Genome-Wide Search Reveals the Existence of a Limited Number of Thyroid Hormone Receptor Alpha Target Genes in Cerebellar Neurons

Thyroid hormone (T3) has a major influence on cerebellum post-natal development. The major phenotypic landmark of exposure to low levels of T3 during development (hypothyroidism) in the cerebellum is the retarded inward migration of the most numerous cell type, granular neurons. In order to identify the direct genetic regulation exerted by T3 on cerebellar neurons and their precursors, we used microarray RNA hybridization to perform a time course analysis of T3 induced gene expression in primary cultures of cerebellar neuronal cell. These experiments suggest that we identified a small set of genes which are directly regulated, both in vivo and in vitro, during cerebellum post-natal development. These modest changes suggest that T3 does not acts directly on granular neurons and mainly indirectly influences the cellular interactions taking place during development

A Bimodal Influence of Thyroid Hormone on Cerebellum Oligodendrocyte Differentiation

International audienceThyroid hormone (T(3)) can trigger a massive differentiation of cultured oligodendrocytes precursor cells (OPC) by binding the nuclear T(3) receptor α1 (TRα1). Whether this reflects a physiological function of TRα1 remains uncertain. Using a recently generated mouse model, in which CRE/loxP recombination is used to block its function, we show that TRα1 acts at two levels for the in vivo differentiation of OPC in mouse cerebellum. At the early postnatal stage, it promotes the secretion of several neurotrophic factors by acting in Purkinje neurons and astrocytes, defining an environment suitable for OPC differentiation. At later stages, TRα1 acts in a cell-autonomous manner to ensure the complete arrest of OPC proliferation. These data explain contradictory observations made on various models and outline the importance of T(3) signaling both for synchronizing postnatal neurodevelopment and restraining OPC proliferation in adult brain

Hormone thyroïdienne et développement du cervelet : effets directs ou indirects ?

International audienceThyroid hormone (T₃) exerts an important influence on neurodevelopment, which can be analysed by using the postnatal development of rodent cerebellum as a model. T₃ acts on all types of neuronal and glial cells, which express at least the TRα1 nuclear receptor, and, for some of them, the TRβ1 isoform. However, as T₃ also activates the secretion of neurotrophins, it can also affect cellular differentiation in an indirect manner. Ongoing experiments, based on mouse genetics and genome wide analysis of gene expression, provide a promising way to study the basic mechanisms of neurodevelopment. This review describes new mouse genetics models and recent advance in this field

Minireview: Deciphering Direct and Indirect Influence of Thyroid Hormone With Mouse Genetics

International audienceT3, the active form of thyroid hormone, binds nuclear receptors that regulate the transcription of a large number of genes in many cell types. Unraveling the direct and indirect effect of this hormonal stimulation, and establishing links between these molecular events and the developmental and physiological functions of the hormone, is a major challenge. New mouse genetics tools, notably those based on Cre/loxP technology, are suitable to perform a multiscale analysis of T3 signaling and achieve this task

Transfection of TRα1 into C17.2 cells restores their response to T3 treatment.

<p>A. T3-induced <i>Hr</i> expression is detected earlier and stronger in transfected C17.2/TRα1 cells (black bars) than in non-transfected cells (white bars), *p<0.05, Student’s t-test difference between non-transfected cells and C17.2/TRα1 cells. B. The level of change in expression induced by T3 and measured by Q-RT-PCR in C17.2/TRα1 cells is indicated for each target gene, using non-treated cultures as reference (represented as log2 of the fold change). White bars indicate T3 treatment in proliferative medium (containing serum), black bars indicated T3 treatment in serum-deprived medium allowing for differentiation. Most genes show a response only in serum-deprived medium, *p<0.05, Student’s t-test, difference between serum containing and serum deprived cultures.</p

Kinetics of T3 target genes expression in wild-type and <i>TRα^AMI/S</i> mice in the cerebellum as measured by Q-RT-PCR.

<p>Expression levels were calculated for each target gene by Q-RT-PCR in wild-type and <i>TRα^AMI/S</i> littermates at P4, P8, P15 and P21 (minimum 3 animals of each genotype for each time point). Data are expressed as mean ± SD using wild-type P4 values (A), for genes with decreasing or stable expression levels over time or P21 (B), for genes with increasing expression levels, as a reference for each genotype. *p<0.05; **p<0.01 for comparisons between wild-type and <i>TRα^AMI/S</i> mice for each time point (Student’s t-test).</p

Chromatin occupancy by TRα1 in C17.2/TRα1 cells.

*<p>Identified using NUBISCAN. Bold characters correspond to TREs with more that 2-fold enrichment after C17.2/TRα1 cells ChAP. ND: not determined, N/A: not relevant. Mean ± SD for three independent experiments.</p

Cell autonomous effect of <i>in vivo</i> expression of a dominant negative TRα1 mutation.

<p><i>TRα^AMI/S</i> data are reported from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030703#pone-0030703-g002" target="_blank">figure 2</a> for comparisons. ND: Not determined. Values are indicated as mean ± SD. Significant changes (Student T-test) are indicated in bold:</p>**<p>: p<0.01,</p>*<p>: p<0.05.</p

Database analysis of expression patterns and gene functions.

<p>Abbreviations: AS: Astrocytes, BC: Basket cells, BG: Bergmann glia, EGL: external granular layer, GI: Golgi interneurons, IGL: internal granular layer, ML: molecular layer, OL:Oligodendrocytes, PC: Purkinje cells, PCL: Purkinje cell layer, SC: Stellate cells, Ubi: ubiquitous, WM: White matter. N/A: not available. First location is the principal location. Data from Allen Brain Atlas, GENSAT and reference <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030703#pone.0030703-Doyle1" target="_blank">[32]</a>.</p

Minireview: Deciphering Direct and Indirect Influence of Thyroid Hormone With Mouse Genetics

International audienceT3, the active form of thyroid hormone, binds nuclear receptors that regulate the transcription of a large number of genes in many cell types. Unraveling the direct and indirect effect of this hormonal stimulation, and establishing links between these molecular events and the developmental and physiological functions of the hormone, is a major challenge. New mouse genetics tools, notably those based on Cre/loxP technology, are suitable to perform a multiscale analysis of T3 signaling and achieve this task