Thyroid Hormone-responsive Genes Research Articles

Current concepts and challenges to unravel the role of iodothyronine deiodinases in human neoplasias

Thyroid hormones (THs) are essential for the regulation of several metabolic processes and the energy consumption of the organism. Their action is exerted primarily through interaction with nuclear receptors controlling the transcription of thyroid hormone-responsive genes. Proper regulation of TH levels in different tissues is extremely important for the equilibrium between normal cellular proliferation and differentiation. The iodothyronine deiodinases types 1, 2 and 3 are key enzymes that perform activation and inactivation of THs, thus controlling TH homeostasis in a cell-specific manner. As THs seem to exert their effects in all hallmarks of the neoplastic process, dysregulation of deiodinases in the tumoral context can be critical to the neoplastic development. Here, we aim at reviewing the deiodinases expression in different neoplasias and exploit the mechanisms by which they play an essential role in human carcinogenesis. TH modulation by deiodinases and other classical pathways may represent important targets with the potential to oppose the neoplastic process.

Overexpression of the Thyroid Hormone-Responsive (THRSP) Gene in the Striatum Leads to the Development of Inattentive-like Phenotype in Mice

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects 8–12% of children globally. Factor analyses have divided ADHD symptoms into two domains: inattention and a combination of hyperactivity and impulsivity. The identification of domain-specific genetic risk variants may help uncover potential genetic mechanisms underlying ADHD. We have previously identified that thyroid hormone-responsive (THRSP) gene expression is upregulated in spontaneously hypertensive rats (SHR/NCrl) and Wistar-Kyoto (WKY/NCrl) rats which exhibited inattention behavior. Thus, we established a line of THRSP overexpressing (OE) mice and assessed their behavior through an array of behavioral tests. The gene and protein overexpression of THRSP in the striatum (STR) was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. The THRSP OE mice exhibited inattention in the novel-object recognition and Y-maze test, but not hyperactivity in the open-field test and impulsivity in the cliff-avoidance and delay-discounting task. We have also found that expression of dopamine-related genes (dopamine transporter, tyrosine hydroxylase, and dopamine D1 and D2 receptors) in the STR increased. Treatment with methylphenidate (5 mg/kg), the most commonly used medication for ADHD, improved attention and normalized expression levels of dopamine-related genes in THRSP OE mice. Our findings suggest that THRSP plays a role in the inattention phenotype of ADHD and that the THRSP OE mice may be used as an animal model to elucidate the genetic mechanisms of the disorder.

Inactivation of hepatic ATRX in Atrx Foxg1cre mice prevents reversal of aging-like phenotypes by thyroxine.

ATRX is an ATP-dependent chromatin remodeler required for the maintenance of genomic integrity. We previously reported that conditional Atrx ablation in the mouse embryonic forebrain and anterior pituitary using the Foxg1cre driver causes reduced health and lifespan. In these mice, premature aging-like phenotypes were accompanied by low circulating levels of insulin-like growth factor 1 (IGF-1) and thyroxine (T4), hormones that maintain stem cell pools and normal metabolic profiles, respectively. Based on emerging evidence that T4 stimulates expression of IGF-1 in pre-pubertal mice, we tested whether T4 supplementation in Atrx Foxg1cre mice could restore IGF-1 levels and ameliorate premature aging-like phenotypes. Despite restoration of normal serum T4 levels, we did not observe improvements in circulating IGF-1. In the liver, thyroid hormone target genes were differentially affected upon T4 treatment, with Igf1 and several other thyroid hormone responsive genes failing to recover normal expression levels. These findings hinted at Cre-mediated Atrx inactivation in the liver of Atrx Foxg1cre mice, which we confirmed. We conclude that the phenotypes observed in the Atrx Foxg1cre mice can be explained in part by a role of ATRX in the liver to promote T4-mediated Igf1 expression, thus explaining the inefficacy of T4 therapy observed in this study.

Identification of hepatic thyroid hormone-responsive genes in neonatal rats: Potential targets for thyroid hormone-disrupting chemicals

There have been many concerns about the possible adverse effects of thyroid hormone-disrupting chemicals in the environment. Because thyroid hormones are essential for regulating the growth and differentiation of many tissues, disruption of thyroid hormones during the neonatal period of an organism might lead to permanent effects on that organism. We postulated that there are target genes that are sensitive to thyroid hormones particularly during the neonatal period and that would thus be susceptible to thyroid hormone-disrupting chemicals. Global gene expression analysis was used to identify these genes in the liver of rat neonates. The changes in hepatic gene expression were examined 24 h after administering 1.0, 10, and 100 ng/g body weight (bw) triiodothyronine (T3) to male rats on postnatal day 3. Thirteen upregulated and four downregulated genes were identified in the neonatal liver. Among these, Pdp2 and Slc25a25 were found to be upregulated and more sensitive to T3 than the others, whereas Cyp7b1 and Hdc were found to be downregulated even at the lowest dose of 1.0 ng/g bw T3. Interestingly, when the responses of gene expression to T3 were examined in adult rats (8-week old), one-third of them did not respond to T3. The environmental chemicals with thyroid hormone-like activity, hydroxylated polybrominated diphenyl ethers, were then administered to neonatal rats to examine the effects on expression of the identified genes. The results showed that these chemicals were indeed capable of changing the expression of Slc25a25 and Hdc. Our results demonstrated a series of hepatic T3-responsive genes that are more sensitive to hormones during the neonatal period than during adulthood. These genes might be the potential targets of thyroid hormone-disrupting chemicals in newborns.

Multiple bioanalytical method to reveal developmental biological responses in zebrafish embryos exposed to triclocarban

Triclocarban (TCC) is a well-known antibacterial agent that is frequently detected in environmental, wildlife and human samples. The potential toxicological effects and action mechanism of TCC on vertebrate development has remained unclear. In the present study, we analyzed phenotypic alterations, thyroid hormone levels, thyroid hormone responsive genes, and proteomic profiles of zebrafish embryos after exposure to a series of concentrations of TCC from 6 h post-fertilization (hpf) to 120 hpf. The most nonlethal concentration (MNLC), lethal concentration 10% (LC10) and lethal concentration 50% (LC50) of TCC for exposures of 96 h were 133.3 μg/L, 147.5 μg/L and 215.8 μg/L, respectively. Our results showed that exposure to TCC decreased heart rate, delayed yolk absorption and swim bladder development at MNLC and LC10. Exposure to MNLC of TCC inhibited thyroid hormone and altered expression of thyroid hormone responsive genes. Furthermore, exposure to 1/20 MNLC of TCC altered expression of proteins related to binding and metabolism, skeletal muscle development and function, as well as proteins involved in nervous system development and immune response, indicating TCC has potential health risks in wildlife and humans at low concentration level.

Inhibited Metamorphosis and Disruption of Antioxidant Defenses and Thyroid Hormone Systems in Bufo gargarizans Tadpoles Exposed to Copper

Copper is a common aqueous pollutant that is known to cause oxidative stress and disrupt the thyroid axis in amphibians. In the present study, tadpoles of the Chinese toad (Bufo gargarizans) were exposed to 1, 6.4, 32, and 64 μg L−1 of copper from Gosner stages 26 to 42. We aimed to examine the influence of copper on thyroid hormone-responsive and stress-associated gene expression in the hind-limb, tail, and liver of B. gargarizans tadpoles. Exposure to 64 μg L−1 copper decreased percent metamorphosis and increased length of both hind-limb and tail of B. gargarizans tadpoles at Gs 42. In addition, according to real-time PCR results, exposure to 64 μg L−1 copper induced downregulation of Dio2, Dio3, TRα, and TRβ mRNA levels in all tissues examined. We inferred that copper might induce a considerable reduction of TH levels through downregulation of Dio2 and Dio3 mRNA levels in peripheral tissues. Decreased TH levels may then decrease the expressions of TRα and TRβ. Also, HSP, SOD, and PHGPx transcript levels were measured to assess cellular stress which might affect TH signaling and metamorphosis. We found that copper significantly downregulated the level of HSP, SOD, and PHGPx transcripts in the hind-limb and tail. This demonstrates that high concentrations of copper could disrupt the antioxidant system of B. gargarizans tadpoles and increase oxidative damage. Therefore, we conclude that copper could disrupt the antioxidant system and cause thyroid hormone disruption in B. gargarizans tadpoles.

Essential Roles of Thyroid Hormone-Regulated Hyaluronan/CD44 Signaling in Adult Stem Cell Development During Xenopus laevis Intestinal Remodeling

In the amphibian intestine during metamorphosis, thyroid hormone (TH) induces some larval epithelial cells to dedifferentiate into stem cells, which generate the adult epithelium analogous to the mammalian intestinal epithelium. We have previously shown that the canonical Wnt signaling pathway is involved in adult epithelial development in the Xenopus laevis intestine. To understand the function of this pathway more precisely, we here focused on CD44, a major Wnt target, which has been identified as a TH response gene in the X. laevis intestine. Our in situ hybridization analysis indicated that CD44 mRNA is detectable in adult epithelial primordia consisting of the adult stem/progenitor cells and is strongly expressed in the connective tissue (CT) cells surrounding them. Interestingly, when the expression of CD44 mRNA is the highest, hyaluronan (HA), a principle ligand of CD44, is newly synthesized and becomes most abundantly distributed in the CT just beneath the adult epithelial primordia that are actively proliferating. Thereafter, as the adult primordia differentiate into the simple columnar epithelium, the expression of CD44 mRNA is gradually downregulated. More importantly, using organ cultures of the X. laevis tadpole intestine in the presence of TH, we have experimentally shown that inhibition of HA synthesis by 4-methylumbelliferone suppresses development of not only the CT but also the epithelial stem cells, resulting in failure to generate the AE. Our findings strongly suggest that TH-upregulated HA/CD44 signaling plays an essential role in formation of the intestinal stem cell niche during vertebrate postembryonic development. Stem Cells 2017;35:2175-2183.

Identification of novel single nucleotide polymorphism at thyroid hormone responsive (THRSP) gene of native goat breeds of India

Precise knowledge about the genes causing variation within a trait will provide an opportunity for more effective marker assisted selection. Thyroid hormone responsive (THRSP) gene encodes for small acidic nuclear protein, associated with growth and lactation. Therefore, the present study was planned to detect single nucleotide variations in THRSP gene of goats. Genomic DNA was isolated from 200 animals belonging to Malabari and Attapady Black goats and PCR was done to amplify intron-1 (472bp) and exon-2 (412bp) region of THRSP gene. Single strand conformation polymorphism (SSCP) technique was used to detect single nucleotide polymorphisms (SNPs).Two unique band patterns were detected in 472bp fragment of THRSP gene. The pooled population frequencies of GG and GA diplotype were 0.88 and 0.12, respectively. The haplotype frequencies were 0.94 for G and 0.06 for a haplotype. Similar pattern of three bands were noticed in exon-2 region of THRSP gene in goats and the population was found to be monomorphic. Sequencing revealed two single nucleotide variations including a novel g.56G>T and g.306A>G in intron-1 of THRSP gene. This study indicates the existence of genetic variability in THRSP gene on goats. Hence, it could be used as a marker for selection to improve growth traits in goats.

CORRIGENDUM.

Molecular EcologyVolume 26, Issue 14 p. 3851-3851 CORRIGENDUMFree Access CORRIGENDUM This article corrects the following: Fine-grained adaptive divergence in an amphibian: genetic basis of phenotypic divergence and the role of nonrandom gene flow in restricting effective migration among wetlands Alex Richter-Boix, María Quintela, Marcin Kierczak, Marc Franch, Anssi Laurila, Volume 22Issue 5Molecular Ecology pages: 1322-1340 First Published online: January 7, 2013 First published: 04 July 2017 https://doi.org/10.1111/mec.14161AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat ALEX RICHTER - BOIX, MARIA QUINTELA, MARCIN KIERCZAK, MARC FRANCH, ANSSI LAURILA In the published paper (Richter-Boix et al. 2013), we incorrectly stated that we sequenced the protein-coding region of the thyroid hormone receptor gene (TRβ). The gene sequenced was in fact the gene C/EBP-1, a thyroid hormone receptor gene and transcription factor. As a consequence, instead of TRβ, it should read “the thyroid hormone receptor gene C/EBP-1” throughout the paper and supporting information of the article online. This error, however, does not strongly affect the main interpretation of our results. The C/EBP-1 gene, as the TRβ gene, is a thyroid hormone receptor with the dual function of repressing or activating thyroid-induced gene expression before or during tadpole metamorphosis. The C/EBP-1 gene, like TRβ, is a primary early TH-response gene during metamorphosis (Becker, Schneider, Davey, & Galton, 1995; Chen & Atkinson, 1997; Mochizuki, Goda, & Yamauchi, 2012; Murata & Yamauchi, 2005). It is not a general TH-receptor, but a specific one involved in the reprogramming of gene expression in the liver during amphibian metamorphosis (Chen & Atkinson, 1997; Chen, Hu, & Atkinson, 1994). The C/EBP-1 gene is a homologue to the mammalian C/EBP-α gene, which is known to play an essential role in cell cycle, hematopoiesis, differentiation and host immune response (Tsukada, Yoshida, Kominato, & Auron, 2011). Metamorphosis of a tadpole to a frog involves coordination between environmental cues, endocrine system and tissue-specific developmental programmes, like the one described in the tadpole liver tissue, which orchestrate changes in form and function required in the transition from aquatic to terrestrial lifestyle. We would like to thank Yvonne Meyer-Lucht for pointing this out. References Becker, K. B., Schneider, M. J., Davey, J. C., & Galton, V. A. (1995). The type III 5-deiodinase in Rana catesbeiana tadpoles is encoded by a thyroid hormone-responsive gene. Endocrinology, 136, 4424– 4431. Chen, Y., & Atkinson, B. G. (1997). Role for the Rana catesbeiana homologue of C/EBP α in the reprogramming of gene expression in the liver of metamorphosing tadpoles. Developmental Genetics, 20, 152– 162. Chen, Y., Hu, H., & Atkinson, B. G. (1994). Characterization and expression of C/EPB-like genes in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis. Developmental Genetics, 15, 366– 377. Mochizuki, K., Goda, T., & Yamauchi, K. (2012). Gene expression profile in the liver of Rana catesbiana tadpoles exposed to low temperature in the presence of thyroid hormone. Biochemical and Biophysical Research Communications, 420, 845– 850. Murata, T., & Yamauchi, K. (2005). Low-temperature arrest of the triiodothyronine-dependent transcription in Rana catesbeiana red blood cells. Endocrinology, 146, 256– 264. Richter-Boix, A., Quintela, M., Kierczak, M., Franch, M., & Laurila, A. (2013). Fine-grained adaptive divergence in an amphibian: Genetic basis of phenotypic divergence and the role of nonrandom gene flow in restricting effective migration among wetlands. Molecular Ecology, 22, 1322– 1340. Tsukada, J., Yoshida, Y., Kominato, Y., & Auron, P. E. (2011). The CCAAT/enhancer (C/EBP) family of basic-leucine zipper (bZIP) transcription factors is a multifaceted highly-regulated system for gene regulation. Cytokine, 54, 6– 19. Volume26, Issue14July 2017Pages 3851-3851 ReferencesRelatedInformation

Nuclear Import and Export of the Thyroid Hormone Receptor.

The thyroid hormone receptors, TRα1 and TRβ1, are members of the nuclear receptor superfamily that forms one of the most abundant classes of transcription factors in multicellular organisms. Although primarily localized to the nucleus, TRα1 and TRβ1 shuttle rapidly between the nucleus and cytoplasm. The fine balance between nuclear import and export of TRs has emerged as a critical control point for modulating thyroid hormone-responsive gene expression. Mutagenesis studies have defined two nuclear localization signal (NLS) motifs that direct nuclear import of TRα1: NLS-1 in the hinge domain and NLS-2 in the N-terminal A/B domain. Three nuclear export signal (NES) motifs reside in the ligand-binding domain. A combined approach of shRNA-mediated knockdown and coimmunoprecipitation assays revealed that nuclear entry of TRα1 is facilitated by importin 7, likely through interactions with NLS-2, and importin β1 and the adapter importin α1 interacting with both NLS-1 and NLS-2. Interestingly, TRβ1 lacks NLS-2 and nuclear import depends solely on the importin α1/β1 heterodimer. Heterokaryon and fluorescence recovery after photobleaching shuttling assays identified multiple exportins that play a role in nuclear export of TRα1, including CRM1 (exportin 1), and exportins 4, 5, and 7. Even single amino acid changes in TRs dramatically alter their intracellular distribution patterns. We conclude that mutations within NLS and NES motifs affect nuclear shuttling activity, and propose that TR mislocalization contributes to the development of some types of cancer and Resistance to Thyroid Hormone syndrome.

Gene Expression Patterns of Geese Expression Patterns of L-FABP, Spot 14, OB and APO A1 Genes in Different Tissues of Overfed and Control Geese

ABSTRACT Ten-week-old Langde geese in similar body weight were randomly selected, four for overfeeding and four for routinly feeding. The abundance of liver fatty acid-binding protein (L-FABP), thyroid hormone-responsive (THRSP or Spot 14), obese (OB), and apolipoprotein A1 (Apo A1) genes in goose were detected by quantitative RT-PCR. L-FABP was higher expressed in liver and intestine than other tissues, but no expression was detected in the pancreas or brain. The other three genes were widely expressed in different tissues, OB was higher expressed in pancreas and abdominal fat, Spot 14 and Apo A1 was higher expressed in sebum and abdominal fat. Spot 14 and Apo A1 genes were up-regulated in overfed goose livers compared with that in the control. Thus, Spot 14 and Apo A1 genes may play important roles in lipid metabolism in goose fat liver.

Editor's Highlight: Congener-Specific Disposition of Chiral Polychlorinated Biphenyls in Lactating Mice and Their Offspring: Implications for PCB Developmental Neurotoxicity.

Chiral polychlorinated biphenyl (PCB) congeners have been implicated by laboratory and epidemiological studies in PCB developmental neurotoxicity. These congeners are metabolized by cytochrome P450 (P450) enzymes to potentially neurotoxic hydroxylated metabolites (OH-PCBs). The present study explores the enantioselective disposition and toxicity of 2 environmentally relevant, neurotoxic PCB congeners and their OH-PCB metabolites in lactating mice and their offspring following dietary exposure of the dam. Female C57BL/6N mice (8-weeks old) were fed daily, beginning 2 weeks prior to conception and continuing throughout gestation and lactation, with 3.1 µmol/kg bw/d of racemic 2,2',3,5',6-pentachlorobiphenyl (PCB 95) or 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) in peanut butter; controls received vehicle (peanut oil) in peanut butter. PCB 95 levels were higher than PCB 136 levels in both dams and pups, consistent with the more rapid metabolism of PCB 136 compared with PCB 95. In pups and dams, both congeners were enriched for the enantiomer eluting second on enantioselective gas chromatography columns. OH-PCB profiles in lactating mice and their offspring were complex and varied according to congener, tissue and age. Developmental exposure to PCB 95 versus PCB 136 differentially affected the expression of P450 enzymes as well as neural plasticity (arc and ppp1r9b) and thyroid hormone-responsive genes (nrgn and mbp). The results suggest that the enantioselective metabolism of PCBs to OH-PCBs may influence neurotoxic outcomes following developmental exposures, a hypothesis that warrants further investigation.

Growth, Development, and Intestinal Remodeling Occurs in the Absence of Thyroid Hormone Receptor α in Tadpoles of Xenopus tropicalis

During development in all vertebrates, thyroid hormone receptors (TRs) are expressed before as well as during and after the peak in plasma thyroid hormone (TH) levels. Previously, we established a role for unliganded TRα in gene repression and developmental timing using tadpoles of TRα knockout (TRαKO) frogs. Here, we examined the role of liganded TRα on growth, development, and intestinal remodeling during natural and TH-induced metamorphosis. Disrupted TRα had little effect on growth during the larval period, but after metamorphosis, TRαKO juveniles grew more slowly than wild-type (WT) juveniles. TRαKO tadpoles developed faster throughout premetamorphosis when TH was low or absent, and despite their decreased responsivity to exogenous TH, TRαKO tadpoles not only were able to complete TH-dependent metamorphosis but also did so earlier than WT tadpoles. In contrast to external morphology, larval epithelial cell apoptosis and adult cell proliferation of intestinal remodeling were delayed in TRαKO tadpoles. Also, TRαKO intestines did not shrink in length to the full extent, and fewer intestinal folds into the lumen were present in TRαKO compared with WT juveniles. Such delayed remodeling occurred despite higher premetamorphic expression levels of TH target genes important for metamorphic progression-namely, TRβ, Klf9, and ST3. Furthermore, the decreased TH-dependent intestinal shrinkage was consistent with reduced TH response gene expression during natural and TH-induced metamorphosis. As in the TRα null mouse model, TRαKO frogs had statistically significant but surprisingly mild growth and development phenotypes with normal survival and fertility.

How thyroid hormone regulates transformation of larval epithelial cells into adult stem cells in the amphibian intestine

In the amphibian intestine during metamorphosis, a small number of larval epithelial cells dedifferentiate into adult stem cells that newly form the adult epithelium analogous to the mammalian counterpart, while most of them undergo apoptosis. Because this larval-to-adult intestinal remodeling can be experimentally induced by thyroid hormone (TH) both in vivo and in vitro, TH response genes identified in the Xenopus intestine provide us valuable clues to investigating how adult stem cells and their niche are formed during postembryonic development. Their expression and functional analyses by using the culture and recent transgenic (Tg) techniques have shed light on key signaling pathways essential for intestinal stem cell development. The present review focuses on such recent findings and discusses the evolutionally conserved roles of TH in development or maintenance of the stem cells which are common to the terrestrial vertebrate intestines.

MCT8 deficiency in Purkinje cells disrupts embryonic chicken cerebellar development.

Inactivating mutations in the human SLC16A2 gene encoding the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) result in the Allan-Herndon-Dudley syndrome accompanied by severe locomotor deficits. The underlying mechanisms of the associated cerebellar maldevelopment were studied using the chicken as a model. Electroporation of an MCT8-RNAi vector into the cerebellar anlage of a 3-day-old embryo allowed knockdown of MCT8 in Purkinje cell precursors. This resulted in the downregulation of the thyroid hormone-responsive gene RORα and the Purkinje cell-specific differentiation marker LHX1/5 at day 6. MCT8 knockdown also results in a smaller and less complex dendritic tree at day 18 suggesting a pivotal role of MCT8 for cell-autonomous Purkinje cell maturation. Early administration of the thyroid hormone analogue 3,5,3'-triiodothyroacetic acid partially rescued early Purkinje cell differentiation. MCT8-deficient Purkinje cells also induced non-autonomous effects as they led to a reduced granule cell precursor proliferation, a thinner external germinal layer and a loss of PAX6 expression. By contrast, at day 18, the external germinal layer thickness was increased, with an increase in presence of Axonin-1-positive post-mitotic granule cells in the initial stage of radial migration. The concomitant accumulation of presumptive migrating granule cells in the molecular layer, suggests that inward radial migration to the internal granular layer is stalled. In conclusion, early MCT8 deficiency in Purkinje cells results in both cell-autonomous and non-autonomous effects on cerebellar development and indicates that MCT8 expression is essential from very early stages of development, providing a novel insight into the ontogenesis of the Allan-Herndon-Dudley syndrome.

Efficacy of protocols for induction of chronic hyperthyroidism in male and female mice.

Protocols for induction of hyperthyroidism in mice are highly variable and mostly involve short-term thyroid hormone(TH) treatment. In addition, little is known about a possible influence of sex on experimental TH manipulation. Here we analyzed the efficacy of intraperitoneal vs. oral levothyroxine (T4) administration to induce chronic hyperthyroidism in male and female mice and asked which T4 dosing intervals are required to achieve stable organ thyrotoxicosis. T4 was administered intraperitoneally or orally over a period of 6/7 weeks. Assessment included monitoring of body weight, TH serum concentrations, and serial quantitative TH target gene expression analysis in liver and heart. Our results show that both intraperitoneal and oral T4 treatment are reliable methods for induction of chronic hyperthyroidism in mice. Thereby T4 injection intervals should not exceed 48 h and oral levothyroxine should be administered continuously during experiments and up to sacrifice to ensure a hyperthyroid organ state. Furthermore, we found a sex-dependent variation in levothyroxine-induced TH serum state, with significantly higher T4 concentrations in female mice, while expression of investigated classical TH responsive genes in liver and heart did not vary with animal's sex. In summary, our study shows that common approaches for rendering rodents thyrotoxic can also be used for induction of chronic hyperthyroidism in male and female mice. Thereby T4 dosing intervals are critical as are read-out parameters to verify a chronic thyrotoxic organ state.

Perinatal Iron Deficiency-Induced Hypothyroxinemia Impairs Early Brain Development Regardless of Normal Iron Levels in the Neonatal Brain.

Both perinatal hypothyroxinemia and perinatal iron deficiency (ID) are associated with poor neurodevelopment in offspring. Iron is an important component of thyroid peroxidase, a key enzyme in the synthesis of thyroid hormone. The authors' previous study demonstrated that perinatal ID can lead to maternal hypothyroxinemia during pregnancy. The goal of this study was to determine whether perinatal ID-associated hypothyroxinemia can cause brain defects prior to neonatal brain iron depletion. Two rat models were established to imitate the two common types of maternal ID (mild ID with anemia [ID + A] and ID without anemia [ID - A]), and iron limitation was initiated two weeks before pregnancy. Maternal and neonatal thyroid hormones in serum were analyzed at postnatal day (P) 0 and P10. Neonatal thyroid hormone, as well as mRNA expression of some thyroid hormone-responsive genes in the cerebral cortex and hippocampus, were measured at P10. Serum iron and brain iron concentrations were analyzed by inductively coupled plasma mass spectrometry. Liver iron concentration was determined using graphite furnace atomic absorption spectroscopy. Hemoglobin was analyzed with an automated blood coagulation analyzer. Surface righting reflex and vibrissae-evoked forelimb placing were measured to assess the sensorimotor behaviors. It was found that pre-pregnant mild ID resulted in maternal hypothyroxinemia, which lasted from gestation day 13 to P10. Pre-pregnant mild ID decreased the neonatal brain total triiodothyronine level at P10. Consistent with a low total triiodothyronine level, the mRNA expression of some thyroid hormone-responsive genes (Mbp, RC3, and Srg1) were significantly reduced in the neonatal cerebral cortex and hippocampus in both ID rat models at P10. Furthermore, ID rat pups at P10 showed retarded sensorimotor skills. No significant difference was found between the control and the ID pups in terms of iron concentrations in the neonatal brain at P10. This study demonstrates that perinatal ID-associated hypothyroxinemia is sufficient to impair early brain development, regardless of whether the neonatal brain iron level is normal, and monitoring thyroid hormone level is indicated in ID pregnant women.

Thyroid hormone activates Wnt/β-catenin signaling involved in adult epithelial development during intestinal remodeling in Xenopus laevis.

During amphibian intestinal remodeling, thyroid hormone (TH) induces some larval epithelial cells to dedifferentiate into adult stem cells, which newly generate the absorptive epithelium analogous to the mammalian epithelium. To clarify molecular mechanisms underlying adult epithelial development, we here focus on TH response genes that are associated with the canonical Wnt pathway. Our quantitative reverse transcription plus polymerase chain reaction and immunohistochemical analyses indicate that all of the genes examined, including β-catenin, c-Myc and secreted frizzle-related protein 2 (SFRP2), are up-regulated in Xenopus laevis intestine during both natural and TH-induced metamorphosis. Moreover, immunoreactivity for nuclear β-catenin becomes detectable in adult stem cells from the start of their appearance and then increases in intensity in adult epithelial primordia derived from the stem cells, which actively proliferate and coexpress Wnt target genes c-Myc and LGR5. These expression profiles strongly suggest the involvement of the canonical Wnt pathway in the maintenance and/or proliferation of adult stem/progenitor cells. More importantly, by using organ cultures of the tadpole intestine, we have experimentally shown that the addition of exogenous SFRP2 protein to the culture medium promotes cell proliferation of the adult epithelial primordia, whereas inhibition of endogenous SFRP2 by its antibody suppresses their proliferation. The inhibition of SFRP2 suppresses larval epithelial changes in shape from simple columnar to stem-cell-like roundish cells, resulting in the failure of epithelial dedifferentiation. Thus, TH-up-regulated SFRP2 in the postembryonic intestine promotes adult stem cell development, possibly by acting as an agonist of both canonical and non-canonical Wnt signaling.

3,5-T2 alters murine genes relevant for xenobiotic, steroid, and thyroid hormone metabolism

The endogenous thyroid hormone (TH) metabolite 3,5-diiodo-l-thyronine (3,5-T2) acts as a metabolically active substance affecting whole-body energy metabolism and hepatic lipid handling in a desirable manner. Considering possible adverse effects regarding thyromimetic action of 3,5-T2 treatment in rodents, the current literature remains largely controversial. To obtain further insights into molecular mechanisms and to identify novel target genes of 3,5-T2 in liver, we performed a microarray-based liver tissue transcriptome analysis of male lean and diet-induced obese euthyroid mice treated for 4 weeks with a dose of 2.5 µg/g bw 3,5-T2 Our results revealed that 3,5-T2 modulates the expression of genes encoding Phase I and Phase II enzymes as well as Phase III transporters, which play central roles in metabolism and detoxification of xenobiotics. Additionally, 3,5-T2 changes the expression of TH responsive genes, suggesting a thyromimetic action of 3,5-T2 in mouse liver. Interestingly, 3,5-T2 in obese but not in lean mice influences the expression of genes relevant for cholesterol and steroid biosynthesis, suggesting a novel role of 3,5-T2 in steroid metabolism of obese mice. We concluded that treatment with 3,5-T2 in lean and diet-induced obese male mice alters the expression of genes encoding hepatic xenobiotic-metabolizing enzymes that play a substantial role in catabolism and inactivation of xenobiotics and TH and are also involved in hepatic steroid and lipid metabolism. The administration of this high dose of 3,5-T2 might exert adverse hepatic effects. Accordingly, the conceivable use of 3,5-T2 as pharmacological hypolipidemic agent should be considered with caution.

Genome-wide association and genomic prediction of breeding values for fatty acid composition in subcutaneous adipose and longissimus lumborum muscle of beef cattle.

BackgroundIdentification of genetic variants that are associated with fatty acid composition in beef will enhance our understanding of host genetic influence on the trait and also allow for more effective improvement of beef fatty acid profiles through genomic selection and marker-assisted diet management. In this study, 81 and 83 fatty acid traits were measured in subcutaneous adipose (SQ) and longissimus lumborum muscle (LL), respectively, from 1366 purebred and crossbred beef steers and heifers that were genotyped on the Illumina BovineSNP50 Beadchip. The objective was to conduct genome-wide association studies (GWAS) for the fatty acid traits and to evaluate the accuracy of genomic prediction for fatty acid composition using genomic best linear unbiased prediction (GBLUP) and Bayesian methods.ResultsIn total, 302 and 360 significant SNPs spanning all autosomal chromosomes were identified to be associated with fatty acid composition in SQ and LL tissues, respectively. Proportions of total genetic variance explained by individual significant SNPs ranged from 0.03 to 11.06 % in SQ, and from 0.005 to 24.28 % in the LL muscle. Markers with relatively large effects were located near fatty acid synthase (FASN), stearoyl-CoA desaturase (SCD), and thyroid hormone responsive (THRSP) genes. For the majority of the fatty acid traits studied, the accuracy of genomic prediction was relatively low (<0.40). Relatively high accuracies (> = 0.50) were achieved for 10:0, 12:0, 14:0, 15:0, 16:0, 9c-14:1, 12c-16:1, 13c-18:1, and health index (HI) in LL, and for 12:0, 14:0, 15:0, 10 t,12c-18:2, and 11 t,13c + 11c,13 t-18:2 in SQ. The Bayesian method performed similarly as GBLUP for most of the traits but substantially better for traits that were affected by SNPs of large effects as identified by GWAS.ConclusionsFatty acid composition in beef is influenced by a few host genes with major effects and many genes of smaller effects. With the current training population size and marker density, genomic prediction has the potential to predict the breeding values of fatty acid composition in beef cattle at a moderate to relatively high accuracy for fatty acids that have moderate to high heritability.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0290-0) contains supplementary material, which is available to authorized users.