Hypotonic male infant and MCT8 deficiency - a diagnosis to think about

[Background]: Thyroid hormone is crucial in the development of different organs, particularly the brain. MCT8 is a specific transporter of triiodothyronine (T3) hormone and MCT8 gene mutations cause a rare X-linked disorder named MCT8 deficiency, also known as Allan-Herndon-Dudley syndrome, characterized by psychomotor retardation and hypotonia. Typically, elevation of T3 and delayed myelination in cerebral magnetic resonance imaging are found. [Case presentation]: We present a 24-month-old boy, born from non-consanguineous healthy parents, with severe motor and cognitive delay and global hypotonia, being unable to hold head upright or sit without support. Deep tendon reflexes were absent bilaterally at the ankles. T3 was elevated and thyroxine slightly decreased, consistent with MCT8 deficiency. Genetic studies confirmed the diagnosis. [Conclusions]: Although a rare disease (MCT8 mutations have been reported in about 50 families all around the world), we illustrate the importance of excluding Allan-Herndon-Dudley syndrome in the evaluation of floppy male infants with development delay, without history of perinatal asphyxia. The simple evaluation of thyroid status, including T3, T4 and TSH can guide the diagnosis, avoiding a number of useless, expensive and invasive investigations and allowing appropriate genetic counseling to the affected families.This is an Open Access article distributed under the terms of the Creative Commons Attribution License.-- et al.Peer Reviewe

Different signalling pathways mediate glucose induction of SUC2, HXT1 and pyruvate decarboxylase in yeast

The glucose sensors Gpr1, Snf3 and Rgt2 generate the earliest signals produced by glucose in yeast. We showed that a lack of Gpr1 or Snf3/Rgt2 decreased by twofold the glucose induction of SUC2, but had no effect on the induction of pyruvate decarboxylase (Pdc). The induction of HXT1 was not affected by the absence of Gpr1. In an hxk1 hxk2 glk1 strain, high glucose fully induced SUC2, caused partial induction of HXT1 and had no effect on Pdc. In this strain, SUC2 induction was dependent on Gpr1, but HXT1 induction was not. Hxk2, required for the high expression of HXT1, was dispensable for the full induction of SUC2 or Pdc. These results indicate that glucose does not induce transcription through a single signalling pathway, but that several pathways may, in different combinations, regulate the transcription of different genes. © 2006 Federation of European Microbiological Societies.This work was supported by grants BMC2001-1690-C02-1 and BFU2004-02855-C02-1 from the Dirección General de Investigación Científica y Técnica (DGICYT) and by the European Union (EU) project BIO-HUG QLK3-CT-1999-00080. M.M.B. was supported by fellowships from the EU and the DGICYT.Peer Reviewe

Glucose controls multiple processes in Saccharomyces cerevisiae through diverse combinations of signaling pathways

We have studied how the lack of glucose sensors in the plasma membrane, or of the enzymes Hxk1, Hxk2, Glk1, which catalyze the first intracellular step in glucose metabolism, affect the different responses of Saccharomyces cerevisiae to glucose. Lack of the G-protein-coupled receptor Gpr1 or of Snf3/Rgt2 did not affect glucose repression of different genes or activation by glucose of plasma membrane ATPase, whereas lack of Gpr1 decreased, in an additive manner with lack of Mth1, the degradation of fructose 1,6-bisphosphatase that takes place in the presence of glucose. In an hxk1 hxk2 glk1 strain, unable to phosphorylate glucose, all of these responses to the sugar were suppressed or strongly reduced. In the absence of Hxk2 (or Hxk1 and Hxk2), glucose repression of SUC2, GAL1 and GDH2 was relieved, but that of FBP1 and ICL1 was maintained. Hxk1 or Hxk2 were needed for activation of plasma membrane ATPase but not for degradation of FbPase. © 2007 Federation of European Microbiological Societies.This work was supported by grants BMC2001-1690-CO2-1 and BFU2004-02855-C02-01 from the Dirección General de Investigación Científica y Técnica, and by the EU project BIO-HUG QLK3-CT-1999-00080. M.M. Belinchón was supported by fellowships from the EU and the DGICYT.Peer Reviewe

Xylose and some non-sugar carbon sources cause catabolite repression in Saccharomyces cerevisiae

Glucose and other sugars, such as galactose or maltose, are able to cause carbon catabolite repression in Saccharomyces cerevisiae. Although glycolytic intermediates have been suggested as signal for repression, no evidence for such a control mechanism is available. The establishment of a correlation between levels of intracellular metabolites and the extent of catabolite repression may facilitate the identification of potential signal molecules in the process. To set a framework for such a study, the repression produced by xylose, glycerol and dihydroxyacetone upon genes belonging to different repressible circuits was tested, using an engineered strain of S. cerevisiae able to metabolize xylose. Xylose decreased the derepression of various enzymes in the presence of ethanol by at least 10-fold; the corresponding mRNAs were not detected in these conditions. Xylose also impaired the derepression of galactokinase and invertase. Glycerol and dihydroxyacetone decreased 2- to 3-fold the derepression observed in ethanol or galactose but did not affect invertase derepression. For yeast cells grown in media with different carbon sources, no correlation was found between repression of fructose-1,6-bisphosphatase and intracellular levels of glucose 6-phosphate or fructose 1,6-bisphosphate.This work was supported by EU project BIO-HUG QLK3-CT-1999-00080 and by grant BMC2001-1690-CO2-01 from the Dirección General de Investigación Científica y Técnica. M.M. had a fellowship from the EU and later from the DGICYT

Critical role of types 2 and 3 deiodinases in the negative regulation of gene expression by T 3 in the mouse cerebral cortex

Thyroid hormones regulate brain development and function through the control of gene expression, mediated by binding of T 3 to nuclear receptors. Brain T 3 concentration is tightly controlled by homeostatic mechanisms regulating transport and metabolism of T 4 and T 3. We have examined the role of the inactivating enzyme type 3 deiodinase (D3) in the regulation of 43 thyroid hormone-dependent genes in the cerebral cortex of 30-d-old mice. D3 inactivation increased slightly the expression of two of 22 positively regulated genes and significantly decreased the expression of seven of 21 negatively regulated genes. Administration of high doses of T 3 led to significant changes in the expression of 12 positive genes and three negative genes in wild-type mice. The response to T 3 treatment was enhanced in D3-deficient mice, both in the number of genes and in the amplitude of the response, demonstrating the role of D3 in modulating T 3 action. Comparison of the effects on gene expression observed in D3 deficiency with those in hypothyroidism, hyperthyroidism, and type 2 deiodinase (D2) deficiency revealed that the negative genes are more sensitive to D2 and D3 deficiencies than the positive genes. This observation indicates that, in normal physiological conditions, D2 and D3 play critical roles in maintaining local T 3 concentrations within a very narrow range. It also suggests that negatively and positively regulated genes do not have the same physiological significance or that their regulation by thyroid hormone obeys different paradigms at the molecular or cellular levels. Copyright © 2012 by The Endocrine Society.This work was supported by Grants SAF2008-01168 and SAF2008-00429-E from the Ministry of Education and Science of Spain, Grant LSHM-CT-2005-018652 from the European Union Integrated ProjectCRESCENDO,a grant from the Center for Biomedical Research on Rare Diseases, an initiative of the Instituto de Salud Carlos III, and by Grant NIMH-083220 from the National Institute of Mental Health. A.C. was recipient of a predoctoral fellowship from the Plan Nacional de I+D+i.Peer Reviewe

Sampling Saccharomyces cerevisiae cells by rapid filtration improves the yield of mRNAs

To optimize the recovery of mRNAs extracted from yeast, different methods for sampling the yeast cells have been compared. For Saccharomyces cerevisiae strains growing on gluconeogenic carbon sources (derepressed cells) rapid filtration allowed much higher yields (3–10 fold) than centrifugation at room temperature or at 4 °C. Recovery of total RNA was similar with the different procedures. For S. cerevisiae growing on glucose, filtration caused a 2–4 fold improvement on the mRNA yields obtained from cells sampled by centrifugation. It was also observed that, when derepressed cells of S. cerevisiae W303-1A were collected by filtration and flash-frozen, part of the 25S and 18S rRNAs (up to 50%) was recovered in an unprocessed 32S or 33S form.This work was supported by Grant BMC2001-1690-CO2-01 from the Dirección General de Investigación Científica y Técnica. M.M.B. was recipient of a fellowship from the DGICYT

Is the intrinsic genomic activity of thyroxine relevant in vivo? Effects on gene expression in primary cerebrocortical and neuroblastoma cells

[Background]: The possibility that the intrinsic genomic activity of thyroxine (T4) is of physiological relevance has been frequently hypothesized. It might explain gene expression patterns in the brain found in type 2-deiodinase (Dio2)-deficient mice. These mice display normal expression of most thyroid hormone–dependent genes, despite decreased brain triiodothyronine (T3).[Methods]: The relative effects of T4 and T3 on gene expression were analyzed in mouse neuro-2a (N2a) cells stably expressing the thyroid hormone receptor α1, and in primary mouse cerebrocortical cells enriched in astrocytes or in neurons. Cortical cells were derived from Dio2-deficient mice to prevent conversion of T4 to T3. T4 and T3 were measured in the media at the beginning and end of incubation, and T4 and T3 antibodies were used to block T4 and T3 action.[Results]: In all cell types, T4 had intrinsic genomic activity. In N2a cells, T4 activity was higher on negative regulation (1/5th of T3 activity) than on positive regulation (1/40th of T3 activity). T4 activity on positive regulation was dependent on the cell context, and was higher in primary cells than in N2a cells.[Conclusion]: T4 has intrinsic genomic activity. Positive regulation depends on the cell context, and primary cells appear much more sensitive than neuroblastoma cells. In all cells, negative regulation is more sensitive to T4 than positive regulation. These properties may explain the mostly normal gene expression in the brain of Dio2-deficient mice.This work was supported by the Center for Biomedical Research on Rare Diseases (Ciberer) under the frame of E-Rare-2 (project acronym THYRONERVE), the ERA-Net for Research on Rare Diseases; grant SAF2014-54919R from Plan Estatal de Investigación Científica, Técnica y de Innovación, Ministerio de Economía y Competititividad, and FEDER funds.Peer reviewe

Thyroid hormone regulation of gene expression in the developing rat fetal cerebral cortex: Prominent role of the Ca2+/calmodulin-dependent protein kinase IV pathway

11 p., 6 figures, 1 table and references.Thyroid hormones influence brain development through regulation of gene expression mediated by nuclear receptors. Nuclear receptor concentration increases rapidly in the human fetus during the secondtrimester,aperiod of high sensitivity of the brain to thyroidhormones.In the rat, the equivalent period is the last quarter of pregnancy. However, little is known about thyroid hormone action in the fetal brain, and in rodents, most thyroid hormone-regulated genes have been identified during the postnatal period. To identify potential targets of thyroid hormone in the fetal brain,weinduced maternal and fetal hypothyroidism by maternal thyroidectomy followed by antithyroid drug (2-mercapto-1-methylimidazole) treatment. Microarray analysis identified differentially expressed genes in the cerebral cortex of hypothyroid fetuses on d 21 after conception. Gene function analysis revealed genes involved in the biogenesis of the cytoskeleton, neuronal migration and growth,and branching of neurites. Twenty percent of the differentially expressed genes were related to each other centered on the Ca2 and calmodulin-activated kinase (Camk4) pathway.Camk4was regulated directly by T3 in primary cultured neurons from fetal cortex, and the Camk4 protein was also induced by thyroid hormone. No differentially expressed genes were recovered when euthyroid fetuses from hypothyroid mothers were compared with fetuses from normal mothers. Although the resultsdonot rule out a specific contribution from the mother, especially at earlier stages of pregnancy, they indicate that the main regulators of thyroid hormone-dependent, fetal brain gene expression near term are the fetal thyroid hormones.This work was supported by Grants BFU2005-01740, SAF2008-01168, and SAF2006-14068 from the Ministry of Science and Innovation, Spain, by the European Union Integrated Project CRESCENDO (LSHM- CT-2005-018652), and by the Center for Biomedical Research on Rare Diseases (CIBERER). D.D. was supported by the I3P program of the Consejo Superior de Investigaciones Científicas, Spain, and by a postdoctoral fellowship from The Japanese Society for the Promotion of Science. D.N. was supported by a predoctoral fellowship of the Spanish Ministry of Science and Innovation.Peer reviewe