The gene for the beta subunit of bovine luteinizing hormone encodes a gonadotropin mRNA with an unusually short 5'-untranslated region

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.

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.

Pitx2 deletion in pituitary gonadotropes is compatible with gonadal development, puberty, and fertility

This report introduces a gonadotrope-specific cre transgenic mouse capable of ablating floxed genes in mature pituitary gonadotropes. Initial analysis of this transgenic line, Tg(Lhb-cre)1Sac, reveals that expression is limited to the pituitary cells that produce luteinizing hormone beta, beginning appropriately at e17.5. Cre activity is detectable by a reporter gene in nearly every LHbeta-producing cell, but the remaining hormone-producing cell types and other organs exhibit little to no activity. We used the Tg(Lhb-cre)1Sac strain to assess the role Pitx2 in gonadotrope function. The gonadotrope-specific Pitx2 knockout mice exhibit normal expression of LHbeta, sexual maturation, and fertility, suggesting that Pitx2 is not required for gonadotrope maintenance or for regulated production of gonadotropins.

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.

Cloning of the elk common glycoprotein alpha-subunit and the FSH and LH beta-subunit cDNAs

We report the nucleotide and deduced amino acid sequences of the pituitary glycoprotein hormone common alpha-subunit, and the FSH and LH beta-subunits of the elk (Cervus elaphus). These sequences were obtained by RT-PCR of pituitary gland polyadenylated RNA. A partial genomic fragment of the elk follicle stimulating hormone beta-subunit was also amplified from genomic DNA and sequenced. These sequences show high similarity to other related domestic species, including sika deer, ovine, bovine, porcine and equine. The presently reported cDNAs were used as probes for Northern analysis of pituitary gland and muscle samples from elk and sheep. Mature mRNA transcripts of approximately 700, 1700 and 550 bases were expressed in the pituitary gland but not in muscle tissue, for the glycoprotein hormone common alpha-subunit and FSH and LH beta-subunits, respectively. These observations are consistent with reports for other related species. The genomic fragment of elk FSH beta-subunit revealed an intronic microsatellite of 6 CT repeats, which differs from the 19 CT repeats documented for the sheep genomic sequence. We propose that differences in the CT repeats of the elk FSH beta-subunit gene may be used as a marker for elk parentage testing. The elk DNA sequences presently reported represent a unique addition to the growing collection of the pituitary hormone genes for various vertebrates, which will facilitate evolutionary and phylogenetic studies of the gonadotropin genes. In addition, this information and the cloned cDNAs will be useful for studying seasonal expression of the elk pituitary glycoprotein genes.

Molecular cloning of the cDNA encoding follicle-stimulating hormone beta subunit of the Chinese soft-shell turtle Pelodiscus sinensis, and its gene expression

Follicle-stimulating hormone (FSH) is a member of the pituitary glycoprotein hormone family. These hormones are composed of two dissimilar subunits, alpha and beta. Very little information is available regarding the nucleotide and amino acid sequence of FSHbeta in reptilian species. For better understanding of the phylogenetic diversity and evolution of FSH molecule, we have isolated and sequenced the complementary DNA (cDNA) encoding the Chinese soft-shell turtle (Pelodiscus sinensis, Family of Trionychidae) FSHbeta precursor molecule by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) methods. The cloned Chinese soft-shell turtle FSHbeta cDNA consists of 602-bp nucleotides, including 34-bp nucleotides of the 5'-untranslated region (UTR), 396-bp of the open reading frame, and 3'-UTR of 206-bp nucleotides. It encodes a 131-amino acid precursor molecule of FSHbeta subunit with a signal peptide of 20 amino acids followed by a mature protein of 111 amino acids. Twelve cysteine residues, forming six disulfide bonds within beta-subunit and two putative asparagine-linked glycosylation sites, are also conserved in the Chinese soft-shell turtle FSHbeta subunit. The deduced amino acid sequence of the Chinese soft-shell turtle FSHbeta shares identities of 97% with Reeves's turtle (Family of Bataguridae), 83-89% with birds, 61-70% with mammals, 63-66% with amphibians and 40-58% with fish. By contrast, when comparing the FSHbeta with the beta-subunits of the Chinese soft-shell turtle luteinizing hormone and thyroid stimulating hormone, the homologies are as low as 38 and 39%, respectively. A phylogenetic tree including reptilian species of FSHbeta subunits, is presented for the first time. Out of various tissues examined, FSHbeta mRNA was only expressed in the pituitary gland and can be up-regulated by gonadotropin-releasing hormone in pituitary tissue culture as estimated by fluorescence real-time PCR analysis.

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.

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.

Change in concentrations of luteinizing hormone subunit messenger ribonucleic acids in the estrous cycle of beef cattle

Changes in the concentrations of LH subunit messenger ribonucleic acids (mRNAs) and in the LH content of the anterior pituitary of beef cattle were studied during the estrous cycle. Japanese beef cows were classified according to the expected day of the estrous cycle: stage I (early-luteal phase, days 1-4; day 1=day of ovulation), stage II (early-mid-luteal phase, days 5-10), stage III (late-mid-luteal phase, days 11-17) and stage IV (follicular phase, days 18-20), according to the morphology of the ovaries. The anterior pituitaries of the cows were collected and the levels of alpha and LHbeta subunit mRNAs were determined by slot-blot analyses. The LH content of the anterior pituitary was measured by radioimmunoassay. The level of alpha subunit mRNA in the pituitary of cows was highest in stage I and decreased significantly by stage II (P<0.05); thereafter it tended to increase. The level of LHbeta subunit mRNA did not change significantly during the estrous cycle. The LH content of the pituitary of cows was low in stage I and tended to increase by stage II, then to decrease from stage II to III, and to increase significantly from stage III to IV (P<0.05). These results suggest that the highest levels of gene expressions of alpha subunit in the anterior pituitary occur in the early-luteal phase of beef cows, while the LH content is increased most in the follicular phase. The enhanced gene expressions of common alpha subunit in the early-luteal phase could be important in replenishing the bovine anterior pituitary with LH, which is depleted of hormone by the LH surge or the enhanced pulsatile release.

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.

Cloning and expression of cynomolgus monkey (Macaca fascicularis) gonadotropins luteinizing hormone and follicle-stimulating hormone and identification of two polymorphic sites in the luteinizing hormone beta subunit

The genes encoding the cynomolgus monkey gonadotropin subunits, alpha, follicle-stimulating hormone (FSH) beta and luteinizing hormone (LH) beta, were cloned by reverse transcriptase polymerase chain reaction (RT-PCR) using pituitary RNA. The predicted amino acid sequences displayed 82, 96 and 87% identity to human subunit sequences, respectively. Northern blot hybridization of monkey tissues revealed pituitary specific transcripts of 1.0 and 0.6 kb for the alpha and LHbeta subunit, respectively, and two bands of 1.8 and 0.65 kb for the FSHbeta. Upon sequencing LHbeta cDNAs from different monkeys, two polymorphic sites were detected, resulting in the amino acid transitions Ser32Thr and His60Arg. Restriction analysis revealed different homo- and heterozygous combinations of the polymorphic sites indicating linkage dysequilibrium. Transient co-expression of the alpha subunit together with the FSHbeta or LHbeta subunit in COS7 and CHO cells resulted in secretion of in vitro bioactive hormones. This work represents a further step towards production of recombinant monkey LH and FSH which can be used in a homologous experimental setting in the cynomolgus monkey.

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.

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.

A new molecular variant of luteinizing hormone associated with female infertility

OBJECTIVE

To investigate whether the newly described G1502 to A1502 mutation in exon 3 of the LH beta-subunit gene, causing the amino acid substitution of Ser102 for Gly102, is related to female infertility.

DESIGN

Screening of fertile and infertile women for the G1502 to A1502 mutation in the LH beta-subunit gene.

SETTING

Clinics and laboratories of the National University Hospital obstetrics and gynecology department, Singapore.

PATIENT(S)

Two hundred twelve healthy fertile women; 40 infertile women with menstrual disorders, polycystic ovary syndrome, and endometriosis; and 12 women with idiopathic infertility.

INTERVENTION(S)

Exon 3 of the LH beta-subunit gene was analyzed using polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), and PCR-mediated direct DNA sequencing.

MAIN OUTCOME MEASURE(S)

The PCR products of patients were analyzed by RFLP, and the results were compared with those of fertile controls. DNA sequencing radiographs were compared between two mutation-bearing patients and four controls.

RESULT(S)

The mutation was identified in only two infertile women with endometriosis; other women studied were found to be negative for this mutation.

CONCLUSION(S)

The missense mutation in the LH beta-subunit gene may be implicated in female infertility, possibly endometriosis-associated infertility in some women.

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.

Cell-specific expression of the mouse gonadotropin-releasing hormone (GnRH) receptor gene is conferred by elements residing within 500 bp of proximal 5' flanking region

Gonadotropin-releasing hormone (GnRH) is a decapeptide produced by the hypothalamus. Upon binding to specific high-affinity receptors on gonadotrope cells of the anterior pituitary gland, GnRH stimulates the synthesis and secretion of LH. In light of the critical role of GnRH in reproduction much effort has been directed toward understanding the regulation of this hormone and its cognate receptor. The recent availability of genomic clones for the GnRH receptor has facilitated research to address the molecular mechanisms underlying regulation of GnRH receptor gene expression. We have expanded the analysis of the promoter for the mouse GnRH receptor gene and report that in addition to transcriptional start sites located within 100 bp of the translation start codon there is a more distal transcriptional start site approximately 200 bp 5' of the initiation codon. The initiation of transcription from this more distal site was sufficient to confer cell-specific expression on luciferase. Further, transient expression assays of constructs containing progressive 5' deletions in the GnRH receptor gene promoter reveal the presence of one or morecis-acting elements located between -500 and -400 (relative to ATG) necessary for transcriptional activity in the gonadotrope-derived αT3 cell line. Finally, αT3 but not COS-7 cell nuclear extract contained protein(s) that bind to at least two separate motifs contained within the -500 to -400 region. We suggest that activation of GnRH receptor gene expression in the αT3 cell line requires the binding of at least two transcriptional regulatory proteins to basal enhancer elements located within a 100 bp region between -500 to -400 relative to the translation start codon in the mouse GnRH receptor gene.

Cloning and analysis of the cDNA encoding the horse and donkey luteinizing hormone beta-subunits

The coding regions of the horse (Equus caballus) and donkey (E. asinus) luteinizing hormone (LH) beta-subunit transcripts were cloned from pituitary gland RNA, in order to investigate their relationships to the corresponding equine chorionic gonadotropin (CG) beta-subunits and to further understand the unusual receptor-binding properties of equine LH and CG. The horse and donkey LH beta-subunit sequences were very similar (97% identity at the nucleotide (nt) level; 93% at the amino acid (aa) level), confirming their very close evolutionary linkage and also indicating that the C-terminal extension in both subunits occurred prior to the divergence of horse and donkeys. Furthermore, sequence comparisons and Southern blot analysis confirmed that in donkeys, as in horses, the pituitary (LH) and placental (CG) beta-subunits are almost certainly derived from a single gene. This contrasts with primates which have a single LH beta gene expressed in the pituitary and a family of separate CG beta genes that are expressed in the placenta. The deduced aa sequences also revealed several differences between the horse and donkey LH/CG beta-subunits that could explain their differences in biological activity. In addition, the study confirmed that the donkey subunit contains an additional Cys residue that is not present in other gonadotropin beta-subunits.

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.

Amphibian lutropin from the bullfrog Rana catesbeiana. Complete amino acid sequence of the beta subunit

The amino acid sequence of lutropin (LH) beta subunit of an amphibian, the bullfrog Rana catesbeiana, has been determined. The primary structure was determined by sequencing the intact protein (residues 1-44) and peptides originated by cyanogen bromide cleavage and lysyl endopeptidase digestion. 12 cysteine residues are conserved in the bullfrog and mammalian LH beta subunit. One sugar-chain-binding site at Asn-8 is also conserved in the bullfrog and in all mammals except humans. This glycoprotein is composed of 112 amino acid residues with a molecular mass of 12675 Da, considering the six cystine bridges and excepting the sugar chain. The bullfrog beta subunit has approximately 50% sequence identity with that of mammals and with the fish gonadotropin beta subunit, and about 40% with bullfrog follicle-stimulating hormone beta subunit.

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.

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.

Cloning and DNA sequence analysis of the cDNA for the precursor of porcine luteinizing hormone (LH) beta subunit

The cDNAs encoding the porcine luteinizing hormone (LH) beta subunit (pLH beta) were isolated from a cDNA library of porcine anterior pituitary constructed in an expression vector lambda gt11 using anti-pituitary glycoprotein hormone antisera. The nucleotide sequence of pLH beta subunit cDNA clone (543 bases) was determined. The cDNA encodes a signal sequence (20 amino acids) and a further 121 amino acids corresponding to the mature LH beta molecule. The predicted protein sequence differs from that determined by direct peptide sequencing at 6 residues and additionally shows an extended carboxyl terminus. The 5' untranslated sequence shows a low homology and is extremely long when compared with other mammalian LH beta subunit cDNAs. Northern analysis showed that the length of the pLH beta subunit mRNA is about 0.85 kb.

A multi-copy gene encodes a potentially protective antigen in Brugia malayi

A genomic library of Brugia malayi was constructed and screened by hybridization with a cDNA clone corresponding to a potentially protective antigen of 63 kDa. The antigen is encoded by a multicopy gene family. Five distinct gene copies were isolated and one was characterized in detail by nucleotide sequence analysis. An apparent pseudogene was also characterized. The organization of genes encoding the antigen is typical of higher eukaryotes in exon/intron organization although the introns have an unusually high A+T content (75%). Organization of the genomic sequence along with S1 nuclease and primer extension analyses indicate that a short untranslated exon is spliced to the 5' end of the mRNAs encoding the antigen.

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.

Measurement of the amount of mRNA for gonadotropins during an estradiol-induced preovulatory-like surge of LH and FSH in ovariectomized ewes

The amount of messenger RNA (mRNA) for luteinizing hormone beta-subunit (LH beta), follicle-stimulating hormone beta-subunit (FSH beta) and alpha-subunit was measured during estradiol-17 beta (E) positive feedback in ovariectomized (OVX) ewes. During the anestrous season, OVX ewes were given an i.m. injection of E (25 micrograms: n = 5) or oil (control; n = 4) and hourly blood samples were collected for 16 hr. After blood collection, ewes were killed and anterior pituitary glands were removed for analysis of hormone and mRNA content. Preovulatory-like increases in serum concentrations of LH and FSH were measured in E-treated OVX ewes. In two E-treated OVX ewes the serum concentrations of LH and FSH were still increasing, whereas in the remaining three E-treated OVX ewes, serum concentrations of LH were on the decreasing portion of the E-induced preovulatory-like surge. Pituitary content of LH was lower (P less than .10) in E-treated OVX ewes when serum concentrations of LH were decreasing than that measured in control ewes or E-treated OVX ewes in which serum concentrations were still increasing. Pituitary content of FSH and prolactin were similar (P greater than .05) among all groups. The amount of mRNA for LH beta-subunit was similar (P greater than .05) in ewes in which serum concentrations of LH were increasing and in control ewes, but was lower (P less than .05) in ewes with decreasing levels of LH. The amount of mRNA for FSH beta-subunit was lower (P less than .05) in all E-treated OVX ewes (independent of whether serum concentrations of FSH were increasing or decreasing) than that measured in control ewes. There was no difference (P greater than .05) in the amount of mRNA for alpha-subunit among any groups. Thus, amounts of mRNA for the beta-subunits of gonadotropins are reduced, while amounts of mRNA for alpha-subunit are unchanged during estradiol positive feedback in OVX ewes.

Identification of specific gene sequences in preimplantation embryos by genomic amplification: detection of a transgene

Endogenous and foreign DNA sequences can be detected in an extremely small number of cells via sequence amplification in vitro. The polymerase chain reaction (PCR) technique applied in multiple cycles allows the amplification of specific short regions of the genome to levels that can be detected by DNA blotting techniques. Cow and mouse blastocysts were analyzed by PCR for the presence of an endogenous singlecopy gene or an integrated foreign gene. The endogenous single-copy gene encoding the beta chain of bovine luteinizing hormone was detectable in cow blastocysts and in purified bovine genomic DNA representing as few as 25 cells. To determine whether exogenous genes (transgenes) can be detected in preimplantation embryos, transgenic male mice hemizygous for the prokaryotic gene encoding neomycin resistance were bred to nontransgenic females, and the resulting blastocysts were analyzed. The neo gene was detected in approximately half of the embryos. The capability to identify specific gene sequences in a limited number of embryonic cells affords investigators the opportunity to study genetics in early development.

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.

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.

Evolution of different transcriptional start sites in the human luteinizing hormone and chorionic gonadotropin beta-subunit genes

To investigate the mechanisms related to the tissue-specific expression of luteinizing hormone (LH) in the pituitary and chorionic gonadotropin (CG) in the placenta, we compared the transcriptional start sites of the common alpha-subunit and structurally related beta-subunit genes encoding human LH and CG. The transcriptional start site of the alpha-subunit gene expressed in human pituitary and placenta is identical, encoding a mRNA with a 5'-untranslated tract of 100 bases. In contrast, the lengths of the 5'-untranslated tracts for human LH beta and CG beta mRNA are different. The human LH beta gene, like the LH beta gene in rat and cattle, transcribes a mRNA with a short 5' untranslated tract of 9 bases. Although the human CG beta gene has a TATAAA box sequence in the same location as the LH beta gene, it is not used for initiation of transcription. Instead, the promoter for the CG beta gene is located at an upstream site resulting in an extended 5' untranslated tract for CG beta mRNA of 366 bases. These results indicate that recognition of the upstream promoter site in the CG beta gene is tissue specific rather than species specific and suggest that the LH beta and CG beta genes evolved distinct regulatory regions which respond differently to intracellular signals in the pituitary and placenta.

Organization and expression of gonadotropin genes

We have examined the question of how hormones regulate the biosynthesis of gonadotropins. In particular we have studied the effects of gonadal sex steroid hormones on the regulation of LH subunit gene expression to determine whether they may occur at the pre-translational level. Success in the molecular cloning of cDNAs in genes encoding the subunits of LH has allowed such studies. It is now known that the subunit genes are located in separate genes on separate chromosomes in man and mouse. These genes must be coordinately expressed in a tissue-specific fashion in gonadotropes to yield subunit mRNAs which are ultimately translated to form the protein backbones of the subunits. It is clear that the gonadal sex steroid hormones in both castration and castration-replacement experimental paradigms negatively regulate the subunit mRNAs in vivo in a rapid and effective manner. Also, it is interesting to note that alpha-subunit RNA is regulated to a lesser extent than the LH beta. This observation is reminiscent of those previously observed in the studies of the biosynthesis of TSH in which the subunit mRNA is less well controlled than the TSH beta mRNA. These studies were performed initially using thyrotropic tumor which lacked confounding gonadotropes. However, studies have also been performed in the pituitary gland of the hypothyroid mouse with similar results. Hence, it appears that the alpha subunit gene is also under regulation by hormones but to a lesser extent than the LH beta. These findings provide hope that future studies will allow us to understand further the molecular mechanisms involved in the regulation of these genes by various hormonal influences.