Molecular cloning of cDNAs for precursors of porcine pituitary glycoprotein hormone common alpha-subunit and of thyroid stimulating hormone beta-subunit

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 and sequence analysis of a cDNA encoding pituitary thyroid stimulating hormone beta-subunit of the Chinese soft-shell turtle Pelodiscus sinensis and regulation of its gene expression

A cDNA encoding thyroid stimulating hormone beta-subunit (TSHbeta) was cloned from pituitary of the Chinese soft-shell turtle, Pelodiscus sinensis, and its regulation of mRNA expression was investigated for the first time in reptile. The Chinese soft-shell turtle TSHbeta cDNA was cloned from pituitary RNA by reverse transcription and polymerase chain reaction (RT-PCR), and rapid amplification cDNA end (RACE) methods. The Chinese soft-shell turtle TSHbeta cDNA consists of 580-bp nucleotides, including 67-bp nucleotides of 5'-untranslated region (UTR), 402-bp of the open reading frame, and 97-bp of 3'-UTR followed by a 14 poly (A) trait. It encodes a precursor protein molecule of 133 amino acids with a putative signal peptide of 19 amino acids and a putative mature protein of 114 amino acids. The number and position of 12 cysteine residues, presumably forming six disulfide bonds, one putative asparagine-linked glycosylation site, and six proline residues that are found at positions for changing the backbone direction of the protein have been conserved in the turtle as in other vertebrate groups. The deduced amino acid sequence of the Chinese soft-shell turtle TSHbeta mature protein shares identities of 82-83% with birds, 71-72% with mammals, 49-57% with amphibians, and 44-61% with fish. The Chinese soft-shell turtle pituitaries were incubated in vitro with synthetic TRH (TSH-releasing hormone), thyroxine and triiodothyronine at doses of 10(-10) and 10(-8)M. TRH stimulated, while thyroid hormones suppressed, TSHbeta mRNA levels in dose-related manner. The sequences of cDNA and its deduced peptide of TSHbeta as well as the regulation of its mRNA level were reported for the first time in reptile.

Analysis of the thyrotropin receptor-thyrotropin interaction by comparative modeling

We have used the most advanced programs currently available to construct the first three-domain structure of the human thyrotropin receptor (TSHR) using comparative modeling. The model consists of a leucine-rich domain (LRD; amino acids 36-281; porcine ribonuclease inhibitor used as a template for modeling), a cleavage domain (CD; amino acids 282-409; tissue inhibitor of matrix metalloproteinases 2 as template) and transmembrane domain (TMD amino acids 410-699; bovine rhodopsin as template). Models of human, porcine, and bovine TSH were also constructed (human chorionic gonadotropin [hCG] and human follicle stimulating hormone [hFSH] as templates). The LRD has a characteristic horseshoe shape with 10 tandem homologous repeats. The CD consists of beta-barrel and alpha helix structures (OB-like fold) with two disulfide bridges and the structure around these disulfide bridges remains stable after cleavage. The TMD presents the typical seven membrane-spanning helices. The TSH, LRD, CD, and TMD models were brought together in an extensive series of docking experiments. Known features of the TSH-TSHR interaction were used for selection of appropriate complexes that were then validated using a different set of experimental data. A similar approach was used to build a model of a complex between the TSHR and a monoclonal TSHR antibody with weak thyroid stimulating activity. Human thyrotropin (hTSH) alpha chains were found to make contact with many amino acids on the LRD surface and CD surface whereas no interaction between the beta chains and the CD were found. The higher affinity of bovine thyrotropin (bTSH) and porcine thyrotropin (pTSH) (relative to hTSH) for the TSHR is explained well by the models in terms of charge-charge interactions between their alpha chains and the receptor. Experimental observations showing increased sensitivity of the TSHR to hCG after mutation of TSHR Lys209 to Glu are explained well by our model. Furthermore, several mutations in the TMD that are associated with increased TSHR basal activity are predicted from our model to be caused by the formation of new interactions that stabilize the activated form of the TMD.

Characteristics and thyroid state-dependent regulation of iodothyronine deiodinases in pigs

Three iodothyronine deiodinases (D1, D2, and D3) regulate local and systemic availability of thyroid hormone. D1 and D2 activate the prohormone T4 to the thyromimetic T3, and D3 inactivates T4 and T3 to rT3 and 3,3'-diiodothyronine, respectively. The expression of the three deiodinases is tightly regulated with regard to developmental stage and cell type to provide fine tuning of T3 supply to target cells. Most studies regarding distribution and regulation of deiodinases have been carried out in rodents. However, in different respects, rodents do not seem to be the optimal experimental model for human thyroid hormone physiology. For instance, D2 expression has been observed in human thyroid and skeletal muscle but not in these tissues in rodents. In this study, we have explored the pig as an alternative model. Porcine D1, D2, and D3 were cloned by RT-PCR, and their catalytic properties were shown to be virtually identical to those reported for human and rodent deiodinases. The tissue distribution of deiodinases was studied in normal pigs and in pigs made hypothyroid by methimazole treatment or in pigs made hyperthyroid by T4 treatment. D1 activity in liver and kidney was increased in T4-treated pigs. D2 activities in cerebrum and pituitary were decreased after T4 treatment and strongly increased after methimazole treatment. Remarkably, D2 activity in thyroid and skeletal muscle was induced in hypothyroid pigs. Significant expression of D3 was observed in cerebrum and was positively regulated by thyroid state. In conclusion, the pig appears to be a valuable model for human thyroid hormone physiology. The expression of D2 activity in thyroid and skeletal muscle is of particular interest for studies on the importance of this enzyme in (hypothyroid) humans.

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

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

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.

Molecular cloning of cDNA encoding thyroid stimulating hormone beta subunit of bighead carp Aristichthys nobilis and regulation of its gene expression

The complementary DNA (cDNA) encoding pituitary thyroid stimulating hormone beta subunit (TSH-beta) of bighead carp was cloned and regulation of its gene expression was investigated for understanding phylogenetic divergence and evolution of TSH molecule. The cDNA was obtained from bighead carp pituitary total RNA by reverse transcription and polymerase chain reaction. Oligonucleotide primers were designed from the sequence of common carp. The full length sequence was then obtained by 3' and 5' rapid amplification of cDNA ends (RACE). The full-length sequence consisting of 3' and 5' untranslated regions was 585 bp long. The predicted amino acid sequence consisted of a signal peptide of 19 amino acid residues and a mature TSH beta subunit protein of 131 residues. The coding sequences of the cDNAs showed variable percentage homologies with those of other teleosts and vertebrate species. The predicted amino acid sequence shared 71% identity with rainbow trout and salmon, 90% with goldfish, 50% with eel and 94% with common carp in the mature protein region. The percentages of identity in the same region in comparison with bovine, porcine, rat, mouse, human and chicken were only 39, 42, 41, 40, 45 and 46%, respectively. TSH beta mRNA expression was found only in the pituitary tissue out of other tissues tested as testis, muscle, brain and heart. For the first time, thyrotropin releasing hormone (TRH) and thyroxine (T4) effects on pituitary TSH mRNA expression were tested in teleosts under in vitro conditions. TRH treatment on pituitary cells increased TSH beta mRNA level, while T4 treatment decreased TSH beta mRNA level. The present study provides a direct evidence, for the first time that TRH directly upregulates TSH beta gene expression in teleosts.

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.

Cloning of cDNAs for the pituitary glycoprotein hormone alpha subunit precursor molecules in three amphibian species, Bufo japonicus, Rana catesbeiana, and Cynops pyrrhogaster

We have isolated cDNA clones encoding molecules of putative glycoprotein hormone alpha subunit precursors from their pituitary cDNA libraries for a toad, bullfrog and newt. The insert of the isolated toad cDNA was 562 bp long containing the 5'-untranlated, coding and 3'-untranslated regions of 38, 363 and 161 bp, respectively. The insert of the bullfrog cDNA was 604 bp long containing the 5'-untranslated, coding and 3'-untranslated regions of 70, 366, and 168 bp, respectively. In the newt, a composite cDNA sequence was estimated from four isolated partial clones. It was 694 bp long and contained the 5'-untranslated region of 89 bp, coding region of 366 bp, and 3'-untranslated region of 91 bp or longer. Amino acid sequences deduced from coding regions of the isolated clones showed that the signal peptides consist of 24 residues and the mature proteins of 96 (toad) or 97 residues (bullfrog and newt). In all three species, an insertion of an amino acid residue was found between residues 26 and 27 of the alpha subunit molecule sequence of all other vertebrate species studied. Interestingly, the percentage identities of the entire amino acid sequence between amphibian and mammalian (or avian) alpha subunits are lower than those between lungfish and mammalian (or avian) alpha subunits. This suggests that amino acid substitutions have occurred more frequently during the course of evolution in the alpha subunit molecule of amphibians than in that of other tetrapod vertebrates, although the biological significance of this is not known.

Cloning of cDNA encoding the common alpha subunit precursor molecule of pituitary glycoprotein hormones in the Australian lungfish, Neoceratodus forsteri

We have isolated cDNA clones encoding a putative glycoprotein hormone alpha subunit precursor molecule from a pituitary cDNA library of the Australian lungfish (Neoceratodus forsteri) by a two-step plaque hybridization technique initially using cDNA encoding the toad glycoprotein hormone alpha subunit precursor molecule as the hybridization probe. The inserts (799 bp) of two of the isolated cDNA clones contained sequences of 5' and 3' untranslated regions, including a poly(A) stretch, and the entire coding sequence of the alpha subunit precursor molecule. The deduced amino acid sequence showed that its signal peptide consists of 24 residues and its mature protein 97 residues. In the mature protein, there is an insert of one residue (Ala) just after the 9th residue. This insert is unique to the Australian lungfish among vertebrate species studied. The amino acid sequence of the mature protein shares the common, or the same-group, amino acid residues at 9 positions with tetrapod and not actinopterygian vertebrates, while only one residue is common to some teleosts and the lungfish to the exclusion of the tetrapods. The overall sequence of the mature protein of the Australian lungfish also shares more similarity with those of tetrapods (69 to 84%) than it does with teleosts (57 to 74%). These results on the relation of the alpha subunit precursor molecule between the lungfish and other vertebrates are consistent with the recent molecular phylogenetic studies suggesting a closer relationship between lungfish and tetrapods than between lungfish and teleosts. We also found that the primary structure of the lungfish alpha subunit is slightly but significantly more similar to that of homeothermic vertebrates than to that of amphibians. This may be due to specialization of the amphibian alpha subunit molecules.

High-level secretion of biologically active recombinant porcine follicle-stimulating hormone by the methylotrophic yeast Pichia pastoris

An active recombinant glycoprotein hormone, porcine follicle-stimulating hormone (recFSH), has been produced for the first time in the methylotrophic yeast, Pichia pastoris. The yield of secreted recFSH (10 mg/l) was the highest ever reached. RecFSH displayed an apparent molecular mass of 41 kDa by SDS-PAGE and was found to bear only N-linked carbohydrates of the high-mannose type. Its in vitro binding and cell-stimulating activities were identical to those of pituitary porcine FSH. The large availability and the noncharged N-glycans of FSHrec should render it highly valuable for structural studies.

Recombinant porcine follicle stimulating hormone produced in baculovirus-insect cells induces rat ovulation in vivo and gene expression of tissue plasminogen activator in vitro

Superovulatory responses in cattle are known to be highly variable. In the present study, a recombinant porcine follicle stimulating hormone (rpFSH) produced in baculovirus-insect cells was utilised to evaluate the role of this recombinant FSH in control of the ovulatory process. Immature hypophysectomised rats were implanted with oestrogen pellet (10 mg diethylstilbestrol) and then primed with pregnant mare serum gonadotropin (PMSG, 17.5 IU, sc). Fifty-two hours later, 100 microg rpFSH or saline was injected (sc) to induce ovulation. All rats that received rpFSH ovulated with about eight ova rat(-1), whereas none of the control animals did. Ovulation induced by rpFSH was associated with an increase in the ovarian activity and message levels of tissue-type plasminogen activator (tPA), a protease important in the preovulatory degradation of the follicle wall. Furthermore, addition of rpFSH to the cultured rat granulosa cells resulted in a significant increase in tPA enzyme activity. These results demonstrate that rpFSH produced in baculovirus-insect cells has biological potency in ovulation as well as gene expression of tPA, providing a large advantage of this massive expression system in the reproduction of domestic animals.

Baculovirus-insect cell production of bioactive porcine FSH

The in vitro and in vivo bioactivity of recombinant porcine FSH (rpFSH) produced from insect cells through use of a baculovirus expression system were studied and compared with those of natural FSH preparations. Determination of in vitro bioactivity, using the rat Sertoli cell aromatase bioassay, indicated that rpFSH is as active as purified pituitary FSH. Determination of in vivo bioactivity, using the mouse uterine weight bioassay, indicated that rpFSH is as active as purified pituitary FSH. Using the mouse Leydig cell testosterone bioassay, it was demonstrated that the intrinsic LH bioactivity of rpFSH is negligible. The increases in ovarian and uterine weight, and the stimulation in follicular growth in immature hypophysectomized rats induced by rpFSH supplemented with hCG were comparable to those induced by natural FSH preparations. Furthermore, rpFSH alone in hypophysectomized mice stimulated preantral follicular growth to preovulatory stages, and the subsequent injection of hCG caused ovulation. These results demonstrate that in vitro and in vivo biological characteristics of rpFSH produced from baculovirus-insect cells are indistinguishable from those of FSH isolated from natural sources.

Presence of the same transcript of pro-opiomelanocortin (POMC) genes in the porcine anterior and intermediate pituitary lobes

The existence of heterogeneous molecular species of pro-opiomelanocortin (POMC) has been reported and it has been inferred that this explains the distinct release patterns of POMC-derived peptide hormones by the anterior and intermediate lobes of the pituitary gland. The aim of this study was to determine the nucleotide sequences of porcine pituitary anterior and intermediate lobar POMC from animals of the same strain. The POMC cDNAs were obtained using immunoscreening (anterior lobe) and the polymerase chain reaction (intermediate lobe), and their nucleotide sequences determined. Comparisons of the coding and the 5'-untranslated regions of the two POMCs demonstrated that their nucleotide sequences were identical and Northern blot analysis showed that both mRNAs were the same length. Therefore, the results of this study confirm that the same POMC transcript is present in both the anterior and intermediate pituitary lobes. The differences between the nucleotide and amino acid sequences of porcine POMC found hitherto may be attributable to strain differences. Comparisons of porcine and several vertebrate POMCs revealed highly conserved amino acid sequences in the regions corresponding to the peptide hormones, but the regions between them show considerable evolutionary divergence.

Molecular structures of glycoprotein hormones and functions of their carbohydrate components

Images

Cloning and sequence analysis of the cDNA for the pituitary glycoprotein hormone alpha-subunit of the European eel

A cDNA library constructed using mRNAs isolated from pituitary glands of estradiol-treated eels was screened with a cDNA fragment for the rat glycoprotein hormone alpha-subunit. Three out of 10,000 cDNA clones were revealed and subcloned in pUC13 for characterization and sequencing. All three had the same nucleotide sequence except for a single, silent change in the coding sequence for one of them, and for the location of the poly(A) tail. Analysis of the deduced amino acid sequence strongly suggests that these cDNA clones encode the precursor for the eel common glycoprotein hormone alpha-subunit. This precursor would therefore consist of a 93 amino acid apoprotein preceded by a 24 amino acid long signal peptide. Alignment with glycoprotein hormone alpha-subunits from fish and mammals reveals high homology, ranging from 60 to 90%. Particularly, the ten cysteines and the two putative N-linked glycosylation sites were at the same position. Comparison between fish and mammals shows also that two regions are highly conserved, comprising about half of the protein length. This high conservation rate through evolution argues for the importance of these regions in the conservation of biological properties of the alpha-subunits. In contrast, other regions are highly variable and could be responsible for the immunological specificity. Northern blot analysis of pituitary RNA from control and estradiol-treated eels showed that estradiol treatment strongly increases the pituitary content of mRNA encoding the glycoprotein hormone alpha-subunit.