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

Identification of a novel ovine LH-beta promoter region, which dramatically enhances its promoter activity

The luteinizing hormone beta subunit (LH-beta) gene plays a critical role in reproduction. In order to characterize and analyze the promoter region of LH-beta in sheep, a genomic library was constructed in phage lambda gt 10 and screened. A novel region of 1,224 bp upstream from the targeted LH-beta gene was identified. Blasting this sequence showed a perfect homology for the first 721 bp sequence with an upstream ovine LH-beta sequence in the database. However, the remaining 5′-503 bp showed no sequence matching. DNA from Moroccan breeds was isolated and the whole region was amplified and confirmed by sequencing. To further confirm the promoter activity of this region, an in vitro analysis using a luciferase assay was carried out. An increase in the promoter activity of the whole region was demonstrated compared to the empty vector. More interestingly, the unpublished region significantly enhanced the promoter activity compared to the known region alone. To predict putative transcription factor binding-sites (TFBSs), an in silico analysis was performed using the TFSEARCH program. The region features many TFBSs and contains two palindrome sequences of 17- and 18-bp. Taken together, a novel region was identified and confirmed in sheep which contained a promoter activity rich with binding sites for a putative regulatory element as shown in silico.

Polymorphisms of LHβ and GnRHR genes and their association with the number of embryos recovered in goats

The objective of the present study was to explore a predictor of superovulation response on the basis of associations between the number of embryos recovered and gene polymorphism. Variation in the goat LHβ and GnRHR genes was investigated using polymerase chain reaction–single-strand conformational polymorphism and DNA sequencing. Two single nucleotide polymorphisms (SNPs) were identified in the 5′-UTR of LHβ gene (A59C, P1 locus) and in the Exon 2 of GnRHR gene (T177A, P6 locus). At the P1 locus in both breeds, the frequencies of one allele were 0.46 and 0.51, respectively. At the P6 locus, the minor allele frequency was 0.23. Associations of both SNPs with the number of embryos recovered and the corpus luteum number were evaluated in Boer and Shaanbei goat breeds. Association analysis showed that both SNPs had significant (P < 0.05) effects on the number of embryos recovered and corpus luteum number. These results indicate that LHβ and GnRHR genes are potential markers for the number of embryos recovered.

Developmental programming: impact of prenatal testosterone excess on pre- and postnatal gonadotropin regulation in sheep

The goal of this study was to explore mechanisms that mediate hypersecretion of LH and progressive loss of cyclicity in female sheep exposed during fetal life to excess testosterone. Our working hypothesis was that prenatal testosterone excess, by its androgenic action, amplifies GnRH-induced LH (but not FSH) secretion and, thus, hypersecretion of LH in adulthood, and that this results from altered developmental gene expression of GnRH and estradiol (E2) receptors, gonadotropin subunits, and paracrine factors that differentially regulate LH and FSH synthesis. We observed that, relative to controls, females exposed during fetal life to excess testosterone, as well as the nor-aromatizable androgen dihydrotestosterone, exhibited enhanced LH but not FSH responses to intermittent delivery of GnRH boluses under conditions in which endogenous LH (GnRH) pulses were suppressed. Luteinizing hormone hypersecretion was more evident in adults than in prepubertal females, and it was associated with development of acyclicity. Measurement of pituitary mRNA concentrations revealed that prenatal testosterone excess induced developmental changes in gene expression of pituitary GnRH and E2 receptors and paracrine modulators of LH and FSH synthesis in a manner consistent with subsequent amplification of LH release. Together, this series of studies suggests that prenatal testosterone excess, by its androgenic action, amplifies GnRH-induced LH response, leading to LH hypersecretion and acyclicity in adulthood, and that this programming involves developmental changes in expression of pituitary genes involved in LH and FSH release.

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.

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.

Transgenesis and neuroendocrine physiology: a transgenic rat model expressing growth hormone in vasopressin neurones

Human growth hormone (hGH) and bovine neurophysin (bNP) DNA reporter fragments were inserted into the rat vasopressin (VP) and oxytocin (OT) genes in a 44 kb cosmid construct used to generate two lines of transgenic rats, termed JP17 and JP59. Both lines showed specific hGH expression in magnocellular VP cells in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). hGH was also expressed in parvocellular neurones in suprachiasmatic nuclei (SCN), medial amygdala and habenular nuclei in JP17 rats; the rat OT-bNP (rOT-bNP) transgene was not expressed in either line. Immunohistochemistry and radioimmunoassay showed hGH protein in the hypothalamus from where it was transported in varicose fibres via the median eminence to the posterior pituitary gland. Immunogold electron microscopy showed hGH co-stored with VP-NP in the same granules. The VP-hGH transgene did not affect water balance, VP storage or release in vivo. Drinking 2 % saline for 72 h increased hypothalamic transgene hGH mRNA expression, and depleted posterior pituitary hGH and VP stores in parallel. In anaesthetised, water-loaded JP17 rats, hGH was released with VP in response to an acute hypovolumic stimulus (sodium nitrosopentacyano, 400 microg I.V.). JP17 rats had a reduced growth rate, lower anterior pituitary rGH contents, and a reduced amplitude of endogenous pulsatile rGH secretion assessed by automated blood microsampling in conscious rats, consistent with a short-loop feedback of the VP-hGH on the endogenous GH axis. This transgenic rat model enables us to study physiological regulation of hypothalamic transgene protein production, transport and secretion, as well as its effects on other neuroendocrine systems in vivo.

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.

An NF-Y binding site is important for basal, but not gonadotropin-releasing hormone-stimulated, expression of the luteinizing hormone beta subunit gene

Regulated synthesis of luteinizing hormone (LH) requires coordinated transcriptional control of the alpha and LHbeta subunits in pituitary gonadotropes. Several cis-acting elements and trans-acting factors have been defined for control of the LHbeta promoter through heterologous cell culture models. In this report, we describe the identification of bipartite NF-Y (CBF/CP1) binding sites within the proximal bovine LHbeta promoter. When multimerized, one of these sites activates the heterologous, minimal HSV thymidine kinase promoter in the gonadotrope-derived cell line alphaT3-1. The functional role of the promoter-distal site in regulating the full-length bovine LHbeta promoter was assessed in vivo using transgenic mice harboring a mutant promoter linked to the chloramphenicol acetyltransferase reporter gene. While this element is important for conferring high level activity of the LHbeta promoter in pituitary, it does not appear to be essential for mediating gonadotropin-releasing hormone (GnRH) regulation. This is the first characterization of a cis-acting element within this GnRH-dependent promoter that is restricted to regulating basal expression and not GnRH-induced activity.

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.

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.

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.

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.

Steroidogenic factor-1 (SF-1) and the regulation of expression of luteinising hormone and follicle stimulating hormone b-subunits in the sheep anterior pituitary in vivo

Luteinising hormone (LH) and follicle stimulating hormone (FSH) comprise a common alpha-subunit and hormone-specific beta-subunit, are expressed in gonadotroph cells of the anterior pituitary and during the sheep oestrous cycle, are regulated by gonadotrophin releasing hormone (GnRH), ovarian peptides and steroids. Transcription factor steroidogenic factor-1 (SF-1) transactivates the common alpha-subunit and LH beta subunit in other species. We investigated whether SF-1 regulates beta-subunit expression and the regulation of SF-1 expression in vivo in sheep. Immunocytochemistry co-localised SF-1, LH and FSH to sheep pituitary gonadotrophs and electrophoretic mobility shift assays (EMSA) demonstrated that SF-1 bound to the LH beta promoter in vitro. No SF-1 DNA binding site was found in the FSH beta promoter. No difference in mean levels of SF-1, FSH beta, LH beta and GnRHr mRNA was measured between the luteal and follicular phases of the oestrous cycle. However SF-1 mRNA levels were correlated to those of LH beta in individual luteal phase animals (r = 0.88, p < 0.05), when the transcription rate of LH beta was significantly higher (p < 0.01). GnRH antagonist treatment of luteal animals did not produce a significant reduction in mRNA levels of LH beta, SF-1 and FSH beta. Administering oestradiol benzoate with GnRH antagonist reduced levels of SF-1 and FSH beta mRNA from luteal values (p < 0.005). We conclude that: (1) expression of SF-1 is not solely dependent on GnRH and is downregulated by oestradiol; (2) the LH beta transcription rate is increased during the luteal phase but is not related to levels of LH beta or SF-1 mRNA; and (3) SF-1 does not appear to directly regulate expression of FSH beta, but may regulate expression indirectly.

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.

Transgenic targeting of neuroendocrine peptide genes in the hypothalamic-pituitary axis

A large number of neuroendocrine peptide genes have been tested for their ability to target expression to the hypothalamus and pituitary in transgenic mice. This has resulted in a number of powerful applications, for example, ablation or immortalization of specific cell types, and analysis of transcription regulatory sequences. The greatest amount of success in targeting cells of the neuroendocrine axis has been in the pituitary and has utilized regulatory sequences of genes that are normally expressed in pituitary. Greater difficulties have been encountered in directing expression to specific neurons in the hypothalamus. A primary goal of this review is to consider collectively the data obtained by a number of laboratories in order to draw conclusions about the general sequence requirements for achieving cell-specific expression. The data suggest that the mechanisms controlling cell-specific expression of neuropeptide genes in the hypothalamus are complex and involve multiple regulatory elements that may reside within the gene or many kilobases away from the promoter. These elements act positively and negatively in different cells to enhance or restrict expression, and may include sequences that shield a transgene from regulatory influences of other genes near the point of chromosomal insertion.