vivo acute ethanol exposure in male rats. Accompanying these changes, a rapid and marked decrease of β-LH mRNA was observed. A similar decrease was not detected in the common α-subunit or β-FSH mRNA. The studies presented here examined the possible mechanisms of decreasing β-LH mRNA by using S1 nuclease protection assay to evaluate the effect of acute ethanol exposure on the levels of β-LH heteronuclear RNA (hnRNA). There was no significant difference detected in the level of β-LH hnRNA after ethanol exposure. Polysome distribution analysis was used to evaluate the association and disassociation of β-LH mRNA with polyribosomes since non-polyribosome associated mRNA may be more vulnerable to degradation by RNAases. The results indicated a decrease in the association of the β-LH mRNA with polysomes following acute ethanol exposure. This decrease in polyribosome association would increase the exposure of the β-LH transcript making it more susceptible to RNases. We conclude that the decrease in steady-state β-LH mRNA levels after ethanol exposure occurs because of increasing degradation of the transcript rendered vulnerable by displacement from polysomes and not through a decreased transcriptional rate.

Antibody response against three epitopic domains on human chorionic gonadotropin (hCG) in women and rodents immunized with a beta hCG-based immunocontraceptive vaccine

The antibody repertoire generated against human chorionic gonadotropin (hCG), following immunization with an immunocontraceptive vaccine based on the beta subunit of the hormone, in humans was compared with that generated in rats. Three epitopic domains represented by the beta hCG loop peptide 38-57, the carboxy-terminal peptide (CTP) 109-145, and a region defined by monoclonal antibody (MAb) 206 were probed. In both species, the titer of antibodies against the MAb 206-defined epitopic domain had a good correlation with the total anti-hCG antibody titers. However, the antibody response against the beta hCG loop peptide (38-57) was not observed in human subjects and there was a weak response against this peptide in rats. Despite the good anti-hCG antibody titers in all animals (n = 8), only two had antibodies against this domain. A good antibody response was observed against CTP in rats, whereas in humans this region was weakly immunogenic. Antibodies against CTP were detected in random samples in only 57% of the subjects and this response had no correlation with the total anti-hCG antibody titers. The high antibody response against CTP in rodents compared to humans may be due to its recognition as a foreign determinant. Our results demonstrate that contraception can be achieved in women despite a poor antibody response against the CTP (109-145) and a receptor binding domain (38-57) of beta hCG.

Characterization of the ovine LH beta-subunit gene: the promoter directs gonadotrope-specific expression in transgenic mice

The alpha- and beta-subunits of the gonadotropin hormones are expressed in the gonadotrope cells of the anterior pituitary. There are no adequate in vitro systems for the analysis of beta-subunit gene expression. In this study, therefore, transgenic mice have been used to investigate the regulation of expression of the ovine luteinizing hormone beta-gene (oLH beta) in vivo. oLH beta was isolated, characterized, and 1.9 kb of the promoter fused to the bacterial reporter chloramphenicol acetyl-transferase (CAT). Three lines of transgenic mice were generated. CAT enzyme was detected in the pituitary of two lines, whereas the third line did not express. Measurement of endogenous luteinizing hormone and follicle stimulating hormone levels in both expressing lines revealed small differences when compared to controls, but these did not affect the fertility of the animals. Immunostaining of the anterior pituitary revealed that the oLH beta CAT transgene was expressed specifically in gonadotrope cells.

The gene encoding ovine follicle-stimulating hormone beta: isolation, characterization, and comparison to a related ovine genomic sequence

Follicle-stimulating hormone (FSH), the primary stimulus for egg and sperm maturation in mammals, is an alpha/beta heterodimer. Each subunit is encoded by a single-copy gene in the human, bovine, and rat genomes. Transcription of both subunits is inhibited by estradiol and progesterone in ovine pituitary cultures. We report the sequence of one ovine FSH-beta gene (-1,527 to +3,664) that is expressed in vivo and the identification of a novel, second ovine FSH-beta-like sequence. Digestion of ovine genomic DNA with Bgl II yielded two fragments of 10 kb and 15 kb that hybridized to a bovine FSH-beta cDNA. The 10-kb fragment contained 6 kb of 5'-flanking region and all but about 200 bp of the 3' terminus of the ovine FSH-beta gene. This FSH-beta gene encodes a protein that differs from the published ovine protein sequence only at the carboxy terminus (Arg-109Glu-110[STOP codon] instead of Glu-109Arg-110[Glx-111]) and at positions 49 (Ala instead of Thr) and 88 (Arg instead of Ser). This gene is organized similarly to the human, bovine, porcine, and rat FSH-beta genes, and its coding sequence is nearly identical (99.5%) to a reported ovine FSH-beta cDNA. Expression of the FSH-beta gene on the 10-kb fragment in vivo was determined by analysis of wether mRNA using the polymerase chain reaction. A 95-bp sequence of the 15-kb fragment was 87% homologous to the corresponding coding region of the 10-kb fragment. This comparison suggested that the 15-kb fragment contains either an FSH-beta-like sequence or a pseudogene. Several potential steroid response elements were found by sequence analysis of the 5'-flanking region of the FSH-beta gene on the 10-kb fragment. A mechanism by which these elements may act is suggested.

Gonadotropin-releasing hormone pulses: regulators of gonadotropin synthesis and ovulatory cycles

The data reviewed present evidence that the pattern of GnRH secretion is an important factor in the regulation of gonadotropin subunit gene expression, gonadotropin synthesis, and secretion. The information on regulation of mRNA expression by GnRH pulses should be considered with some caution, as the experiments were performed in male rats and may not accurately reflect events in female primates or humans. However, an overall pattern emerges which suggests that common factors may be involved in all mammalian species. If current evidence is correct, and only a single gonadotropin-releasing hormone exists, then mechanisms to differentially regulate the three gonadotropin genes may involve changes in GnRH secretion. Alterations in GnRH pulse frequency and amplitude are recognized by the pituitary gonadotrope cell and could be the mechanism used to effect differential expression of the gonadotropin subunit genes. Differential regulation of subunit gene expression would be expected to be critically important in the establishment of pubertal maturation, and subsequently in the maintenance of ovulatory cycles in women. Our hypotheses, proposing a major role of pulsatile GnRH secretion in the regulation of human reproduction, are summarized in schematic form in Fig. 14 for men and Fig. 15 for women. In utero and during the first few months of life, GnRH is secreted at a relatively fast frequency (approximately 1 pulse/hour). During the first year, GnRH secretion is inhibited and both the amplitude and apparent frequency of pulsatile release is markedly reduced. The mechanisms involved in inhibiting GnRH release remain unclear in humans. Similarly, the mechanisms involved in the disinhibition of GnRH secretion, which first occurs during sleep at the initiation of puberty, are unclear, but in humans do not appear to involve opiates. In males, the increased frequency and amplitude of GnRH secretion favor LH synthesis and release, which in turn stimulates testosterone secretion (Fig. 14). Testosterone acts at the hypothalamus, perhaps through opioid mechanisms, to inhibit GnRH pulse frequency and to maintain a regular pattern of pulses occurring approximately every 90-110 min in adult males. In females, the mechanisms involving alterations in the patterns of GnRH secretion to regulate reproduction appear more complex. This may reflect the need to differentially synthesize and secrete FSH and LH at different times during reproductive cycles to allow orderly follicular maturation and ovulation. As shown in Fig. 15, we hypothesize that the events during the first decade of life and through the initiation of nocturnal GnRH secretion at puberty are similar in both sexes.(ABSTRACT TRUNCATED AT 400 WORDS)

DNA sequences required for expression of the LH beta promoter in primary cultures of rat pituitary cells

To begin analysis of the DNA sequences necessary for luteinizing hormone (LH) gene transcription, fusion genes containing the 5' flanking region of the rat LH beta or the human alpha-subunit gene linked to luciferase were transfected into primary cultures of rat pituitary cells. The LH beta-luciferase construct was expressed in the primary cultures at a level 50 times greater than a promoterless luciferase control plasmid. Little or no expression of the LH beta-luciferase construct was detected following transfection of MCF-7, JAR or GH3 tumor cell lines. Treatment of transfected cells with gonadotropin-releasing hormone resulted in a modest induction of LH beta-luciferase activity. Considerably higher levels of LH beta-luciferase activity were obtained with cultures from ovariectomized rats than were obtained with cultures from intact female rats. Analysis of 5' deletions of the LH beta-luciferase construct demonstrated that activity was well maintained even after substantial deletions. The shortest construct, which contained 75 base pairs of 5' flanking sequence had 38% of the activity of the longest which contained 1.7 kilobase pairs of flanking sequence. These findings demonstrate that transfection of primary cultures of rat pituitary cells may provide a useful system for analysis of the cis-acting sequences and trans-acting factors required for LH gene expression.

Isolation and characterization of the gene encoding the beta-subunit of rat follicle-stimulating hormone

Follicle-stimulating hormone (FSH) is a pituitary glycoprotein hormone that is comprised of two dissimilar subunits, alpha and beta, encoded by separate genes. We have isolated the gene encoding the beta-subunit of rat FSH by screening a rat genomic DNA-library by filter hybridization with bovine FSH-beta cDNA. Southern blot analysis of rat genomic DNA suggests that there is a single copy of the FSH-beta gene per haploid genome in the rat. The nucleotide sequence of the rat FSH-beta gene was determined and the amino acid sequence of the subunit was deduced. The gene is composed of three exons and two introns. The predicted amino acid sequence reveals that there is a 20-amino-acid signal peptide followed by a mature protein of 110 amino acid residues. Exons I, II, and III are 36, 187, and 1221 bp, respectively. Intron 1 (640 bp) interrupts the 5'-untranslated (UT) region (61 bp) and intron 2 (approximately 1 kb) interrupts the coding region between amino acid residues +34 and +35. Comparison of the amino acid sequence to those of the human and bovine FSH-beta subunits reveals 80% similarity to both species. The "CAGY" sequence, or the Cys-Ala-Gly-Tyr quartet of amino acids encoded by exon II is present in every other glycoprotein beta-subunit sequenced thus far, is altered in rat FSH-beta, with the Ala residue replaced by Glu. Primer extension analysis demonstrated that there is a single transcriptional start site. The nucleotide sequence of the 5'-flanking region (1 kb) was determined and compared to the nucleotide sequences of corresponding regions in the bovine and human genes. This analysis revealed that there are three regions in the 5'-flanking region of the rat FSH-beta gene that display greater than 80% sequence similarity to regions in the bovine and human genes. The second of these regions also shares similarity to segments within the 5'-flanking regions of the rat alpha- and LH beta-subunit genes. The characterization of the rat FSH-beta gene will enable further study of the regulation of rat FSH using in vitro systems.

Isolation and characterization of the gene encoding the alpha-subunit of the rat pituitary glycoprotein hormones

The gene encoding the common alpha subunit of the rat pituitary glycoprotein hormones was isolated from a rat genomic DNA library. The gene spans approximately 8 kb, and contains four exons and three intervening sequences of 5.4 kb, 1.1 kb and 0.6 kb. Blot hybridization of restriction enzyme digests of rat genomic DNA suggests that the alpha gene is present in a single copy. The coding region and 424 bp of the 5'-flanking region of the gene were sequenced. Primer extension and S1 nuclease analyses revealed a single transcriptional start point downstream from consensus promoter elements. The organization of the rat alpha-subunit gene is similar to that of the human and bovine genes including the sizes and locations of the four exons and three introns. In addition, a region of strong sequence similarity has been identified in the 5'-flanking region of the rat, human and bovine genes. This region includes sequences which are similar to a putative triiodothyronine regulatory element and the previously identified cAMP regulatory region; such sequences may mediate the known effects of these factors on alpha-subunit gene expression.

Nucleotide sequence of the bovine gene for follicle-stimulating hormone beta-subunit

The gene for the beta-subunit of follicle-stimulating hormone (FSH-beta) was isolated from a library of bovine DNA fragments cloned in bacteriophage gamma and the complete nucleotide sequence of the gene was determined. The bovine FSH-beta gene contains approximately 4000 nucleotides and consists of three exons separated by two intervening sequences. The transcription initiation site of the gene was mapped by nuclease protection experiments. Analysis of RNA species present in pituitary mRNA demonstrated the presence of a 4.0-kb RNA containing FSH-beta sequences, which is the appropriate size for the primary transcript of the gene. Comparison of nucleotide sequence of the 5'-flanking sequence of the FSH-beta gene to the 5'-flanking regions of other pituitary glycoprotein hormone genes reveals little sequence similarity.

Structure of vertebrate genes: a statistical analysis implicating selection

This paper conducts a statistical analysis of the size distribution of exons and six other gene parts [the transcription unit, introns, intervening DNA (sum of introns), mRNA (sum of exons), and leader and trailer regions of mRNA] as well as the number of exons, the percentage of introns, the placement of introns within the gene, and the potential for frameshifts from coding exon shifts. The first seven variables measured in base pairs fit log-normal distributions. Significant correlations between the sizes of intervening DNA and mRNA, the sizes of leader and trailer regions, and the sizes of introns and flanking exons exist. Introns occur at nonrandom frequencies within the codon frame, in untranslated regions, and relative to the frameshift potential from exon movement or duplication. These nonrandom patterns in gene structure demonstrate that models of gene evolution must incorporate selective processes.

Organization and nucleotide sequence of the gene encoding the beta-subunit of murine thyrotropin

We constructed a murine genomic DNA library in lambda EMBL3 and have isolated and determined the nucleotide sequence of the murine thyrotropin beta-subunit (TSH beta) gene. The cloned gene was derived from a thyrotropic tumor and had no detectable rearrangements when compared to the murine TSH beta gene in total genomic DNA. The murine TSH beta gene is 5 kb in size and consists of five exons and four introns. The 5' untranslated region of the mRNA is encoded except for a single nucleotide by exons 1, 2, and 3. The protein-coding regions are encoded by exons 4 and 5 while the 3' untranslated region is entirely contained in exon 5. Primer extension analysis using an exon 1-specific primer was used to map the 5' end of the gene. Two transcriptional start sites are present in the murine TSH beta gene which appear to be positioned by two TATAAA sequences located 40 bp apart. In all, 99% of transcripts initiate at the downstream site. Transcription from both start sites is affected by thyroidal status in both murine pituitaries and in TtT97 thyrotropic tumors. Finally, sequences homologous with putative thyroid-responsive elements and cyclic AMP-responsive elements are present in the 5'-flanking region and may be important in regulating negative and positive effects on TSH beta gene expression.

LH subunit mRNA concentrations during LH surge in ovariectomized estradiol-replaced rats

In cycling rats, pituitary concentrations of luteinizing hormone (LH) beta-subunit mRNA increase two- to threefold before the afternoon proestrus LH surge without a corresponding increase in alpha-subunit mRNA. Estradiol (E2) treatment is known to allow expression of daily LH surges in ovariectomized (OVX) rats, and the timing, magnitude, and duration of LH secretion is similar to the LH surge on proestrus. The present study was conducted to examine whether the regulation of LH subunit mRNAs during the LH surge in OVX-E2-treated rats is similar to that present on proestrus. Female Holtzman rats were OVX and Silastic implants containing E2 were inserted subcutaneously under ether anesthesia. Some animals received bromocriptine (0.6 mg sc, twice/day beginning 1 h before surgery). On the 2nd day after surgery, groups of animals (n = 4-10/group) were decapitated at intervals between 1000 and 2100. LH and prolactin (PRL) levels were measured in trunk blood. LH subunit mRNA concentrations in the pituitaries were measured by dot-blot hybridization assay. In OVX-E2 rats the LH surge occurred at 1830 and was accompanied by a selective twofold increase in alpha-subunit mRNA (from 266 +/- 18 to 459 +/- 61 pg cDNA bound/100 micrograms pituitary DNA) and maximum values were present at 1730. LH beta-subunit mRNA (m = 29 +/- 1 pg cDNA bound/100 micrograms pituitary DNA) was unchanged throughout the day. Bromocriptine treatment resulted in the suppression of serum PRL (m = 23 +/- 2 ng/ml) and the LH surge was delayed by 1-1.5 h and somewhat blunted.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of the organization and nucleotide sequence of the chromosomal gene for the beta-subunit of rat thyrotropin

The gene for the beta-subunit of rat thyrotropin has been isolated from a library of rat DNA fragments cloned in bacteriophage lambda. The complete nucleotide sequence of the gene has been determined including a portion of 5'- and 3'-flanking regions. The rat TSH-beta gene contains approximately 4879 nucleotides which ultimately lead to the production of a mRNA of about 554 nucleotides, exclusive of the 3' poly(A) tract. The first exon which represents only 5' untranslated sequences of the mRNA, is separated from the second exon by a very large, 3.9-kbp intervening sequence. The second and third exons are separated by a small, 377-bp intervening sequence. Southern blot analysis of total genomic DNA demonstrated that the rat genome contains sequences similar to the cloned gene, suggesting that no rearrangements occurred during the cloning process.