The transcription factor TTF-1 is expressed at the onset of thyroid and lung morphogenesis and in restricted regions of the foetal brain

Thyroid development and its disorders: genetics and molecular mechanisms

Thyroid gland organogenesis results in an organ the shape, size, and position of which are largely conserved among adult individuals of the same species, thus suggesting that genetic factors must be involved in controlling these parameters. In humans, the organogenesis of the thyroid gland is often disturbed, leading to a variety of conditions, such as agenesis, ectopy, and hypoplasia, which are collectively called thyroid dysgenesis (TD). The molecular mechanisms leading to TD are largely unknown. Studies in murine models and in a few patients with dysgenesis revealed that mutations in regulatory genes expressed in the developing thyroid are responsible for this condition, thus showing that TD can be a genetic and inheritable disease. These studies open the way to a novel working hypothesis on the molecular and genetic basis of this frequent human condition and render the thyroid an important model in the understanding of molecular mechanisms regulating the size, shape, and position of organs.

Nkx2.1 transcription factor in lung cells and a transforming growth factor-beta1 heterozygous mouse model of lung carcinogenesis

The Nkx2.1 homeobox gene and transforming growth factor-beta1 (TGF-beta1) are essential for organogenesis and differentiation of the mouse lung. NKX2.1 is a marker of human lung carcinomas, but it is not known whether this gene participates in early tumorigenesis. Addition of TGF-beta1 to TGF-beta1-responsive nontumorigenic mouse lung cells cotransfected with a NKX2.1Luc luciferase reporter and either a Sp1 or Sp3 plasmid showed a significant increase or decrease, respectively, in NKX2.1Luc transcription. Cotransfection of Sp3 and dominant-negative TGF-beta type II receptor plasmids negated the effect of Sp1. Cotransfected Sp1 plasmid with either dominant-negative Smad2 or Smad3 or Smad4 plasmids significantly decreased NKX2.1Luc transcription. Electrophoretic mobility shift assays revealed binding of Sp1 and Smad4 to the NKX2.1 promoter. With a TGF-beta1 heterozygous mouse model, Nkx2.1 mRNA and protein in lungs of TGF-beta1 heterozygous mice were significantly lower compared to wildtype (WT) littermates. Competitive reverse transcription (RT)-polymerase chain reaction (PCR) and immunostaining showed that Nkx2.1 mRNA and protein decreased significantly in adenomas and adenocarcinomas compared to normal lung tissue. Our in vitro data showed that regulation of Nkx2.1 by TGF-beta1 occurs through TGF-beta type II receptor and Smad signaling, with Sp1 and Sp3 in lung cells. Our in vivo data showed reduced Nkx2.1 in lungs of TGF-beta1 heterozygous mice compared to WT mice, that is detectable in adenomas, and that is further reduced in carcinogenesis, and that correlates with reduction of Sp1, Sp3, and Smads in lung adenocarcinomas. Our findings suggest that reduced Nkx2.1 and TGF-beta1 signaling components may contribute to tumorigenesis in the lungs of TGF-beta1 heterozygous mice.

In vivo characterization of the Nkx2.1 promoter/enhancer elements in transgenic mice

Nkx2.1 encodes a homeodomain transcription factor whose expression is restricted to the thyroid, lung and specific regions of the forebrain. NKX2.1 plays a key role in the development of the latter organs. In lung epithelial cells, two regions of promoter activity, designated as proximal and distal promoters, map to DNA elements located upstream of exons 1 and 2 (within intron 1). That both promoters are active in vivo has been demonstrated by the presence of multiple Nkx2.1 mRNA species with distinct and appropriate exonic composition. The mechanisms of Nkx2.1 tissue selective gene expression remain entirely unknown. We have examined the potential of three overlapping DNA fragments, representing a total of approximately 4 kb of potential regulatory DNA from the baboon Nkx2.1 5' flanking region to direct expression of LacZ in transgenic mice during embryonic development. The three constructs include sequences in proximal, distal and both promoters separately. All three fragments directed LacZ expression to the brain of transgenic E15 and E18 mouse embryos. In addition to a number of other sites, all three constructs were active in subgroups of cells localized in the hypothalamus, a well-established site of endogenous Nkx2.1 gene expression. Two of the fragments conferred tracheal epithelial-specific LacZ gene expression, but parenchymal lung expression was not observed. None of the three fragments had activity in the thyroid. These data demonstrate the complexity of the Nkx2.1 tissue specific gene regulation and suggest that cis-active elements required for tracheal versus lung morphogenesis may be distinct. The same applies to the brain, which provides the most permissive environment for recognition of Nkx2.1 tissue specific cis-active elements.

The utility and limitation of thyroid transcription factor-1 protein in primary and metastatic pulmonary neoplasms

Thyroid transcription factor-1 (TTF-1) is a tissue-specific transcription factor expressed in the thyroid and lung. The clinical utility and limitation of TTF-1 in primary or metastatic carcinomas of the lung have not been previously studied in detail. We examined TTF-1 expression in 510 primary lung and 107 metastatic neoplasms. TTF-1 was detectable in 4/99 (4%) squamous cell carcinomas, 169/176 (96%) solitary adenocarcinomas, 34/34 (100%) multifocal adenocarcinomas, 1/1 (100%) signet ring cell carcinoma, 16/20 (80%) mucinous adenocarcinomas, 23/23 (100%) nonmucinous bronchioloalveolar carcinomas, 19/36 (53%) small cell carcinomas, and 39/44 (89%) sclerosing hemangioma. TTF-1 was absent in all eight carcinoids, three atypical carcinoids, 23 pleomorphic carcinomas, 25 lymphoepithelioma-like carcinomas, the sarcomatous component of one pseudomesotheliomatous carcinoma, and one mesothelioma. In four combined small cell carcinomas and 12 adenosquamous carcinomas, TTF-1 expression was only demonstrated in the adenocarcinoma component. There were 78 TTF-1 non-immunoreactive metastatic cases from 22 livers, 20 colorectums, 10 breasts, six nasopharynx, four larynx, four ovaries, three salivary glands, three esophagus, two adrenal glands, two kidneys, one bile duct, and one endometrium. TTF-1 was also detected in all 10 cervical lymph nodes, seven brain, and 6/7 (86%) bony tissues of 24 patients with metastatic carcinomas of unknown primary site, but it was absent in 125 patients with metastatic carcinomas other than lung origin in cervical lymph nodes, brain, and bony tissues. These results indicate the clinical usefulness and limitation in certain primary and metastatic lung neoplasms.

Growth hormone deficiency and related disorders: insights into causation, diagnosis, and treatment

Advances in molecular biology have led to the identification of mutations within several novel genes associated with the phenotype of isolated growth hormone deficiency, combined pituitary hormone deficiency, and syndromes such as septo-optic dysplasia. Progress has also been made in terms of the optimum diagnosis of disorders of stature and their treatment. The use of growth hormone for the treatment of adults with growth hormone deficiency and conditions such as Turner's syndrome, Prader-Willi syndrome, intrauterine growth restriction, and chronic renal failure has changed the practice of endocrinology, although cost-benefit implications remain to be established.

Transcriptional repressor DREAM interacts with thyroid transcription factor-1 and regulates thyroglobulin gene expression

Tissue-specific gene expression depends on the interaction between tissue-specific and general transcription factors. DREAM is a Ca2+-dependent transcriptional repressor widely expressed in the brain where it participates in nociception through its control of prodynorphin gene expression. In the periphery, DREAM is highly expressed in the thyroid gland, the immune system, and the reproductive organs. Here, we show that DREAM interacts with thyroid-specific transcription factor TTF-1 and regulates the expression of the thyroglobulin (Tg) gene. The mechanism also involves binding of DREAM to the thyroglobulin promoter and blockage of TTF-1-mediated transactivation. The TSH/cAMP pathway and Ca2+ signaling regulate DREAM-mediated transcriptional repression of the thyroglobulin gene. Furthermore, chromatin immunoprecipitation experiments in FRTL-5 cells confirmed that Tg is a bona fide target gene for DREAM transrepression in thyroid follicular cells.

Genetic deletion of sonic hedgehog causes hemiagenesis and ectopic development of the thyroid in mouse

Thyroid dysgenesis encountered in 85% of patients with congenital hypothyroidism is a morphologically heterogeneous condition with primarily unknown pathogenesis. Here we identify sonic hedgehog (Shh) as a novel regulator of thyroid development. In Shh knockout mice the thyroid primordium is correctly specified in the pharyngeal endoderm, but budding and dislocation are slightly delayed. In late development the thyroid fails to form a bilobed gland. Instead a single thyroid mass is found unilaterally and mostly to the left of the midline. Thyroid-specific transcription factors (TTF-1 and TTF-2) and thyroglobulin are expressed indicating terminal differentiation. Strikingly, TTF-1- and TTF-2-positive cells aberrantly develop in the presumptive trachea of Shh-/- embryos. The ectopic tissue buds ventrolaterally into the adjacent mesenchyme, and less extensively into the tracheal lumen, forming follicle-like structures that accumulate thyroglobulin. Shh mRNA is not expressed in the thyroid precursor cells at any developmental stage. The results indicate that Shh signaling indirectly governs the symmetric bilobation of the thyroid during late organogenesis. Shh also seems to repress inappropriate thyroid differentiation in nonthyroid embryonic tissues. This study provides clues to the molecular mechanisms that might be dysregulated in thyroid hemiagenesis and development of ectopic thyroid tissue outside the thyroglossal duct.

Prostatic neuroendocrine tumor in multiple endocrine neoplasia Type 2B

We report the unusual occurrence of a neuroendocrine prostatic tumor in two young males with multiple endocrine neoplasia (MEN) 2B. Immunohistochemistry of the tumor markers may help differentiate a primary neuroendocrine prostate tumor from the metastasis of a medullary thyroid carcinoma of poor prognosis. MEN 2B hallmarks (i.e. plasma thyrocalcitonin and urinary metanephrines) may be systematically investigated in neuroendocrine tumors of the prostate, and conversely prostate examination may be performed in the periodic screening of MEN 2B male patients.

Thyroid transcription factor-1, but not p53, is helpful in distinguishing moderately differentiated neuroendocrine carcinoma of the larynx from medullary carcinoma of the thyroid

Moderately differentiated neuroendocrine carcinoma/atypical carcinoid tumor is the most common nonsquamous malignancy in the larynx; however, due to morphologic overlap and calcitonin immunoreactivity, it can be difficult to distinguish from thyroid medullary carcinoma. Currently, low serum calcitonin is the most reliable means for distinguishing primary laryngeal moderately differentiated neuroendocrine carcinoma from metastatic medullary carcinoma. Thyroid transcription factor-1 (TTF-1) is positive in at least 80% of medullary carcinomas, but has not been evaluated in laryngeal moderately differentiated neuroendocrine carcinomas. Additionally, it has been suggested that p53 is positive in laryngeal moderately differentiated neuroendocrine carcinomas and negative in other neuroendocrine tumors, but this has not been validated. The purpose of this study was to determine if the immunohistochemical markers TTF-1 and p53 could be used to discriminate between laryngeal moderately differentiated neuroendocrine carcinomas and thyroid medullary carcinomas. Eight laryngeal moderately differentiated neuroendocrine carcinomas and 10 thyroid medullary carcinomas were identified from the archival files of the BWH and MGH Pathology Departments. Hematoxylin and eosin slides were reviewed, and immunohistochemistry was performed using antibodies to calcitonin, TTF-1, and p53. Calcitonin immunohistochemistry demonstrated immunoreactivity in 100% of laryngeal moderately differentiated neuroendocrine carcinomas (N=8) and 100% of thyroid medullary carcinomas (N=10). There was weak, focal immunoreactivity with TTF-1 in one of eight (13%) laryngeal moderately differentiated neuroendocrine carcinomas, whereas nine of ten (90%) medullary carcinomas were positive for TTF-1, with strong diffuse staining in seven of these cases (78%). p53 was positive in three of six (50%) laryngeal moderately differentiated neuroendocrine carcinomas, and three of ten (30%) medullary carcinomas. Our data demonstrate that immunoreactivity for TTF-1, but not calcitonin or p53, may be helpful in distinguishing laryngeal moderately differentiated neuroendocrine carcinoma and thyroid medullary carcinoma. In particular, diffuse and/or strong TTF-1 immunoreactivity favors a diagnosis of primary thyroid medullary carcinoma over laryngeal moderately differentiated neuroendocrine carcinoma.

Diagnostic strategies for unknown primary cancer

Unknown primary cancer (UPC) is defined by the presence of metastatic disease for which a primary site is undetectable on presentation. Computed tomography scan of the body was performed routinely in search of the primary cancer and invasive procedures were pursued in selective cases. Magnetic resonance imaging of the breast enables identification of an occult breast primary tumor in < or = 75% of women who present with adenocarcinoma in the axillary lymph nodes and can influence surgical management. Positron emission tomography scan also can be used in the diagnosis of UPCs, but its value is controversial. Cytokeratins 7 and 20 and thyroid transcription factor are some of the histochemical markers used in most patients who present with metastatic adenocarcinoma. Some of the newly discovered immunohistochemical markers further assist in narrowing the differential diagnosis. The role of molecular profiling to make the diagnosis, establish the prognosis, and assess the response to treatment in UPCs is evolving. The authors discuss the role of histochemical markers in the diagnosis of UPC and the most recent data regarding the use of imaging and invasive diagnostic modalities and gene expression profiles.

NKX2.1 regulates transcription of the gene for human bone morphogenetic protein-4 in lung epithelial cells

Bone morphogenetic protein 4, BMP4, plays an important role in the development of various organs including the lungs. Little is known regarding the regulation of Bmp4 gene expression in any organ. In the lung, indirect evidence indicates that NKX2.1, a homeodomain transcriptional factor with a demonstrated role in lung morphogenesis, may be a potential upstream regulator of Bmp4 gene expression. In particular, Bmp4 mRNA is reduced or absent in Nkx2.1(-/-) lungs. The human Bmp4 gene has been reported to include two regions of promoter activity in an embryonal carcinoma cell line, Tera2EC. The hBmp4.1 promoter is located upstream of exon I, whereas the second promoter, hBmp4.2, is localized within intron 1 and upstream of exon II. In the current study, we used a co-transfection assay in lung epithelial cells to examine the response of the two hBmp4 promoters to transcriptional stimulation by NKX2.1. Two DNA sequences were identified on the hBmp4.1 promoter that bind NKX2.1 and serve as functional cis-active NKX2.1-responsive elements. Similarly, NKX2.1 stimulated transcription from the hBmp4.2 promoter through two consensus binding sites localized within 412 nucleotides from the site of transcriptional initiation. Thus, both hBmp4 promoters include specific cis-active elements that bind to and mediate transcriptional regulation by NKX2.1. These findings bear functional implications regarding the regulation of a key signaling molecule by a homeodomain transcriptional regulator of lung epithelial morphogenesis.

TAZ Interacts with TTF-1 and Regulates Expression of Surfactant Protein-C

Thyroid transcription factor-1 (TTF-1/Nkx-2.1) is required for formation of the lung and differentiation of peripheral respiratory epithelial cells. TTF-1 activates transcription of target genes, including the surfactant proteins critical for lung function. A recently identified protein TAZ (transcriptional co-activator with PDZ-binding motif) contains a WW domain and a COOH-terminal PDZ-binding motif that are proposed to mediate its interactions with various transcriptional proteins. To determine the role of TAZ in the regulation of gene expression in the lung, the sites of TAZ expression and the role of TAZ in the regulation of respiratory epithelial gene expression were assessed. TAZ mRNA was detected in immortalized mouse lung epithelial cells, primary isolates of mouse alveolar type II epithelial cells, and epithelial cells of fetal lung. Sites of TAZ mRNA and protein overlapped with those of TTF-1 and surfactant protein C (SP-C) in the respiratory epithelial cells of the mouse lung. In the presence of TTF-1, TAZ synergistically activated the expression of mouse SP-C-luciferase reporter constructs. Mammalian two-hybrid assays and pull-down experiments demonstrated that the TAZ directly interacted with TTF-1. Further, deletion analysis demonstrated that TAZ binds to the NH(2)-terminal domain of TTF-1. TAZ binds to TTF-1, increasing the transcriptional activity of TTF-1 on the SP-C promoter. Developmental and cell-selective regulation of TAZ provides a mechanism by which the activity of TTF-1 on target genes is modulated.

Clear cells and thyroid transcription factor I reactivity in sclerosing mucoepidermoid carcinoma of the thyroid gland

Clear cells have been described in mucoepidermoid carcinoma of the salivary glands, but to our knowledge these cells have not been recognized as a distinctive component of sclerosing mucoepidermoid carcinoma with eosinophilia of the thyroid gland. We report four examples in which sclerosing mucoepidermoid carcinoma of the thyroid gland contained a minor component (10% to 30%) of clear cells. The four tumors occurred in women with Hashimoto's thyroiditis whose ages ranged from 38 to 52 years. All four patients presented with thyroid nodules, but two also had enlarged cervical lymph nodes. Although two tumors metastasized to multiple cervical lymph nodes and one recurred in the soft tissues of the neck, all four patients are disease-free 6 months to 6 years after surgical treatment. The locally aggressive behavior of the first three tumors was probably related to their size, rather than to the presence of clear cells. Microscopically, these tumors showed the classical features of sclerosing mucoepidermoid carcinoma with eosinophilia, as well as nests of clear cells that appeared to be glycogen-rich squamous cells. Although the four tumors were thyroglobulin negative, two were immunoreactive to thyroid transcription factor 1 (TTF-1), supporting the idea that they originated from squamous metaplasia of follicular epithelium rather than from solid cell nests of the ultimobranchial body.

Zebrafish hhex, nk2.1a, and pax2.1 regulate thyroid growth and differentiation downstream of Nodal-dependent transcription factors

During zebrafish development, the thyroid primordium initiates expression of molecular markers such as hhex and nk2.1a in the endoderm prior to pharynx formation. As expected for an endodermally derived organ, initiation of thyroid development depends on Nodal signalling. We find that it also depends on three downstream effectors of Nodal activity, casanova (cas), bonnie and clyde (bon), and faust (fau)/gata5. Despite their early Nodal-dependent expression in the endoderm, both hhex and nk2.1a are only required relatively late during thyroid development. In hhex and nk2.1a loss-of-function phenotypes, thyroid development is initiated and arrests only after the primordium has evaginated from the pharyngeal epithelium. Thus, like pax2.1, both hhex and nk2.1a have similarly late roles in differentiation or growth of thyroid follicular cells, and here, we show that all three genes act in parallel rather than in a single pathway. Our functional analysis suggests that these genes have similar roles as in mammalian thyroid development, albeit in a different temporal mode of organogenesis.

C/EBP transcription factors in the lung epithelium

During recent years, the biological roles of CCAAT/enhancer binding proteins (C/EBPs) in the lung have started to be uncovered. C/EBPs form a family within the basic region-leucine zipper class of transcription factors. In the lung epithelium C/EBPalpha, -beta, and -delta are expressed. Lung-specific target genes for these transcription factors include the surfactant proteins A and D, the Clara cell secretory protein, and the P450 enzyme CYP2B1. As more information is gathered, a picture is emerging in which C/EBPalpha has a role in regulating proliferation as well as differentiation-dependent gene expression, whereas C/EBPbeta and -delta, in addition to a partly overlapping role in regulating expression of differentiation markers, also seem to be involved in responses to injury and hormones.

Production and application of polyclonal antibody to human thyroid transcription factor 2 reveals thyroid transcription factor 2 protein expression in adult thyroid and hair follicles and prepubertal testis

Germline mutations in thyroid transcription factor 2 (TTF2) cause thyroid agenesis, spiky hair, and cleft palate, indicating thyroidal and extrathyroidal expression. We sought to investigate this by producing and applying an antibody to human TTF2. The coding region of human TTF2 was cloned into a bacterial expression vector, production of the soluble TTF2 protein optimized, and pure TTF2 obtained by nickel chromatography. Rabbits were immunized and the resulting TTF2 polyclonal titrated on formalin-fixed, paraffin-embedded sections of thyroid. The optimized protocol was applied to a range of tissues. Nine milligrams of TTF2 protein was obtained per liter of culture and a high-titer antibody produced. This displayed specific staining of thyroid follicular cell nuclei/cytoplasm and not of the interstitium, connective tissue, smooth muscle, or endothelium. No staining was obtained with the preimmune serum in the same conditions, or with the majority of other tissues tested with the TTF2 polyclonal. The exceptions were testis and skin, in which nuclear TTF2 immunoreactivity was present in the seminiferous tubules and cells in the follicular outer root sheath, respectively. In conclusion, we have produced a polyclonal antibody for human TTF2 and demonstrated immunoreactivity for this transcription factor in adult human thyroid and hair follicles and prepubertal testis.

Multiple mechanisms for oxygen-induced regulation of the Clara cell secretory protein gene

The Clara cell secretory protein (CCSP) imparts a protective effect to the lung during oxidant injury. However, exposure to supplemental oxygen, a common therapeutic modality for lung disease, represses the expression of CCSP in the adult mouse lung. We investigated the mechanisms of hyperoxia-induced repression of the mouse CCSP promoter. Deletion experiments in vivo and in vitro indicated that the hyperoxia-responsive elements are localized to the proximal -166 bp of the CCSP promoter. Electrophoretic mobility shift and supershift analyses demonstrated increased binding of c-Jun at the activator protein-1 site, increased binding of CCAAT/enhancer binding protein (C/EBP) beta at the C/EBP sites, and decreased binding at the Nkx2.1 sites. Western analyses revealed that hyperoxia exposure induced an increase in the expression of the C/EBPbeta isoform liver-inhibiting protein (LIP) and an increase in cytoplasmic Nkx2.1. Cotransfection of LIP or c-Jun expression plasmids decreased the transcriptional activity of the proximal -166-bp CCSP promoter. These observations suggest that hyperoxia-induced repression of the CCSP gene is mediated, at least in part, at the level of transcription and that multiple mechanisms mediate this repression. Moreover, these novel observations may provide insights for generation of therapeutic interventions for the amelioration of oxidant-induced lung injury.

Dkk1 and noggin cooperate in mammalian head induction

Growth factor antagonists play important roles in mediating the inductive effects of the Spemann organizer in amphibian embryos and its equivalents in other vertebrates. Dual inhibition of Wnt and BMP signals has been proposed to confer head organizer activity. We tested the requirement of this coinhibition in Xenopus and mice. In Xenopus, simultaneous reduction of the BMP antagonists chordin and noggin, and the Wnt antagonist dickkopf1 (dkk1) leads to anterior truncations. In mice, compound mutants for dkk1 and noggin display severe head defects, with deletion of all head structures anterior to the mid-hindbrain boundary. These defects arise as a result of a failure in anterior specification at the gastrula stage. The results provide genetic evidence for the dual inhibition model and indicate that dkk1 and noggin functionally cooperate in the head organizer.

TTF-1 phosphorylation is required for peripheral lung morphogenesis, perinatal survival, and tissue-specific gene expression

Thyroid transcription factor-1 (TTF-1) is a 43-kDa, phosphorylated member of the Nkx2 family of homeodomain-containing proteins expressed selectively in lung, thyroid, and the central nervous system. To assess the role of TTF-1 and its phosphorylation during lung morphogenesis, mice bearing a mutant allele, in which seven serine phosphorylation sites were mutated, Titf1PM/PM, were generated by homologous recombination. Although heterozygous Titf1PM/+ mice were unaffected, homozygous Titf1PM/PM mice died immediately following birth. In contrast to Titf1 null mutant mice, which lack peripheral lung tissues, bronchiolar and peripheral acinar components of the lung were present in the Titf1PM/PM mice. Although lobulation and early branching morphogenesis were maintained in the mutant mice, abnormalities in acinar tubules and pulmonary hypoplasia indicated defects in lung morphogenesis later in development. Although TTF-1PM protein was readily detected within the nuclei of pulmonary epithelial cells at sites and abundance consistent with that of endogenous TTF-1, expression of a number of known TTF-1 target genes, including surfactant proteins and secretoglobulin 1A, was variably decreased in the mutant mice. Vascular endothelial growth factor mRNA was decreased in association with decreased formation of peripheral pulmonary blood vessels. Genes mediating surfactant homeostasis, vasculogenesis, host defense, fluid homeostasis, and inflammation were highly represented among those regulated by TTF-1. Thus, in contrast to the null Titf1 mutation, the Titf1PM/PM mutant substantially restored lung morphogenesis. Direct and indirect transcriptional targets of TTF-1 were identified that are likely to play important roles in lung formation and function.

A disrupted balance between Bmp/Wnt and Fgf signaling underlies the ventralization of the Gli3 mutant telencephalon

Regionalization of the neural plate and the early neural tube is controlled by several signaling centers that direct the generation of molecularly distinct domains. In the developing telencephalon, the anterior neural ridge (ANR) and the roof and floor plate act as such organizing centers via the production of Fgfs, Bmps/Wnts, and Shh, respectively. It remains largely unknown, however, how the combination of these different signals is used to coordinate the generation of different telencephalic territories. In the present study, we report on telencephalic development in Pdn mutant mice, which carry an integration of a retrotransposon in the Gli3 locus. Homozygous mutant animals are characterized by a partial dorsal-to-ventral transformation of the telencephalon and by an increased size of the septum. On a molecular level, these alterations correlate with a reduction and/or loss of Bmp/Wnt expression and a concomitant expansion of Fgf8 transcription. Finally, we provide evidence that the ectopic activation of Fgf signaling in the dorsal telencephalon provides an explanation for the ventralization of the Gli3 mutant telencephalon as application of Fgf8-soaked beads to dorsal telencephalic explants led to the specific induction and repression of ventral marker and dorsal marker genes, respectively.

DNA testing in patients with GH deficiency at the time of transition

Over the last 10 years, major advances in the understanding of pituitary gland development in the mouse have led to the identification of mutations in a number of genes that then lead to delineation of the phenotype of growth hormone deficiency (GHD), either in isolation (IGHD) or in combination with a number of other hormone deficiencies (CPHD) or syndromic features (e.g., septo-optic dysplasia, SOD). The genetic abnormalities include mutations within: (1) Hesx1 (IGHD, SOD or CPHD); (2) Lhx3 (CPHD with preservation of cortisol secretion and a short stiff neck); (3) Lhx4 (GH, TSH and ACTH deficiency with cerebellar hypoplasia); (4) Prop1 (variable CPHD often associated with pituitary masses); (5) POU1F1 (GH, prolactin and TSH deficiency); (6) GHRHR (IGHD) and (7) GH1 (IGHD). There can be variations in inheritance, phenotype and penetrance patterns. Nevertheless, establishing the genetic diagnosis can help in predicting the evolution of the phenotype and in genetic counselling. Therefore, for these reasons it is recommended that all patients with GHD should undergo testing for genetic mutations within the genes associated with IGHD, CPHD and SOD.

Expression of classical cadherins in thyroid development: maintenance of an epithelial phenotype throughout organogenesis

The long distance between the final location of the thyroid gland in front of the trachea and the site of embryological specification at the tongue base suggests that active migration of the thyroid progenitor cells is required. During embryogenesis, similar morphogenetic events often involve epithelial to mesenchymal transition (EMT), which promotes the acquisition of a migrating phenotype. EMT is characterized by an altered expression of cadherin cell adhesion molecules, most notably loss of E-cadherin. To investigate whether a similar mechanism operates in thyroid development, we studied the expression of classical cadherins in the thyroid primordium of mouse embryos by immunohistochemistry. E-Cadherin was expressed at high levels in thyroid cells at all developmental stages. In contrast, R-cadherin expression was induced in the embryonic thyroid coinciding with the onset of folliculogenesis and was maintained in the adult thyroid along with E-cadherin. N-Cadherin, often associated with increased migrating capacity, was not detected in the thyroid primordium, but was expressed in the surrounding mesenchyme. These findings indicate that the epithelial phenotype is maintained in thyroid progenitor cells throughout organogenesis and favor the idea that translocation of the developing thyroid does not involve active migration of individual cells, but rather is secondary to movements of surrounding tissues.

The different cardiac expression of the type 2 iodothyronine deiodinase gene between human and rat is related to the differential response of the Dio2 genes to Nkx-2.5 and GATA-4 transcription factors

By producing T3 from T4, type 2 iodothyronine deiodinase (D2) catalyzes the first step in the cascade underlying the effect exerted by thyroid hormone. Type 2 iodothyronine deiodinase mRNA is expressed at high levels in human heart but is barely detectable in the corresponding rodent tissue. Although the heart is a major target of thyroid hormone, the role of cardiac D2 and the factors that regulate its expression are unknown. Here we report that the human Dio2 promoter is very sensitive to the cardiac transcription factors Nkx-2.5 and GATA-4. Nkx-2.5 transactivates a 6.5-kb human (h)Dio2-chloramphenicol acetyltransferase construct, with maximal induction reached with a 633-bp proximal promoter region. Interestingly, despite 73% identity with the corresponding human region, the rat Dio2 promoter is much less responsive to Nkx-2.5 induction. Using EMSA, we found that two sites in the human promoter (C and D) specifically bind Nkx-2.5. In coexpression studies, GATA-4 alone was a poor inducer of the hDio2 promoter; however in synergy with Nkx-2.5, it activated D2 reporter gene expression in the human, but not the rat promoter. Functional analysis showed that both C and D sites are required for the complete Nkx-2.5 response and for the Nkx-2.5/GATA-4 synergistic effect. In neonatal rat primary myocardiocytes, most of the hDio2-chloramphenicol acetyltransferase activity was suppressed by mutation of the Nkx-2.5 binding sites. Finally, a mutant Nkx-2.5 protein (N188K), which causes, in heterozygosity, congenital heart diseases, did not transactivate the Dio2 promoter and interfered with its activity in cardiomyocytes, possibly by titrating endogenous Nkx-2.5 protein away from the promoter. In conclusion, this study shows that Nkx-2.5 and GATA-4 play prime roles in Dio2 gene regulation in the human heart and suggests that it is their synergistic action in humans that causes the differential expression of the cardiac Dio2 gene between humans and rats.

TTF-1, a homeodomain-containing transcription factor, participates in the control of body fluid homeostasis by regulating angiotensinogen gene transcription in the rat subfornical organ

In recent years, it has become increasingly evident that angiotensins synthesized in the brain contribute to regulating body fluid homeostasis. Although angiotensinogen, the unique angiotensin precursor, is produced in the brain, the factors that regulate its gene expression remain unknown. We recently found that TTF-1, a homeodomain-containing transcription factor essential for the development of the fetal diencephalon, is postnatally expressed in discrete areas of the hypothalamus. We now report that the subfornical organ, an important site of angiotensinogen synthesis, is an extra-hypothalamic site of TTF-1 expression. Double in situ hybridization histochemistry demonstrated the presence of TTF-1 mRNA in angiotensinogen-producing cells of the rat subfornical organ. RNase protection assays showed that TTF-1 and angiotensinogen mRNA levels are simultaneously increased in the subfornical organ by water deprivation. The angiotensinogen promoter contains seven presumptive TTF-1 binding motifs, four of which are recognized by the TTF-1 homeodomain. In the C6 glioma cell line, TTF-1 transactivates the angiotensinogen promoter in a dose-dependent manner. This transactivation is abolished by deletion of the TTF-1 binding motif at -125. Intracranial administration of an antisense TTF-1 oligodeoxynucleotide decreased angiotensinogen mRNA in the subfornical organ and dramatically reduced the animal's water intake while increasing urine excretion. Moreover, plasma arginine vasopressin content was decreased by the same treatment. These results demonstrate a novel role for TTF-1 in the regulation of body fluid homeostasis, exerted via the transactivational control of angiotensinogen synthesis in the subfornical organ.

Aberrant trajectory of ascending dopaminergic pathway in mice lacking Nkx2.1

In the embryonic brain, the transcription factor Nkx2.1 is localized in the medial ganglionic eminence and the ventromedial part of the hypothalamus. In the present study, we examined the development of mesencephalic dopamine (DA) neuron system in mice lacking Nkx2.1. In normal mice, tyrosine hydroxylase-immunoreactive axons from mesencephalic DA cells extended bilaterally in the lateral hypothalamus at embryonic day 12.5 (E12.5) and project to the ipsilateral striatum by E14.5. In the mutant brain, mesencephalic DA cell groups appeared to develop normally, but the majority of their ascending axons were observed to cross the ventral midline of the caudal hypothalamus and project to the contralateral striatum. DiI, a fluorescent dye, placed in the ventrolateral mesencephalon of E14.5 mutant mice, further revealed that majority of DiI-labeled axons projected to the contralateral striatum, while a minor ipsilateral projection was also observed. In the ventromedial hypothalamus of mutants, the neuroepithelium of third ventricle was missing, and immunoreactivity of semaphorin 3A, a soluble type of axon repellent, which was normally localized in the neuroepithelium, was remarkably reduced. Together with the recent evidence that the expression of slit2, another axon-repellent diffusible factor, is also eliminated in the hypothalamic neuroepithelium of Nkx2.1-deficient mice, the abnormal crossing of ascending DA axons observed may be attributed to the elimination of these chemorepulsive signals in the medial part of the mutant hypothalamus.

Perturbed thyroid morphology and transient hypothyroidism symptoms in Hoxa5 mutant mice

The Hox family of transcriptional regulators has been extensively studied for their role in axial and appendicular patterning. Genetic analyses have also unveiled Hox gene function in organogenesis and postnatal development. A phenotypical survey of the Hoxa5(-/-) mutant mice shows that the surviving mutants display symptoms of hypothyroidism, including transient growth retardation, and delayed eye opening and ear elevation. Thyroid gland morphogenesis initiates normally, but follicle formation and thyroglobulin processing are abnormal at late gestation. The expression of several molecular markers essential for thyroid gland formation and function, namely Nkx2.1, Pax8, and Titf2, is affected in the developing thyroid gland of Hoxa5(-/-) mutants. As a consequence, the expression of thyroid effector genes, including the thyroglobulin and thyroperoxidase genes, is perturbed. Our characterization reveals that the loss of Hoxa5 function transiently affects thyroid development in a non-cell autonomous manner.

Thyroid transcription factor (TTF) -1 regulates the expression of midkine (MK) during lung morphogenesis

Midkine (MK) is a 13-kDa heparin-binding growth factor that is thought to mediate developmental processes, including vasculogenesis, cell migration, and proliferation in various organs. To determine whether MK plays a role during lung morphogenesis, immunostaining for MK was assessed in mouse lung from embryonic day (E) 13 to postnatal day (PN) 24. MK was detected in mesenchymal and respiratory epithelial cells of the peripheral mouse lung from E13.0 to E15.5. From E18.5 to PN1, MK was observed primarily in epithelial cells lining conducting airways and peripheral lung saccules. By PN10, expression was no longer observed in respiratory epithelial cells but was readily detected in small blood vessels in the alveolar region of the lung. Although most respiratory epithelial cells uniformly expressed MK before E13.0, MK was restricted to subsets of cells by E18.5, colocalizing with the Clara cell secretory protein (CCSP) marker in conducting airways and with pro-SPC, a marker specific for alveolar type II pneumocytes. By PN10, MK was not detected in respiratory epithelial cells of the conducting airways and was closely associated with capillary networks. The sites of intense MK staining in the respiratory epithelial cells correlated with sites of expression of thyroid transcription factor (TTF) -1, a transcription factor regulating formation and gene expression in the lung parenchyma. TTF-1 enhanced transcription of the mouse MK gene promoter, acting on TTF-1 regulatory elements located in the 5'-region of the gene. Furthermore, MK expression was not detected in lungs of TTF-1 null mice. TTF-1 regulates expression of MK in the lung. The temporal/spatial distribution of midkine is consistent with a potential role in paracrine signaling during lung morphogenesis.

Thyroid transcription factor-1 expression prevalence and its clinical implications in non-small cell lung cancer: a high-throughput tissue microarray and immunohistochemistry study

Thyroid transcription factor 1 (TTF-1), a homeodomain-containing transcription factor, plays a pivotal role in lung development, cell growth, and differentiation processes. The current literature reports considerable variation in frequency of TTF-1 protein expression in human non-small cell lung cancer (NSCLC). TTF-1 expression has not been extensively investigated as a prognostic marker in NSCLC. To assess the prevalence of TTF-1 expression, and to evaluate its potential role in disease prognosis, 140 stage I-IIIA NSCLCs with long-term follow-up were studied under uniform conditions using high-density tissue microarray (TMA) combined with immunohistochemistry. Patient survival and association of TTF-1 expression with clinicopathologic parameters were analyzed. One hundred twenty-six tumor samples were fully assessable after tissue processing. Sixty-four samples (50.8%) expressed TTF-1 and 62 (49.2%) displayed no expression. TTF-1 expression was significantly (P < 0.001) correlated with histological subtype: 51 adenocarcinomas (AdCs) (51 of 75; 68%) versus 9 squamous cell carcinomas (SCCs) (9 of 43; 21%) were TTF-1 positive. TTF-1 expression, performance status, nodal status, and tumor stage were significantly related to patient survival. In multivariate analysis, positive TTF-1 expression tended to favor a better patient outcome (P = 0.05). Overall, NSCLC patients with positive TTF-1 expression had a median survival of greater than 57.3 months, whereas those with negative expression had a median survival of 39.4 +/- 5.2 months (log-rank test, P = 0.0067). In this study we found that TTF-1 is predominately expressed in adenocarcinoma. The loss of TTF-1 expression was associated with aggressive behavior of NSCLCs. The results from this study strongly indicate that further investigation is warranted to better define the role of TTF-1 as a prognostic factor in this malignancy.

CDX2, a highly sensitive and specific marker of adenocarcinomas of intestinal origin: an immunohistochemical survey of 476 primary and metastatic carcinomas

CDX2 is a recently cloned homeobox gene that encodes an intestine-specific transcription factor, expressed in the nuclei of epithelial cells throughout the intestine, from duodenum to rectum. While expression of CDX2 protein in primary and metastatic colorectal carcinomas has been previously documented, neither the sensitivity nor the specificity of CDX2 expression, as determined by immunohistochemistry, for colorectal adenocarcinoma has been determined. We performed an immunohistochemical survey of 476 tumors with a monoclonal antibody, CDX2-88, including 89 tumors from the colon and duodenum and 95 tumors from other gastrointestinal sites, including the esophagus, stomach, pancreatobiliary system, gastrointestinal carcinoids, and liver. CDX2 was expressed uniformly (that is, in 76-100% of tumor cells) in all but one of the evaluated colorectal and duodenal tumors. High-level expression of CDX2 was also found, however, in mucinous ovarian carcinomas and adenocarcinomas primary to the urinary bladder of which 64% and 100% were positive, respectively. Gastric, gastroesophageal, and pancreatic adenocarcinomas and cholangiocarcinomas all showed similar, heterogeneous patterns of CDX2 expression. Most tumors in each group showed CDX2 expression by a minority of cells, whereas a substantial minority of cases in each group was completely negative and a smaller minority was uniformly positive. Gastrointestinal carcinoids gave similarly varied results, but the majority (58%) was negative. Hepatocellular carcinomas showed no expression of CDX2. Only very rare examples of carcinomas of the genitourinary and gynecologic tracts, breast, lung, and head and neck showed significant levels of CDX2 expression. In this study of primary and metastatic epithelial tumors, uniform CDX2 expression is demonstrated to be an exquisitely sensitive and highly, but incompletely, specific marker of intestinal adenocarcinomas. Compared with villin, a previously described marker of GI adenocarcinomas, CDX2 demonstrated superior sensitivity and comparable specificity. CDX2 expression can be seen, however, in selected non-GI adenocarcinomas such as mucinous ovarian carcinomas and adenocarcinomas of the urinary bladder.

An enhancer region determines hSP-B gene expression in bronchiolar and ATII epithelial cells in transgenic mice

Regulation of the surfactant protein B gene (SP-B) is developmentally controlled and highly tissue specific. To elucidate the SP-B gene temporal/spatial expression pattern in lung development at the transcriptional level, a transgenic mouse model line carrying the human SP-B (hSP-B) 1.5-kb 5'-flanking regulatory region and the lacZ gene was established. Expression of hSP-B 1.5-kb lacZ gene started at the onset of lung formation [embryonic day 9 (E9)] and was restricted to epithelial cells throughout prenatal and postnatal lung development. In the adult lung, hSP-B 1.5-kb lacZ gene expression was restricted to bronchiolar and alveolar type II epithelial cells. In lung explant culturing studies, the hSP-B 1.5-kb lacZ gene was highly expressed in newly formed epithelial tubules during the respiratory branching process. In a second transgenic mouse line, an enhancer region, which binds to thyroid transcription factor-1, retinoic acid receptor, signal transducers and activators of transcription 3, and nuclear receptor coactivators (SRC-1, ACTR, TIF2, and CBP/p300), was deleted from the hSP-B 1.5-kb lacZ gene. The deletion abolished hSP-B lacZ gene expression in bronchiolar epithelial cells and significantly reduced its expression level in alveolar type II epithelial cells in transgenic mice.

Six3 repression of Wnt signaling in the anterior neuroectoderm is essential for vertebrate forebrain development

In vertebrate embryos, formation of anterior neural structures requires suppression of Wnt signals emanating from the paraxial mesoderm and midbrain territory. In Six3(-/-) mice, the prosencephalon was severely truncated, and the expression of Wnt1 was rostrally expanded, a finding that indicates that the mutant head was posteriorized. Ectopic expression of Six3 in chick and fish embryos, together with the use of in vivo and in vitro DNA-binding assays, allowed us to determine that Six3 is a direct negative regulator of Wnt1 expression. These results, together with those of phenotypic rescue of headless/tcf3 zebrafish mutants by mouse Six3, demonstrate that regionalization of the vertebrate forebrain involves repression of Wnt1 expression by Six3 within the anterior neuroectoderm. Furthermore, these results support the hypothesis that a Wnt signal gradient specifies posterior fates in the anterior neural plate.

Pax-8 expression correlates with type II 5' deiodinase expression in thyroids from patients with Graves' disease

Transcription factors TTF-1 and Pax-8 control the expression of thyroid-specific genes crucial for thyroid function. It has been postulated that they may play a role in thyrotropin (TSH)-mediated augmentation of gene expression observed in some thyroid diseases including Grave's hyperthyroidism. Recently, we and others described the expression of two genes participating in thyroid hormone metabolism type I and type II deiodinase (D1 and D2, respectively) that are upregulated by TSH, although the mechanisms responsible for this effect are likely to be different. The aim of this study was to investigate whether there is a correlation between TTF-1 and Pax-8 mRNA levels and type I or type II 5' deiodinases expression in Graves' disease. D1 activity and mRNA level, as well as D2 activity and mRNA level, were significantly increased in Graves' disease in comparison to control tissues. D1, but not D2, activity correlated with its mRNA level in Graves' disease and toxic multinodular goitre. The TTF-1 mRNA level was not different between Graves' disease and control thyroids and no correlation between TTF-1 mRNA level and either D1 or D2 mRNA levels were found. The Pax-8 mRNA level was significantly increased in Graves' disease in comparison to control tissues and correlated with D2, but not D1, mRNA levels among all investigated groups of tissues. Our data suggest that transcription factor Pax-8 could be involved in the upregulation of D2 expression in the thyroid of Graves' patients.

The paired domain-containing factor Pax8 and the homeodomain-containing factor TTF-1 directly interact and synergistically activate transcription

Pax genes encode for transcription factors essential for tissue development in many species. Pax8, the only member of the family expressed in the thyroid tissue, is involved in the morphogenesis of the gland and in the transcriptional regulation of thyroid-specific genes. TTF-1, a homeodomain-containing factor, is also expressed in the thyroid tissue and has been demonstrated to play a role in thyroid-specific gene expression. Despite the presence of Pax8 and TTF-1 also in a few other tissues, the simultaneous expression of the two transcription factors occurs only in the thyroid, supporting the idea that Pax8 and TTF-1 might cooperate to influence thyroid-specific gene expression. In this report, we describe a physical and functional interaction between these two factors. The fusion protein GST-Pax8 is able to bind TTF-1 present in thyroid or in non-thyroid cell extracts, and by using bacterial purified TTF-1 we demonstrate that the interaction is direct. By co-immunoprecipitation, we also show that the interaction between the two proteins occurs in vivo in thyroid cells. Moreover, Pax8 and TTF-1 when co-expressed in HeLa cells synergistically activate Tg gene transcription. The synergism requires the N-terminal activation domain of TTF-1, and deletions of Pax8 indicate that the C-terminal domain of the protein is involved. Our results demonstrate a functional cooperation and a physical interaction between transcription factors of the homeodomain-containing and of the paired domain-containing gene families in the regulation of tissue-specific gene expression.

Expression of thyroid transcription factor-1 in 16 human lung cancer cell lines

It has been suggested that thyroid transcription factor-1 (TTF-1) is frequently expressed in human lung cancer, especially in adenocarcinoma and small cell lung cancer, and the TTF-1 expression is closely related with the expression of surfactant protein. We hypothesized that TTF-1 is expressed in human lung cancer cell lines and its expression might be related to the expression of surfactant protein. To test this, expressions of TTF-1 and surfactant protein A (SP-A) were immunohistochemically evaluated in 16 human lung cancer cell lines. In addition, expressions of mRNAs for TTF-1 and SP-A were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing. As a result, nuclear staining of TTF-1 was observed in two of six adenocarcinoma cell lines, none of seven small cell lung cancer cell lines, and none of three squamous lung cancer cell lines. Among the 16 cell lines, six cell lines (PC3, LC2/Ad, A549, RERF-LC-OK, HI1017, and PC9) expressed significant amounts of mRNA for TTF-1. In contrast, cytoplasmic staining of TTF-1 was observed in five of six adenocarcinoma cell lines, in six of seven small cell lung cancer cell lines, and in all three squamous cell lung cancer cell lines. One of the two adenocarcinoma cell lines those showed positive nuclear staining and cytoplasmic SP-A staining released a significant amount of SP-A in culture supernatant. Our present study demonstrates that the frequency of TTF-1 expression in the nucleus was very low in human lung cancer cell lines; however, their cytoplasmic positivities should be further investigated.

Glia-to-neuron signaling and the neuroendocrine control of female puberty

The sine qua non event of puberty is an increase in pulsatile release of gonadotrophin hormone releasing hormone (GnRH). It is now clear that this increase and, therefore, the initiation of the pubertal process itself, require both changes in transsynaptic communication and the activation of glia-to-neuron signaling pathways. While neurons that utilize excitatory and inhibitory amino acids as transmitters represent major players in the transsynaptic control of puberty, glial cells utilize a combination of trophic factors and small cell-cell signaling molecules to regulate neuronal function and, thus, promote sexual development. A coordinated increase in glutamatergic transmission accompanied by a decrease in inhibitory GABAergic tone appears to initiate the transsynaptic cascade of events leading to the pubertal increase in GnRH release. Glial cells facilitate GnRH secretion via cell-cell signaling loops mainly initiated by members of the EGF and TGF- families of trophic factors, and brought about by either these factors themselves or by chemical messengers released in response to growth factor stimulation. In turn, a neuron-to-glia communication pathway mediated by excitatory amino acids serves to coordinate the simultaneous activation of transsynaptic and glia-to-neuron communication required for the advent of sexual maturity. A different--and perhaps higher--level of control may involve the transcriptional regulation of subordinate genes that, by contributing to neuroendocrine maturation, are required for the initiation of the pubertal process.

Regional expression of the homeobox gene NKX2-1 defines pallidal and interneuronal populations in the basal ganglia of amphibians

The distribution of gene expression domains during development constitutes a novel tool for the identification of distinct brain regions. This is particularly useful in the brain of amphibians where cell migration is very limited and most neurons organize in a periventricular layer. Here we report the expression pattern of NKX2-1 protein in the developing Xenopus telencephalon. In mammals, the Nkx2-1 gene is expressed in distinct subpallial regions such as the septum, the medial ganglionic eminence and preoptic region. The results of the present study demonstrate that the expression of NKX2-1 delineates the pallidal anlage and its derivatives in amphibians, as in mammals and birds. In addition, double-labeling immunohistochemistry and the combination of tracing experiments with NKX2-1 immunohistochemistry demonstrate that the amphibian striatum contains interneurons, which express NKX2-1 and produce, among other possible neurotransmitters, nitric oxide and acetylcholine. In sum, the results of the present study strengthen the notion that similar developmental programs exist during basal ganglia development in all tetrapods.

Specification of developmental fates in ascidian embryos: molecular approach to maternal determinants and signaling molecules

Tadpole larvae of ascidians represent the basic body plan of chordates with a relatively small number and few types of cells. Because of their simplicity, ascidians have been intensively studied. More than a century of research on ascidian embryogenesis has uncovered many cellular and molecular mechanisms responsible for cell fate specification in the early embryo. This review describes recent advances in our understanding of the molecular mechanisms of fate specification mainly uncovered in model ascidian species--Halocynthia roretzi, Ciona intestinalis, and Ciona savignyi. One category of developmentally important molecules represents maternal localized mRNAs that are involved in cell-autonomous processes. In the second category, signaling molecules and downstream transcription factors are involved in inductive cell interactions. Together with genome-wide information, there is a renewed interest in studying ascidian embryos as a fascinating model system for understanding how single-celled eggs develop a highly organized chordate body plan.

Defining thyrotropin-dependent and -independent steps of thyroid hormone synthesis by using thyrotropin receptor-null mice

The thyrotropin (TSH) receptor (TSHR) is a member of the heterotrimeric G protein-coupled family of receptors whose main function is to regulate thyroid cell proliferation as well as thyroid hormone synthesis and release. In this study, we generated a TSHR knockout (TSHR-KO) mouse by homologous recombination for use as a model to study TSHR function. TSHR-KO mice presented with developmental and growth delays and were profoundly hypothyroid, with no detectable thyroid hormone and elevated TSH. Heterozygotes were apparently unaffected. Knockout mice died within 1 week of weaning unless fed a diet supplemented with thyroid powder. Mature mice were fertile on the thyroid-supplemented diet. Thyroid glands of TSHR-KO mice produced uniodinated thyroglobulin, but the ability to concentrate and organify iodide could be restored to TSHR-KO thyroids when cultured in the presence of the adenylate cyclase agonist forskolin. Consistent with this observation was the lack of detectable sodium-iodide symporter expression in TSHR-KO thyroid glands. Hence, by using the TSHR-KO mouse, we provided in vivo evidence, demonstrating that TSHR expression was required for expression of sodium-iodide symporter but was not required for thyroglobulin expression, suggesting that the thyroid hormone synthetic pathway of the mouse could be dissociated into TSHR-dependent and -independent steps.

Role of the thyroid-stimulating hormone receptor signaling in development and differentiation of the thyroid gland

The thyroid-stimulating hormone/thyrotropin (TSH) is the most relevant hormone in the control of thyroid gland physiology in adulthood. TSH effects on the thyroid gland are mediated by the interaction with a specific TSH receptor (TSHR). We studied the role of TSHTSHR signaling on gland morphogenesis and differentiation in the mouse embryo using mouse lines deprived either of TSH (pit(dw)pit(dw)) or of a functional TSHR (tshr(hyt)tshr(hyt) and TSHR-knockout lines). The results reported here show that in the absence of either TSH or a functional TSHR, the thyroid gland develops to a normal size, whereas the expression of thyroperoxidase and the sodium/iodide symporter are reduced greatly. Conversely, no relevant changes are detected in the amounts of thyroglobulin and the thyroid-enriched transcription factors TTF-1, TTF-2, and Pax8. These data suggest that the major role of the TSH/TSHR pathway is in controlling genes involved in iodide metabolism such as sodium/iodide symporter and thyroperoxidase. Furthermore, our data indicate that in embryonic life TSH does not play an equivalent role in controlling gland growth as in the adult thyroid.

Testing putative hemichordate homologues of the chordate dorsal nervous system and endostyle: expression of NK2.1 (TTF-1) in the acorn worm Ptychodera flava (Hemichordata, Ptychoderidae)

Recent phylogenetic investigations have confirmed that hemichordates and echinoderms are sister taxa. However, hemichordates share several cardinal characterstics with chordates and are thus an important taxon for testing hypotheses of homology between key chordate characters and their putative hemichordate antecedents. The chordate dorsal nervous system (DNS) and endostyle are intriguing characters because both hemichordate larval and adult structures have been hypothesized as homologues. This study attempts to test these purported homologies through examination of the expression pattem of a Ptychodera flava NK2 gene, PfNK2.1, because this gene is expressed both in the DNS and endostyle/thyroid in a wide range of chordate taxa. We found that PfNK2.1 is expressed in both neuronal and pharyngeal structures, but its expression pattem is broken up into distinct embryonic and juvenile phases. During embryogenesis, PfNK2.1 is expressed in the apical ectoderm, with transcripts later detected in presumable neuronal structures, including the apical organ and ciliated feeding band. In the developing juvenile we detected PfNK2.1 signal throughout the pharynx, including the stomochord, and later in the hindgut. We conclude that the similar utilization of NK2.1 in apical organ development and chordate DNS is probably due to a more general role for NK2.1 in neurogenesis and that hemichordates do not possess a homologue of the chordate DNS. In addition, we conclude that P. flava most likely does not possess a true endostyle; rather during the evolution of the endostyle NK2.1 was recruited from its more general role in pharynx development.

Thyroid transcription factor 1: a marker for lung adenoarinoma in body cavity fluids

BACKGROUND

Adenocarcinomas are the most common epithelial malignancies in body cavity fluids. Subclassification of adenocarcinomas according to primary site can be a challenging task. Thyroid transcription factor 1 (TTF-1) is a nuclear transcription factor that is expressed in normal lung, in thyroid, and in their neoplasms. Because thyroid carcinomas rarely metastasize to the serosal surfaces, the authors used TTF-1 as a marker to distinguish adenocarcinomas of the lung from carcinomas of other organs.

METHODS

The authors studied 113 body cavity fluids (92 pleural fluid samples and 21 ascitic samples) from 113 patients with a diagnosis of adenocarcinoma on the basis of routine cytology. The primary sites of origin were confirmed clinically or histologically for all patients. There were 39 adenocarcinomas of the lung, 24 adenocarcinomas of the breast, 34 adenocarcinomas of the genitourinary tract, and 16 adenocarcinomas of the gastrointestinal tract. Archival Papanicolaou-stained, cytocentrifuged slides were used without destaining for immunocytochemistry with the monoclonal TTF-1 antibody using a commercial available method.

RESULTS

TTF-1 was expressed in 21 of 39 lung adenocarcinomas (54%). Intense nuclear staining was present in tumor cells that occurred in groups or in isolated form. In contrast, none of the other types of adenocarcinomas expressed TTF-1.

CONCLUSIONS

TTF-1 is a highly specific marker for adenocarcinomas of the lung in body cavity fluids. Immunocytochemistry using this antibody can be performed easily on archival Papanicolaou-stained, cytocentrifuged slides of fluid specimens.

Synergistic transactivation of the differentiation-dependent lung gene Clara cell secretory protein (secretoglobin 1a1) by the basic region leucine zipper factor CCAAT/enhancer-binding protein alpha and the homeodomain factor Nkx2.1/thyroid transcription factor-1

The basic region-leucine zipper transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) and the homeodomain transcription factor Nkx2.1/thyroid transcription factor-1 are essential for normal lung morphogenesis. Nkx2.1 is expressed from the onset of lung development, whereas C/EBPalpha expression is turned on at later stages. The expression of C/EBPalpha correlates to the appearance of lung-specific proteins with differentiation-dependent expression patterns, such as the Clara cell secretory protein (secretoglobin 1a1 (Scgb1a1), CCSP). In this study, we demonstrate synergistic transactivation by C/EBPalpha and Nkx2.1 in the regulation of the CCSP gene. We show that the synergistic activity of C/EBPalpha and Nkx2.1 originates from cis-acting elements in the proximal promoter of CCSP and that the synergism is dependent on NH(2)-terminal transactivation domains of C/EBPalpha and Nkx2.1. Our results suggest that the cooperation of C/EBPalpha and Nkx2.1 is a major determinant for the high level, lung epithelial-specific expression of CCSP during the later stages of lung development and in the adult lung.

Expression pattern of the homeobox protein NKX2-1 in the developing Xenopus forebrain

Although morphological data suggest that the amphibian forebrain contains similar subdivisions to those observed in birds and mammals, it is presently unclear whether the same patterning mechanisms are conserved among all three classes of tetrapods. Here we report that NKX2-1, a transcription factor that is essential for the ventral patterning of the forebrain in birds and mammals, is expressed in corresponding (homologous) domains in the developing Xenopus forebrain. NKX2-1 expression is restricted to two domains in the amphibian forebrain: (1) a ventral diencephalic domain, with expression limited to hypothalamic structures; and (2) a telencephalic domain, with expression in the medial ganglionic eminence, preoptic area and part of the septum. Thus, the detailed analysis of the distribution of NKX2-1 provides the first unequivocal evidence for distinct progenitor zones within the amphibian forebrain through embryonic and larval development.

Regulation of pituitary adenylate cyclase-activating polypeptide gene transcription by TTF-1, a homeodomain-containing transcription factor

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an important hypophysiotrophic factor as well as a regulator for immune, reproductive, and neural tissues. We recently found that TTF-1, a homeodomain-containing transcription factor essential for the development of the fetal diencephalon, is postnatally expressed in the hypothalamic area and plays a transcription regulatory role for certain neurohormones. Based on the similarity of synthesis sites between PACAP and TTF-1 and, moreover, on the presence of conserved core TTF-1 binding motifs in the 5'-flanking region of the PACAP gene, we sought to uncover a regulatory role of TTF-1 in PACAP gene transcription. The TTF-1 homeodomain binds to six of the seven putative binding domains observed in the 5'-flanking region of the PACAP gene. In the C6 glioma cell-line, TTF-1 activates the PACAP promoter in a dose-dependent manner. This transactivation of PACAP by TTF-1 was totally removed when the core TTF-1 binding motif at -369 was deleted. RNase protection assays showed that TTF-1 and PACAP mRNAs have daily fluctuations in the rat hypothalamus. They both were at low levels during the day and high levels during the night. Intracerebroventricular administration of an antisense TTF-1 oligodeoxynucleotide significantly decreased the PACAP mRNA level as well as TTF-1 protein content in the rat hypothalamus, suggesting that TTF-1 also regulates PACAP transcription in vivo. Moreover, the TTF-1 promoter was inhibited by molecular oscillators of CLOCK and BMAL-1. Taken together, these data suggest that TTF-1 plays an important regulatory role in the gene transcription for PACAP, which may be important for the generation of a daily rhythm of hypothalamic PACAP gene expression.

Distribution of the titf2/foxe1 gene product is consistent with an important role in the development of foregut endoderm, palate, and hair

Titf2/foxe1 is a forkhead domain-containing gene expressed in the foregut, in the thyroid, and in the cranial ectoderm of the developing mouse. Titf2 null mice exhibit cleft palate and either a sublingual or completely absent thyroid gland. In humans, mutations of the gene encoding for thyroid transcription factor-2 (TTF-2) result in the Bamforth syndrome, characterized by thyroid agenesis, cleft palate, spiky hair, and choanal atresia. Here, we report a detailed expression pattern of TTF-2 protein during mouse embryogenesis and show its presence in structures where it has not been described yet. At embryonic day (E) 10.5, TTF-2 is expressed in Rathke's pouch, in thyroid, and in the epithelium of the pharyngeal wall and arches, whereas it is absent in the epithelium of the pharyngeal pouches. According to this expression, at E13.5, TTF-2 is present in endoderm derivatives, such as tongue, palate, epiglottis, pharynx, and oesophagus. Later in embryogenesis, we detect TTF-2 in the choanae and whiskers. This pattern of expression helps to define the complex phenotype displayed by human patients. Finally, we show that TTF-2 is a phosphorylated protein. These results help to characterize the domains of TTF-2 expression, from early embryogenesis throughout organogenesis, providing more detail on the potential role of TTF-2 in the development of endoderm and ectoderm derived structures.

Immunohistochemical detection of thyroid transcription factor-1, thyroglobulin, and calcitonin in canine normal, hyperplastic, and neoplastic thyroid gland

Immunohistochemistry for thyroid transcription factor-1 (TTF-1), thyroglobulin, and calcitonin was done in normal, hyperplastic, and neoplastic canine thyroid glands that had been fixed in formalin and embedded in paraffin. Prolonged fixation did not significantly alter the immunostaining for TTF-1. Staining for TTF-1 was always nuclear and usually strong. One of two C-cell adenomas, five of five follicular cell adenomas, 5 of 11 C-cell carcinomas, 38 of 42 follicular cell carcinomas, two of five cases of C-cell hyperplasia, two of two cases of follicular epithelial hyperplasia, one of two metastatic C-cell carcinomas, and three of four metastatic follicular carcinomas were positive for TTF-1. One follicular carcinoma that was positive for TTF-1 was negative for thyroglobulin. Thirty-nine of 42 follicular cell carcinomas were positive for thyroglobulin, including two cases that were negative for TTF-1. All C-cell lesions were positive for calcitonin. Of a variety of normal canine tissues and 278 nonthyroid tumors, only normal lung (airway and alveolar epithelial cells) and four of five pulmonary carcinomas were positive for TTF-1. TTF-1 is a good marker of thyroid differentiation and can be used in conjunction with thyroglobulin and calcitonin to increase the detection and differentiation of thyroid tumors and their metastases.

Expression of thyroid transcription factor-1 in strumal carcinoid and struma ovarii: an immunohistochemical study

Strumal carcinoid is an ovarian teratoma composed of thyroid tissue and carcinoid, intimately admixed in variable proportions. To further elucidate the histogenesis of strumal carcinoid, the expression pattern of thyroid transcription factor-1 (TTF-1) was evaluated in two cases of strumal carcinoid using immunohistochemical techniques. TTF-1 is a nuclear transcription protein that is selectively expressed in the thyroid and respiratory epithelium, and is thought to be expressed specifically in pulmonary and thyroid neoplasms. While the follicular lining cells of the strumal carcinoid showed positive staining for TTF-1, the carcinoid element was, for the most part, negative. These results confirm that TTF-1 is expressed in the thyroidal element of ovarian teratomas and also provide further evidence that the carcinoid component of the strumal carcinoid bears no relation to thyroidal differentiation.