Thyroid development and its disorders: genetics and molecular mechanisms

Regulators of thyroid hormone availability and action in embryonic chicken brain development

Thyroid hormones (THs) are crucial elements in vertebrate brain development. They exert their action mainly through binding of 3,5,3'-triiodothyronine (T3) to nuclear receptors that directly influence the expression of TH-regulated genes. Intracellular TH action is therefore dependent on both the availability of T3 and its receptors. TH uptake in cells is regulated by specific TH transporters and local activation and inactivation is regulated by deiodinases. This review provides an overview of the general expression pattern of TH transporters, deiodinases and receptors during embryonic chicken brain development and compares it to the situation in mammals. It is clear that THs and their regulators are present in the embryonic brain from the early stages of development, long before the onset of embryonic thyroid gland functioning. The mechanism of TH uptake across the brain barriers during development is only partly understood. At the developing blood-brain-barrier expression of the TH-activating type 2 deiodinase is closely associated with the blood vessels, but contrary to the situation in (adult) mammals no expression of MCT8 or OATP1C1 TH transporters is found at that level in the developing chicken. At the blood-cerebrospinal fluid-barrier co-expression of the TH-inactivating type 3 deiodinase and MCT8 and OATP1C1 is found in birds and mammals. These comparative data show overlapping patterns, pointing to general mechanisms, but also indicate specific interspecies differences that may help to understand species-specific responses to regulator gene knockout/mutation.

The molecular causes of thyroid dysgenesis: a systematic review

BACKGROUND

Congenital hypothyroidism (CH) is a frequent disease occurring with an incidence of about 1/2500 newborns/year. In 80-85% of the cases CH is caused by alterations in thyroid morphogenesis, generally indicated by the term "thyroid dysgenesis" (TD). TD is generally a sporadic disease, but in about 5% of the cases a genetic origin has been demonstrated. In these cases, mutations in genes playing a role during thyroid morphogenesis (NKX2-1, PAX8, FOXE1, NKX2-5, TSHR) have been reported.

AIM

This work reviews the main steps of thyroid morphogenesis and all the genetic alterations associated with TD and published in the literature.

A new PAX8 mutation causing congenital hypothyroidism in three generations of a family is associated with abnormalities in the urogenital tract

BACKGROUND

Although thyroid dysgenesis is the most common cause of congenital hypothyroidism (CH), its molecular basis remains largely elusive. Indeed, in only a minority of cases with thyroid dysgenesis (2%-3%) was it possible to identify an underlying genetic defect. The objective of this study was to screen the PAX8 gene and the PAX2 gene in a family with six cases of CH spanning three generations and presenting urogenital malformations. Herein, we report a case series and in vitro characterization of the PAX8 gene mutation.

METHODS

Investigations were conducted at a tertiary care referral center. The index case was diagnosed to have congenital hypothyroidism at 7 months of age when he presented with severe impairment of suckling, constipation, and poor development. Treatment with levothyroxine corrected the symptoms and was associated with catch-up growth. His progeny, including two sons, one daughter, and two granddaughters, were affected by CH, and three of them received the diagnosis at neonatal screening. Ultrasound demonstrated normally located thyroid glands with reduced volumes. Five of the six affected family members, including the index case, had urogenital malformations, including incomplete horseshoe kidney, undescended testicles, hydrocele, and ureterocele. Strabismus was found in three out of six affected patients. No other somatic malformations were found.

RESULTS

Direct sequencing of the PAX8 gene revealed a new heterozygous mutation (c.74C > G) in all affected individuals. This mutation leads to substitution of proline with arginine at codon 25 (P25R). Fluorescence microscopy showed that P25R is normally located in the nucleus. In transient transfection studies, this mutation causes reduced transcriptional activation ability when using a luciferase reporter construct under the control of a thyroglobulin promoter. This diminished transactivation ability is due to loss of DNA binding capability as shown in electrophoresis mobility shift assay. The sequencing analysis of the PAX2 gene was normal.

CONCLUSIONS

We conclude that this novel PAX8 mutation is responsible for a severe form of dominantly inherited CH. The mutation seems to be associated with abnormalities of the urogenital tract.

Medical management of thyroid ectopia:report of three cases

Thyroid ectopia (TE) is an embryological aberration of the thyroid gland migration most commonly observed in the lingual region followed by the sublingual, hyoid, and mediastinal regions. TE is often complicated by local compressive symptoms resulting in dysphagia, dysphonia, and dyspnea. Surgical removal of TE is frequently complicated by difficulties in intubation, increased perioperative bleeding, and severe primary hypothyroidism; on the other hand, I131 ablation is limited by high doses needed and the concern for long-term effects especially in children. We report three children with TE who all presented with compressive symptoms and were managed conservatively with levothyroxine resulting in resolution of compressive symptoms and favorable outcomes. Levothyroxine supplementation is effective and has an important role in managing TE, not only in correcting the associated hypothyroidism but also in resolving the associated compressive symptoms by reducing the size of the ectopic thyroid tissue.

The follicular thyroid cell line PCCL3 responds differently to laminin and to polylaminin, a polymer of laminin assembled in acidic pH

The extracellular-matrix protein laminin forms polymers both in vivo and in vitro. Acidification of pH leads to the formation of an artificial polymer with biomimetic properties, named polylaminin (polyLM). Follicle cells in the thyroid are in close contact with laminin, but their response to this important extracellular signal is still poorly understood. PCCL3 thyroid follicular cells cultured on glass, on regular laminin (LM) or on laminin previously polymerized in acidic pH (polyLM) showed different cell morphologies and propensities to proliferate, as well as differences in the organization of their actin cytoskeleton. On polyLM, cells displayed a typical epithelial morphology and radially organized actin fibers; whereas on LM, they spread irregularly on the substrate, lost cell contacts, and developed thick actin fibers extending through the entire cytoplasm. Iodide uptake decreased similarly in response to both laminin substrates, in comparison to glass. On both the LM and polyLM substrates, the expression of the sodium iodide symporter (NIS) decreased slightly but not significantly. NIS showed dotted immunostaining at the plasma membrane in the cells cultured on glass; on polyLM, NIS was observed mainly in the perinuclear region, and more diffusely throughout the cytoplasm on the LM substrate. Additionally, polyLM specifically favored the maintenance of cell polarity in culture. These findings indicate that PCCL3 cells can discriminate between LM and polyLM and that they respond to the latter by better preserving the phenotype observed in the thyroid tissue.

Pax8 has a critical role in epithelial cell survival and proliferation

The transcription factor Pax8, a member of the Paired-box gene family, is a critical regulator required for proper development and differentiation of thyroid follicular cells. Despite being Pax8 well characterized with respect to its role in regulating genes responsible for thyroid differentiation, its involvement in cell survival and proliferation has been hypothesized but remains unclear. Here, we show that Pax8 overexpression significantly increases proliferation and colony-forming efficiency of Fischer rat thyroid line 5 epithelial cells, although it is not sufficient to overcome their hormone dependence. More interestingly, we show that Pax8-specific silencing induces apoptosis through a p53-dependent pathway that involves caspase-3 activation and cleavage of poly(ADP)ribose polymerase. Our data indicate that tumor protein 53 induced nuclear protein 1 (tp53inp1), a positive regulator of p53-dependent cell cycle arrest and apoptosis, is a transcriptional target of Pax8 and is upregulated by Pax8 knockdown. Remarkably, tp53inp1 silencing significantly abolishes Pax8-induced apoptosis thus suggesting that tp53inp1 may be the mediator of the observed effects. In conclusion, our data highlight that Pax8 is required for the survival of differentiated epithelial cells and its expression levels are able to modulate the proliferation rate of such cells.

Two cases of thyroid dysgenesis caused by different novel PAX8 mutations in the DNA-binding region: in vitro studies reveal different pathogenic mechanisms

BACKGROUND

Mutations in PAX8, a transcription factor gene, cause thyroid dysgenesis (TD). The extreme variability of the thyroid phenotype makes it difficult to identify individuals harboring PAX8 gene mutations. Here we describe two patients with TD and report two novel PAX8 gene mutations (S54R and R133Q). We performed in vitro studies to functionally characterize these mutations.

METHODS

Using PAX8 expression vectors, we investigated whether the PAX8 mutants localized correctly to the nucleus. To analyze the DNA-binding properties of S54R and R133Q, electrophoretic mobility shift assays were performed. Furthermore, we measured whether the mutant PAX8 proteins were able to activate the thyroglobulin (TG)- and the thyroperoxidase (TPO)-promoters.

RESULTS

S54R had an impaired binding to DNA and a negligible activity on the TG- and the TPO-promoters. The DNA-binding property of R133Q, which is located in the highly conserved terminal portion of the PAX8 DNA-binding domain, was normal. Interestingly, it also exhibited dramatically impaired activation of the TG- and TPO-promoters. However, R133Q has no dominant negative effect on the WT protein in vitro. Thus, the underlying molecular mechanism by which the function of R133Q is impaired remains to be elucidated.

CONCLUSIONS

We identified and functionally characterized two novel mutations of the PAX8 gene that lead to TD by distinct mechanisms. A structural defect of the mutant R133Q leading to a reduced capability for induced fit upon DNA interaction might explain the disparity between its apparently normal binding to DNA, but lack of promoter activation.

A case of hemiagenesis of thyroid with double ectopic thyroid tissue

Developmental abnormalities of the thyroid gland are very rare. The most common abnormalities include ectopic thyroid tissues that are commonly seen in lingual or sublingual location, agenesis, and hemiagenesis of the thyroid gland. These developmental defects may or may not be associated with thyroid dysfunction. Our case is an 18-year-old male who presented with swelling in the neck of 4-year duration. Clinical examination revealed an oval-shape swelling in the left side of the thyroid gland. The ultrasound and the nuclear scan report revealed the presence of thyroid hemiagenesis of the right lobe with isthmus along with double ectopic thyroid tissue at suprahyoid and infrahyoid region. His thyroid function test showed elevated thyroid-stimulating hormone (TSH) and normal free T4. We report a very rare case of thyroid hemiagenesis with double ectopic thyroid tissue; and to the best of our knowledge, this is the first report in the world literature.

Identification and functional characterization of a novel mutation in the NKX2-1 gene: comparison with the data in the literature

BACKGROUND

NKX2-1 mutations have been described in several patients with primary congenital hypothyroidism, respiratory distress, and benign hereditary chorea, which are classical manifestations of the brain-thyroid-lung syndrome (BTLS).

METHODS

The NKX2-1 gene was sequenced in the members of a Brazilian family with clinical features of BTLS, and a novel monoallelic mutation was identified in the affected patients. We introduced the mutation in an expression vector for the functional characterization by transfection experiments using both thyroidal and lung-specific promoters.

RESULTS

The mutation is a deletion of a cytosine at position 834 (ref. sequence NM_003317) (c.493delC) that causes a frameshift with formation of an abnormal protein from amino acid 165 and a premature stop at position 196. The last amino acid of the nuclear localization signal, the whole homeodomain, and the carboxy-terminus of NKX2-1 are all missing in the mutant protein, which has a premature stop codon at position 196 (p.Arg165Glyfs*32). The p.Arg165Glyfs*32 mutant does not bind DNA, and it is unable to transactivate the thyroglobulin (Tg) and the surfactant protein-C (SP-C) promoters. Interestingly, a dose-dependent dominant negative effect of the p.Arg165Glyfs*32 was demonstrated only on the Tg promoter, but not on the SP-C promoter. This effect was also noticed when the mutation was tested in presence of PAX8 or cofactors that synergize with NKX2-1 (P300 and TAZ). The functional effect was also compared with the data present in the literature and demonstrated that, so far, it is very difficult to establish a specific correlation among NKX2-1 mutations, their functional consequence, and the clinical phenotype of affected patients, thus suggesting that the detailed mechanisms of transcriptional regulation still remain unclear.

CONCLUSIONS

We describe a novel NKX2-1 mutation and demonstrate that haploinsufficiency may not be the only explanation for BTLS. Our results indicate that NKX2-1 activity is also finely regulated in a tissue-specific manner, and additional studies are required to better understand the complexities of genotype-phenotype correlations in the NKX2-1 deficiency syndrome.

Reciprocal epithelial:endothelial paracrine interactions during thyroid development govern follicular organization and C-cells differentiation

The thyroid is a highly vascularized endocrine gland, displaying a characteristic epithelial organization in closed spheres, called follicles. Here we investigate how endothelial cells are recruited into the developing thyroid and if they control glandular organization as well as thyrocytes and C-cells differentiation. We show that endothelial cells closely surround, and then invade the expanding thyroid epithelial cell mass to become closely associated with nascent polarized follicles. This close and sustained endothelial:epithelial interaction depends on epithelial production of the angiogenic factor, Vascular Endothelial Growth Factor-A (VEGF-A), as its thyroid-specific genetic inactivation reduced the endothelial cell pool of the thyroid by > 90%. Vegfa KO also displayed decreased C-cells differentiation and impaired organization of the epithelial cell mass into follicles. We developed an ex vivo model of thyroid explants that faithfully mimicks bilobation of the thyroid anlagen, endothelial and C-cells invasion, folliculogenesis and differentiation. Treatment of thyroid explants at e12.5 with a VEGFR2 inhibitor ablated the endothelial pool and reproduced ex vivo folliculogenesis defects observed in conditional Vegfa KO. In the absence of any blood supply, rescue by embryonic endothelial progenitor cells restored folliculogenesis, accelerated lumen expansion and stimulated calcitonin expression by C-cells. In conclusion, our data demonstrate that, in developing mouse thyroid, epithelial production of VEGF-A is necessary for endothelial cells recruitment and expansion. In turn, endothelial cells control epithelial reorganization in follicles and C-cells differentiation.

New insights into FoxE1 functions: identification of direct FoxE1 targets in thyroid cells

BACKGROUND

FoxE1 is a thyroid-specific forkhead transcription factor essential for thyroid gland development, as well as for the maintenance of the thyroid differentiated state in adults. FoxE1 recognizes and binds to a short DNA sequence present in thyroglobulin (Tg) and thyroperoxidase (Tpo) promoters, but FoxE1 binding to regulatory regions other than Tg and Tpo promoters remains almost unexplored. Improving knowledge of the regulatory functions of FoxE1 is necessary to clarify its role in endocrine syndromes and cancer susceptibility.

METHODOLOGY/PRINCIPAL FINDING

In order to further investigate downstream FoxE1 targets, we performed a genome-wide expression screening after knocking-down FoxE1 and obtained new insights into FoxE1 transcriptional networks in thyroid follicular cells. After validation, we confirmed Adamts9, Cdh1, Duox2 and S100a4 as upregulated genes and Casp4, Creld2, Dusp5, Etv5, Hsp5a, Nr4a2 and Tm4sf1 as downregulated genes when FoxE1 was silenced. In promoter regions of putative FoxE1-regulated genes and also in the promoters of the classical thyroid genes Nis, Pax8 and Titf1, we performed an in silico search of the FoxE1 binding motif that was in close proximity to the NF1/CTF binding sequence, as previously described for other forkhead factors. Using chromatin immunoprecipitation we detected specific in vivo FoxE1 binding to novel regulatory regions in two relevant thyroid genes, Nis and Duox2. Moreover, we demonstrated simultaneous binding of FoxE1 and NF1/CTF to the Nis upstream enhancer region, as well as a clear functional activation of the Nis promoter by both transcription factors.

CONCLUSIONS/SIGNIFICANCE

In search for potential downstream mediators of FoxE1 function in thyroid cells, we identified two novel direct FoxE1 target genes. To our knowledge, this is the first evidence regarding the implication of Nis and Duox2 in executing the transcriptional program triggered by FoxE1. Furthermore, this study points out the important role of FoxE1 in the regulation of a large number of genes in thyroid cells.

Pitfalls in the staging of cancer of thyroid

Thyroid cancer includes several neoplasms originating from the thyroid gland-from indolent and curable histologies of differentiated thyroid carcinoma to aggressive anaplastic thyroid carcinoma. Differentiation of thyroid nodules is problematic on CT and MR imaging unless there is evidence of extrathyroidal extension. Evaluation of regional lymph nodes is often performed clinically or with ultrasound. The retropharyngeal and mediastinal lymph nodes are better evaluated by CT and MR imaging. Nuclear scintigraphy is useful for staging and treatment of distant metastasis in differentiated thyroid carcinoma. PET may have a role in aggressive cancers. Accurate staging affects surgical management and subsequent therapy.

A case of mediastinal ectopic thyroid presenting with a paratracheal mass

Mediastinal ectopic thyroid is a very rare condition, with few reported cases in the literature and no reported cases in Korea. This report describes an asymptomatic 65-year-old man with a right paratracheal mass compressing the superior vena. Additionally, the epidemiology, clinical manifestation, diagnosis, and management of mediastinal ectopic thyroids are discussed. A mediastinal ectopic thyroid should be considered in the differential diagnosis of all mediastinal masses. Surgical excision is recommended for both the diagnosis and treatment of this condition, because of its potential for malignancy and compression of mediastinal structures. This case demonstrates the clinical importance of mediastinal etopic thyroid.

Thyroid papillary carcinoma arising in ectopic thyroid tissue within a branchial cleft cyst

Ectopic thyroid tissue comprises a rare clinical entity which can clinically manifest with the whole spectrum of thyroid disorders, including thyroid malignancy. Thyroid carcinoma arising in ectopic thyroid tissue is extremely rare, with only a few cases described in the literature so far. We present a very unusual case of a primary papillary thyroid carcinoma arising in a left lateral branchial cyst, describing our diagnostic and therapeutic approach for this uncommon clinical entity. This is the first case where recombinant thyrotropin was used along with radioiodine treatment in primary ectopic thyroid cancer.

Functional analysis of the murine Pax8 promoter reveals autoregulation and the presence of a novel thyroid-specific DNA-binding activity

BACKGROUND

Organogenesis of the thyroid gland requires the Pax8 protein. Absence or reduction of Pax8 results in congenital hypothyroidism in animal models and humans, respectively. This study aims at elucidating the regulatory mechanism leading to the expression of Pax8 in thyroid cells.

METHODS

The murine Pax8 gene promoter was functionally dissected by mutagenesis and transfection in the thyroid cell line FRTL-5. Nuclear factors important for thyroid-specific gene expression were identified by DNA-binding assays.

RESULTS

We show that Pax8 binds to and controls the expression of its own promoter. Furthermore, we identify a novel, thyroid-specific, DNA-binding activity (denominated nTTF [for novel Thyroid Transcription Factor]) that recognizes a specific region of the Pax8 promoter.

CONCLUSIONS

The Pax8 promoter appears to be autoregulated, a feature that might be responsible for the haploinsufficiency displayed by this gene.

Recent insights into the cell biology of thyroid angiofollicular units

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

Carcinoma of dual ectopic thyroid gland in a patient with cyanotic congenital heart disease--a case report and review of literature

Carcinoma arising from an ectopic thyroid gland in the absence of a normal thyroid gland is uncommon. There is a clinically relevant and unique association of ectopic thyroid with congenital heart disease which in turn is related to thyroid embryogenesis. The median thyroid anlage develops adjacent to the newly differentiated myocardium during the 3rd week of intrauterine life. The downward pull exerted by continued descent of heart is postulated to assist in the descent of the thyroid to its final location in the lower cervical position. Ectopic thyroid tissue can result from abnormal heart development or abnormal interaction between thyroid primordium and heart. We present a rare association of cancer of the ectopic thyroid gland in a patient with congenital heart disease.

Maternal thyroid dysfunction and neonatal thyroid problems

Aim. To investigate obstetric features of pregnant women with thyroid disorders and thyroid function tests of their newborn infants. Methods. Women with hypothyroidism and having anti-thyroglobulin (ATG) and anti-thyroid peroxidase (anti-TPO) antibodies were assigned as group I, women with hypothyroidism who did not have autoantibodies were assigned as group II, and women without thyroid problems were assigned as group III. Results. Pregnant women with autoimmune hypothyroidism (group I) had more preterm delivery and their babies needed more frequent neonatal intensive care unit (NICU) admission. In group I, one infant was diagnosed with compensated hypothyroidism and one infant had transient hyperthyrotropinemia. Five infants (23.8%) in group II had thyroid-stimulating hormone (TSH) levels >20 mIU/mL. Only two of them had TSH level >7 mIU/L at the 3rd postnatal week, and all had normal free T4 (FT4). Median maternal TSH level of these five infants with TSH >20 mIU/mL was 6.6 mIU/mL. In group III, six infants (6.5%) had TSH levels above >20 mIU/mL at the 1st postnatal week. Conclusion. Infants of mothers with thyroid problems are more likely to have elevated TSH and higher recall rate on neonatal thyroid screening. Women with thyroid disorders and their newborn infants should be followed closely for both obstetrical problems and for thyroid dysfunction.

Mechanisms of thyroid development and dysgenesis: an analysis based on developmental stages and concurrent embryonic anatomy

Thyroid dysgenesis is the most common cause of congenital hypothyroidism that affects 1 in 3000 newborns. Although a number of pathogenetic mutations in thyroid developmental genes have been identified, the molecular mechanism of disease is unknown in most cases. This chapter summarizes the current knowledge of normal thyroid development and puts the different developmental stages in perspective, from the time of foregut endoderm patterning to the final shaping of pharyngeal anatomy, for understanding how specific malformations may arise. At the cellular level, we will also discuss fate determination of follicular and C-cell progenitors and their subsequent embryonic growth, migration, and differentiation as the different thyroid primordia evolve and merge to establish the final size and shape of the gland.

Adenomas of cervical maldescended parathyroid glands: pearls and pitfalls

BACKGROUND

Missed parathyroid adenoma (PTA) is the commonest cause of persistent hyperparathyroidism. Although many are subsequently found in well-described locations, some are found in unusual regions of the neck. This paper presents the combined experience of three large tertiary endocrine surgery centres with maldescended PTA (MD-PTA).

METHODS

Patients were recruited from the endocrine surgical databases of three tertiary endocrine surgery units. Patients with PTA found >1 cm above the superior thyroid pole or other cervical locations as a result of abnormal or incomplete descent were included for analysis.

RESULTS

MD-PTA was identified in 16 patients out of a total of 5241 patients who had undergone parathyroidectomies in the 7-year study period (incidence 0.3%). Seven (44%) patients had minimally invasive parathyroidectomy, while nine (56%) had bilateral neck exploration. The mean excised gland weight was 750 + 170 mg. Cure was achieved in all patients with a minimum follow-up of 6 months. The locations of MD-PTA in this study included submandibular triangle, retropharyngeal space, carotid sheath (at carotid bifurcation and intravagal), parapharyngeal space (superior to thyroid cartilage or superior thyroid pole) and cricothyroid space.

CONCLUSIONS

Despite their rare occurrence, incompletely or abnormally descended PTAs can be encountered by any surgeon who performs parathyroidectomies. It is important to develop a strategy to systematically locate these glands. High cure rates can still be achieved with minimally invasive parathyroidectomy if confident preoperative localization is available. A sound knowledge of embryology and a thorough exploration also facilitate an overall high success rate with open exploration.

Thyroid peroxidase gene expression is induced by lipopolysaccharide involving nuclear factor (NF)-κB p65 subunit phosphorylation

Thyroid peroxidase (TPO), a tissue-specific enzyme expressed in differentiated thyroid follicular cells, is a major antigen that has been linked to autoimmune thyroid disease. We have previously reported the functional expression of the lipopolysaccharide (LPS) receptor Toll-like receptor 4 on thyroid follicular cells. Here we investigated the effect of LPS in TPO expression and analyzed the mechanisms involved. We found a dose-dependent enhancement of TSH-induced TPO expression in response to LPS stimulation. EMSAs demonstrated that LPS treatment increased thyroid transcription factor-1 and -2 binding to the B and Z regions of TPO promoter, respectively. Moreover, LPS increased TSH-stimulated TPO promoter activity. Using bioinformatic analysis, we identified a conserved binding site for transcription nuclear factor-κB (NF-κB) in the TPO promoter. Chemical inhibition of NF-κB signaling and site-directed mutagenesis of the identified κB-cis-acting element abolished LPS stimulation. Furthermore, chromatin immunoprecipitation assays confirmed that TPO constitutes a novel NF-κB p65 subunit target gene in response to LPS. Additionally, our results indicate that p65 phosphorylation of serine 536 constitutes an essential step in the p65-dependent, LPS-induced transcriptional expression of TPO. In conclusion, here we demonstrated that LPS increases TPO expression, suggesting a novel mechanism involved in the regulation of a major thyroid autoantigen. Our results provide new insights into the potential effects of infectious processes on thyroid homeostasis.

Dual thyroid ectopia with graves' disease: a case report and a review of the literature

Ectopic thyroid or thyroid ectopia is a rare developmental anomaly with the prevalence of 1 per 100,000-300,000 population. Even rarer, such an anomaly manifests as dual thyroid ectopia. To our best knowledge, only one case has been reported on dual thyroid ectopia with Graves' disease in the English literature. We present here a case of dual thyroid ectopia complicated by Graves' disease, whereby the diagnosis was rendered through judicious use of various diagnostic modalities coupled with a close clinical follow-up. In this case, therapeutic consideration should be personalized with proper informed consent of the patient.

Detection of ectopic thyroid remnants: a serious diagnostic dilemma. When molecular biology and immunohistochemistry can solve the problem

The presence of ectopic thyroid tissue is a frequent diagnostic feedback related to a possible histogenetic abnormality or a result of post-surgical seeding. The important challenge is the diagnostic definition of its nature, which could lead to a different therapeutic approach. We describe a case with all the possible implications and differential diagnoses supported by the application of immunohistochemistry and BRAF-V600E molecular detection. A 36-year-old girl with a left thyroid nodule underwent surgery with a diagnosis of angio-invasive tall cell variant of papillary carcinoma without lymph-node metastases. The patient history revealed a previous right lobectomy in another institution ten years before. The right neck dissection was histologically characterized by the presence of thymic residual and evidence of microfollicular microfoci (less than 1mm) of thyroid tissue. Thyroid tumor cells were positive for thyroglobulin, TTF-1, HBME-1 and Galectin-3, while the residual ectopic thyroid tissue showed positivity only for TTF-1 and thyroglobulin. The molecular tests on the thyroid nodule revealed the presence of BRAF-V600E mutation, but wild type BRAF in the ectopic tissue. The histo-morphological definition of these remnants plays the most important role, but the application of immunohistochemistry and molecular biology may help to reach a conclusive diagnosis.

Pyrene exposure influences the thyroid development of Sebastiscus marmoratus embryos

Thyroid hormones play crucial roles in regulating development, morphogenesis, growth, and behavior in fishes. Some environmental pollutants have adverse effects on either development or function of the thyroid gland in fish. However, there are few reports on the effects of polycyclic aromatic hydrocarbons (PAHs) on fish thyroid. In the present study, rockfish (Sebastiscus marmoratus) embryos were exposed to pyrene (Py) for 5 days at the concentrations of 0.5, 5, and 50 nmol/L. The results showed that Py exposure decreased the expression of thyroid primordium markers, Pax2.1 and Nk2.1a as detected by quantitative PCR and in situ hybridization, and reduced the concentration of T(3), but not T(4). Thyroid receptor genes (TRα and TRβ) expression was down-regulated by Py. At the same time, Py exposure impaired the expression of thyroid development related genes, Fgfr2 and Hoxa3a expression, and altered the mRNA levels of thyroid function related genes, Deio1, Ttr, and Tg. In conclusion, the results demonstrated Py exposure inhibited thyroid development and influenced the function of thyroid system in rockfish embryos.

Disruptions of global and JAGGED1-mediated notch signaling affect thyroid morphogenesis in the zebrafish

The mechanisms underlying the early steps of thyroid development are largely unknown. In search for novel candidate genes implicated in thyroid function, we performed a gene expression analysis on thyroid cells revealing that TSH regulates the expression of several elements of the Notch pathway, including the ligand Jagged1. Because the Notch pathway is involved in cell-fate determination of several foregut-derived endocrine tissues, we tested its contribution in thyroid development using the zebrafish, a teleost model recapitulating the mammalian molecular events during thyroid development. Perturbing the Notch signaling (e.g. mib mutants, γ-secretase inhibition, or Notch intracellular domain overexpression), we obtained evidence that this pathway has a biological role during the earlier phases of thyroid primordium induction, limiting the number of cells that proceed to a specialized fate and probably involving actions from surrounding tissues. Moreover, we were able to confirm the expression of Jagged1 during different phases of zebrafish thyroid development, as well as in mouse and human thyroid tissues. The two orthologues to the single jagged1 gene (JAG1) in humans, jag1a and jag1b, are expressed with different spatiotemporal patterns in the developing zebrafish thyroid. Both jag1a and jag1b morphants, as well as jag1b mutant fish line, display thyroid hypoplasia and impaired T(4) production; this thyroid phenotype was rescued by coinjection of human JAG1 mRNA. In conclusion, Notch pathway is involved in the early steps of thyroid morphogenesis, and Jagged1-Notch signal is required for zebrafish thyroid development and function. Thus, genetic alterations affecting the Notch pathway may confer susceptibility for thyroid dysgenesis.

Generation of functional thyroid from embryonic stem cells

The primary function of the thyroid gland is to metabolize iodide by synthesizing thyroid hormones, which are critical regulators of growth, development and metabolism in almost all tissues. So far, research on thyroid morphogenesis has been missing an efficient stem-cell model system that allows for the in vitro recapitulation of the molecular and morphogenic events regulating thyroid follicular-cell differentiation and subsequent assembly into functional thyroid follicles. Here we report that a transient overexpression of the transcription factors NKX2-1 and PAX8 is sufficient to direct mouse embryonic stem-cell differentiation into thyroid follicular cells that organize into three-dimensional follicular structures when treated with thyrotropin. These in vitro-derived follicles showed appreciable iodide organification activity. Importantly, when grafted in vivo into athyroid mice, these follicles rescued thyroid hormone plasma levels and promoted subsequent symptomatic recovery. Thus, mouse embryonic stem cells can be induced to differentiate into thyroid follicular cells in vitro and generate functional thyroid tissue.

Single lobe disease in cases of advanced endemic goiter: a new phenotype

OBJECTIVES

To report a new phenotype of advanced endemic goiter that affects only one lobe of the thyroid gland.

PATIENTS AND METHODS

This study included 60 patients from the west of Sudan with long-standing unilateral simple endemic goiter that required obectomy, with emphasis on the gross appearance, measurements and cytological features of the contralateral lobe.

RESULTS

Out of 60 patients with unilateral goiter, 50 (83%) were found to have the disease on the ipsilateral lobe only (monolobar goiter). The contralateral lobe in these 50 patients showed no nodularity, and its volume was within the normal limits. All patients with monolobar disease had total lobectomy on the affected side, and postoperatively they continued to have normal blood levels of T3, T4 and TSH.

CONCLUSION

We report a new phenotype of advanced endemic goiter that affects only one lobe of the thyroid gland, and in the presence of a structurally and functionally normal contralateral lobe.

Transgenic zebrafish illuminate the dynamics of thyroid morphogenesis and its relationship to cardiovascular development

Among the various organs derived from foregut endoderm, the thyroid gland is unique in that major morphogenic events such as budding from foregut endoderm, descent into subpharyngeal mesenchyme and growth expansion occur in close proximity to cardiovascular tissues. To date, research on thyroid organogenesis was missing one vital tool-a transgenic model that allows to track the dynamic changes in thyroid size, shape and location relative to adjacent cardiovascular tissues in live embryos. In this study, we generated a novel transgenic zebrafish line, tg(tg:mCherry), in which robust and thyroid-specific expression of a membrane version of mCherry enables live imaging of thyroid development in embryos from budding stage throughout formation of functional thyroid follicles. By using various double transgenic models in which EGFP expression additionally labels cardiovascular structures, a high coordination was revealed between thyroid organogenesis and cardiovascular development. Early thyroid development was found to proceed in intimate contact with the distal ventricular myocardium and live imaging confirmed that thyroid budding from the pharyngeal floor is tightly coordinated with the descent of the heart. Four-dimensional imaging of live embryos by selective plane illumination microscopy and 3D-reconstruction of confocal images of stained embryos yielded novel insights into the role of specific pharyngeal vessels, such as the hypobranchial artery (HA), in guiding late thyroid expansion along the pharyngeal midline. An important role of the HA was corroborated by the detailed examination of thyroid development in various zebrafish models showing defective cardiovascular development. In combination, our results from live imaging as well es from 3D-reconstruction of thyroid development in tg(tg:mCherry) embryos provided a first dynamic view of late thyroid organogenesis in zebrafish-a critical resource for the design of future studies addressing the molecular mechanisms of these thyroid-vasculature interactions.

Thyroid function is maintained despite increased oxidative stress in mice lacking selenoprotein biosynthesis in thyroid epithelial cells

AIMS

We have tested the hypothesis that selenium (Se)-containing antioxidative enzymes protect thyroid epithelial cells from oxidative damage associated with enzymatic production of hydrogen peroxide required for thyroid hormone biosynthesis. Thyroid epithelial cells therefore express antioxidative enzymes, including catalase, peroxiredoxins, thioredoxin reductases, and glutathione peroxidases (GPxs). The latter two enzyme families contain highly active peroxide-degrading enzymes that carry selenocysteine (Sec) in their active centers. Since low Se status has been associated with thyroid disorders, selenoproteins are considered essential for thyroid integrity and function. We have conditionally inactivated selenoprotein biosynthesis in thyrocytes by targeting Sec tRNA.

RESULTS

Constitutive and inducible Cre/loxP-mediated recombination of tRNA([Ser]Sec) drastically reduced activities of selenoenzymes GPx and type I-deiodinase in thyroid extracts. Immunohistochemical staining revealed increased 4-hydroxynonenal and 3-nitro-tyrosine levels consistent with increased oxidative stress. However, gross thyroid morphology remained intact for at least 6 months after recombination. Circulating thyroid hormone levels remained normal in mutant mice, while thyrotropin (TSH) levels were moderately elevated. Challenging mutant mice with low iodine diet increased TSH, but did not lead to destruction of selenoprotein-deficient thyroids.

INNOVATION

This is the first report probing the assumed physiological roles of selenoproteins in the thyroid using a genetic loss-of-function approach.

CONCLUSION

We conclude that selenoproteins protect thyrocytes from oxidative damage and modulate thyroid hormone biosynthesis, but are not essential for thyrocyte survival.

Molecular characterization and functional analysis of sheep thyroid transcription factor-1

Thyroid transcription factor-1 (TTF-1), a member of the Nkx2 family of homeodomain-containing proteins, is involved in binding to and in activating the promoters of several important genes in the thyroid, lungs, and brain, and in regulating expression of these tissue-specific genes. We investigated potential roles of sheep (Ovis aries) TTF-1 in regulating cell fate and organ morphogenesis and in controlling puberty and reproductive capability of females. We amplified and cloned the sheep TTF-1 full-length DNA for the first time, analyzed its functional domains and regions, predicted molecular structure of its homeodomain and DNA-binding sites, and examined its expression in pituitary, brain, thyroid gland, ovary, and hypothalamus. We found that sheep TTF-1 has a high degree of homologous identity with that of other mammals, and it has several important domains including domain N, DNA-binding domain, domain C, TN-domain, domain I, and NK2-SD. The DNA-binding domain of sheep TTF-1 has 10 potential DNA-binding sites and is a novel mammalian homeodomain that shows considerable sequence homology with the corresponding rat homeodomain. Several functional regions in sheep TTF-1 share high sequence identity with rat TTF-1, indicating that these regions may have the same activity as in the rat. Expression of TTF-1 in several specific tissues implies that sheep TTF-1 in involved in sheep sexual development and reproductive capability. These results suggest a role of sheep TTF-1 in enhancing sheep reproduction performance and we propose it as a candidate gene for selection.

Functional inactivation of thyroid transcription factor-1 in PCCl3 thyroid cells

Thyroid transcription factor-1 (TTF-1) is a key regulator of thyroid development and function. In order to identify the genes whose expression depends on TTF-1 transcriptional activity within the thyrocyte we analyzed the consequence of the functional inactivation of this factor in PCCl3 cells. The expression of a fusion protein composed of the DNA binding domain of TTF-1 and of the strong repressive domain of the engrailed protein resulted in a dramatic loss of epithelial cell morphology and in proliferation arrest. These changes were reversed when the inhibition of endogenous TTF-1 was relieved. No change was observed when a similar fusion protein containing point mutations abolishing DNA binding activity was produced in the cells. Besides the expected down-regulation of expression of the main genes linked to the differentiated thyroid function, we observed a decreased expression of the transcription factors Hhex, Pax 8 and TTF-2 and of E-cadherin. By contrast, both ThOX-1 and DUOXA-1 genes were up-regulated, as well as the ones encoding vimentin and several proteins involved in cell cycle arrest. Our data thus extend the known roles of TTF-1 in thyroid development and in the expression of differentiated function in the adult organ to the control of epithelial morphology and of cell division in mature thyrocytes.

Common genetic variants in metabolism and detoxification pathways and the risk of papillary thyroid cancer

Relationships are unclear between polymorphisms in genes involved in metabolism and detoxification of various chemicals and papillary thyroid cancer (PTC) risk as well as their potential modification by alcohol or tobacco intake. We evaluated associations between 1647 tagging single nucleotide polymorphisms (SNPs) in 132 candidate genes/regions involved in metabolism of exogenous and endogenous compounds (Phase I/II, oxidative stress, and metal binding pathways) and PTC risk in 344 PTC cases and 452 controls. For 15 selected regions and their respective SNPs, we also assessed interaction with alcohol and tobacco use. Logistic regression models were used to evaluate the main effect of SNPs (P(trend)) and interaction with alcohol/tobacco intake. Gene- and pathway-level associations and interactions (P(gene interaction)) were evaluated by combining P(trend) values using the adaptive rank-truncated product method. While we found associations between PTC risk and nine SNPs (P(trend) ≤ 0.01) and seven genes/regions (P(region)<0.05), none remained significant after correction for the false discovery rate. We found a significant interaction between UGT2B7 and NAT1 genes and alcohol intake (P(gene interaction)=0.01 and 0.02 respectively) and between the CYP26B1 gene and tobacco intake (P(gene interaction)=0.02). Our results are suggestive of interaction between the genetic polymorphisms in several detoxification genes and alcohol or tobacco intake on risk of PTC. Larger studies with improved exposure assessment should address potential modification of PTC risk by alcohol and tobacco intake to confirm or refute our findings.

Serum copper as a novel biomarker for resistance to thyroid hormone

Thyroid hormone action is mediated by the thyroid hormone receptors TRα1 and TRβ. Defects in TRβ lead to RTH (resistance to thyroid hormone) β, a syndrome characterized by high levels of thyroid hormone and non-suppressed TSH (thyroid-stimulating hormone). However, a correct diagnosis of RTHβ patients is difficult as the clinical picture varies. A biochemical serum marker indicative of defects in TRβ signalling is needed and could simplify the diagnosis of RTHβ, in particular the differentiation to TSH-secreting pituitary adenomas, which present with clinically similar symptoms. In the present paper we show that serum copper levels are regulated by thyroid hormone, which stimulates the synthesis and the export of the hepatic copper-transport protein ceruloplasmin into the serum. This is accompanied by a concerted reduction in the mRNA levels of other copper-containing proteins such as metallothioneins 1 and 2 or superoxide dismutase 1. The induction of serum copper is abolished in genetically hyperthyroid mice lacking TRβ and human RTHβ patients, demonstrating an important role of TRβ for this process. Together with a previously reported TRα1 specific regulation of serum selenium, we show that the ratio of serum copper and selenium, which is largely independent of thyroid hormone levels, volume changes or sample degradation, can constitute a valuable novel biomarker for RTHβ. Moreover, it could also provide a suitable large-scale screening parameter to identify RTHα patients, which have not been identified to date.

Influence of neonatal hypothyroidism on hepatic gene expression and lipid metabolism in adulthood

Thyroid hormones are required for normal growth and development in mammals. Congenital-neonatal hypothyroidism (CH) has a profound impact on physiology, but its specific influence in liver is less understood. Here, we studied how CH influences the liver gene expression program in adulthood. Pregnant rats were given the antithyroid drug methimazole (MMI) from GD12 until PND30 to induce CH in male offspring. Growth defects due to CH were evident as reductions in body weight and tail length from the second week of life. Once the MMI treatment was discontinued, the feed efficiency increased in CH, and this was accompanied by significant catch-up growth. On PND80, significant reductions in body mass, tail length, and circulating IGF-I levels remained in CH rats. Conversely, the mRNA levels of known GH target genes were significantly upregulated. The serum levels of thyroid hormones, cholesterol, and triglycerides showed no significant differences. In contrast, CH rats showed significant changes in the expression of hepatic genes involved in lipid metabolism, including an increased transcription of PPARα and a reduced expression of genes involved in fatty acid and cholesterol uptake, cellular sterol efflux, triglyceride assembly, bile acid synthesis, and lipogenesis. These changes were associated with a decrease of intrahepatic lipids. Finally, CH rats responded to the onset of hypothyroidism in adulthood with a reduction of serum fatty acids and hepatic cholesteryl esters and to T3 replacement with an enhanced activation of malic enzyme. In summary, we provide in vivo evidence that neonatal hypothyroidism influences the hepatic transcriptional program and tissue sensitivity to hormone treatment in adulthood. This highlights the critical role that a euthyroid state during development plays on normal liver physiology in adulthood.

Genome-wide analysis of Pax8 binding provides new insights into thyroid functions

Background

The transcription factor Pax8 is essential for the differentiation of thyroid cells. However, there are few data on genes transcriptionally regulated by Pax8 other than thyroid-related genes. To better understand the role of Pax8 in the biology of thyroid cells, we obtained transcriptional profiles of Pax8-silenced PCCl3 thyroid cells using whole genome expression arrays and integrated these signals with global cis-regulatory sequencing studies performed by ChIP-Seq analysis

Results

Exhaustive analysis of Pax8 immunoprecipitated peaks demonstrated preferential binding to intragenic regions and CpG-enriched islands, which suggests a role of Pax8 in transcriptional regulation of orphan CpG regions. In addition, ChIP-Seq allowed us to identify Pax8 partners, including proteins involved in tertiary DNA structure (CTCF) and chromatin remodeling (Sp1), and these direct transcriptional interactions were confirmed in vivo. Moreover, both factors modulate Pax8-dependent transcriptional activation of the sodium iodide symporter (Nis) gene promoter. We ultimately combined putative and novel Pax8 binding sites with actual target gene expression regulation to define Pax8-dependent genes. Functional classification suggests that Pax8-regulated genes may be directly involved in important processes of thyroid cell function such as cell proliferation and differentiation, apoptosis, cell polarity, motion and adhesion, and a plethora of DNA/protein-related processes.

Conclusion

Our study provides novel insights into the role of Pax8 in thyroid biology, exerted through transcriptional regulation of important genes involved in critical thyrocyte processes. In addition, we found new transcriptional partners of Pax8, which functionally cooperate with Pax8 in the regulation of thyroid gene transcription. Besides, our data demonstrate preferential location of Pax8 in non-promoter CpG regions. These data point to an orphan CpG island-mediated mechanism that represents a novel role of Pax8 in the transcriptional output of the thyrocyte.

Identifying thyroid stem/progenitor cells: advances and limitations

Continuing advances in stem cell science have prompted researchers to envisage the potential application of stem cells for the management of several debilitating disorders, thus raising the expectations of transplant clinicians. In particular, in order to find a source of adult stem cells alternative to embryonic stem cells (ESCs) for the exploration of novel strategies in regenerative medicine, researchers have attempted to identify and characterise adult stem/progenitor cells resident in compact organs, since these populations appear to be responsible for physiological tissue renewal and regeneration after injury. In particular, recent studies have also reported evidence for the existence of adult stem/progenitor cell populations in both mouse and human thyroids. Here, I provide a review of published findings about ESC lines capable of generating thyroid follicular cells, thyroid somatic stem cells and cancer stem cells within the thyroid. The three subjects are analysed by also considering the criticism recently raised against their existence and potential utility. I comment specifically on the significance of resident thyroid stem cells in the developmental biology of the gland and their putative role in the pathogenesis of thyroid disorders and on the protocols employed for their identification. I finally provide my opinion on whether from basic science results obtained to date it is possible to extrapolate any convincing basic for future treatment of thyroid disorders.

Lateral Ectopic Thyroid: A Case Diagnosed Preoperatively

Ectopic thyroid is an uncommon condition defined as the presence of thyroid tissue at a site other than the pretracheal area. When the process of embryologic migration is disturbed, aberrant thyroid tissue may appear. In most cases, ectopic thyroid is located along the embryologic descent path of migration as either a lingual thyroid or a thyroglossal duct cyst. In rare cases, aberrant migration can result in lateral ectopic thyroid tissue. Approximately 1 to 3% of all ectopic thyroids are located in the lateral neck. Ectopic tissue frequently represents the only presence of thyroid tissue; a second site of orthotopic or ectopic thyroid tissue is found in other cases. The presentation of ectopic thyroid as a lateral mass should be differentiated from metastatic thyroid cancer; other differential diagnoses include a submandibular tumor, branchial cleft cyst, carotid body tumor, and lymphadenopathy of various etiologies. In addition to the history and physical examination, the workup for a patient with a submandibular mass suspicious for ectopic thyroid should include (1) technetium-99m or iodine-131 scintigraphy, (2) ultrasonography and either computed tomography or magnetic resonance imaging, (3) fine-needle aspiration biopsy, and (4) thyroid function testing. No treatment is required for asymptomatic patients with normal thyroid function and cytology, but hypothyroid patients should be placed on thyroid hormone replacement therapy. Most cases are diagnosed postoperatively. Surgical treatment of ectopic thyroid should be considered when a malignancy is suspected or diagnosed, when the patient is symptomatic, or when thyroid suppression therapy fails.

Absence of mutations in PAX8, NKX2.5, and TSH receptor genes in patients with thyroid dysgenesis

OBJECTIVES: To precisely classify the various forms of TD, and then to screen for mutations in transcription factor genes active in thyroid development. SUBJECTS AND METHODS: Patients underwent ultrasound, thyroid scan, and serum thyroglobulin measurement to accurately diagnose the form of TD. DNA was extracted from peripheral leukocytes. The PAX8, and NKX2.5 genes were evaluated in all patients, and TSH receptor (TSHR) gene in those with hypoplasia. RESULTS: In 27 nonconsanguineous patients with TD, 13 were diagnosed with ectopia, 11 with hypoplasia, and 3 with athyreosis. No mutations were detected in any of the genes studied. CONCLUSION: Sporadic cases of TD are likely to be caused by epigenetic factors, rather than mutations in thyroid transcription factors or genes involved in thyroid development.

Growth and development in a child with resistance to thyroid hormone and ectopic thyroid gland

Resistance to thyroid hormone is an uncommon problem, which has rarely been associated with thyroid dysgenesis. We report a case with both thyroid gland ectopy and resistance to thyroid hormone and, thus, a reduced capacity to produce and respond to thyroid hormone. The patient presented at 2 years of age with developmental delay, dysmorphic features, and elevation in both thyroxine and thyrotropin. We document her response to therapy with thyroxine, with particular regard to her growth and development. Persistent elevation of thyrotropin is commonly recognized during treatment of congenital hypothyroidism. Resistance to thyroid hormone may be an important additional diagnosis to consider in cases where thyrotropin remains persistently elevated.

Evidence for calcitonin-producing cells in human lingual thyroids

CONTEXT

The thyroid contains two types of cells, the thyroid follicular cells and the calcitonin-producing cells. The site of origin of the thyroid follicular cells is the median thyroid anlage, an endothelial diverticulum in the midline of the ventral pharynx between the first and the second pharyngeal pouches. The ultimobranchial bodies (UBB), a pair of transient embryonic structures evaginated from the fourth pharyngeal pouch and located symmetrically on the sides of the developing neck, are the source of calcitonin-producing cells. In human embryos, the thyroid bud starts its migration at embryonic day 24 and reaches its final location in front of the trachea at embryonic day 45-50. The UBB fuse with the primitive thyroid when thyroid migration is completed. Lingual thyroids result from the failure of the thyroid precursor cells to migrate from the primordial pharynx to the anterior part of the neck. Therefore, calcitonin-producing cells are not expected to be present in lingual thyroids.

OBJECTIVE

Our objective was to determine whether calcitonin-producing C cells are present in ectopic lingual thyroids.

DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE

We performed calcitonin immunolabeling and transcript detection on four flash-frozen ectopic lingual thyroids. Additional calcitonin immunolabeling was performed on two other paraffin-embedded ectopic lingual thyroids.

RESULTS

We report evidence of calcitonin-producing cells in six independent cases of ectopic lingual thyroids.

CONCLUSION

The UBB are not the only source of calcitonin-producing cells in humans. Interactions between calcitonin-producing and thyroid follicular cells occur earlier than previously accepted.

Ectopic thyroid tissue in the anterior mediastinum with a normally located gland: a case report

Ectopic thyroid tissue occurs in about 7 to 10% of the general population. Localization in the anterior mediastinum is rare: seven cases reported in the literature, most associated with thyroid dysfunction. We report the case of a 77-year-old woman who presented ectopic thyroid tissue in the anterior mediastinum and a normally-located normally-functioning gland.

[Genetic disorders of surfactant]

Lung diseases associated with surfactant metabolism disorders represent a significant but heterogeneous group of rare disorders. Intra-alveolar accumulation of protein related to surfactant dysfunction leads to cough, hypoxemia and radiological diffuse infiltration. Inherited deficiency of pulmonary surfactant protein B (SP-B) was initially described in term newborns who develop severe respiratory failure at birth. More recently, mutations in surfactant protein C (SP-C) or in proteins required for surfactant synthesis such as ATP-binding cassette, sub-family A, member 3 (ABCA3) or NK2 homeobox 1 (NKX2-1) were identified in newborns with respiratory distress but also in children with diffuse infiltrative pneumonia. The aim of this review is to describe the clinical presentation of these diseases but also the diagnostic tools and the treatments options available.

Deletion of the RNaseIII enzyme dicer in thyroid follicular cells causes hypothyroidism with signs of neoplastic alterations

Micro-RNAs (miRNAs) are small non-coding RNAs that regulate gene expression, mainly at mRNA post-transcriptional level. Functional maturation of most miRNAs requires processing of the primary transcript by Dicer, an RNaseIII-type enzyme. To date, the importance of miRNA function for normal organogenesis has been demonstrated in several mouse models of tissue-specific Dicer inactivation. However, the role of miRNAs in thyroid development has not yet been addressed. For the present study, we generated mouse models in which Dicer expression has been inactivated at two different stages of thyroid development in thyroid follicular cells. Regardless of the time of Dicer invalidation, the early stages of thyroid organogenesis, preceding folliculogenesis, were unaffected by the loss of small RNAs, with a bilobate gland in place. Nevertheless, Dicer mutant mice were severely hypothyroid and died soon after weaning unless they were substituted with T4. A conspicuous follicular disorganization was observed in Dicer mutant thyroids together with a strong down regulation of Nis expression. With increasing age, the thyroid tissue showed characteristics of neoplastic alterations as suggested by a marked proliferation of follicular cells and an ongoing de-differentiation in the center of the thyroid gland, with a loss of Pax8, FoxE1, Nis and Tpo expression. Together, our data show that loss of miRNA maturation due to Dicer inactivation severely disturbs functional thyroid differentiation. This suggests that miRNAs are mandatory to fine-tune the expression of thyroid specific genes and to maintain thyroid tissue homeostasis.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.

Ectopic thyroid masquerading as submandibular tumour: a case report

An ectopic thyroid gland may be present in any location along the path of migration from the foramen caecum to the mediastinum. The most common locations for an ectopic thyroid are the lingual thyroid followed by median cervical cysts. An ectopic thyroid in the submandibular region is extremely rare. We present the case of a 44-year-old patient with ectopic thyroid tissue in submandibular space and a review of the literature related to it.

Congenital hypothyroidism with neurological and respiratory alterations: a case detected using a variable diagnostic threshold for TSH

We report a case of congenital hypothyroidism (CH) with neurological and respiratory alterations due to a heterozygotic c.374-1G > A mutation of TITF1/NKX2-1. The hypothyroidism was detected using a neonatal screening protocol in which the thyroid stimulating hormone (TSH) threshold is re-set each day on the basis of within-day variability and between-day variation. In this case, the threshold on the day of the initial analysis was 8.2 mIU/L, and the measured TSH level in heel-prick blood was 8.3 mIU/L.

The microRNA-processing enzyme Dicer is essential for thyroid function

Dicer is a type III ribonuclease required for the biogenesis of microRNAs (miRNAs), a class of small non-coding RNAs regulating gene expression at the post-transcriptional level. To explore the functional role of miRNAs in thyroid gland function, we generated a thyrocyte-specific Dicer conditional knockout mouse. Here we show that development and early differentiation of the thyroid gland are not affected by the absence of Dicer, while severe hypothyroidism gradually develops after birth, leading to reduced body weight and shortened life span. Histological and molecular characterization of knockout mice reveals a dramatic loss of the thyroid gland follicular architecture associated with functional aberrations and down-regulation of several differentiation markers. The data presented in this study show for the first time that an intact miRNAs processing machinery is essential for thyroid physiology, suggesting that deregulation of specific miRNAs could be also involved in human thyroid dysfunctions.