Morphogenesis of the thyroid gland

Advancing thyroid disease research: The role and potential of zebrafish model

Thyroid disorders significantly affect human metabolism, cardiovascular function, skeletal health, and reproductive systems, presenting a complex challenge due to their multifactorial nature. Understanding the underlying mechanisms and developing novel therapeutic approaches require appropriate models. Zebrafish, with their genetic tractability, short life cycle, and physiological relevance, have emerged as a valuable model for investigating thyroid diseases. This review provides a comprehensive analysis of the zebrafish thyroid gland's structure and function, explores its application in modeling thyroid pathologies such as hypothyroidism, hyperthyroidism, and thyroid cancer, and discusses current limitations and possible improvements. Furthermore, it outlines future directions for zebrafish-based research, focusing on enhancing the model's relevance to human thyroid disease and its potential to expedite the development of clinical therapies.

Modelling Functional Thyroid Follicular Structures Using P19 Embryonal Carcinoma Cells

Thyroid gland diseases remain clinical challenges due to the lack of reliable in vitro models to examine molecular pathways of thyrocytes development, maturation, and functional maintenance. This study aimed to develop in vitro thyrocytes model using a stem cell culture, P19 embryonal carcinoma which requires no feeder layer, differentiation into mature and functional thyrocytes that allow molecular and genetic manipulation for studying thyroid diseases. The procedure utilizes Activin A and thyroid stimulating hormone (TSH) to first induce embryoid body endoderm formation enriched in thyrocyte progenitors. Following dissociating embryoid bodies, thyrocyte progenitors are plated in Matrigel as monolayer cultures that allows thyrocyte progenitors mature to functional thyrocytes. These thyrocytes further maturate to form follicle-like structures expressing and accumulating thyroglobulin that can be secreted into the medium upon TSH stimulation. Thyrocyte differentiation-maturation process is monitored by the expression of essential transcriptional factors and thyrocyte-specific functional genes. Further, the applicability of this system is validated by introducing a siRNA control. Following molecular manipulation, the system can still be guided to differentiate into mature and functional thyrocytes. This system spans a time frame of 14 days, suitable for detailed molecular studies to dissect pathways and molecular players in thyrocytes development and functional maintenance.

Should there be a paradigm shift for the evaluation of isthmic thyroid nodules?

PURPOSE

Although the thyroid isthmus seems like a rudimentary structure that connects bilateral lobes, it is an undiscovered area that needs to be explored. Currently, the data is evolving that the increase in the risk of malignancy is higher in the isthmic nodules, and extrathyroidal extensions and lymph node metastases are more common in isthmic-derived malignant thyroid nodules. Therefore, we aimed to compare the malignancy rate of isthmic and lobar nodules, the ultrasonographic features of isthmic and lobar nodules, and presence of lymph node metastases, distant metastases, and extrathyroidal invasions in malignant isthmic nodules.

METHODS

In this retrospective study, we enrolled patients between the ages of 18-80 years, who had thyroid nodule/nodules cytology and/or pathology results from January 2009 to November 2022. 9504 nodules were selected for the analysis of US findings, cytopathology results, and malignancy rates.

RESULTS

A mean ± SD age of 55.3 ± 13.0 years with a female to male ratio of [7618 (80.2%)/1886(19.8%)] were included in the study. 962 of the nodules were at isthmic localization; whereas 8542 nodules were at lobar localization. 1188 nodules were resulted as malignant from histopathological evaluation. Of the 1188 malignant nodules, 986 nodules were (83.0%) PTC, 114 nodules (9.6%) were FTC, 55 nodules were (4.6%) MTC, 16 nodules 1.3% were Hurtle cell carcinoma, 8 nodules (0.7%) were anaplastic thyroid carcinoma, and 9 nodules (0.8%) were thyroid tumors of uncertain malignant potential (TT-UMP). 156 of the malignant nodules (13.1%) were located in the isthmus, whereas the majority of the malignant nodules (n = 1032, 86.9%) were located at the lobar parts (right or left) of the thyroid. When the metastasis patterns of isthmic and lobar thyroid cancers were examined, no significant relationship was found between isthmic and lobar cancers in terms of capsule invasion (p = 0.435), muscle invasion (p = 0.294), and lymph node metastasis (p = 0.633). A significant relation was found between nodule localization (isthmus-upper-middle and lower lobes) and malignancy (p < 0.001). In our logistic regression analysis, isthmic and upper pole nodule localizations, age and TI-RADS were evaluated as independent risk factors for malignancy (p < 0.001 for all factors).

CONCLUSION

We recommend nodule localization has to be considered an additional risk factor when performing a Fine Needle Aspiration Biopsy for the increased malignancy risk in this localization.

TAF1 is needed for the proliferation and maturation of thyroid follicle cells via Notch signaling

Thyroid dysgenesis (TD) is the common pathogenic mechanism of congenital hypothyroidism (CH). In addition, known pathogenic genes are limited to those that are directly involved in thyroid development. To identify additional candidate pathogenetic genes, we performed forward genetic screening for TD in zebrafish, followed by positional cloning. The candidate gene was confirmed in vitro using the Nthy-ori 3.1 cell line and in vivo using a zebrafish model organism. We obtained a novel zebrafish line with thyroid dysgenesis and identified the candidate pathogenetic mutation TATA-box binding protein associated Factor 1 (taf1) by positional cloning. Further molecular studies revealed that taf1 was needed for the proliferation of thyroid follicular cells by binding to the NOTCH1 promoter region. Knockdown of TAF1 impaired the proliferation and maturation of thyroid cells, thereby leading to thyroid dysplasia. This study showed that TAF1 promoted Notch signaling and that this association played a pivotal role in thyroid development.NEW & NOTEWORTHY In our study, we obtained a novel zebrafish line with thyroid dysgenesis (TD) and identified the candidate pathogenetic mutation TATA-box binding protein associated Factor 1 (taf1). Further researches revealed that taf1 was required for thyroid follicular cells by binding to the NOTCH1 promoter region. Our findings revealed a novel role of TAF1 in thyroid morphogenesis.

Myeloid cells interact with a subset of thyrocytes to promote their migration and follicle formation through NF-κB

The pathogenesis of thyroid dysgenesis (TD) is not well understood. Here, using a combination of single-cell RNA and spatial transcriptome sequencing, we identify a subgroup of NF-κB-activated thyrocytes located at the center of thyroid tissues in postnatal mice, which maintained a partially mesenchymal phenotype. These cells actively protruded out of the thyroid primordium and generated new follicles in zebrafish embryos through continuous tracing. Suppressing NF-κB signaling affected thyrocyte migration and follicle formation, leading to a TD-like phenotype in both mice and zebrafish. Interestingly, during thyroid folliculogenesis, myeloid cells played a crucial role in promoting thyrocyte migration by maintaining close contact and secreting TNF-α. We found that cebpa mutant zebrafish, in which all myeloid cells were depleted, exhibited thyrocyte migration defects. Taken together, our results suggest that myeloid-derived TNF-α-induced NF-κB activation plays a critical role in promoting the migration of vertebrate thyrocytes for follicle generation.

Developmental changes of the fetal and neonatal thyroid gland and functional consequences on the cardiovascular system

Thyroid hormones play an important role in the development and function of the cardiac myocyte. Dysregulation of the thyroid hormone milieu affects the fetal cardiac cells via complex molecular mechanisms, either by altering gene expression or directly by affecting post-translational processes. This review offers a comprehensive summary of the effects of thyroid hormones on the developing cardiovascular system and its adaptation. Furthermore, we will highlight the gaps in knowledge and provide suggestions for future research.

Approach to the Patient With Congenital Hypothyroidism

Congenital hypothyroidism (CH) is the most frequent neonatal endocrine disorder and the most common preventable cause of development delay and growth failure if diagnosed and treated early. The thyroid is the first endocrine gland to develop during embryonic life and to be recognizable in humans. Thyroid development and maturation can be divided into 2 phases: a first phase of embryogenesis and a second phase of folliculogenesis and differentiation with thyroid hormone production at the final steps. Regulation of the thyroid function requires normal development of the hypothalamic-pituitary-thyroid axis, which occurs during the embryonic and neonatal period. Defects in any of steps of thyroid development, differentiation, and regulation lead to permanent CH. Newborn screening programs, established in only one-third of countries worldwide, detect CH and are cost-effective and highly sensitive and specific. During the last decade, epidemiology of CH has changed with increased frequency of thyroid in situ in primary CH. Advances in molecular testing have expanded knowledge and understanding of thyroid development and function. However, a molecular cause is identified in only 5% of CH due to thyroid dysgenesis. The purpose of this article is to describe the clinical approach to the child with CH, focusing on diagnostic work-up and future challenges on optimizing thyroid replacement therapy and regenerative medicine. The review is written from the perspective of the case of 2 girls referred for CH after newborn screening and diagnosed with thyroid ectopy. The genetic work-up revealed novel mutations in TUBB1 gene, associated with large platelets and abnormal platelet physiology.

The Importance of the Thyroid Nodule Location in Determining the Risk of Malignancy: A Retrospective Study

Introduction

Thyroid nodules are very common. However, the majority of thyroid nodules are benign. Ultrasound is the first-line imaging investigation of choice for thyroid nodules. Certain sonographic features are associated with an increased risk of malignancy. Recent studies suggested that the location of the nodule may be associated with the malignancy risk. Hence, this study aims to investigate this association.

Methods

After obtaining approval from the ethics committee, we conducted a retrospective study that involved all patients who attended our hospital, and who underwent fine-needle aspiration cytology for the evaluation of suspicious thyroid nodules (TR3-5). Electronic medical records were used to obtain data about the ultrasound and cytology reports. A multivariable binary logistic regression analysis model was conducted to identify the independent factors significantly associated with malignant thyroid nodules.

Results

The study included 366 patients who underwent fine-needle aspiration cytology for suspicious nodules on thyroid ultrasound. In total, 52 (14.2%) nodules were found to be malignant on cytology. By far, the most common thyroid malignancy was papillary carcinoma. The multivariable analysis model revealed that women were 24% less likely to have malignant thyroid nodules compared with men. After adjusting for the age, gender, and Thyroid Imaging Reporting and Data System (TI-RADS) group, the nodules located within the isthmus were four times more likely to be malignant compared to those located in the right or left lobes.

Conclusions

The study demonstrates that the isthmus location of thyroid nodules is associated with a higher risk of malignancy. Physicians should have a lower threshold to biopsy such nodules. Further studies are needed to confirm this interesting finding.

Zebrafish as an emerging tool for drug discovery and development for thyroid diseases

Zebrafish is a useful model for understanding human genetics and diseases and has evolved into a prominent scientific research model. The genetic structure of zebrafish is 70% identical to that of humans. Its small size, low cost, and transparent embryo make it a valuable tool in experimentation. Zebrafish and mammals possess the same molecular mechanism of thyroid organogenesis and development. Thus, thyroid hormone signaling, embryonic development, thyroid-related disorders, and novel genes involved in early thyroid development can all be studied using zebrafish as a model. Here in this review, we emphasize the evolving role of zebrafish as a possible tool for studying the thyroid gland in the context of physiology and pathology. The transcription factors nkx2.1a, pax2a, and hhex which contribute a pivotal role in the differentiation of thyroid primordium are discussed. Further, we have described the role of zebrafish as a model for thyroid cancer, evaluation of defects in thyroid hormone transport, thyroid hormone (TH) metabolism, and as a screening tool to study thyrotoxins. Hence, the present review highlights the role of zebrafish as a novel approach to understand thyroid development and organogenesis.

Differentiation of endostyle cells by Nkx2-1 and FoxE in the ascidian Ciona intestinalis type A: insights into shared gene regulation in glandular- and thyroid-equivalent elements of the chordate endostyle

Due to similarities in iodine concentrations and peroxidase activities, the thyroid in vertebrates is considered to originate from the endostyle of invertebrate chordates even though it is a glandular (mucus-producing) organ for aquatic suspension feeding. Among chordates with an endostyle, urochordates are useful evolutionary research models for the study of vertebrate traits. The ascidian Ciona intestinalis forms an endostyle with specific components of glandular- and thyroid-related elements, and molecular markers have been identified for these components. Since we previously examined a simple endostyle in the larvacean Oikopleura dioica, the expression of the thyroid-related transcription factor genes, Ciona Nkx2-1 and FoxE, was perturbed by TALEN-mediated gene knockout in the present study to elucidate the shared and/or divergent features of a complex ascidian endostyle. The knockout of Ciona Nkx2-1 and FoxE exerted different effects on the morphology of the developing endostyle. The knockout of Nkx2-1 eliminated the expression of both glandular and thyroidal differentiation marker genes, e.g., vWFL1, vWFL2, CiEnds1, TPO, and Duox, while that of FoxE eliminated the expression of the differentiation marker genes, TPO and CiEnds1. The supporting element-related expression of Pax2/5/8a, Pax2/5/8b, FoxQ1, and β-tubulin persisted in the hypoplastic endostyles of Nkx2-1- and FoxE-knockout juveniles. Although the gene regulation of ascidian-specific CiEnds1 remains unclear, these results provide insights into the evolution of the vertebrate thyroid as well as the urochordate endostyle.

Development of Functional Thyroid C Cell-like Cells from Human Pluripotent Cells in 2D and in 3D Scaffolds

Medullary thyroid carcinoma contributes to about 3–4% of thyroid cancers and affects C cells rather than follicular cells. Thyroid C cell differentiation from human pluripotent stem cells has not been reported. We report the stepwise differentiation of human embryonic stem cells into thyroid C cell-like cells through definitive endoderm and anterior foregut endoderm and ultimobranchial body-like intermediates in monolayer and 3D Matrigel culture conditions. The protocol involved sequential treatment with interferon/transferrin/selenium/pyruvate, foetal bovine serum, and activin A, then IGF-1 (Insulin-like growth factor 1), on the basis of embryonic thyroid developmental sequence. As well as expressing C cell lineage relative to follicular-lineage markers by qPCR (quantitative polymerase chain reaction) and immunolabelling, these cells by ELISA (enzyme-linked immunoassay) exhibited functional properties in vitro of calcitonin storage and release of calcitonin on calcium challenge. This method will contribute to developmental studies of the human thyroid gland and facilitate in vitro modelling of medullary thyroid carcinoma and provide a valuable platform for drug screening.

Shaping the thyroid: From peninsula to de novo lumen formation

A challenging and stimulating question in biology deals with the formation of organs from groups of undifferentiated progenitor cells. Most epithelial organs indeed derive from the endodermal monolayer and evolve into various shape and tridimensional organization adapted to their specialized adult function. Thyroid organogenesis is no exception. In most mammals, it follows a complex and sequential process initiated from the endoderm and leading to the development of a multitude of independent closed spheres equipped and optimized for the synthesis, storage and production of thyroid hormones. The first sign of thyroid organogenesis is visible as a thickening of the anterior foregut endoderm. This group of thyroid progenitors then buds and detaches from the foregut to migrate caudally and then laterally. Upon reaching their final destination in the upper neck region on both sides of the trachea, thyroid progenitors mix with C cell progenitors and finally organize into hormone-producing thyroid follicles. Intrinsic and extrinsic factors controlling thyroid organogenesis have been identified in several species, but the fundamental cellular processes are not sufficiently considered. This review focuses on the cellular aspects of the key morphogenetic steps during thyroid organogenesis and highlights similarities and common mechanisms with developmental steps elucidated in other endoderm-derived organs, despite different final architecture and functions.

Nkx2-1 and FoxE regionalize glandular (mucus-producing) and thyroid-equivalent traits in the endostyle of the chordate Oikopleura dioica

The endostyle is a ventral pharyngeal organ used for internal filter feeding of basal chordates and is considered homologous to the follicular thyroid of vertebrates. It contains mucus-producing (glandular) and thyroid-equivalent regions organized along the dorsoventral (DV) axis. Although thyroid-related genes (Nkx2-1, FoxE, and thyroid peroxidase (TPO)) are known to be expressed in the endostyle, their roles in establishing regionalization within the organ have not been demonstrated. We report that Nkx2-1 and FoxE are essential for establishing DV axial identity in the endostyle of Oikopleura dioica. Genome and expression analyses showed von Willebrand factor-like (vWFL) and TPO/dual oxidase (Duox)/Nkx2-1/FoxE as orthologs of glandular and thyroid-related genes, respectively. Knockdown experiments showed that Nkx2-1 is necessary for the expression of glandular and thyroid-related genes, whereas FoxE is necessary only for thyroid-related genes. Moreover, Nkx2-1 expression is necessary for FoxE expression in larvae during organogenesis. The results demonstrate the essential roles of Nkx2-1 and FoxE in establishing regionalization in the endostyle, including (1) the Nkx2-1-dependent glandular region, and (2) the Nkx2-1/FoxE-dependent thyroid-equivalent region. DV axial regionalization may be responsible for organizing glandular and thyroid-equivalent traits of the pharynx along the DV axis.

From Endoderm to Progenitors: An Update on the Early Steps of Thyroid Morphogenesis in the Zebrafish

The mechanisms underlying thyroid gland development have a central interest in biology and this review is aimed to provide an update on the recent advancements on the early steps of thyroid differentiation that were obtained in the zebrafish, because this teleost fish revealed to be a suitable organism to study the early developmental stages. Physiologically, the thyroid precursors fate is delineated by the appearance among the endoderm cells of the foregut of a restricted cell population expressing specific transcription factors, including pax2a, nkx2.4b, and hhex. The committed thyroid primordium first appears as a thickening of the pharyngeal floor of the anterior endoderm, that subsequently detaches from the floor and migrates to its final location where it gives rise to the thyroid hormone-producing follicles. At variance with mammalian models, thyroid precursor differentiation in zebrafish occurs early during the developmental process before the dislocation to the eutopic positioning of thyroid follicles. Several pathways have been implicated in these early events and nowadays there is evidence of a complex crosstalk between intrinsic (coming from the endoderm and thyroid precursors) and extrinsic factors (coming from surrounding tissues, as the cardiac mesoderm) whose organization in time and space is probably required for the proper thyroid development. In particular, Notch, Shh, Fgf, Bmp, and Wnt signaling seems to be required for the commitment of endodermal cells to a thyroid fate at specific developmental windows of zebrafish embryo. Here, we summarize the recent findings produced in the various zebrafish experimental models with the aim to define a comprehensive picture of such complicated puzzle.

Thyroid disrupting effects of low-dose dibenzothiophene and cadmium in single or concurrent exposure: New evidence from a translational zebrafish model

Thyroid hormones (THs) are major regulators of biological processes essential for correct development and energy homeostasis. Although thyroid disruptors can deeply affect human health, the impact of exogenous chemicals and in particular mixture of chemicals on different aspects of thyroid development and metabolism is not yet fully understood. In this study we have used the highly versatile zebrafish model to assess the thyroid axis disrupting effects of cadmium (Cd) and dibenzothiophene (DBT), two environmental endocrine disruptors found to be significantly correlated in epidemiological co-exposure studies. Zebrafish embryos (5hpf) were exposed to low concentrations of Cd (from 0.05 to 2 μM) and DBT (from 0.05 to 1 μM) and to mixtures of them. A multilevel assessment of the pollutant effects has been obtained by combining in vivo morphological analyses allowed by the use of transgenic fluorescent lines with liquid chromatography mass spectrometry determination of TH levels and quantification of the expression levels of key genes involved in the Hypothalamic-Pituitary-Thyroid Axis (HPTA) and TH metabolism. Our results underscore for the first time an important synergistic toxic effect of these pollutants on embryonic development and thyroid morphology highlighting differences in the mechanisms through which they can adversely impact on multiple physiological processes of the HPTA and TH disposal influencing also heart geometry and function.

Identification of Transient Receptor Potential Channel 4-Associated Protein as a Novel Candidate Gene Causing Congenital Primary Hypothyroidism

BACKGROUND

Congenital primary hypothyroidism (CH) is the most common endocrine disorder in neonates.

METHODS

To identify novel genes, we performed whole exome sequencing (WES) in 6 patients with CH due to thyroid dysgenesis (TD). The potential effects of the most relevant variants were analyzed using in silico prediction tools. The most promising candidate gene, transient receptor potential channel 4-associated protein (TRPC4AP), was sequenced in 179 further patients with TD. Expression of TRPC4AP in human thyroid was investigated using RT-PCR. Trpc4ap- functional analysis was performed in Xenopus laevis using Morpholino (MO) antisense oligomers.

RESULTS

WES identified a likely damaging mutation in TRPC4AP leading to a de novo stop codon p.Q552*. Targeted sequencing of TRPC4AP demonstrated gene variants with predicted damaging potential in 5 patients resulting each in an amino acid exchange (p.P706S, p.F729L, p.S777C, and p.N229S). We demonstrated that TRPC4AP is expressed in human thyroid gland tissue. Using Xenopus laevis, we showed that the volume of the tadpole thyroid anlage was reduced by 20% in Trpc4ap MO knockdowns compared to controls and by 41% in "Clustered Regularly Interspaced Short Palindromic Repeats"/Cas9-mediated gene knockout experiments.

DISCUSSION

A recognized interaction of TRPC4AP and the NF-kappa-B-essential-modulator encoded by IKBKG gene was identified by IPA analysis. IKBKG plays a role in activation of the NF-κB-signaling pathway and regulates genes involved in proliferation and survival of thyrocytes and expression of key enzymes of thyroid hormone synthesis.

CONCLUSION

TRPC4AP was identified as a novel candidate gene in TD, but further studies are needed to validate its role in thyroid function.

Molecular and clinical characteristics of congenital hypothyroidism in a large cohort study based on comprehensive thyroid transcription factor mutation screening in Henan

BACKGROUND

Congenital hypothyroidism (CH), the most common neonatal endocrine disorder worldwide, can be caused by variants in thyroid transcription factor (TTF) genes including NKX2-1, FOXE1, PAX8, NKX2-5 and HHEX. This study aims to perform targeted next-generation sequencing (NGS) panel for comprehensive mutation screening on these genes in a cohort of 606 CH patients with various types from Henan Province, China, to investigate the mutation rate of TTF genes, and to analyze the clinical, biochemical and molecular characteristics of our CH cohort.

METHODS

High-throughput sequencing combined with statistical calculation were applied for mutation screening and analyses of the clinical data.

RESULTS

Twenty-two likely disease-causing monoallelic mutations in the TTF genes were identified in our cohort (3.63%, 22/606). Mutated PAX8 was the most predominant genetic alteration among these TTF mutations. Interestingly, PAX8 defects were only found in TD cases and variants in the five TTF genes were detected in gland in situ (GIS) patients. CH patients with the same genotype may have significant phenotypic variability and permanent CH (PCH) patients in the GIS group were significantly fewer than those in the TD group.

CONCLUSIONS

Our study showed the estimated TTF mutation rate among CH cases was 3.63% in Henan Province and genetic alternations in TTF genes played a role not only in TD but also in GIS, especially in goiter. Although we speculated that the five TTF genes may be involved in certain steps of thyroid hormone biosynthesis, more researches are needed to verify the conclusions of the present study.

Enhanced Canonical Wnt Signaling During Early Zebrafish Development Perturbs the Interaction of Cardiac Mesoderm and Pharyngeal Endoderm and Causes Thyroid Specification Defects

Background: Congenital hypothyroidism due to thyroid dysgenesis is a frequent congenital endocrine disorder for which the molecular mechanisms remain unresolved in the majority of cases. This situation reflects, in part, our still limited knowledge about the mechanisms involved in the early steps of thyroid specification from the endoderm, in particular the extrinsic signaling cues that regulate foregut endoderm patterning. In this study, we used small molecules and genetic zebrafish models to characterize the role of various signaling pathways in thyroid specification. Methods: We treated zebrafish embryos during different developmental periods with small-molecule compounds known to manipulate the activity of Wnt signaling pathway and observed effects in thyroid, endoderm, and cardiovascular development using whole-mount in situ hybridization and transgenic fluorescent reporter models. We used the antisense morpholino (MO) technique to create a zebrafish acardiac model. For thyroid rescue experiments, bone morphogenetic protein (BMP) pathway induction in zebrafish embryos was obtained by manipulation of heat-shock inducible transgenic lines. Results: Combined analyses of thyroid and cardiovascular development revealed that overactivation of Wnt signaling during early development leads to impaired thyroid specification concurrent with severe defects in the cardiac specification. When using a model of MO-induced blockage of cardiomyocyte differentiation, a similar correlation was observed, suggesting that defective signaling between cardiac mesoderm and endodermal thyroid precursors contributes to thyroid specification impairment. Rescue experiments through transient overactivation of BMP signaling could partially restore thyroid specification in models with defective cardiac development. Conclusion: Collectively, our results indicate that BMP signaling is critically required for thyroid cell specification and identify cardiac mesoderm as a likely source of BMP signals.

Bethesda System Categories of Fine Needle Aspiration Cytology Are Not Associated with Thyroid Nodule Location: A Single Institution Experience

INTRODUCTION

Thyroid isthmus is defined as the thin band connecting thyroid tissue between both lateral thyroid lobes. Recently, a possible association between thyroid nodules located in the isthmus and malignancy was proposed. The aim of this study was to compare the frequency of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) categories between nodules from the isthmus and nodules from both thyroid lobes.

METHODS

All fine needle aspiration cytology procedures performed between January 2016 and December 2019 at the Pathology Institute of Araçatuba, São Paulo, Brazil, were analyzed. For each nodule, at least 2 conventional slides were produced (1 stained by Giemsa and the other by hematoxylin and eosin). All cases were reported according to the TBSRTC. Clinical information (gender, age, and localization) and ultrasound data (size of nodules) were collected from medical requisition forms. To assess the association between the frequency of TBSRTC categories and nodule location, univariate analysis was performed using the χ2 test or Fisher's exact test, as appropriate. A p value <0.05 was considered statistically significant. Nodules located in transition between the isthmus and a right or left lobe were included in the isthmus group.

RESULTS

Considering the p value between the TBSRTC categories and thyroid nodule location, statistic association was not observed: nondiagnostic or unsatisfactory (p = 0.1442), atypia of undetermined significance or follicular lesion of undetermined significance (p = 0.3296), follicular neoplasm or suspicious for a follicular neoplasm (p = 0.0817), suspicious for malignancy (p = 0.8464), and malignant (p = 0.1082).

CONCLUSION

In the studied population, nodules located in the isthmus were not related to any Bethesda System category.

Effects of repetitive Iodine thyroid blocking on the foetal brain and thyroid in rats: a systems biology approach

A single administration of an iodine thyroid blocking agent is usually sufficient to protect thyroid from radioactive iodine and prevent thyroid cancer. Repeated administration of stable iodine (rKI) may be necessary during prolonged or repeated exposure to radioactive iodine. We previously showed that rKI for eight days offers protection without toxic effects in adult rats. However, the effect of rKI administration in the developing foetus is unknown, especially on brain development, although a correlation between impaired maternal thyroid status and a decrease in intelligence quotient of the progeny has been observed. This study revealed distinct gene expression profiles between the progeny of rats receiving either rKI or saline during pregnancy. To understand the implication of these differentially expressed (DE) genes, a systems biology approach was used to construct networks for each organ using three different techniques: Bayesian statistics, sPLS-DA and manual construction of a Process Descriptive (PD) network. The PD network showed DE genes from both organs participating in the same cellular processes that affect mitophagy and neuronal outgrowth. This work may help to evaluate the doctrine for using rKI in case of repetitive or prolonged exposure to radioactive particles upon nuclear accidents.

Small-Molecule Screening in Zebrafish Embryos Identifies Signaling Pathways Regulating Early Thyroid Development

Background: Defects in embryonic development of the thyroid gland are a major cause for congenital hypothyroidism in human newborns, but the underlying molecular mechanisms are still poorly understood. Organ development relies on a tightly regulated interplay between extrinsic signaling cues and cell intrinsic factors. At present, however, there is limited knowledge about the specific extrinsic signaling cues that regulate foregut endoderm patterning, thyroid cell specification, and subsequent morphogenetic processes in thyroid development. Methods: To begin to address this problem in a systematic way, we used zebrafish embryos to perform a series of in vivo phenotype-driven chemical genetic screens to identify signaling cues regulating early thyroid development. For this purpose, we treated zebrafish embryos during different developmental periods with a panel of small-molecule compounds known to manipulate the activity of major signaling pathways and scored phenotypic deviations in thyroid, endoderm, and cardiovascular development using whole-mount in situ hybridization and transgenic fluorescent reporter models. Results: Systematic assessment of drugged embryos recovered a range of thyroid phenotypes including expansion, reduction or lack of the early thyroid anlage, defective thyroid budding, as well as hypoplastic, enlarged, or overtly disorganized presentation of the thyroid primordium after budding. Our pharmacological screening identified bone morphogenetic protein and fibroblast growth factor signaling as key factors for thyroid specification and early thyroid organogenesis, highlighted the importance of low Wnt activities during early development for thyroid specification, and implicated drug-induced cardiac and vascular anomalies as likely indirect mechanisms causing various forms of thyroid dysgenesis. Conclusions: By integrating the outcome of our screening efforts with previously available information from other model organisms including Xenopus, chicken, and mouse, we conclude that signaling cues regulating thyroid development appear broadly conserved across vertebrates. We therefore expect that observations made in zebrafish can inform mammalian models of thyroid organogenesis to further our understanding of the molecular mechanisms of congenital thyroid diseases.

Slc:Wistar/ST rats develop unilateral thyroid dysgenesis: A novel animal model of thyroid hemiagenesis

Developmental anomalies of the thyroid gland lead to congenital malformations such as thyroglossal duct cysts and thyroid dysgenesis. However, the pathogenesis of thyroid dysgenesis remains unclear due to the lack of suitable animal models. This study demonstrated that Slc:Wistar/ST rats frequently developed unilateral thyroid dysgenesis, including hemiagenesis, characterized by the absence of one lobe. In Wistar/ST rats, each thyroid lobe was frequently different in size, and approximately 27% and 20% of the rats presented with hemihypoplasia and hemiagenesis of the thyroid gland, respectively. Dysgenesis was predominant on the left side in both sexes, without sex differences. At a young age, thyroid hemiagenesis did not alter body weight. In rats of both sexes with thyroid hemiagenesis, plasma total triiodothyronine and total triiodothyronine levels remained unchanged while plasma thyroid-stimulating hormone levels were significantly elevated in young rats. The remaining thyroid lobes increased in weight, but the follicular epithelial cells appeared normal in terms of their height and proliferating activities. On the side of thyroid dysgenesis, the parathyroid glands were normally localized and were situated at the same location as the contralateral glands. The ultimobranchial body remnants were localized at the level of the thyroid gland along with the cranial thyroid artery and vein, forming cell clusters or cystic structures and containing calcitonin-positive C-cells. In conclusion, Wistar/ST rats developed unilateral thyroid dysgenesis and may be novel and useful animal models for thyroid hemiagenesis in humans and for morphogenesis of pharyngeal pouch-derived organs.

Molecular defects in thyroid dysgenesis

Congenital hypothyroidism (CH) is a neonatal endocrine disorder that might occur as itself or be associated to congenital extra-thyroidal defects. About 85% of affected subjects experience thyroid dysgenesis (TD), characterized by defect in thyroid gland development. In vivo experiments on null mice paved the way for the identification of genes involved thyroid morphogenesis and development, whose mutation has been strongly associated to TD. Most of them are thyroid-specific transcription factors expressed during early thyroid development. Despite the arduous effort in unraveling the genetics of TD in animal models, up to now these data have been discontinuously confirmed in humans and only 5% of TD have associated with known null mice-related mutations (mainly PAX8 and TSHR). Notwithstanding, the advance in genetic testing represented by the next-generation sequencing (NGS) approach is steadily increasing the list of genes whose highly penetrant mutation predisposes to TD. In this review we intend to outline the molecular bases of TD, summarizing the current knowledge on thyroid development in both mice and humans and delineating the genetic features of its monogenetic forms. We will also highlight current strategies to enhance the insight into the non-Mendelian mechanisms of abnormal thyroid development.

Effects of thyroid hormone disruption on the ontogenetic expression of thyroid hormone signaling genes in developing zebrafish (Danio rerio)

Thyroid hormones (THs) regulate neurodevelopment, thus TH disruption is widely posited as a mechanism of developmental neurotoxicity for diverse environmental chemicals. Zebrafish have been proposed as an alternative model for studying the role of TH in developmental neurotoxicity. To realize this goal, it is critical to characterize the normal ontogenetic expression profile of TH signaling molecules in the developing zebrafish and determine the sensitivity of these molecules to perturbations in TH levels. To address these gaps in the existing database, we characterized the transcriptional profiles of TH transporters, deiodinases (DIOs), receptors (TRs), nuclear coactivators (NCOAs), nuclear corepressors (NCORs), and retinoid X receptors (RXRs) in parallel with measurements of endogenous TH concentrations and tshβ mRNA expression throughout the first five days of zebrafish development. Transcripts encoding these TH signaling components were identified and observed to be upregulated around 48-72 h post fertilization (hpf) concurrent with the onset of larval production of T4. Exposure to exogenous T4 and T3 upregulated mct8, dio3-b, trα-a, trβ, and mbp-a levels, and downregulated expression of oatp1c1. Morpholino knockdown of TH transporter mct8 and treatment with 6-propyl-2-thiouracil (PTU) was used to reduce cellular uptake and production of TH, an effect that was associated with downregulation of dio3-b at 120 hpf. Collectively, these data confirm that larval zebrafish express orthologs of TH signaling molecules important in mammalian development and suggest that there may be species differences with respect to impacts of TH disruption on gene transcription.

Is Benign Hereditary Chorea Really Benign? Brain-Lung-Thyroid Syndrome Caused by NKX2-1 Mutations

BACKGROUND

Since its localization to the NKX2-1 gene in 2002, the phenotype of the disorder historically called "benign hereditary chorea" has been expanding beyond chorea.

METHODS

The phenomenology of movement disorders and other symptomatology associated with mutations in NKX2-1 were characterized after a detailed evaluation of consecutive patients evaluated in our clinic over the past 3 years.

RESULTS

We studied 5 patients (3 females), ages 2 to 31 years, with confirmed pathogenic variants in NKX2-1. All patients exhibited chorea, gross motor delay, and gait impairment. Other symptoms included neonatal respiratory failure (n = 4), cognitive deficits (n = 3), hypothyroidism (n = 4), joint laxity (n = 2), myoclonus (n = 1), hypotonia (n = 3), and seizures (n = 1). Chorea often proved refractory to medical therapies.

CONCLUSIONS

The phenotype associated with pathogenic variants in NKX2-1 frequently includes disabling and often medically refractory neurological and non-neurological abnormalities. We therefore suggest that the term benign hereditary chorea be abandoned in favor of its genetic designation as NKX2-1-related disorder.

Mutation screening in the genes PAX-8, NKX2-5, TSH-R, HES-1 in cohort of 63 Brazilian children with thyroid dysgenesis

OBJECTIVE

To evaluate the candidate genes PAX-8, NKX2-5, TSH-R and HES-1 in 63 confirmed cases of thyroid dysgenesis.

SUBJECTS AND METHODS

Characterization of patients with congenital hypothyroidism into specific subtypes of thyroid dysgenesis with hormone levels (TT4 and TSH), thyroid ultrasound and scintigraphy. DNA was extracted from peripheral blood leukocytes and the genetic analysis was realized by investigating the presence of mutations in the transcription factor genes involved in thyroid development.

RESULTS

No mutations were detected in any of the candidate genes. In situ thyroid gland represented 71.1% of all cases of permanent primary congenital hypothyroidism, followed by hypoplasia (9.6%), ectopia (78%), hemiagenesis (6.0%) and agenesis (5.5%). The highest neonatal screening TSH levels were in the agenesis group (p < 0.001).

CONCLUSIONS

Thyroid dysgenesis is possibly a polygenic disorder and epigenetic factors could to be implicated in these pathogeneses.

DIAGNOSIS OF ENDOCRINE DISEASE: Congenital hypothyroidism: update and perspectives

Congenital hypothyroidism (CH) may be primary, due to a defect affecting the thyroid gland itself, or central, due to impaired thyroid-stimulating hormone (TSH)-mediated stimulation of the thyroid gland as a result of hypothalamic or pituitary pathology. Primary CH is the most common neonatal endocrine disorder, traditionally subdivided into thyroid dysgenesis (TD), referring to a spectrum of thyroid developmental abnormalities, and dyshormonogenesis, where a defective molecular pathway for thyroid hormonogenesis results in failure of hormone production by a structurally intact gland. Delayed treatment of neonatal hypothyroidism may result in profound neurodevelopmental delay; therefore, CH is screened for in developed countries to facilitate prompt diagnosis. Central congenital hypothyroidism (CCH) is a rarer entity which may occur in isolation, or (more frequently) in association with additional pituitary hormone deficits. CCH is most commonly defined biochemically by failure of appropriate TSH elevation despite subnormal thyroid hormone levels and will therefore evade diagnosis in primary, TSH-based CH-screening programmes. This review will discuss recent genetic aetiological advances in CH and summarize epidemiological data and clinical diagnostic challenges, focussing on primary CH and isolated CCH.

Histopathological Characterization and Whole Exome Sequencing of Ectopic Thyroid: Fetal Architecture in a Functional Ectopic Gland from Adult Patient

Ectopic thyroid results from a migration defect of the developing gland during embryogenesis causing congenital hypothyroidism. But it has also been detected in asymptomatic individuals. This study aimed to investigate the histopathological, functional, and genetic features of human ectopic thyroids. Six samples were histologically examined, and the expression of the specific thyroid proteins was assessed by immunohistochemistry. Two samples were submitted to whole exome sequencing. An oropharynx sample showed immature fetal architecture tissue with clusters or cords of oval thyrocytes and small follicles; one sample exhibited a normal thyroid pattern while four showed colloid goiter. All ectopic thyroids expressed the specific thyroid genes and T4 at similar locations to those observed in normal thyroid. No somatic mutations associated with ectopic thyroid were found. This is the first immature thyroid fetal tissue observed in an ectopic thyroid due to the arrest of structural differentiation early in the colloid stage of development that proved able to synthesize thyroid hormone but not to respond to TSH. Despite the ability of all ectopic thyroids to synthetize specific thyroid proteins and T4, at some point in life, it may be insufficient to support body growth leading to hypothyroidism, as observed in some of the patients.

DUOX2 Mutations Are Associated With Congenital Hypothyroidism With Ectopic Thyroid Gland

CONTEXT

Thyroid dysgenesis (TD) is the leading cause of congenital hypothyroidism (CH). The etiology of TD remains unknown in ∼90% of cases, the most common form being thyroid ectopia (TE) (48% to 61%).

OBJECTIVE

To search for candidate genes in hypothyroid children with TE.

DESIGN, SETTING, AND PARTICIPANTS

We followed a cohort of 268 children with TD and performed whole-exome sequencing (WES) in three children with CH with TE (CHTE) and compared them with 18 thyroid-healthy controls. We then screened an additional 41 children with CHTE by Sanger sequencing and correlated the WES and Sanger molecular findings with in vitro functional analysis.

MAIN OUTCOME MEASURES

Genotyping, mutation prediction analysis, and in vitro functional analysis.

RESULTS

We identified seven variants in the DUOX2 gene, namely G201E, L264CfsX57, P609S, M650T, E810X, M822V, and E1017G, and eight known variations. All children carrying DUOX2 variations had high thyroid-stimulating hormone levels at neonatal diagnosis. All mutations were localized in the N-terminal segment, and three of them led to effects on cell surface targeting and reactive oxygen species generation. The DUOX2 mutants also altered the interaction with the maturation factor DUOXA2 and the formation of a stable DUOX2/DUOXA2 complex at the cell surface, thereby impairing functional enzymatic activity. We observed no mutations in the classic genes related to TD or in the DUOX1 gene.

CONCLUSION

Our findings suggest that, in addition to thyroid hormonogenesis, the DUOX2 N-terminal domain may play a role in thyroid development.

Development of the thyroid gland

Thyroid hormones are crucial for organismal development and homeostasis. In humans, untreated congenital hypothyroidism due to thyroid agenesis inevitably leads to cretinism, which comprises irreversible brain dysfunction and dwarfism. Elucidating how the thyroid gland - the only source of thyroid hormones in the body - develops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro that might be used for cell-based therapies. Here, we review the principal mechanisms involved in thyroid organogenesis and functional differentiation, highlighting how the thyroid forerunner evolved from the endostyle in protochordates to the endocrine gland found in vertebrates. New findings on the specification and fate decisions of thyroid progenitors, and the morphogenesis of precursor cells into hormone-producing follicular units, are also discussed.

Mechanisms involved in hearing disorders of thyroid ontogeny: a literature review

Endocochlear, retrocochlear and/or central origin hearing damage may be related to the absence of appropriate levels of thyroid hormone during morphogenesis and/or auditory system development. Hearing disorders related to the thyroid are not well studied, despite speculation on the pathophysiological mechanisms. The objective of this review was to characterize the main pathophysiological mechanisms of congenital hypothyroidism and to evaluate the relationship with central and peripheral hearing disorders. We conducted a literature review using the databases MedLine, LILACS, Cochrane Library, SciELO, Institute for Scientific Information (ISI), Embase, and Science Direct between July and September on 2016. We identified the studies that address hearing disorder mechanisms on the congenital hypothyroidism. Congenital hypothyroidism may have clinical and subclinical manifestations that affect the auditory system and may be a potential risk factor for hearing impairment. Hearing impairment can severely impact quality-of-life, which emphasizes the importance of monitoring and evaluating hearing during the clinical routine of these patients.

Mutations in BOREALIN cause thyroid dysgenesis

Congenital hypothyroidism is the most common neonatal endocrine disorder and is primarily caused by developmental abnormalities otherwise known as thyroid dysgenesis (TD). We performed whole exome sequencing (WES) in a consanguineous family with TD and subsequently sequenced a cohort of 134 probands with TD to identify genetic factors predisposing to the disease. We identified the novel missense mutations p.S148F, p.R114Q and p.L177W in the BOREALIN gene in TD-affected families. Borealin is a major component of the Chromosomal Passenger Complex (CPC) with well-known functions in mitosis. Further analysis of the missense mutations showed no apparent effects on mitosis. In contrast, expression of the mutants in human thyrocytes resulted in defects in adhesion and migration with corresponding changes in gene expression suggesting others functions for this mitotic protein. These results were well correlated with the same gene expression pattern analysed in the thyroid tissue of the patient with BOREALIN-p.R114W. These studies open new avenues in the genetics of TD in humans.

Morphological and molecular evolution of the ultimobranchial gland of nonmammalian vertebrates, with special reference to the chicken C cells

This review summarizes the current understanding of the nonmammalian ultimobranchial gland from morphological and molecular perspectives. Ultimobranchial anlage of all animal species develops from the last pharyngeal pouch. The genes involved in the development of pharyngeal pouches are well conserved across vertebrates. The ultimobranchial anlage of nonmammalian vertebrates and monotremes does not merge with the thyroid, remaining as an independent organ throughout adulthood. Although C cells of all animal species secrete calcitonin, the shape, cellular components and location of the ultimobranchial gland vary from species to species. Avian ultimobranchial gland is unique in several phylogenic aspects; the organ is located between the vagus and recurrent laryngeal nerves at the upper thorax and is densely innervated by branches emanating from them. In chick embryos, TuJ1-, HNK-1-, and PGP 9.5-immunoreactive cells that originate from the distal vagal (nodose) ganglion, colonize the ultimobranchial anlage and differentiate into C cells; neuronal cells give rise to C cells. Like C cells of mammals, the cells of fishes, amphibians, reptiles, and also a subset of C cells of birds, appear to be derived from the endodermal epithelium forming ultimobranchial anlage. Thus, the avian ultimobranchial C cells may have dual origins, neural progenitors and endodermal epithelium. Developmental Dynamics 246:719-739, 2017. © 2017 Wiley Periodicals, Inc.

Can Medullary Thyroid Carcinoma Arise in Thyroglossal Duct Cysts? A Search for Parafollicular C-cells in 41 Resected Cases

Thyroglossal duct cysts (TGDCs) are present in ~7% of adults and develop from the midline migratory tract between the foramen cecum and anatomic location of the thyroid. Thyroid tissue can be identified in 2/3 of TGDCs, and up to 1% develop associated malignancy, 90% of which are papillary thyroid carcinoma. Cases of follicular and anaplastic carcinoma have been documented, but there are no reports of medullary thyroid carcinoma arising in a TGDC. This is presumably due to the distinct embryologic origin of parafollicular C-cells, from which medullary carcinoma arises. The goal of this study is to determine whether parafollicular C-cells are present in TGDCs. H&E sections from 41 TGDC cases were examined for thyroid tissue, thyroglossal duct remnants, ultimobranchial remnants, and parafollicular C-cells. Immunohistochemistry was performed for TTF-1 and calcitonin. Eighty three percent (34/41) of cases contained thyroid tissue on H&E and by TTF-1. No cases (0/41) had ultimobranchial remnants or parafollicular C-cells on H&E or with calcitonin. One case of papillary carcinoma in a TGDC was identified. These cases illustrate that although TGDCs often contain thyroid tissue, parafollicular C-cells are absent. Therefore, unlike other thyroid neoplasms, there is no evidence to support the possibility of medullary carcinoma arising in a TGDC.

Immunohistochemical profiling of the ultimobranchial remnants in the rat postnatal thyroid gland

Ultimobranchial (UB) remnants are a constant presence in the thyroid throughout rat postnatal life; however, the difficulty in identifying the most immature forms from the surrounding thyroid tissue prompted us to search for a specific marker. With that objective, we applied a panel of antibodies reported to be specific for their human counterpart, solid cell nests (SCNs), using double immunohistochemistry and immunofluorescence. Our results demonstrated that cytokeratin 34βE12 and p63 are highly sensitive markers for the immunohistologic screening of UB-remnants, independently of their maturity or size. Furthermore, rat UB-follicles (UBFs) coincided with human SCNs in the immunohistochemical pattern exhibited by both antigens. In contrast, the pattern displayed for calcitonin and thyroglobulin differs considerably but confirm the hypothesis that rat UB-cells can differentiate into both types of thyroid endocrine cells. This hypothesis agrees with recent findings that thyroid C-cells share an endodermic origin with follicular cells in rodents. We suggest that the persistence of p63-positive undifferentiated cells in UB-remnants may constitute a reservoir of basal/stem cells that persist beyond embryogenesis from which, in certain unknown conditions, differentiated thyroid cells or even unusual tumors may arise.

Regenerative therapy for hypothyroidism: Mechanisms and possibilities

The ability to derive functional thyroid follicular cells from embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) would provide potential therapeutic benefit for patients with congenital or post-surgical hypothyroidism. Furthermore, understanding the process by which thyroid follicular cells develop will also provide great insight into the key steps that regulate the development of other tissues derived from endoderm. Here we review the advances in our understanding of the process of thyroid follicular cell development including the creation of two models that have allowed for the rescue of hypothyroid mouse recipients through the transplantation of thyroid follicular cells derived from mouse ESCs. Rapid progress in the field suggests that the same success should be achievable with human ESCs or iPSCs in the near future. Additionally, the availability of ESC or iPSC-derived thyroid follicular cell models will provide ideal systems to explore how genetic mutations, drugs or illness impact thyroid function in a cell-autonomous fashion.

Disorders of thyroid morphogenesis

Developmental anomalies of the thyroid gland, defined as thyroid dysgenesis, underlie the majority of cases of congenital hypothyroidism. Thyroid dysgenesis is predominantly a sporadic disorder although a reported familial enrichment, variation of incidence by ethnicity and the monogenic defects associated mainly with athyreosis or orthotopic thyroid hypoplasia, suggest a genetic contribution. Of note, the most common developmental anomaly, thyroid ectopy, remains unexplained. Ectopy may result from multiple genetic or epigenetic variants in the germline and/or at the somatic level. This review provides a brief overview of the monogenic defects in candidate genes that have been identified so far and of the syndromes which are known to be associated with thyroid dysgenesis.

Rtfc (4931414P19Rik) Regulates in vitro Thyroid Differentiation and in vivo Thyroid Function

Thyroid is a one of the most important endocrine organs. Understanding the molecular mechanism underlying thyroid development and function, as well as thyroid diseases, is beneficial for the clinical treatment of thyroid diseases and tumors. Through genetic linkage analysis and exome sequencing, we previously identified an uncharacterized gene C14orf93 (RTFC, mouse homolog: 4931414P19Rik) as a novel susceptibility gene for familial non-medullary thyroid carcinoma, and demonstrated its function in promoting thyroid tumor. However, the role of RTFC in thyroid development and function remains unexplored. In this study, we found that knockout of Rtfc compromises the in vitro thyroid differentiation of mouse embryonic stem cells. In contrast, Rtfc^−/− mice are viable and fertile, and the size and the morphology of thyroid are not affected by Rtfc knockout. However, female Rtfc^−/− mice, but not male Rtfc^−/− mice, display mild hypothyroidism. In summary, our data suggest the roles of Rtfc in in vitro thyroid differentiation of embryonic stem cells, and in vivo thyroid function.

TAZ Induction Directs Differentiation of Thyroid Follicular Cells from Human Embryonic Stem Cells

OBJECTIVE

The differentiation program for human thyroid follicular cells (TFCs) relies on the interplay between sequence-specific transcription factors and transcriptional co-regulators. Transcriptional co-activator with PDZ-binding motif (TAZ) is a co-activator that regulates several transcription factors, including PAX8 and NKX2-1, which play a central role in thyroid-specific gene transcription. TAZ and PAX8/NKX2-1 are co-expressed in the nuclei of thyroid cells, and TAZ interacts directly with both PAX8 and NKX2-1, leading to their enhanced transcriptional activity on the thyroglobulin (TG) promoter and additional genes.

METHODS

The use of a small molecule, ethacridine, recently identified as a TAZ activator, in the differentiation of thyroid cells from human embryonic stem (hES) cells was studied. First, endodermal cells were derived from hES cells using Activin A, followed by induction of differentiation into thyroid cells directed by ethacridine and thyrotropin (TSH).

RESULTS

The expression of TAZ was increased in the Activin A-derived endodermal cells by ethacridine in a dose-dependent manner and followed by increases in PAX8 and NKX2-1 when assessed by both quantitative polymerase chain reaction and immunostaining. Following further differentiation with the combination of ethacridine and TSH, the thyroid-specific genes TG, TPO, TSHR, and NIS were all induced in the differentiated hES cells. When these cells were cultured with extracellular matrix-coated dishes, thyroid follicle formation and abundant TG protein expression were observed. Furthermore, such hES cell-derived thyroid follicles showed a marked TSH-induced and dose-dependent increase in radioiodine uptake and protein-bound iodine accumulation.

CONCLUSION

These data show that fully functional human thyroid cells can be derived from hES cells using ethacridine, a TAZ activator, which induces thyroid-specific gene expression and promotes thyroid cell differentiation from the hES cells. These studies again demonstrate the importance of transcriptional regulation in thyroid cell development. This approach also yields functional human thyrocytes, without any gene transfection or complex culture conditions, by directly manipulating the transcriptional machinery without interfering with intermediate signaling events.

Update of Thyroid Developmental Genes

Thyroid dysgenesis (TD) is the most common cause of congenital hypothyroidism in iodine-sufficient regions and includes a spectrum of developmental anomalies. The genetic components of TD are complex. Although a sporadic disease, advances in developmental biology have revealed monogenetic forms of TD. Inheritance is not based on a simple Mendelian pattern and additional genetic elements might contribute to the phenotypic spectrum. This article summarizes the key steps of normal thyroid development and provides an update on responsible genes and underlying mechanisms of TD. Up-to-date technologies in genetics and biology will allow us to advance in our knowledge of TD.

Thyroid follicle development requires Smad1/5- and endothelial cell-dependent basement membrane assembly

Thyroid follicles, the functional units of the thyroid gland, are delineated by a monolayer of thyrocytes resting on a continuous basement membrane. The developmental mechanisms of folliculogenesis, whereby follicles are formed by the reorganization of a non-structured mass of non-polarized epithelial cells, are largely unknown. Here we show that assembly of the epithelial basement membrane is crucial for folliculogenesis and is controlled by endothelial cell invasion and by BMP-Smad signaling in thyrocytes. Thyroid-specific Smad1 and Smad5 double-knockout (Smad1/5(dKO)) mice displayed growth retardation, hypothyroidism and defective follicular architecture. In Smad1/5(dKO) embryonic thyroids, epithelial cells remained associated in large clusters and formed small follicles. Although similar follicular defects are found in Vegfa knockout (Vegfa(KO)) thyroids, Smad1/5(dKO) thyroids had normal endothelial cell density yet impaired endothelial differentiation. Interestingly, both Vegfa(KO) and Smad1/5(dKO) thyroids displayed impaired basement membrane assembly. Furthermore, conditioned medium (CM) from embryonic endothelial progenitor cells (eEPCs) rescued the folliculogenesis defects of both Smad1/5(dKO) and Vegfa(KO) thyroids. Laminin α1, β1 and γ1, abundantly released by eEPCs into CM, were crucial for folliculogenesis. Thus, epithelial Smad signaling and endothelial cell invasion promote folliculogenesis via assembly of the basement membrane.

Graves' disease in a mediastinal mass presenting after total thyroidectomy for nontoxic multinodular goiter: a case report

BACKGROUND

Thyrotoxicosis after total thyroidectomy is mostly iatrogenic. Rarely, a hyperfunctional thyroid remnant or ectopic tissue may be the cause. There are few cases of Graves' disease arising from thyroid tissue located in the mediastinum and none in which Graves' disease was diagnosed only after surgery. We report the case of a patient with Graves's disease in a mediastinal thyroid mass presenting 7 years after total thyroidectomy for nontoxic goiter.

CASE PRESENTATION

A 67-year-old Caucasian woman presented with palpitations, fatigue and weight loss. She had a history of total thyroidectomy for nontoxic multinodular goiter at the age of 60 without any signs of malignancy on microscopic examination. She had been medicated with levothyroxine 100 μg/day since the surgery without follow-up. She was tachycardic, had no cervical mass or eye involvement. Her thyroid-stimulating hormone levels were suppressed (0.000 μU/mL) and her free thyroxine (3.22 ng/dL) and free triiodothyronine (8.46 pg/mL) levels increased. Neither mediastinal enlargement nor trachea deviation was found on chest roentgenogram. Levothyroxine treatment was stopped but our patient showed no improvement on free thyroxine or free triiodothyronine 10 days later. Thyroglobulin was increased to 294 mg/mL. A cervical ultrasound scan revealed no thyroid remnant. Her anti-thyroid-stimulating hormone receptor antibodies were high (19.7 U/L). Corporal scintigraphy demonstrated increased intrathoracic radioiodine uptake. A computed tomography scan confirmed a 60 × 40 mm mediastinal mass. Methimazole 10 mg/day was started. Three months later, her thyroid function was normal and she underwent surgical resection. Microscopic examination showed thyroid tissue with no signs of malignancy.

CONCLUSIONS

Although thyrotoxicosis after total thyroidectomy is mostly due to excessive supplementation, true hyperthyroidism may rarely be the cause, which should be kept in mind. The presence of thyroid tissue after total thyroidectomy in our patient may correspond to a remnant or ectopic thyroid tissue that became hyperfunctional in the presence of anti- thyroid-stimulating hormone receptor antibodies.

PHACE syndrome and congenitally absent thyroid gland at MR imaging

PHACE syndrome is a rare neurocutaneous disorder characterized by posterior fossa malformations, hemangiomas, arterial anomalies, cardiac defects, and abnormalities of the eye. Thyroid disorders associated with PHACE syndrome have been described, although there are limited reports of this rare occurrence. We report a case of PHACE syndrome with congenital hypothyroidism in an infant, for which absent thyroid gland was diagnosed at magnetic resonance imaging.

Screening of HHEX Mutations in Chinese Children with Thyroid Dysgenesis

OBJECTIVE

Congenital hypothyroidism (CH) is a frequent neonatal endocrine disease with an incidence of about 1:2500 worldwide. Although thyroid dysgenesis (TD) is the most frequent cause of CH cases, its pathogenesis remains unclear. The aim of this study was to screen the hematopoietically-expressedhomeobox gene (HHEX) mutations in Chinese children with TD.

METHODS

Genomic deoxyribonucleic acid was extracted from peripheral blood leukocytes in 234 TD patients from Shandong Province. Mutations in all exons and nearby introns of HHEX were analyzed by direct sequencing after polymerase chain reaction amplification.

RESULTS

Sequencing analysis of HHEX indicated that no causative mutations were present in the coding regionof the TD patients. However, a genetic variant (IVS2+ 127 G/T, 10.26%) was observed in the intron 2 in HHEX.

CONCLUSION

Our results indicate that the frequency of HHEX mutation is very low and may not be the main causative factor in Chinese TD patients. However, these results need to be replicated using larger datasets collected from different populations.