Nucleotide sequence of the cDNA encoding the precursor of the beta subunit of rat lutropin

Expression of Luteinizing Hormone (LH) Subunit Genes in Mouse Testis

Gonadotropins are heterodimers consisting an alpha chain (Cgα) and a beta chain. Interestingly, presence of complicated LH-β transcripts in rat testis was accidently found; testicular LH-β transcripts were confined in seminiferous tubules to spermatids, and the translated products were localized in the elongated spermatids. We hypothesized that mouse testis has potential to produce the tissue specific LH-β with similar structure to the rat testicular forms. To verify our hypothesis, we examined the adult mouse (ICR) testis using RT-PCR and immunohistochemistry. The PCR revealed the presence of the identical products in the reactions for three LH subunit types. The expected product sizes for mouse Cgα and LH-β known as pituitary type were 224 bp and 503 bp, respectively. The testicular type LH-β products were produced by a primer set based on the rat sequences, with unexpected size of 800 bp. Sequencing revealed that the proximal and distal parts (2-82 and 661- 773 bp, respectively) were homologous to rat testicular LH-β cDNA, and middle part (83-660 bp) was a unique mouse-specific region. Both Cgα and LH-β positive signals were in the round and elongated spermatids and mature sperms, and the LH-β signals were more intense. In conclusion, our study demonstrated that the presence and localization of the LH subunits in mouse testis. Further studies will be needed to understand the precise structure and function of mouse testicular LH.

Aryl hydrocarbon receptor activation in lactotropes and gonadotropes interferes with estradiol-dependent and -independent preprolactin, glycoprotein alpha and luteinizing hormone beta gene expression

Arylhydrocarbon receptor (Ahr) activation by 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) interferes with female reproductive functions, but there is little information on the specific targets of TCDD in the hypothalamic-pituitary-gonadal (HPG) axis. In these studies, we found that TCDD upregulated known AhR target genes, cytochrome p450 1a1 (Cyp1a1), Cyp1a2 and Cyp1b1 in the rat pituitary gland. Moreover, 75% of pituitary lactotropes and 45% of gonadotropes contained Ahr mRNA, and most Ahr-containing cells were estrogen receptor 1 (Esr1)-positive. TCDD abrogated estradiol (E(2))-induced prolactin (Prl) expression in vivo and in vitro; conversely, E(2) blocked TCDD upregulation of luteinizing hormone beta (Lhb) and glycoprotein hormone alpha polypeptide (Cga) expression. TCDD had no effect on levels of Ahr mRNA, but upregulated Esr1 mRNA. E(2) independently repressed Ahr and Esr1 expression and blocked TCDD upregulation of Esr1. Thus, complex interactions between Ahr and Esr alter Prl and luteinizing hormone (LH) synthesis by direct actions in lactotropes and gonadotropes. These findings provide important insights into how TCDD disrupts female reproductive functions.

The mechanism responsible for the supraphysiologic gonadotropin surge in females treated with gonadotropin-releasing hormone (GnRH) agonist and primed with GnRH antagonist

OBJECTIVE

To elucidate the physiologic mechanism responsible for the supraphysiologic gonadotropin release from the pituitary induced by gonadotropin-releasing hormone (GnRH) agonist in female rats primed with GnRH antagonist.

DESIGN

Controlled experimental intervention.

SETTING

Government research facility.

ANIMAL(S)

Forty 8-week-old Sprague-Dawley rats.

INTERVENTION(S)

Forty oophorectomized rats were randomized into four treatment groups of 10: group A, control vehicles; group B, GnRH agonist (leuprolide acetate; 1.7 microg/kg twice a day) on day 4; group C, GnRH antagonist (Nal-Lys; 3 mg/kg each day) days 1 to 4; or group D, GnRH antagonist (Nal-Lys; 3 mg/kg each day) days 1 to 4 plus GnRH agonist (1.7 microg/kg twice a day) on day 4.

MAIN OUTCOME MEASURE(S)

Immunohistochemical methods, Northern and in situ hybridization to quantitate pituitary follicle-stimulating hormone beta (FSH-beta), luteinizing hormone beta (LH-beta), and GnRH receptor (GnRH-R) messenger RNA (mRNA), and receptor protein levels in all treatment groups.

RESULT(S)

Treatment with GnRH antagonist was associated with increased storage of gonadotropin in the pituitary for FSH-beta and LH-beta, but mRNA levels were unchanged. The GnRH-R mRNA decreased after GnRH-agonist treatment but remained stable in the GnRH-antagonist treatment groups. Levels of GnRH-R were decreased after GnRH-antagonist treatment.

CONCLUSION(S)

These data indicate that the in vivo mechanism responsible for the exaggerated release of gonadotropins in rats primed with GnRH antagonist and treated with GnRH agonist was an increase in releasable gonadotropin pools coupled with a reduction in GnRH-R, but receptor function was preserved.

Dietary daidzein and puerarin do not affect pituitary LH expression but exert uterotropic effects in ovariectomized rats

OBJECTIVE

To investigate the potency of LH suppression, as an indirect measure of alleviation of postmenopausal vasomotor symptoms, as well as the uterotropic effects of two isoflavones: daidzein and puerarin in an ovariectomized (ovx) rat model and compare them with the effects of 17beta-estradiol benzoate (E2B).

DESIGN

Eighty female Sprague-Dawley rats were ovx and divided into six different treatment groups and one control group (11-12 animals per group). Daidzein, puerarin and E2B were added to the soy free rodent chow in low and high doses (250 mg and 1000 mg per kg, 600 mg and 3000 mg per kg and 4.3 mg and 17.3 mg per kg, respectively). After 3 months of treatment, animals were sacrificed and using real time RT-PCR, pituitary LHbeta and uterine IGF-1, PR and C3 mRNA levels were measured. Additionally serum LH levels were measured in a radioimmunoassay.

RESULTS

Both of our tested isoflavones at low and high doses had no effect on the expression of the pituitary LH at the mRNA and protein level. Only E2B at both doses significantly decreased pituitary LHbeta gene expression and serum LH levels. Daidzein and puerarin at high dose increased significantly uterine weights. Uterine IGF-1 gene expression was only upregulated in puerarin high group. Uterine PR mRNA levels were higher in animals fed with low dose daidzein and high dose puerarin. Uterine C3 gene expression was upregulated in animals fed with daidzein and puerarin at high doses. Although statistically significant, all these effects were however very discrete compared to those of E2B at low and high doses.

CONCLUSION

We speculate that due to the lack of LH suppressing effects in our model, it is very unlikely for daidzein and puerarin to alleviate vasomotor symptoms in postmenopausal women. In contrast, due to their uterotropic effects, high dose consumption of commercially available preparations containing daidzein or puerarin may expose women with an intact uterus to the risk of endometrial hyperplasia.

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.

Molecular cloning of cDNAs and structural model analysis of two gonadotropin beta-subunits of snakehead fish (Channa maculata)

The cDNAs encoding beta-subunits of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) have been cloned from the pituitary of snakehead fish, Channa maculata, and the three-dimensional structural models of the encoded FSH and LH were investigated. The cloned cDNAs, including 5'-untranslated region (UTR), open-reading frame, and 3'-UTR followed by a poly(A) tail, were obtained by reverse transcription-polymerase chain reaction and rapid amplification of cDNA end methods. The open-reading frames of FSH-beta cDNA encodes a 120-amino acid protein with a signal peptide of 18 amino acids and a mature protein of 102 amino acids; while LH-beta cDNA encodes a 140-amino acid protein with a signal peptide of 33 amino acids and a mature protein of 115 amino acids. The amino acid sequence identities of snakehead fish FSH-beta and LH-beta in comparison with other fish are 27.8-81.9% and 45.2-88.8%, respectively; while in comparison with tetrapods are 26.2-28.9% and 37.5-51.2%, respectively. Both FSH-beta and LH-beta of snakehead fish resemble most to those of Perciformes, implying their closer phylogenetic relationship. All 12 cysteine residues are conserved in snakehead fish LH-beta; while 11 cysteine residues are conserved in its FSH-beta. The third cysteine is absent in snakehead fish FSH-beta; instead, a positionally shifted cysteine residue is present at the N-terminus, as found in some phylogenetic related fish. The structure models of snakehead fish FSH and LH, constructed by using the crystal structures of human FSH and human chorionic gonadotropin as respective template, showed that the positionally shifted N-terminal cysteine residue of snakehead fish FSH-beta likely can substitute the third cysteine to form a disulfide bond with the 12th cysteine.

Differential regulation of gonadotropins and glycoprotein hormone alpha-subunit by IGF-I in anterior pituitary cells from male rats

IGF-I has been demonstrated to stimulate basal and GnRH-induced gonadotropin release. IGF-I also elicites alpha-subunit secretion in human pituitary tumor cells. The aims of this study were to evaluate both the effect of IGF-I on gonadotropin LH-beta and FSH-beta mRNA levels and glycoprotein alpha-subunit gene expression in cultured rat anterior pituitary cells. The exposure of pituitary cells to recombinant human IGF-I (rhlGF-I; 2 microg/ml) for 72 h markedly stimulated basal LH and FSH release whereas their mRNA levels remained unmodified. IGF-I elicited a-subunit release from pituitary cells (p < 0.01) and augmented its mRNA levels. Exposure to IGF-I consistently reduced GH release from pituitary cells. This study shows that the gonadotropin-releasing effects of IGF-I are not paralleled by changes in their mRNAs whereas IGF-I stimulates not only alpha-subunit release but also its mRNA levels. This study provides the first observation of alpha-subunit regulation by IGF-I in normal pituitary cells, where a differential regulation between release and synthesis for gonadotropin a-and 1-subunits is also shown.

Cloning and sequence analysis of FSH and LH in the giant panda (Ailuropoda melanoleuca)

The giant panda (Ailuropoda melanoleuca) is an endangered species and indigenous to China. It has been proposed that it has a highly specialized reproductive pattern with low fecundity, but little is known about its basic reproductive biology at the molecular level. In this report the genes encoding gonadotropin subunits alpha, follicle-stimulating hormone (FSH) beta and luteinizing hormone (LH) beta of the giant panda were amplified for the first time by RT-PCR from pituitary total RNA, and were cloned, sequenced and analyzed. The results revealed that the open reading region (ORF) of gonadotropin subunits alpha, FSH beta and LH beta are 363, 390 and 426 bp long, respectively. They displayed a reasonably high degree (74-94, 85-93, 75-91%, for alpha, FSH beta and LH beta subunits, respectively) of identity when deduced amino acids were compared with homologous sequences from partial available mammals including human, cattle, sheep, pig, rat, mouse. Three distinct differences were found at the site of 59 aa of the alpha subunit and 55 aa, 68 aa of FSH beta subunit. Our results provide an insight into understanding the mechanism of reproduction regulation and genetic characteristics of giant panda which will make an actual contribution to its conservation. In addition they lay a foundation for a further study towards producing recombinant panda FSH and LH which can be used in artificial breeding aimed to increase its captive reproductive efficiency.

Sequence analysis and expressional regulation of messenger RNAs encoding beta subunits of follicle-stimulating hormone and luteinizing hormone in the red-bellied newt, Cynops pyrrhogaster

Two distinct cDNAs encoding beta subunits of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were cloned from the cDNA library constructed for the pituitary of the red-bellied newt, Cynops pyrrhogaster, and sequenced. The newt FSHbeta and LHbeta cDNAs encode polypeptides of 129 and 131 amino acids, including signal peptides of 20 and 19 amino acids, respectively. The number and position of cysteine and N-glycosylation in each of the beta subunits of FSH and LH, which are considered essential for assembly of the alpha subunit, are well conserved between the newt and other tetrapods. The high homology (41.6%) between the beta subunits of newt FSH and LH imply less specificity of FSH and LH in gonadal function. One cDNA encoding the common polypeptide chain alpha subunit of FSH and LH was also isolated from the newt pituitary gland. The mRNAs of FSHbeta, LHbeta, and the alpha subunit were expressed only in the pituitary gland among various newt tissues. Double-staining with in situ hybridization and immunohistochemistry revealed coexpression of FSHbeta and LHbeta in the same newt pituitary cells. Ovariectomy induced a significant increase in FSHbeta mRNA levels, but there was no significant change in LHbeta or alpha subunit mRNA levels compared with those in control animals. Taken together, these data suggest that two kinds of gonadotropins, namely FSH and LH, are expressed in the same gonadotropin-producing cells in the pars distalis of the newt as well as in other tetrapods and that the expression of FSHbeta is negatively regulated by the ovaries.

Comparative analysis of different puberty inhibiting mechanisms of two GnRH agonists and the GnRH antagonist cetrorelix using a female rat model

GnRH agonists are the established treatment of precocious puberty caused by premature stimulation of gonadotropin secretion. It has been reported that after an initial stimulation ("flare-up") they reduce LH secretion by desensitization of pituitary GnRH receptors. Little has been published about the use of GnRH antagonists such as cetrorelix to control the onset of puberty and whether they are potentially advantageous compared with GnRH agonists. We conducted two multigroup experiments (12 and 10 d, respectively) treating prepubertal/peripubertal female rats with either the GnRH agonist triptorelin or buserelin and compared them with rats treated with the GnRH antagonist cetrorelix and controls to assess the effects on pubertal progress and serum hormones. In the second experiment, the effects of buserelin and cetrorelix on gene expression of the GnRH receptor, LH-beta, FSH-beta, and the alpha subunit genes in the pituitary were also investigated. Cetrorelix, triptorelin, and buserelin retarded the onset of puberty as determined by delayed vaginal opening, lower ovarian weights, and lower serum estradiol levels. However, although LH and FSH levels were stimulated by both agonists, they were inhibited by cetrorelix. In the cetrorelix versus buserelin experiment, pituitary gene expression of the GnRH receptor and LH-beta subunit were significantly lower in cetrorelix treated rats compared with controls whereas buserelin had little effect. Expression of FSH-beta and alpha subunit were stimulated by buserelin but not by cetrorelix. Even though all three of these GnRH analogues inhibited gonadal development and delayed the onset of puberty, the GnRH agonists had stimulating and inhibiting effects on the pituitary-gonadal axis whereas cetrorelix exerted only inhibiting effects. We conclude from this female rat model that cetrorelix may offer advantages for a more controlled medical treatment of precocious puberty compared with GnRH agonist treatment.

Differential regulation of pituitary gonadotropin subunit messenger ribonucleic acid levels in photostimulated Siberian hamsters

FSH levels begin to rise 3-5 days after male Siberian hamsters are transferred from inhibitory short photoperiods to stimulatory long photoperiods. In contrast, LH levels do not increase for several weeks. This differential pattern of FSH and LH secretion represents one of the most profound in vivo examples of differential regulation of the gonadotropins. The present study was undertaken to characterize the molecular mechanisms controlling differential FSH and LH synthesis and secretion in photostimulated Siberian hamsters. First, we cloned species-specific cDNAs for the three gonadotropin subunits: the common alpha subunit and the unique FSHbeta and LHbeta subunits. All three subunits share high nucleotide and predicted amino acid sequence identity with the orthologous cDNAs from rats. We then used these new molecular probes to examine the gonadotropin subunit mRNA levels from pituitaries of short-day male hamsters transferred to long days for 2, 5, 7, 10, 15, or 20 days. Short-day (SD) and long-day (LD) controls remained in short and long days, respectively, from the time of weaning. We measured serum FSH and LH levels by RIA. FSHbeta, LHbeta, and alpha subunit mRNA levels were measured from individual pituitaries using a microlysate ribonuclease protection assay. Serum FSH and pituitary FSHbeta mRNA levels changed similarly following long-day transfer. Both were significantly elevated after five long days (2.3- and 3.6-fold, respectively; P < 0.02) and declined thereafter, but they remained above SD control values through 20 long days. Alpha subunit mRNA levels also increased significantly relative to SD control values (maximum 2-fold increase after seven long days; P < 0.03), although to a lesser extent than FSHbeta. Neither serum LH nor pituitary LHbeta mRNA levels changed significantly following long-day transfer. The results indicate that long-day-associated increases in serum FSH levels in Siberian hamsters reflect an underlying increase in pituitary FSHbeta and alpha subunit mRNA accumulation.

Male reproductive toxicity and beta-luteinizing hormone gene expression in sexually mature and immature rats exposed to 2-bromopropane

1. The reproductive effects of 2-bromopropane (2-BP) in sexually mature and immature male Sprague-Dawley rats were investigated. The animals were randomly divided into three treatment groups and one control group each of which comprised six mature and six immature rats. The treated groups were injected s.c. 200, 600 and 1800 mg/kg of 2-BP on 5 days a week for 5 - 7 weeks and the control group received the vehicle. 2. The absolute and relative testis weights were significantly reduced in 600 and 1800 mg/kg b.w. dose groups in both mature and immature rats. The absolute epididymis, prostate, seminal vesicle, and pituitary weights and the relative epididymis weights, however, were significant only at the highest dose level used in both mature and immature rats. 3. The sperm concentration and sperm viability in epididymal duct decreased and the percentage of abnormal sperm increased in a dose-dependent manner in both mature and immature rats. Additionally, serum testosterone level was significantly decreased in all dose groups in mature rats, and was significantly reduced only in the group treated with the middle and highest dose in immature rats. 4. In both mature and immature rats treated with 200 and 600 mg/kg, the seminiferous tubules were atrophied and all types of germ cells were decreased in number. At the highest dose level, the effect was more marked showing severely atrophied seminiferous tubules and a complete loss of all types of germ cells. 5. The mating, pregnancy and fertility indices were significantly reduced in the 600 and 1800 mg/kg groups. Additionally, at the highest dose group the number of implantations and viable fetuses per litter were reduced and the resorption rate was increased significantly. 6. In the mature rats, the beta-LH gene expression increased significantly in the 1800 mg/kg group when compared to the control group. 7. It can be concluded that 2-BP induces alterations in both neuro-endocrine axis and the reproductive tract under the present experimental conditions. The no observed adverse effect level (NOAEL) in this study could be estimated to be lower than 200 mg/kg/b.w. based on the alteration in testicular morphology as well as on sperm parameters observed at the dose level of 200 mg/kg.

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.

Steroid feedback on gonadotropin release and pituitary gonadotropin subunit mRNA in mice lacking a functional estrogen receptor alpha

Steroid hormones regulate levels of gonadotropin mRNA in the pituitary, and gonadotropic hormones in plasma. To determine whether estrogen receptor alpha (ERalpha) mediates steroid negative feedback, wild type (WT) and estrogen receptor alpha knockout (ERalphaKO) mice of both sexes were gonadectomized and implanted with a Silastic capsule containing either estradiol (E2), dihydrotestosterone (DHT), testosterone, or a blank capsule. Ten days later, plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were measured. Pituitary mRNA levels of gonadotropin subunit (alpha, LHbeta, FSHbeta) and prolactin (PRL) were quantified. LH levels in gonad-intact ERalphaKO females were elevated, similar to values seen following gonadectomy. By contrast, serum LH concentrations in gonad-intact ERalphaKO males were low and rose following gonadectomy, suggesting androgen feedback. Estradiol treatment significantly decreased plasma LH in WT animals, but not in ERalphaKOs. In fact, in female ERalphaKOs, our dose of E2 increased plasma levels of LH as compared with untreated, ovariectomized ERalphaKOs. All the steroid treatments suppressed LH in WT animals whereas only DHT consistently suppressed LH concentrations in ERalphaKO mice. The postgonadectomy rise in plasma FSH was prevented by steroid treatments in WT females, but not in any of the other groups. Gonadotropin subunit and PRL mRNA responses to E2 treatment (both inhibitory and stimulatory) were absent in ERalphaKO mice, suggesting a critical role for ERalpha. Although E2 can exert negative feedback effects on LH release in both males and females by actions at the ERalpha, the androgen receptor plays the primary physiological role in the male mouse.

Reduction of luteinzing hormone secretion induced by long-term feed restriction in male rats is associated with increased expression of GABA-synthesizing enzymes without alterations of GnRH gene expression

In rats, fasting or restriction of feed intake impairs the activity of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator which results in reduced luteinizing hormone (LH) secretion. It is still unknown which neurotransmitters are involved in this phenomenon. However, it is known that increased GABA concentrations in the hypothalamus reduce GnRH biosynthesis and release. Therefore, we examined whether 17 days of feed restriction in male rats affected the hypothalamic gene expression of GnRH and the GABA-synthesizing enzymes glutaminase (GLS) and glutamic acid decarboxylase-which exists in two forms, GAD67 and GAD65-in the mammalian brain. Furthermore, the expression of the GnRH receptor (GnRH-R) and the GABA transporter 1 (GAT-1) were investigated. Feed restriction resulted in a 75% reduction in body weight (b.w.) compared to rats fed ad libitum. Serum concentrations of LH and testosterone in the feed restricted group were significantly reduced to approximately 15% of that of rats fed ad libitum, while the FSH concentration remained unchanged. In the mediobasal hypothalamus (MBH) where GnRH is released into the portal vessels, mRNA levels of GAD67 and GLS were increased twofold compared to rats fed ad libitum while no changes were observed in the preoptic area of the hypothalamus (POA) where GnRH is biosynthesised. Neither the expression of preoptic GnRH mRNA nor the expression of GAD65 and of GnRH-R mRNA in both hypothalamic structures was affected by feed restriction. In the anterior pituitary, a significant reduction of the expression of GnRH-R, LH-beta and the alpha subunit was observed in the feed restricted rats, whereas FSH-beta mRNA levels remained constant. Thus, feed restriction selectively increased the expression of GABA-synthesizing enzymes in the MBH but did not modify GnRH expression in the POA. However, the reduced expression of the LH-beta- and alpha-subunit and of the GnRH-R in the anterior pituitary indicates that pulsatile GnRH release may have been attenuated or even abolished. We suggest, that enhanced expression of GABA-synthesizing enzymes reflects increased GABAergic neurotransmission and thereby reducing GnRH release from the MBH.

The gonadotropin-releasing hormone receptor gene promoter directs pituitary-specific oncogene expression in transgenic mice

Our previous work has shown that 1.2 kb of the 5' flanking region of the mouse GnRH receptor (mGnRH-R) gene is sufficient to direct tissue-specific expression in vitro. In this study, we have used the cell-specific regulatory sequences of the mGnRH-R gene promoter to target the expression of the simian virus 40 virus T antigen (TAg) to the pituitary gland of transgenic mice. A hybrid transgene, GnRH-R/TAg, was prepared using the -1164/+52 region of the mGnRH-R gene and +2533/+5234 sequences encoding the large T antigen of the simian virus 40. Two founders developed tumors of apparent pituitary origin at 44 (M28, female) and 50 (M25, male) days of age. M28 and M25 mice were about 50% underweight, and their gonads were grossly underdeveloped compared with wild-type litter mates. A third male founder, M29, developed a tumor at a later time (109 days). M29 was able to breed successfully and stably transmit the GnRH-R/TAg transgene. Mice of the M29 transgene line developed tumors at 4-5 months of age. Gross examination showed that the tumors extend from the sella and infiltrate into the inferior surface of the brain. In small tumors collected from young transgenic animals, normal pituitary cells as well as transition areas of increasing cellular atypia are evident. Frankly malignant cells are seen in all tumors. The pituitary tumors express the alpha-, FSHbeta-, and LHbeta-subunits and the GnRH-R messenger RNA, all markers of a gonadotrope but not of other anterior pituitary cell lineages. In summary, our studies indicate that 1.2 kb of the 5'-flanking region of the mGnRH-R gene can be used to target expression specifically to the gonadotropes of the pituitary gland in transgenic mice. The GnRH-R gene promoter-directed expression appears to be cell-specific and results in the formation of tumors that are primarily of gonadotropic origin.

Cloning of complementary deoxyribonucleic acid for the follicle-stimulating hormone-beta subunit in the Japanese quail

Complementary DNA clones encoding the luteinizing hormone-beta and common alpha subunits have been isolated not only in mammals but also in some nonmammalian tetrapod vertebrates. However, cloning of cDNA encoding the follicle-stimulating hormone (FSH)-beta subunit is limited to mammals, and no clone for the FSH-beta subunit has been isolated for nonmammalian vertebrates. We report here the isolation and characterization of cDNA encoding the FSH-beta subunit precursor molecule in the Japanese quail from a cDNA library of the pituitary gland of this bird. As the hybridization probe for the screening, we used a cDNA clone prepared by the polymerase chain reaction (PCR) with primers designed from known nucleotide sequence data of cDNA for FSH-beta subunit precursors of mammals. The FSH-beta subunit precursor cDNA we isolated was longer than any other FSH-beta subunit precursor cDNAs previously reported. This is due to the extraordinarily long 3'-untranslated region (2135 bp). This region is extremely rich in consensus sequences reported to cause instability of mRNA, suggesting that mRNA for the FSH-beta subunit, especially that of the Japanese quail, is unstable. Northern blot analysis of mRNA for the FSH-beta subunit revealed that the pituitary content of mRNA in the nonbreeding season was about 1/5 to 1/10 that in the breeding season in male Japanese quail kept in an outdoor cage. The profile of the seasonal change in FSH-beta subunit mRNA in the quail pituitary gland was similar to that of the seasonal change in the concentration of FSH in plasma reported previously. The deduced amino acid sequence of the mature protein region showed that the quail FSH-beta subunit is more similar to the opossum FSH-beta subunit than to the other mammalian FSH-beta subunits.

Chicken lutropin acts like follitropin in rat ovarian follitropin receptor: an isoelectric focusing study

This study investigates whether chicken lutropin (LH) specifically binds to rat ovarian follitropin (FSH) receptor and exerts FSH-like bioactivity. Glycoprotein fraction, prepared from the chicken anterior pituitary gland, was fractionated using isoelectric focusing within a pH range of 3.5-11. Analysis of the focused fractions, by a radioreceptor assay (RRA) specific for FSH in rats using rat ovarian homogenate as receptor source, and 125I-labeled rat FSH as radioligand, detected a large component having an isoelectric point of 10.25. This focusing profile obtained by RRA was quite similar to that obtained by a specific radioimmunoassay (RIA) for chicken LH, but clearly different from that obtained by a specific RIA for chicken FSH, indicating this RRA specifically recognizes chicken LH. Chicken LH fraction prepared from the electrofocused material was used for further studies. The chicken LH preparation was three times more potent than rat FSH in the RRA in displacing the radioligand bound to rat ovarian receptor, while chicken LH facilitated an 8-fold less production of estradiol in dispersed rat granulosa cells than rat FSH. These results suggest that chicken LH acts like rat FSH in rat ovarian FSH receptor, but receptor-binding activity is much higher than biological activity.

Effects of sex steroids on secretory granule formation in gonadotropes of castrated male rats with respect to granin expression

Pituitary gonadotropes show sex-related differences in their ultrastructure. Typical gonadotropes of male rats exhibit both large granules, which contain chromogranin A (CgA), and small granules, which contain secretogranin II (SgII). In contrast, typical female rat gonadotropes show only a very few large granules among the numerous small granules. To clarify the nature of the biogenesis of these secretory granules and the effects of sex steroids, the ultrastructural and immunocytochemical changes in gonadotropes were examined in castrated male rats supplied with a testosterone or estradiol implant. In castrated rats, pituitary expression and plasma levels of LH increased drastically, but the pituitary content of CgA decreased. The majority of gonadotropes then showed features of "castration cells" containing many small secretory granules. A testosterone implant to castrated rats remarkably suppressed the expression and circulating levels of LH and increased the CgA content in the pituitary to near-normal levels. In this situation, immunocytochemical studies demonstrated that gonadotropes again exhibited large and small secretory granules with the respective localization of CgA and SgII. On the contrary, in castrated rats supplied with an estradiol implant, the expression and content of CgA in the pituitary were remarkably suppressed, and large secretory granules disappeared from gonadotropes. These results suggest that the expression of CgA in gonadotropes is regulated differently by male and female sex steroids. These different effects of androgen and estrogen on the expression level of CgA are closely associated with the sex-related differences in the ultrastructure of secretory granules within gonadotropes.

Recombinant rat luteinizing hormone; production by Chinese hamster ovary cells, purification and functional characterization

Rat recombinant (rec) luteinizing hormone (LH) was produced in Chinese hamster ovary (CHO) cells, to enable studies on LH physiology in this species with homologous hormone. The synthesized hormone was purified, and characterized physico-chemically and biologically in comparison with highly purified preparations of rat pituitary (pit) LH (NIDDK-rLH-I-7 and I-9) and to highly purified urinary (NIH, CR-121) and rec forms of human chorionic gonadotropin (hCG). The 33 kD molecular mass of rat recLH, as determined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot, was comparable with the 32 kD size of pitLH. In chromatofocusing, the isoforms of rat recLH distributed in the pI range 6.5-7.8, similar to rat pitLH. In receptor binding assays using rat testicular membranes, and physiologic salt concentration, rat recLH displayed a 5-10-fold higher affinity than rat pitLH, but about 100-fold lower affinity than hCG. In contrast, in low salt concentrations the affinities of rat recLH and rechCG to rat LH receptor were rather similar. The differences in potency in the mouse Leydig cell in vitro bioassay were in agreement with the receptor binding data at physiologic salt concentration. Neither rat recLH nor pitLH stimulated cAMP production or bound specifically to HEK 293 cells expressing the rec human LH receptor. When injected subcutaneously on four consecutive days to male rats (8.4-33.7 microg/rat/day) rat recLH did not induce seminal vesicle growth in comparison with a significant effect of human menopausal gonadotropin (hMG; 12.5-50 IU/rat/day). In contrast, ovulation was induced in 5/6 and 6/6 female rats following single injections of 3.75 and 7.5 microg of rat recLH, respectively, after pretreatment with 10 microg/kg of a GnRH-antagonist (Org 30850). In conclusion, rat recLH displays clearly lower in vivo and in vitro bioactivity than hCG. Nevertheless, it binds effectively to the rat LH receptor (with affinity dependent on salt concentration) and is bioactive in the mouse Leydig cell bioassay. This newly synthesized recombinant hormone provides a useful tool for further studies on the physiology of LH action in the rat, the most common animal model in reproduction research.

Complete amino acid sequences of follitropin and lutropin in the ostrich, Struthio camelus

We determined the complete amino acid sequences of two pituitary gonadotropins, follitropin and lutropin in the ostrich, thereby providing the first information on the structure of avian follitropin. Ostrich follitropin and lutropin both consist of two subunits: a common alpha-subunit and a hormone-specific beta-subunit. The alpha-subunit is composed of 96 amino acid residues and has 70-80% sequence identity with the alpha-subunits of most vertebrates. The ostrich follitropin beta-subunit consists of 106 amino-acid residues, and shows 70-74% sequence identity with mammalian follitropins beta, 61% with amphibian follitropin beta, 39-46% with teleost gonadotropins II beta and 32-44% with teleost gonadotropins I beta. The ostrich lutropin beta-subunit consists of 128 amino-acid residues, and exhibits 76-78% sequence identity with other avian lutropins beta, 44-50% with teleost gonadotropins II beta, 45% with amphibian lutropin beta, 41-44% with mammalian lutropins beta, and 25-36% with teleost gonadotropins I beta. Sequence comparison revealed that lutropin beta-subunits are more class-specific and have diversified approximately twice as fast follitropin beta-subunits, although segments essential for maintaining higher-order structures have been conserved.

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.

Effects of corticosterone and testosterone on pituitary gonadotropin content, secretion, bioactivity and messenger RNA levels in the presence or absence of GnRH in male rats

The effects of corticosterone (B) and testosterone (T) on pituitary and serum bioactive and immunoreactive gonadotropins and on gonadotropin hormone subunit messenger RNA levels were compared in the absence of GnRH. Male rats were implanted with pellets of either cholesterol, B or T. At implantation, 2 and 4 days later half of each group received GnRH antagonist and animals were killed 5 days after implantation. As expected, GnRH antagonist lowered bioactive and immunoreactive serum FSH and LH, pituitary FSH, LHβ and FSHβ mRNA. B treatment alone lowered bioactive and immunoreactive serum FSH and immunoreactive serum LH. B reversed the antagonist effect on bioactive and immunoreactive pituitary FSH and FSHβ mRNA. T alone lowered bioactive and immunoreactive serum FSH and LH levels. T reversed the antagonist effect on bioactive and immunoreactive pituitary FSH. T lowered bioactive and immunoreactive pituitary LH and LHβ mRNA and partially reversed the antagonist effect on FSHβ mRNA. The data suggest that either B or T enhance FSH synthesis by acting directly at the gonadotrope, but that B does not affect LH variables to the same extent as T. The results suggest that in stressed animals, when T levels are reduced, B can substitute for T in sustaining FSH synthesis.

Isolation and characterization of two distinct gonadotropins, GTHI and GTHII, from bonito (Katsuwonus plelamis) pituitary glands

Two distinct glycoproteins homologous to chum salmon GTHI and GTHII were isolated from the pituitary glands of a marine fish, the bonito (Katsuwonus plelamis), and characterized by amino acid sequence analysis in order to obtain additional evidence for duality of teleost GTHs. Glycoproteins were extracted from the pituitary glands, and intact GTHI and GTHII, consisting of two distinct subunits, were purified by ion-exchange chromatography on DEAE-cellulose, rpHPLC on Asahipak C4P-50 in alkaline buffer, and gel filtration on Superdex 75. The association of the subunits was stable in GTHI (39 kD) and unstable in GTHII (30 kD) in acidic conditions. Immunoblotting revealed that antisera against beta subunits of chum salmon GTHs reacted with GTHII, but not with GTHI. In addition, none of the GTHs was stained with antiserum against human TSH beta. Sequence analysis demonstrated that bonito GTHI beta is homologous to salmon GTHI beta with 43% sequence identity, and bonito GTHII beta is homologous to salmon GTHII beta with 67% identity. Sequence identity between bonito GTHI beta and GTHII beta was only 28%. Thus, it is evident that the bonito pituitary gland produces two chemically distinct gonadotropins homologous to chum salmon GTHs.

Dissociation between release and gene expression of gonadotropin alpha-subunit in gonadotropin-releasing hormone-stimulated alpha T3-1 cell line

The alpha T3-1 cell line which was derived by targeted tumorigenesis in transgenic mice [Windle et al. (1990) Mol. Endocrinol. 4, 597-603] possesses high-affinity binding sites for GnRH analogs coupled to enhanced phosphoinositide turnover and phospholipase D activity. Incubation of alpha T3-1 cells with [D-Trp6]-GnRH analog (GnRH-A) resulted in a rapid increase in gonadotropin alpha-subunit mRNA levels which was detected already at 30 min of incubation (0.1 nM GnRH-A, 3-fold, p < 0.01). The effect diminished with time to reach basal levels at about 12 h of incubation, with a secondary rise in alpha mRNA levels between 12 and 24 h of incubation. Addition of the protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 ng/mL) or the Ca2+ ionophore ionomycin (1 microM) to alpha T3-1 cells also resulted in a rapid increase in alpha-subunit mRNA levels. Surprisingly, GnRH-induced alpha-subunit release was detected only after a lag of 4 h of incubation. Thus, dissociation between exocytosis and gene expression can be demonstrated in GnRH-stimulated alpha T3-1 cell line.

Molecular structures of glycoprotein hormones and functions of their carbohydrate components

Images

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.

Effect of Ovariectomy or Oestrogen Implants upon Pituitary Function in Female Hypogonadal Mice Bearing Normal Fontal Preoptic Area Grafts

Abstract The effects of ovariectomy and oestrogen feedback for 10 days upon pituitary and serum luteinizing hormone (LH) content, pituitary glycoprotein subunit messenger ribonucleic acid (mRNA) and prolactin mRNA content in normal females, female hypogonadal mice and hypothalamic grafted female hypogonadal mice, bearing a graft of normal mouse preoptic area tissue into the third ventricle, have been investigated. In normal females ovariectomy resulted in a rise in serum LH, LHbeta-subunit and common alpha-subunit mRNAs with no significant change in pituitary LH content or follicle-stimulating hormone (FSH) beta-subunit mRNA. In the hypogonadal females, preoptic area grafting resulted in an elevation in all of the above parameters into the normal range. Ovariectomy in this group resulted in a further elevation of serum LH, LHbeta-subunit and alpha-subunit mRNAs with no change in pituitary LH content or FSHbeta-subunit mRNA, which in all cases were comparable to ovariectomized normal animals. Oestrogen treatment caused a fall in pituitary LH content and the serum LH fell below the detection of the assay. LHbeta-subunit and a-subunit mRNA mirrored this fall but there was no change in FSHbeta-subunit hybridization. These experiments suggest that even though normal neuronal input to the gonadotrophin-releasing hormone neurons is disrupted, oestrogen-induced negative feedback can still occur in grafted female hypogonadal animals. Gonadotrophin-releasing hormone neurons are reported to lack oestrogen receptors but feedback within this graft by co-transplanting oestrogen-sensitive neurons remains a possibility, as does feedback at the level of the host median eminence where graft axons extend to the pituitary portal vessels. The similarity of the response in normal and grafted animals indicates that these actions of oestrogen may be effected predominantly at the pituitary level.

Molecular cloning and sequence analysis of chum salmon gonadotropin cDNAs

cDNAs encoding alpha and beta subunits of salmon gonadotropins, sGTHI and sGTHII, have been isolated from the cDNA library prepared from salmon pituitary mRNA. sGTHI alpha, sGTHI beta, and sGTHII beta cDNAs encode polypeptides of 114, 137, and 142 amino acids, including signal peptides of 22, 24, and 23 amino acids, respectively. The deduced amino acid sequence for sGTHI alpha revealed rather high homology (66-69%) to mammalian alpha chains, whereas sGTHI beta and sGTHII beta show lower homology (30%) to each other and to mammalian beta subunits. The existence of two distinct beta-subunit cDNAs in the teleost suggests that divergence of the GTH gene took place earlier than divergence of teleosts from the main line of evolution leading to tetrapods.

Nucleic acid composition, codon usage, and the rate of synonymous substitution in protein-coding genes

Based on the rates of synonymous substitution in 42 protein-coding gene pairs from rat and human, a correlation is shown to exist between the frequency of the nucleotides in all positions of the codon and the synonymous substitution rate. The correlation coefficients were positive for A and T and negative for C and G. This means that AT-rich genes accumulate more synonymous substitutions than GC-rich genes. Biased patterns of mutation could not account for this phenomenon. Thus, the variation in synonymous substitution rates and the resulting unequal codon usage must be the consequence of selection against A and T in synonymous positions. Most of the variation in rates of synonymous substitution can be explained by the nucleotide composition in synonymous positions. Codon-anticodon interactions, dinucleotide frequencies, and contextual factors influence neither the rates of synonymous substitution nor codon usage. Interestingly, the nucleotide in the second position of codons (always a nonsynonymous position) was found to affect the rate of synonymous substitution. This finding links the rate of nonsynonymous substitution with the synonymous rate. Consequently, highly conservative proteins are expected to be encoded by genes that evolve slowly in terms of synonymous substitutions, and are consequently highly biased in their codon usage.

Isolation and nucleotide sequence analysis of a cloned cDNA encoding the beta-subunit of bovine follicle-stimulating hormone

Two different cDNAs containing sequences coding for the beta-subunit of bovine follicle stimulating hormone (FSH-beta) have been isolated from a phage lambda gt11 bovine pituitary cDNA library. The complete nucleotide sequence of both clones was determined, and the combined sequence represents most of FSH-beta mRNA. The combined sequence contains 46 nucleotides of 5'-untranslated sequence followed by 387 nucleotides of coding sequence. The coding sequence predicts a 19-amino-acid amino-terminal precursor segment followed by the 110-amino-acid sequence of mature bovine FSH-beta. The cDNA sequence demonstrates the presence of a long 3'-untranslated region containing 1295 bases followed by a segment representing the poly(A) portion of the mRNA. Thus, the combined sequence of the cDNAs suggests a minimal size of 1.7 kb for FSH-beta mRNA. Analysis of FSH-beta sequences present in bovine pituitary mRNA demonstrated the presence of an mRNA with a size of about 2.0 kb. This apparent discrepancy is probably due to the presence of a several-hundred nucleotide tract of poly(A) at the 3' terminus of the mRNA. Comparison of the amino acid sequence predicted from the cDNA with the known amino acid sequence of the beta-subunit of FSH from several different species demonstrates that the protein has been highly conserved.

Cloning and DNA sequence analysis of the cDNA for the precursor of the beta chain of bovine follicle stimulating hormone

Follicle stimulating hormone (FSH) plays essential roles in the maintenance and development of oocytes and spermatozoa in normal reproductive physiology. FSH possesses two subunits, alpha and beta, the latter being responsible for FSH biological specificity. We have cloned and sequenced the cDNA encoding the FSH beta chain from a bovine anterior pituitary cDNA library. The mature molecule is 109 amino acids long and is preceded by a 20-amino acid putative signal peptide. RNA gel blot analysis of bovine pituitary RNA shows that the mRNA encoding beta chain of FSH is approximately 1.7 kilobases in length.

Gonadotropin-releasing hormone differentially regulates expression of the genes for luteinizing hormone alpha and beta subunits in male rats

Gonadotropin-releasing hormone (GnRH) and gonadal steroids regulate synthesis and release of luteinizing hormone (LH). GnRH is secreted intermittently by the hypothalamus, producing pulsatile LH release, and a pulsatile GnRH stimulus is required to maintain LH secretion. We report the regulatory effects of GnRH pulse injections on pituitary concentrations of LH alpha and beta subunit mRNAs in a castrated/testosterone-replaced male rat model. Replacement with physiologic amounts of testosterone decreased concentrations of both LH subunit mRNAs. GnRH pulse injections (10-250 ng per pulse given every 30 min for 48 hr) increased both mRNA concentrations, but the dose response patterns were markedly different. alpha subunit mRNA was increased by all GnRH doses but not the levels seen after castration alone. In contrast, LH beta subunit mRNA concentrations showed a marked dependence on GnRH dose. Maximal responses, to values similar to those in castrates, occurred after 25-ng GnRH pulses, and larger doses produced a smaller increase in LH beta subunit mRNA. Both the acute LH secretory response to GnRH and the number of GnRH receptors followed a pattern similar to the LH beta subunit mRNA concentration and were maximal after the 25-ng GnRH dose. These results show that GnRH can differentially regulate LH subunit mRNAs and suggest that concentrations of LH beta subunit mRNA may be a limiting factor in GnRH-stimulated LH release.

Regulation of rat luteinizing hormone subunit messenger ribonucleic acids by gonadal steroid hormones

Little is known about the hormonal regulation of luteinizing hormone (LH) biosynthesis. We have studied the regulation of LH messenger RNA (mRNA) levels by gonadal-steroid hormones in the rat. In one set of experiments, male and female rats were surgically gonadectomized (GDX) and killed 1, 3, 7, 14, 22, and 31 d postoperatively. In another set of experiments, male and female rats were surgically GDX and were injected subcutaneously with testosterone propionate (500 micrograms/100 g body wt per d) or 17 beta-estradiol 3-benzoate (10 micrograms/100 g body wt per d), respectively, beginning 3 wk postoperatively. Levels of serum LH were determined by radioimmunoassay and levels of LH subunit mRNAs in single pituitary glands were determined by blot hybridization analysis using labeled synthetic oligodeoxyribonucleotide probes that correspond to portions of the coding regions of the rat alpha- and LH beta-subunit mRNAs. 4 wk after gonadectomy, serum LH levels rose nine- and 20-fold, while alpha-subunit mRNA levels rose six- and 10-fold, and LH beta-subunit levels rose seven- and 14-fold, compared with controls in males and females, respectively. In gonadal-steroid hormone-treated male and female GDX rats, serum LH levels fell to 8 and 36% of control values, while alpha-subunit mRNA levels declined to 22 and 19%, and LH beta-subunit mRNA levels declined to 6 and 10% of control values, 48 h after injections were initiated, in males and females, respectively. We conclude that gonadal-steroid hormones negatively regulate the levels of both subunit mRNAs in GDX rats in a pattern that parallels the changes in serum LH values. These data suggest that gonadal-steroid hormone regulation of LH biosynthesis occurs, at least in part, at the level of LH subunit mRNAs due to effects at the transcriptional and/or RNA stability levels.

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.

Molecular cloning of the human thyrotropin-beta subunit gene

Genomic DNA fragments that carried a gene for human thyrotropin-beta (hTSH beta) subunit were isolated. Nucleotide sequence analysis of the gene showed that the hTSH beta subunit precursor consists of 138 amino acid residues. There is an N-terminal sequence of 20 amino acids as a signal peptide, followed by 112 amino acids, whose sequence is in agreement with that known for the secretory form of hTSH beta subunit. This is followed by an additional stretch of 6 hydrophobic amino acids, which may be eliminated post-translationally. The coding region is separated by an intron of about 460 bp. Genomic Southern blot hybridization analysis suggested that the hTSH beta gene is a unique single copy gene.

Analysis of the distribution of charged residues in the N-terminal region of signal sequences: implications for protein export in prokaryotic and eukaryotic cells

A statistical analysis of the distribution of charged residues in the N-terminal region of 39 prokaryotic and 134 eukaryotic signal sequences reveals a remarkable similarity between the two samples, both in terms of net charge and in terms of the position of charged residues within the N-terminal region, and suggests that the formyl group on Metf is not removed in prokaryotic signal sequences.