Thyrotropin-releasing hormone regulation of human TSHB expression: role of a pituitary-specific transcription factor (Pit-1/GHF-1) and potential interaction with a thyroid hormone-inhibitory element

The ageing thyroid: implications for longevity and patient care

Thyroid hormones have vital roles in development, growth and energy metabolism. Within the past two decades, disturbances in thyroid hormone action have been implicated in ageing and the development of age-related diseases. This Review will consider results from biomedical studies that have identified the importance of precise temporospatial regulation of thyroid hormone action for local tissue maintenance and repair. Age-related disturbances in the maintenance of tissue homeostasis are thought to be important drivers of age-related disease. In most iodine-proficient human populations without thyroid disease, the mean, median and 97.5 centile for circulating concentrations of thyroid-stimulating hormone are progressively higher in adults over 80 years of age compared with middle-aged (50-59 years) and younger (20-29 years) adults. This trend has been shown to extend into advanced ages (over 100 years). Here, potential causes and consequences of the altered thyroid status observed in old age and its association with longevity will be discussed. In about 5-20% of adults at least 65 years of age, thyroid-stimulating hormone concentrations are elevated but circulating concentrations of thyroid hormone are within the population reference range, a condition referred to as subclinical hypothyroidism. Results from randomized clinical trials that have tested the clinical benefit of thyroid hormone replacement therapy in older adults with mild subclinical hypothyroidism will be discussed, as well as the implications of these findings for screening and treatment of subclinical hypothyroidism in older adults.

Bisphenol analogues induce thyroid dysfunction via the disruption of the thyroid hormone synthesis pathway

Bisphenol analogues are widely used in industrial and daily-use consumer products having imperfect thyroid hormones (THs) structures. Widespread exposure interferes with thyroid-related health outcomes in human. The mechanisms of disruption on TH synthesis and subsequent thyroid dysfunction by different bisphenol analogues remain unclear. Here, we evaluated bisphenol-induced thyroid endocrine disruption in C57BL/6 mice at doses of 0.002, 0.02, 2, and 20 mg/kg body weight/day (BW/d) for five consecutive weeks. Administration of 20 mg/kg BW/d bisphenol S (BPS) and 2 mg/kg BW/d tetrabromobisphenol S (TBBPS) significantly increased serum thyrotropin (TSH) levels to 1.21-fold and 1.20-fold of control group, respectively, indicating that bisphenols induced thyroid dysfunction in mice. Height of the thyroid follicle epithelium significantly increased to 1.27-, 1.24-, 1.26-, and 1.36-fold compared to control group with BPA, BPS, TBBPA, and TBBPS at 20 mg/kg BW/d, respectively, indicating impairment of the thyroid gland structure, and TBBPS showed potent effect. Exposure to bisphenol analogues of 0.02 mg/kg BW/d downregulated the protein expression levels of thyrotropin receptor, the sodium/iodide symporter, thyroperoxidase. The TH-dependent effects were further determined using the T-Screen assay at 10-11 M to 10-5 M concentrations. Bisphenol analogues significantly decreased TH-dependent GH3 cell proliferation, indicating the antagonistic activity of bisphenol analogues. The gene responsible for THs synthesis of thyrotropin releasing hormone receptor and TSH were upregulated, but downregulation of thyroid receptor β was observed. Our results suggest that bisphenol analogues distinctly induce thyroid dysfunction via TH synthesis, implying adverse effect of bisphenol analogues on TH homeostasis and subsequent physiological processes.

Effects of intracerebroventricular MOTS-c infusion on thyroid hormones and uncoupling proteins

This study was conducted to determine the possible effects of intracerebroventricular MOTS-c infusion on thyroid hormones and uncoupling proteins (UCPs) in rats. Forty male Wistar Albino rats were divided into 4 groups with 10 animals in each group: control, sham, 10 and 100 µM MOTS-c. Hypothalamus, blood, muscle, adipose tissues samples were collected for thyrotropin-releasing hormone (TRH), UCP1 and UCP3 levels were determined by the RT-PCR and western blot analysis. Serum thyroid hormone levels were determined by the ELISA assays. MOTS-c infusion was found to increase food consumption but it did not cause any changes in the body weight. MOTS-c decreased serum TSH, T3, and T4 hormone levels. On the other hand, it was also found that MOTS-c administration increased UCP1 and UCP3 levels in peripheral tissues. The findings obtained in the study show that central MOTS-c infusion is a directly effective agent in energy metabolism.

Discoveries Around the Hypothalamic-Pituitary-Thyroid Axis

Many members of the American Thyroid Association played prominent roles in discovering the various aspects of the hypothalamic-pituitary-thyroid axis. This axis is fundamental for maintaining the normal serum levels of circulating thyroid hormones (THs) and thus the euthyroid state. The pituitary glycoprotein hormone, thyrotropin (TSH), controls the activity of the thyroid gland. Thyrotropin-releasing hormone and the negative feedback mechanism of circulating TH regulate the synthesis and the secretion of TSH. The dynamic interplay of these two dominant mechanisms has essential effects on TSH release. Therefore, the finding of abnormal serum levels of TSH often indicates the presence of a disorder of thyroid gland function. A summary of key historical discoveries in the understanding of the hypothalamic-pituitary axis is presented.

PFOS-induced thyroid hormone system disrupted rats display organ-specific changes in their transcriptomes

Perfluorooctanesulfonic acid (PFOS) is a persistent anthropogenic chemical that can affect the thyroid hormone system in humans and animals. In adults, thyroid hormones (THs) are regulated by the hypothalamic-pituitary-thyroid (HPT) axis, but also by organs such as the liver and potentially the gut microbiota. PFOS and other xenobiotics can therefore disrupt the TH system at various locations and through different mechanisms. To start addressing this, we exposed adult male rats to 3 mg PFOS/kg/day for 7 days and analysed effects on multiple organs and pathways simultaneously by transcriptomics. This included four primary organs involved in TH regulation, namely hypothalamus, pituitary, thyroid, and liver. To investigate a potential role of the gut microbiota in thyroid hormone regulation, two additional groups of animals were dosed with the antibiotic vancomycin (8 mg/kg/day), either with or without PFOS. PFOS exposure decreased thyroxine (T4) and triiodothyronine (T3) without affecting thyroid stimulating hormone (TSH), resembling a state of hypothyroxinemia. PFOS exposure resulted in 50 differentially expressed genes (DEGs) in the hypothalamus, 68 DEGs in the pituitary, 71 DEGs in the thyroid, and 181 DEGs in the liver. A concomitant compromised gut microbiota did not significantly change effects of PFOS exposure. Organ-specific DEGs did not align with TH regulating genes; however, genes associated with vesicle transport and neuronal signaling were affected in the hypothalamus, and phase I and phase II metabolism in the liver. This suggests that a decrease in systemic TH levels may activate the expression of factors altering trafficking, metabolism and excretion of TH. At the transcriptional level, little evidence suggests that the pituitary or thyroid gland is involved in PFOS-induced TH system disruption.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

Establishing gene Amelogenin as sex-specific marker in yak by genomic approach

Yak, an economically important bovine species considered as lifeline of the Himalaya. Indeed, this gigantic bovine is neglected because of the scientific intervention for its conservation as well as research documentation for a long time. Amelogenin is an essential protein for tooth enamel which eutherian mammals contain two copies in both X and Y chromosome each. In bovine, the deletion of a fragment of the nucleotide sequence in Y chromosome copy of exon 6 made Amelogenin an excellent sex-specific marker. Thus, an attempt was made to use the gene as an advanced molecular marker of sexing of the yak to improve breeding strategies and reproduction. The present study confirmed that the polymerase chain reaction amplification of the Amelogenin gene with a unique primer is useful in sex identification of the yak. The test is further refined with qPCR validation by quantifying the DNA copy number of the Amelogenin gene in male and female. We observed a high level of sequence polymorphisms of AMELX and AMELY in yak considered as novel identification. These tests can be further extended into several other specialized fields including forensics, meat production and processing, and quality control.

Association of polymorphisms in Pit-1 gene with growth and feed efficiency in meat-type chickens

OBJECTIVE

The pituitary specific transcription factor-1 (Pit-1) gene is responsible for pituitary development and growth hormone expression and is regarded as a pivotal candidate gene for growth and production in chickens. Therefore, the aim of this study was to investigate the association of Pit-1 polymorphisms with growth and feed efficiency traits in yellow meat-type chickens.

METHODS

In the present study, five single nucleotide polymorphisms (SNPs) of Pit-1 were selected and genotyped by high-throughput matrix-assisted laser desorption-ionization time-of-flight mass spectrometry in 724 meat-type chickens.

RESULTS

Association analysis showed that rs13687126 of Pit-1 was strongly associated with body weight gain (BWG) and feed intake (FI) (p<0.05), and that rs13687128 was significantly correlated with body weight at 70 days of age (BW70), BWG and feed conversion ratio (FCR) (p<0.05). SNP rs13905622 was strongly related to BW70 and FCR (p<0.05). Furthermore, birds with the GG genotype of rs13687126 had larger BWG and FI than those with the AG genotype (p<0.05). Individuals with the TT genotype of rs13687128 were significantly higher BW70 and BWG than those of the CT and CC genotype, while FCR was just the opposite (p<0.05). For rs13905622, the AA chickens showed strongly larger BW70 and lower FCR compared with the AT and TT chickens (p<0.05). Additionally, an ACA haplotype based on rs13687126, rs13687128, and rs13905622 had significant effects on BW70 and FCR (p<0.05).

CONCLUSION

Our studies thus provide crucial evidence for the relationship between polymorphisms of Pit-1 and growth and feed efficiency traits which may be useful for meat-type chicken breeding programs.

Pituitary NR4A1 is negatively regulated by thyroid hormone without direct binding of thyroid hormone receptors on the gene

We previously reported that TRH stimulated pituitary TSHβ gene expression via an immediate increase in NR4A1 in thyrotrophs. We demonstrated that NR4A1 mRNA levels are regulated by thyroid hormone. Pituitary NR4A1 mRNA levels were decreased in mice injected with L-T4. NR4A1 promoter activity was increased by the overexpression of TRβs, and these increases were decreased by T3, and the -27∼+152 bp region was responsible for these changes in vitro. An EMSA showed the lack of TRβs-isoforms binding, and a ChIP assay demonstrated the recruitment of TRβs and NCoR in the -147∼+148 bp region in the absence of T3, whereas T3 induced their release. Experiments on the overexpression and knockdown of NCoR, and using the mutant TRs supported the involvement of NCoR in the TR-induced stimulation. These results demonstrate that thyroid hormone down-regulated basal NR4A1 mRNA levels in the pituitary, and the direct binding of TR was not required.

Pituitary genomic expression profiles of steers are altered by grazing of high vs. low endophyte-infected tall fescue forages

Consumption of ergot alkaloid-containing tall fescue grass impairs several metabolic, vascular, growth, and reproductive processes in cattle, collectively producing a clinical condition known as "fescue toxicosis." Despite the apparent association between pituitary function and these physiological parameters, including depressed serum prolactin; no reports describe the effect of fescue toxicosis on pituitary genomic expression profiles. To identify candidate regulatory mechanisms, we compared the global and selected targeted mRNA expression patterns of pituitaries collected from beef steers that had been randomly assigned to undergo summer-long grazing (89 to 105 d) of a high-toxic endophyte-infected tall fescue pasture (HE; 0.746 μg/g ergot alkaloids; 5.7 ha; n = 10; BW = 267 ± 14.5 kg) or a low-toxic endophyte tall fescue-mixed pasture (LE; 0.023 μg/g ergot alkaloids; 5.7 ha; n = 9; BW = 266 ± 10.9 kg). As previously reported, in the HE steers, serum prolactin and body weights decreased and a potential for hepatic gluconeogenesis from amino acid-derived carbons increased. In this manuscript, we report that the pituitaries of HE steers had 542 differentially expressed genes (P < 0.001, false discovery rate ≤ 4.8%), and the pattern of altered gene expression was dependent (P < 0.001) on treatment. Integrated Pathway Analysis revealed that canonical pathways central to prolactin production, secretion, or signaling were affected, in addition to those related to corticotropin-releasing hormone signaling, melanocyte development, and pigmentation signaling. Targeted RT-PCR analysis corroborated these findings, including decreased (P < 0.05) expression of DRD2, PRL, POU1F1, GAL, and VIP and that of POMC and PCSK1, respectively. Canonical pathway analysis identified HE-dependent alteration in signaling of additional pituitary-derived hormones, including growth hormone and GnRH. We conclude that consumption of endophyte-infected tall fescue alters the pituitary transcriptome profiles of steers in a manner consistent with their negatively affected physiological parameters.

PROP1 triggers epithelial-mesenchymal transition-like process in pituitary stem cells

Mutations in PROP1 are the most common cause of hypopituitarism in humans; therefore, unraveling its mechanism of action is highly relevant from a therapeutic perspective. Our current understanding of the role of PROP1 in the pituitary gland is limited to the repression and activation of the pituitary transcription factor genes Hesx1 and Pou1f1, respectively. To elucidate the comprehensive PROP1-dependent gene regulatory network, we conducted genome-wide analysis of PROP1 DNA binding and effects on gene expression in mutant mice, mouse isolated stem cells and engineered mouse cell lines. We determined that PROP1 is essential for stimulating stem cells to undergo an epithelial to mesenchymal transition-like process necessary for cell migration and differentiation. Genomic profiling reveals that PROP1 binds to genes expressed in epithelial cells like Claudin 23, and to EMT inducer genes like Zeb2, Notch2 and Gli2. Zeb2 activation appears to be a key step in the EMT process. Our findings identify PROP1 as a central transcriptional component of pituitary stem cell differentiation.

Hypothalamus-Pituitary-Thyroid Axis

The hypothalamus-pituitary-thyroid (HPT) axis determines the set point of thyroid hormone (TH) production. Hypothalamic thyrotropin-releasing hormone (TRH) stimulates the synthesis and secretion of pituitary thyrotropin (thyroid-stimulating hormone, TSH), which acts at the thyroid to stimulate all steps of TH biosynthesis and secretion. The THs thyroxine (T4) and triiodothyronine (T3) control the secretion of TRH and TSH by negative feedback to maintain physiological levels of the main hormones of the HPT axis. Reduction of circulating TH levels due to primary thyroid failure results in increased TRH and TSH production, whereas the opposite occurs when circulating THs are in excess. Other neural, humoral, and local factors modulate the HPT axis and, in specific situations, determine alterations in the physiological function of the axis. The roles of THs are vital to nervous system development, linear growth, energetic metabolism, and thermogenesis. THs also regulate the hepatic metabolism of nutrients, fluid balance and the cardiovascular system. In cells, TH actions are mediated mainly by nuclear TH receptors (210), which modify gene expression. T3 is the preferred ligand of THR, whereas T4, the serum concentration of which is 100-fold higher than that of T3, undergoes extra-thyroidal conversion to T3. This conversion is catalyzed by 5'-deiodinases (D1 and D2), which are TH-activating enzymes. T4 can also be inactivated by conversion to reverse T3, which has very low affinity for THR, by 5-deiodinase (D3). The regulation of deiodinases, particularly D2, and TH transporters at the cell membrane control T3 availability, which is fundamental for TH action. © 2016 American Physiological Society. Compr Physiol 6:1387-1428, 2016.

All Hormone-Producing Cell Types of the Pituitary Intermediate and Anterior Lobes Derive From Prop1-Expressing Progenitors

Mutations in PROP1, the most common known cause of combined pituitary hormone deficiency in humans, can result in the progressive loss of all hormones of the pituitary anterior lobe. In mice, Prop1 mutations result in the failure to initiate transcription of Pou1f1 (also known as Pit1) and lack somatotropins, lactotropins, and thyrotropins. The basis for this species difference is unknown. We hypothesized that Prop1 is expressed in a progenitor cell that can develop into all anterior lobe cell types, and not just the somatotropes, thyrotropes, and lactotropes, which are collectively known as the PIT1 lineage. To test this idea, we produced a transgenic Prop1-cre mouse line and conducted lineage-tracing experiments of Prop1-expressing cells. The results reveal that all hormone-secreting cell types of both the anterior and intermediate lobes are descended from Prop1-expressing progenitors. The Prop1-cre mice also provide a valuable genetic reagent with a unique spatial and temporal expression for generating tissue-specific gene rearrangements early in pituitary gland development. We also determined that the minimal essential sequences for reliable Prop1 expression lie within 10 kilobases of the mouse gene and demonstrated that human PROP1 can substitute functionally for mouse Prop1. These studies enhance our understanding of the pathophysiology of disease in patients with PROP1 mutations.

Selective deletion of leptin receptors in gonadotropes reveals activin and GnRH-binding sites as leptin targets in support of fertility

The adipokine, leptin (LEP), is a hormonal gateway, signaling energy stores to appetite-regulatory neurons, permitting reproduction when stores are sufficient. Dual-labeling for LEP receptors (LEPRs) and gonadotropins or GH revealed a 2-fold increase in LEPR during proestrus, some of which was seen in LH gonadotropes. We therefore investigated LEPR functions in gonadotropes with Cre-LoxP technology, deleting the signaling domain of the LEPR (Lepr-exon 17) with Cre-recombinase driven by the rat LH-β promoter (Lhβ-cre). Selectivity of the deletion was validated by organ genotyping and lack of LEPR and responses to LEP by mutant gonadotropes. The mutation had no impact on growth, body weight, the timing of puberty, or pregnancy. Mutant females took 36% longer to produce their first litter and had 50% fewer pups/litter. When the broad impact of the loss of gonadotrope LEPR on all pituitary hormones was studied, mutant diestrous females had reduced serum levels of LH (40%), FSH (70%), and GH (54%) and mRNA levels of Fshβ (59%) and inhibin/activin β A and β B (25%). Mutant males had reduced serum levels of GH (74%), TSH (31%), and prolactin (69%) and mRNA levels of Gh (31%), Ghrhr (30%), Fshβ (22%), and glycoprotein α-subunit (Cga) (22%). Serum levels of LEP and ACTH and mRNA levels of Gnrhr were unchanged. However, binding to GnRH receptors was reduced in LEPR-null LH or FSH gonadotropes by 82% or 89%, respectively, in females (P < .0001) and 27% or 53%, respectively, in males (P < .03). This correlated with reductions in GnRH receptor protein immunolabeling, suggesting that LEP's actions may be posttranscriptional. Collectively, these studies highlight the importance of LEP to gonadotropes with GnRH-binding sites and activin as potential targets. LEP may modulate population growth, adjusting the number of offspring to the availability of food supplies.

TSH Measurement and Its Implications for Personalised Clinical Decision-Making

Advances in assay technology have promoted thyrotropin (TSH) measurements from participation in a multi-analyte assessment of thyroid function to a statistically defined screening parameter in its own right. While this approach has been successful in many ways, it has some grave limitations. This includes the basic question of what constitutes an agreed reference range and the fact that the population-based reference range by far exceeds the variation of the intraindividual set point. Both problems result in a potential misdiagnosis of normal and pathological thyroid function in a substantial proportion of patients. From a physiological perspective, TSH plays an integrated role in thyroid homeostasis. Few attempts have been made to adopt physiological insights into thyroid homeostasis for medical decision-making. Some emerging novel findings question the widely assumed log-linear TSH-FT₄ relationship over the entire thyroid function spectrum. This data favours more complex hierarchically structured models. With a better understanding of its role in thyroid homeostasis in thyroid health and disease, TSH can be revisited in the context of thyroid regulation. This, in turn, could help overcome some of the limitations arising from its isolated statistical use and offer new prospects towards a more personalised interpretation of thyroid test results.

Estudio del polimorfismo Hinfi del gen Pit-1 y su asociación con características de tipo, producción de leche y días abiertos de vacas Holstein en el departamento de Antioquia, Colombia

El objetivo de este estudio fue determinar las frecuencias alélicas y fenotípicas del polimorfismo de nucleótido simple (SNP) del exón VI del gen Pit-1 y su asociación con características de tipo, producción de leche y días abiertos. Se muestrearon un total de 390 vacas Holstein del departamento de Antioquia (Colombia), genotipificadas para el polimorfismo Hinfi de Pit-1 por PCR-RFLP. Se encontraron los genotipos AA, AB y BB con frecuencia de 0,03, 0,43 y 0,53, respectivamente. El alelo A tuvo frecuencia de 0,35 y su presencia en el genotipo se asoció con mayor producción de leche, profundidad de la ubre y del cuerpo; la ausencia del alelo A en el genotipo se asoció con menores días abiertos. Este estudio indica que es posible desarrollar programas de selección usando el gen Pit-1 en bovinos Holstein del departamento de Antioquia.

Pit-1w may regulate prolactin gene expression in mouse testis

Pit-1 is a POU-domain transcription factor that promotes growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone β subunit (TSHβ) gene expression in the pituitary gland. Alternative splicing of Pit-1 gene transcripts has been shown to give rise to several variants with discrete transactivation properties. Recently, we identified a mouse Pit-1 w that is generated by alternative promoter usage and is expressed in a variety of tissues including the testis. Using a combination of reverse-transcription polymerase chain reaction analyses and luciferase reporter gene assays, we investigated the possible role of Pit-1 w in the mouse testis. In postnatal testicular development, the expression of Pit-1 w mRNA was significantly up-regulated between 18 and 20 days after birth when the numbers of secondary spermatocytes and spermatids have been reported to increase in mice. The PRL mRNA, but not the mRNAs for GH or TSHβ, showed intratesticular expression patterns that were similar to those of the Pit-1 w mRNA. In experimental unilaterally cryptorchid testes of adult mice, spermatid numbers were extremely low and the expression levels of both the Pit-1 w and PRL mRNAs dropped dramatically. Furthermore, in the luciferase reporter gene assays, we found that Pit-1 w specifically transactivated the PRL promoter but had no effect on the promoters of GH or TSHβ. These results suggested that Pit-1 w could be involved in the paracrine/autocrine system in mice and may be necessary for normal testicular function via its possible role in regulating PRL expression in testicular germ cells. This is the first report demonstrating the possible role of Pit-1 w in mammals.

Identification of mammalian Pit-1w, possibly involved in spermatogenesis in mice

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Alternative splicing of Pit-1 gene transcripts has been shown to give rise to several variants with discrete transactivation properties; however, those arising from alternative promoters such as avian Pit-1 w have not yet been identified in mammals. Here, comparative genomics analysis followed by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of 5' cDNA ends (5'RACE) were used in identifying Pit-1 w mRNA in the mouse pituitary. The mouse Pit-1 w mRNA is generated by using an alternative promoter located in the first intron, as with chicken Pit-1 w, and is expressed in a wide variety of tissues besides the pituitary. In the testis, Pit-1 w is expressed as the predominant variant and a protein of 33 kDa. During the first wave of spermatogenesis, expression of Pit-1 w mRNA at substantial levels was observed from 3 weeks, but not at 1 or 2 weeks after birth. A combination of immunohistochemistry and in situ hybridization detected Pit-1 mRNA and Pit-1 immunoreactivity in the spermatogonia, spermatocytes, and spermatids in the testis of adult mice. Because secondary spermatocytes and haploid spermatids increase in number between 18 and 20 days after birth in mice, it is possible that mouse Pit-1 w plays a role in spermatogenesis. This is the first report demonstrating the expression of Pit-1 variants arising from alternative promoters in mammals.

Research resource: T-antigen transformation of pituitary cells captures three novel cell lines in the Pit-1 lineage

We report the establishment of three distinct pituitary-derived murine cell lines generated by targeted T-antigen-induced transformation. The Pit1/0 line expresses pituitary-specific transcription factor-1 (Pit-1) but lacks expression of GH, prolactin (Prl), or TSH, and the Pit1/Prl line is selectively positive for Pit-1 and Prl. The third line, Pit1/Triple, expresses Pit-1 and all three of the Pit-1-dependent hormones: GH, Prl, and TSHβ/glycoprotein hormone α-subunit. The three corresponding transformation events appear to have captured pituitary cells representing: 1) an initial step in the Pit-1(+) lineage, 2) a cell line that corresponds to the differentiated lactotrope, and 3) a novel tri-hormone intermediate that may represent a pivotal step in Pit-1(+) cell lineage differentiation. The documented dependence of the tri-hormone expression in the Pit-1/Triple line on Pit-1 activity supports its potential role in the pathway of pituitary cell differentiation. The presence of a 123-kb human transgene encompassing the hGH locus (hGH/bacterial artificial chromosome) in two of these lines, Pit1/0 and Pit1/Prl, further expands their potential utility to the analysis of gene activation within the hGH gene cluster.

A Pit-1 threonine 220 phosphomimic reduces binding to monomeric DNA sites to inhibit Ras and estrogen stimulation of the prolactin gene promoter

Pit-1 is a POU-homeodomain transcription factor that dictates the ontogeny of pituitary somatotrophs, lactotrophs, and thyrotrophs through regulation of their respective protein hormone genes: GH, prolactin (PRL), and TSHbeta. Although Pit-1 threonine 220 (T220) and serine 115 are protein kinase phospho-acceptor sites, the transcriptional role of Pit-1 phosphorylation remains unclear. In the rat PRL promoter (rPRL), Ras-stimulated transcription is mediated by binding of Ets-1 and Pit-1 at a composite site (FPIV). Ets-1 and Pit-1 physically interact, and Pit-1 T220 is a major Ets-1 contact point. T220 was mutated to aspartic acid (D, to mimic phosphorylation) or a neutral alanine (A), and DNA binding and transcriptional activity were tested. The Pit-1 T220D mutation reduced binding at monomeric Pit-1 sites (FPIV, PRL-1d), but not dimeric Pit-1 sites (FPI). Pit-1 T220A bound all sites with wild-type (WT) affinity. In transfections of HeLa cells, each Pit-1 mutant transcriptionally activated the -425rPRL promoter and cooperated with Ets-1 to WT levels. In contrast, Pit-1-mediated Ras activation of the -425 rPRL promoter was significantly inhibited by T220D. Finally, Pit-1 synergistic activation of the 2500-bp rPRL promoter with estrogen receptor was reduced by T220D compared with T220A and WT Pit-1. Thus, phosphorylation of Pit-1 T220 reduces binding to monomeric sites blunting Ras and estrogen/estrogen receptor stimulation of the rPRL gene promoter. Consequently, T220 phosphorylation of Pit-1 by protein kinase A, protein kinase C, or cell cycle-dependent kinases appears to serve as a regulatory switch, inhibiting Ras and estrogen/estrogen receptor regulatory pathways, while enhancing the cAMP/protein kinase A response, thus allowing a more precise integration of pituitary responses to distinct signaling stimuli.

High levels of thyrotropin-releasing hormone receptors activate programmed cell death in human pancreatic precursors

OBJECTIVES

Thyrotropin-releasing hormone (TRH) is expressed in rodent and human adult pancreata and in mouse pancreas during embryonic development. However, expression of TRH receptors (TRHRs) in the pancreas is controversial. We sought to provide evidence that the TRH/TRHR system might play a role in fetal development.

METHODS

We used quantitative reverse transcription-polymerase chain reaction to measure TRH and TRHR messenger RNA (mRNA). To study the effects of TRHR expression in a pancreatic progenitor population, we expressed TRHRs in human islet-derived precursor cells (hIPCs) by infection with adenoviral vector AdCMVmTRHR. Thyrotropin-releasing hormone receptor signaling was measured as inositol phosphate production and intracellular calcium transients. Thyrotropin-releasing hormone receptor expression was measured by [H]methyl-TRH binding. Apoptosis was monitored by release of cytochrome c from mitochondria.

RESULTS

We show that TRH mRNA is expressed in human fetal and adult pancreata, and that TRHR mRNA is expressed in fetal human pancreas but not in adult human pancreas. Thyrotropin-releasing hormone receptors expressed in hIPCs were shown to signal normally. Most importantly, TRH treatment for several days stimulated apoptosis in hIPCs expressing approximately 400,000 TRHRs per cell.

CONCLUSIONS

These findings suggest a possible role for TRH/TRHR signaling in pancreatic precursors to promote programmed cell death, a normal constituent of morphogenesis during embryonic development in humans.

Minireview: Thyrotropin-releasing hormone and the thyroid hormone feedback mechanism

Thyroid hormone (TH) plays a critical role in development, growth, and cellular metabolism. TH production is controlled by a complex mechanism of positive and negative regulation. Hypothalamic TSH-releasing hormone (TRH) stimulates TSH secretion from the anterior pituitary. TSH then initiates TH synthesis and release from the thyroid gland. The synthesis of TRH and TSH subunit genes is inhibited at the transcriptional level by TH, which also inhibits posttranslational modification and release of TSH. Although opposing TRH and TH inputs regulate the hypothalamic-pituitary-thyroid axis, TH negative feedback at the pituitary was thought to be the primary regulator of serum TSH levels. However, study of transgenic animals showed an unexpected, dominant role for TRH in regulating the hypothalamic-pituitary-thyroid axis and an unanticipated involvement of the thyroid hormone receptor ligand-dependent activation function (AF-2) domain in TH negative regulation. These results are summarized in the review.

Involvement of mPOU (Brn-5), a class VI POU protein, in the gene expression of Pit-1 as well as PRL

PRL is mainly expressed in the pituitary and its gene expression is regulated by a variety of transcription factors including Pit-1. Brn-5 is a transcription factor that binds to Pit-1 binding elements and stimulates PRL reporter gene expression. In this study, the role of Brn-5 was examined. RNA interference (RNAi) against Brn-5 leaded to reduction in PRL content of GH3 cells, indicating endogenous Brn-5 may play a role in PRL gene expression. Furthermore Brn-5 RNAi decreased Pit-1 mRNA. Transfection of expression vectors for mPOU (human ortholog of Brn-5) modestly but significantly stimulated activities of PRL-Luc and Pit-1-Luc reporter genes in GH3 and HEK 293 cells. In addition, mPOU showed synergistic action with Pit-1 and CBP on PRL-Luc expression. mPOU-FL, a splicing variant of mPOU, showed weaker activity than mPOU. Chip assay suggested binding of mPOU to PRL and Pit-1 promoters of genomic DNA. Taken together, these results suggest that mPOU (Brn-5) enhances PRL gene expression directly in association with Pit-1 and CBP, and indirectly via the activation of Pit-1 gene expression.

Activation of the thyroid-stimulating hormone beta-subunit gene by LIM homeodomain transcription factor Lhx2

Although there is evidence that the LIM homeodomain transcription factor, Lhx2, can stimulate transcription of the glycoprotein hormone alpha-subunit gene, the role of Lhx2 in regulating TSH beta-subunit has not been established. In the present studies, the ability of Lhx2 to regulate transcription of the TSH beta-subunit gene was examined. In the thyrotrope-derived TalphaT1 cell line, Lhx2 expression was found to be induced by treatment with either TRH or cAMP, consistent with the possibility that Lhx2 may play a role in mediating the ability of this signaling pathway to stimulate TSH gene expression. Transient, forced overexpression of Lhx2 stimulated activity of a TSH beta-subunit reporter gene. Deletion studies provided evidence that the -177 to -79 region of the TSH beta-subunit promoter was necessary for stimulation of reporter gene activity by Lhx2. A gel mobility shift assay provided the evidence that Lhx2 can bind to this region of DNA. DNase I footprinting studies demonstrated that two distinct regions of the TSHbeta promoter, -118 to -108 and -86 to -68, are protected by Lhx2 from nuclease digestion. These regions contain repeats of the sequence, 5'-(G/T)CAAT(T/A)-3'. Mutation of this sequence, especially in the -86 to -68 region, substantially decreased Lhx2 responsiveness of the TSH beta-subunit reporter gene. In addition, a DNA fragment containing the -177 to -79 region of the TSHbeta promoter was found to confer Lhx2 responsiveness to a minimal promoter. These results provide multiple lines of evidence consistent with a role for Lhx2 in modulating expression of the TSH beta-subunit gene.

Comparison of the rapid pro-apoptotic effect of trans-ß-nitrostyrenes with delayed apoptosis induced by the standard agent 5-fluorouracil in colon cancer cells

Trans-beta-nitrostyrene (TBNS) has been reported to be a potent inhibitor of protein phosphatases PTB1 and PP2A and to display a pro-apoptotic effect even in multidrug resistant tumour cells. Here we compared the anti-tumour potential of TBNS with 5-fluorouracil (5-FU) as the standard chemotherapeutic agent for colorectal cancer in LoVo cells. Resistance to 5-FU based therapy might be a consequence of 5-FU's delayed effect requiring long-term effective concentrations in the tumour tissue. Thus, alternatives like platin containing drugs with a more rapid effect have been introduced recently. Compared to 5-FU TBNS displayed a faster cytotoxic and pro-apoptotic effect. A 50% decrease in viability was observed already after 8 h with TBNS while 5-FU displayed no significant effect before 48 h. DNA fragmentation and caspase-3 assays confirmed the more rapid apoptotic effect of TBNS. Since apoptosis affects individual cells these results about a rapidly induced apoptosis were further studied on a single cell level in microscopic assays of caspase-3 and caspase-8 activation. Adducts of trans-beta-nitrostyrene displayed an anti-tumour effect comparable to TBNS which suggests the possibility of creating adducts with optimised tissue targeting. Finally, the calculation of a drug combination index displayed a synergistic effect for the combination of TBNS and 5-FU in Lovo as well as in HT-29 and HCT116 colon cancer cells.

Activin inhibits the human Pit-1 gene promoter through the p38 kinase pathway in a Smad-independent manner

The pituitary transcription factor Pit-1 regulates hormonal production from the anterior pituitary gland. However, the mechanisms by which Pit-1 gene expression is regulated in humans are poorly understood. Activin, a member of the TGFbeta superfamily, acts as a negative regulator of cell growth and prolactin gene expression in lactotrope cells. In this study, we show that activin negatively regulates the human Pit-1 gene promoter. We defined a 117-bp element within the Pit-1 promoter that is sufficient to relay these inhibitory effects. We further investigated the signaling pathways that mediate activin-induced inhibition of Pit-1 gene promoter in pituitary lactotrope cells. We found that the activin effects on Pit-1 gene regulation are Smad independent and require the p38 MAPK pathway. Specifically, blocking p38 kinase activity reverses activin-mediated inhibition of the Pit-1 gene promoter. Together, our results highlight the p38 MAPK pathway as a key regulator of activin function in pituitary lactotrope cells and further emphasizes the critical role played by activin in regulating hormonal production in the pituitary gland.

Dominant Role of Thyrotropin-releasing Hormone in the Hypothalamic-Pituitary-Thyroid Axis

Hypothalamic thyrotropin-releasing hormone (TRH) stimulates thyroid-stimulating hormone (TSH) secretion from the anterior pituitary. TSH then initiates thyroid hormone (TH) synthesis and release from the thyroid gland. Although opposing TRH and TH inputs regulate the hypothalamic-pituitary-thyroid axis, TH negative feedback is thought to be the primary regulator. This hypothesis, however, has yet to be proven in vivo. To elucidate the relative importance of TRH and TH in regulating the hypothalamic-pituitary-thyroid axis, we have generated mice that lack either TRH, the beta isoforms of TH receptors (TRbeta KO), or both (double KO). TRbeta knock-out (KO) mice have significantly higher TH and TSH levels compared with wild-type mice, in contrast to double KO mice, which have reduced TH and TSH levels. Unexpectedly, hypothyroid double KO mice also failed to mount a significant rise in serum TSH levels, and pituitary TSH immunostaining was markedly reduced compared with all other hypothyroid mouse genotypes. This impaired TSH response, however, was not due to a reduced number of pituitary thyrotrophs because thyrotroph cell number, as assessed by counting TSH immunopositive cells, was restored after chronic TRH treatment. Thus, TRH is absolutely required for both TSH and TH synthesis but is not necessary for thyrotroph cell development.

The mimecan gene expressed in human pituitary and regulated by pituitary transcription factor-1 as a marker for diagnosing pituitary tumors

CONTEXT

Mimecan, a secretory protein, belongs to a family of small leucine-rich proteoglycans (SLRPs). The physiological functions of mimecan have not been fully understood.

OBJECTIVE

We hypothesize that the mimecan gene expressed in the human pituitary and regulated by pituitary transcription factor-1 (Pit-1) might act as a marker for diagnosing pituitary tumors.

DESIGN

The clinical aspect of our work was a cross-sectional study.

SETTING AND PATIENTS

In total, 20 pituitary tumor samples were collected from January 1, 2002, to December 30, 2002, in Ruijin Hospital, Shanghai, China.

INTERVENTION

The number of pituitary tumors was limited. Collection of more pituitary tumor samples for additional observation will be necessary.

MAIN OUTCOME MEASURES

The main outcomes were measured by Northern blot, in situ hybridization, immunohistochemical analysis, and so on.

RESULTS

The mimecan gene was expressed at a moderate level in the mouse pituitary gland by Northern blot analysis. Expression of mimecan mRNA and protein is also observed in the human anterior pituitary gland. Luciferase reporter analysis and electrophoretic mobility shift assays show that Pit-1 activates the human mimecan promoter through Pit-1 response element sites. In addition, our data also show that almost all the ACTH- or GH-positive pituitary tumors likely express mimecan protein, and only a portion of prolactin-, TSH-, FSH-, and LH-positive pituitary tumors express mimecan protein.

CONCLUSIONS

This work provides insight into the regulating mechanism of mimecan in pituitary and suggests that mimecan may be an unidentified pituitary secretory protein, and certain pituitary cells secreting ACTH or GH also secrete mimecan.

Hypothalamic control of the thyroidal axis in the chicken: over the boundaries of the classical hormonal axes

The pituitary gland, occupying a central position in the hypothalamo-pituitary thyroidal axis, produces thyrotropin (TSH), which is known to stimulate the thyroid gland to synthetize and release its products, thyroid hormones. TSH is produced by a specific cell population in the pituitary, the so-called thyrotropes. Their secretory activity is controlled by the hypothalamus, releasing both stimulatory and inhibitory factors that reach the pituitary through a portal system of blood vessels. Based on early experiments in mammals, thyrotropin-releasing hormone (TRH) is generally mentioned as the main stimulator of the thyrotropes. During the past few decades, it has become clear that the hypophysiotropic function of the hypothalamus is more complex, with different hormonal axes interacting with each other. In the chicken, it was found that not only TRH, but also corticotropin-releasing hormone (CRH), the main stimulator of corticotropin release, is a potent stimulator of TSH secretion. Somatostatin (SRIH), a hypothalamic factor known for its inhibitory effect on growth hormone secretion, was demonstrated to blunt the TSH response to TRH and CRH. In this review we summarize the latest studies concerning the "interaxial" hypothalamic control of TSH release in the chicken, with a special emphasis on the molecular components of these control mechanisms. It remains to be demonstrated if these findings could also be extrapolated to other species or classes of vertebrates.

Associations of polymorphisms in the Pit-1 gene with growth and carcass traits in Angus beef cattle12

The Pit-1 gene was studied as a candidate for genetic markers of growth and carcass traits. Angus beef cattle that were divergently selected for high- or low-blood serum IGF-I concentration were used in this study. The single-strand conformation polymorphism method was used to identify polymorphism in the Pit-1 gene including regions from intron 2 to exon 6. Two polymorphisms, Pit1I3H (HinfI) and Pit1I3NL (NlaIII), were detected in intron 3 of the Pit-1 gene. One polymorphism, Pit1I4N (BstNI), was found in intron 4, and a single nucleotide polymorphism, Pit1I5, was found in intron 5. The previously reported polymorphism in exon 6, Pit1E6H (HinfI), was also studied in 416 Angus beef cattle. Associations of the polymorphisms with growth traits, carcass traits, and IGF-I concentration were analyzed using a general linear model procedure. No significant associations were observed between these polymorphisms and growth and carcass traits.

Mice lacking the thyrotropin-releasing hormone gene: what do they tell us?

Thyrotropin-releasing hormone (TRH) is localized in the brain hypothalamus and stimulates the secretion and synthesis of pituitary thyrotropin (TSH). Although TRH deficiency caused by artificial hypothalamic destructions has been reported to result in significant decreases in TSH secretion in rodents, clinical observations from the patients with possible TRH deficiency did not entirely agree with these animal results. Because of its ubiquitous distribution throughout the brain and in the peripheral tissues, TRH has been suggested to possess a wide variety of functions in these regions. However, the neurobehavioral and peripheral actions of TRH still remains to be established. It has been, therefore, anticipated that detailed analysis of TRH-knockout mice might provide insight into the physiological significance of endogenous TRH. The present review focuses on the phenotypic findings of mice deficient in TRH.

Regulation of the intronic promoter of rat estrogen receptor alpha gene, responsible for truncated estrogen receptor product-1 expression

We have characterized the intronic promoter of the rat estrogen receptor (ER) alpha gene, responsible for the lactotrope-specific truncated ER product (TERP)-1 isoform expression. Transcriptional regulation was investigated by transient transfections using 5'-deletion constructs. TERP promoter constructs were highly active in MMQ cells, a pure lactotrope cell line, whereas a low basal activity was detected in alphaT3-1 gonadotrope cells or in COS-7 monkey kidney cells. Serial deletion analysis revealed that 1) a minimal -693-bp region encompassing the TATA box is sufficient to allow lactotrope-specific expression; 2) the promoter contains strong positive cis-acting elements both in the distal and proximal regions, and 3) the region spanning the -1698/-1194 region includes repressor elements. Transient transfection studies, EMSAs, and gel shifts demonstrated that estrogen activates the TERP promoter via an estrogen-responsive element (ERE1) located within the proximal region. Mutation of ERE1 site completely abolishes the estradiol-dependent transcription, indicating that ERE1 site is sufficient to confer estrogen responsiveness to TERP promoter. In addition, ERalpha action was synergized by transfection of the pituitary-specific factor Pit-1. EMSAs showed that a single Pit-1 DNA binding element in the vicinity of the TATA box is sufficient to confer response by the TERP promoter. In conclusion, we demonstrated, for the first time, that TERP promoter regulation involves ERE and Pit-1 cis-elements and corresponding trans-acting factors, which could play a role in the physiological changes that occur in TERP-1 transcription in lactotrope cells.

Thyroid hormone receptor DNA binding is required for both positive and negative gene regulation

The beta isoform of thyroid hormone receptor (TR-beta) has a key role in the feedback regulation of the hypothalamic-pituitary-thyroid (H-P-T) axis. The mechanism of trans-repression of the hypothalamic thyrotropin-releasing hormone (TRH) and pituitary thyroid-stimulating hormone (TSH) subunit genes, however, remains poorly understood. A number of distinct mechanisms for TR-beta-mediated negative regulation by thyroid hormone have been proposed, including those that require and do not require DNA binding. To clarify the importance of DNA binding in negative regulation, we constructed a DNA-binding mutant of TR-beta in which two amino acids within the P box were altered (GSG for EGG) to resemble that found in the glucocorticoid receptor (GR). We termed this mutant GS125, and as expected, it displayed low binding affinities for positive and negative thyroid hormone-response element (pTRE and nTRE, respectively) in gel-mobility shift assays. In transient transfection assays, the GS125 mutant abolished transactivation on three classic pTREs (DR+4, LAP, and PAL) and all negatively regulated promoters in the H-P-T axis (TRH, TSH-beta, and TSH-alpha). However, GS125 TR-beta bound to a composite TR/GR-response element and was fully functional on this hybrid TR/GR-response element. Moreover, the GS125 TR-beta mutant displayed normal interactions with transcriptional cofactors in mammalian two-hybrid assays. These data do not support a DNA-binding independent mechanism for thyroid hormone negative regulation in the H-P-T axis.

Expression of Fushi tarazu factor 1 homolog and Pit-1 genes in the pituitaries of pre-spawning chum and sockeye salmon

Fushi tarazu factor-1 (FTZ-F1) and Pit-1 are major pituitary transcription factors, controlling expression of genes coding for gonadotropin (GTH) subunits and growth hormone/prolactin/somatolactin family hormone, respectively. As a first step to investigate physiological factors regulating gene expression of these transcription factors, we determined their mRNA levels in the pituitaries of chum salmon (Oncorhynchus keta) at different stages of sexual maturation. FTZ-F1 gene expression was increased in males at the stage before spermiation, where the levels of GTH alpha and IIbeta subunit mRNAs were elevated. Pit-1 mRNA showed maximum levels at the final stage of sexual maturation in both sexes, when expression of somatolactin gene peaked. To clarify whether gonadotropin-releasing hormone (GnRH) is involved in these increases in FTZ-F1 and Pit-1 gene expression, we examined effects of GnRH analog (GnRHa) administration on their gene expression in maturing sockeye salmon (Oncorhynchus nerka). GnRHa stimulated Pit-1 gene expression in females only, but failed to stimulate FTZ-F1 gene expression in both sexes. The up-regulated expression of FTZ-F1 and Pit-1 genes at the pre-spawning stages suggest that the two transcription factors have roles in sexual maturation of salmonids. Physiological factors regulating gene expression of FTZ-F1 and Pit-1 are discussed in this review.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

cAMP response element-binding protein-binding protein mediates thyrotropin-releasing hormone signaling on thyrotropin subunit genes

Transcription of pituitary alpha-glycoprotein hormone subunit (alpha-GSU) and thyrotropin beta subunit (TSH-beta) genes is stimulated by thyrotropin-releasing hormone (TRH). Since cAMP response element-binding protein (CREB)-binding protein (CBP) integrates a number of cell signaling pathways, we investigated whether CBP is important for TRH stimulation of the TSH subunit genes. Cotransfection of E1A in GH(3) cells completely blocked TRH stimulation of the TSH subunit genes, suggesting that CBP is a key factor for TRH signaling in the pituitary. CBP and Pit-1 acted synergistically in TRH stimulation of the TSH-beta promoter, and amino acids 1-450 of CBP were sufficient for the TRH effect. In contrast, on the human alpha-GSU promoter, CREB and P-Lim mediated TRH signaling. Intriguingly, CREB was phosphorylated upon TRH stimulation, leading to CBP recruitment to the alpha-GSU promoter. CBP also interacted with P-Lim in a TRH-dependent manner, suggesting that P-Lim is an important factor for non-cAMP response element-mediated TRH stimulation of this promoter. Distinct domains of CBP were required for TRH signaling by CREB and P-Lim on the alpha-GSU promoter, amino acids 450-700 and 1-450, respectively. Thus, the amino terminus of CBP plays a critical role in TRH signaling in the anterior pituitary via both Pit-1-dependent and -independent pathways, yielding differential regulation of pituitary gene products.

Expression of pituitary homeo box 1 (Ptx1) in human non-neoplastic pituitaries and pituitary adenomas

We investigated the localization of pituitary homeo box 1 (Ptx1) protein in five human non-neoplastic pituitaries and 73 of all types of pituitary adenomas using immunohistochemistry, and the expression of Ptx1 messenger RNA (mRNA) in 18 representative pituitary adenomas using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. By immunohistochemical analysis, Ptx1 protein was extensively detected in the nuclei of normal human pituitary cells. Ptx1 was detected in 10/14 (71.4%) of growth hormone (GH)-secreting adenomas, 12/12 (100%) of prolactin (PRL)-secreting adenomas, 18/20 (90%) of adrenocorticotropic hormone (ACTH)-secreting adenomas, 6/7 (85.7%) of thyroid-stimulating hormone (TSH)-secreting adenomas, and 17/20 (85%) of clinically non-functioning adenomas, including 9/10 (90%) of gonadotropin-subunit-positive adenomas. Thus, there was no relationship between Ptx1 expression and a particular type of pituitary adenomas. By RT-PCR analysis, Ptx1 mRNA was expressed in all 18 cases of pituitary adenomas, including two cases negative for Ptx1 protein by immunohistochemistry. These results suggested that Ptx1 may be an universal transcription factor in both neoplastic and non-neoplastic conditions in human pituitaries. The synergistic action with other transcription factors may be speculated to determine the specific production of the anterior pituitary hormones.

Contributions of immunohistochemistry and in situ hybridization to the functional analysis of pituitary adenomas

Immunohistochemistry (IHC) and recently in situ hybridization (ISH) have elucidated various aspects of human pituitary adenomas, i.e., functional differentiation and classification, transcription factors and mechanism of hormone production, regulation of hormone secretion, and processing of prohormones. Recently, the use of tyramide (catalyzed signal amplification; TSA or CSA) and RT-PCR has been effective for detection of trivial amount of proteins (peptides) and mRNA, respectively. Immunomolecular histochemistry is expected to further clarify the function and biology of human pituitary adenomas.

Thyroid hormone suppression of pituitary hormone gene expression

T3 suppression of TSH subunit gene transcription is an important step in maintaining thyroid hormone homeostasis, and recent investigations have increased our understanding of this process. Thyrotrope-specific proteins play a critical role in TSH subunit gene expression, and influence T3-mediated regulatory mechanisms. The structure and placement of the TSH gene TREs define suppressive regulation by T3, and this process is favored by the TR isoforms expressed in the pituitary. Elimination of TR beta function compromises the pituitary response to T3. TR beta 2, the isoform specifically expressed in pituitary and neural tissue, contains a transferable domain that both increases T3-independent gene transcription and enhances T3-suppressed transcription. The functional interaction of TR beta 2 with other regulatory proteins is distinct from that of other TR isoforms, and likely plays a critical role in pituitary physiology and in pituitary resistance to thyroid hormone. The development of novel thyrotrope cell lines will allow investigators to define new proteins and molecular mechanisms that distinguish negative from positive T3 transcriptional regulation.

Combined pituitary hormone deficiency: role of Pit-1 and Prop-1

During fetal development of the anterior pituitary gland, a number of sequential processes occur that affect cell differentiation and proliferation. Molecular analyses have revealed several steps that are required for pituitary cell line specification and have identified specific factors that control these steps. The gene encoding the pituitary transcription factor 1 (Pit-1) is expressed during differentiation steps that take place quite late in the development of the anterior pituitary gland. Clinically, patients with mutations of the PIT1 gene are characterized by severe deficiencies in growth hormone (GH) and prolactin (PRL), and often develop secondary hypothyroidism. A second pituitary transcription factor is known as Prophet of Pit-1 (Prop-1), and a mutation of the Prop1 gene has been detected in Ames dwarf mice. Several Prop1 mutations have been identified that structurally affect the 'paired-like' DNA-binding domain of the Prop-1 protein molecule. Patients with PROP1 mutations show combined pituitary hormone deficiency. These patients exhibit secondary hypogonadism in addition to the deficiencies of GH, PRL and thyroid-stimulating hormone (TSH) also seen in patients with PIT1 mutations. Although all are in the subnormal range, the levels of GH, PRL and TSH in patients with PROP1 mutations are, on average, slightly higher than in patients with PIT1 mutations. Some degree of hypocortisolism may necessitate cortisol substitution in patients with PROP1 mutations.

Candidate gene markers associated with somatotropic axis and milk selection

One of the obstacles to progress in dairy cattle selection is that milk production traits are only expressed after the first calving. However, the use of the quantitative trait loci (QTL) technology will improve the efficiency of dairy industry with a positive image for the consumers. QTL are part of the genome showing a preponderant action and explaining the major part of variation of the trait production. At the present time, the two major strategies developed to detect such QTL are the candidate gene approach and the positional genetics approach. The somatotropic axis contains the most promising candidates in this respect, as it strongly regulates milk production. Then, the identification of favorable QTL associated with the somatotropic axis that are significantly correlated with genetic merits for milk production could lead to more effective selection programs.

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

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