HAL (Le Centre pour la Communication Scientifique Directe), 2004
Thyroid hormones are involved in the regulation of many physiological processes and regulate gene... more Thyroid hormones are involved in the regulation of many physiological processes and regulate gene transcription by binding to their nuclear receptors TRalpha and TRbeta. In the absence of triiodothyronine (T3), the unliganded receptors (aporeceptors) do bind DNA and repress the transcription of target genes. The role of thyroid hormone aporeceptors as repressors was observed in hypothyroid adult mice, but its physiological relevance in nonpathological hypothyroid conditions remained to be determined. Here we show that, in the normal mouse fetus, TRalpha aporeceptors repress heart rate as well as the expression of TRbeta and several genes encoding ion channels involved in cardiac contractile activity. Right after birth, when T3 concentration sharply increases, liganded TRalpha (holoreceptors) turn on the expression of some of these same genes concomitantly with heart rate increase. These data describe a physiological situation under which conversion of TRalpha from apo-receptors into holo-receptors, upon changes in T3 availability, plays a determinant role in a developmental process.
HAL (Le Centre pour la Communication Scientifique Directe), 2007
Thyroid hormones act directly on transcription by binding to TRalpha1, TRbeta1, and TRbeta2 nucle... more Thyroid hormones act directly on transcription by binding to TRalpha1, TRbeta1, and TRbeta2 nuclear receptors, regulating many aspects of postnatal development and homeostasis. To analyze precisely the implication of the widely expressed TRalpha1 isoform in this pleiotropic action, we have generated transgenic mice with a point mutation in the TRalpha1 coding sequence, which is expressed only after CRE/loxP-mediated DNA recombination. The amino acid change prevents interaction between TRalpha1 and histone acetyltransferase coactivators and the release of corepressors. Early expression of this dominant-negative receptor deeply affects postnatal development and adult homeostasis, recapitulating many aspects of congenital and adult hypothyroidism, except in tissues and cells where TRbeta1 and TRbeta2 are predominantly expressed. Both respective abundance and intrinsic properties of TRalpha1 and TRbeta1/2 seem to govern specificity of action.
Thyroid hormones act directly on transcription by binding to TR1, TRb1, TRb2 nuclear receptors, ... more Thyroid hormones act directly on transcription by binding to TR1, TRb1, TRb2 nuclear receptors, regulating many aspects of post-natal development and homeostasis. To precisely analyze the implication of the widely expressed TR1 isoform in this pleiotropic action, we have generated transgenic mice with a point mutation in the TR1 coding sequence, which is expressed only after CRE/loxP mediated DNA recombination. The amino-acid change prevents interaction between TR1 and histone acetyltransferase coactivators and the release of corepressors. Early expression of this dominant-negative receptor deeply affects post-natal development and adult homeostasis, recapitulating many aspects of congenital and adult hypothyroidism, except in tissues and cells where TRb1 and TRb2 are predominantly expressed. Both respective abundance and intrinsic properties of TRa1 and TRb1/2 seems to govern specificity of action.
The International journal of developmental biology, 1994
A new procedure, virofection, designed to stabilize the expression of transfected DNA has been de... more A new procedure, virofection, designed to stabilize the expression of transfected DNA has been developed. It exploits the capacity of retroviruses to integrate their genome into the chromosomes of host cells. The co-transfection of two plasmids, one carrying the genome of a defective retrovirus vector, the other one encoding all the retroviral proteins, results in a transient production of infectious virus particles. These particles can infect the neighboring cells and this leads to the stable integration of the vector genome. This procedure is time-saving and appears to be quite efficient. When applied to chicken embryonic fibroblasts cultured in vitro, it resulted in the stable expression of the lacZ gene in more than 30% of the cells, and did not induce chronic viremia. Stable lacZ expression was also achieved in chicken embryos in ovo. Virofection appears to be a promising and generally applicable method for implementing stable, safe and efficient gene transfer in vitro and in v...
Proceedings of the National Academy of Sciences, 2017
Significance Thyroid hormone (T3) controls both developmental and physiological processes. Its nu... more Significance Thyroid hormone (T3) controls both developmental and physiological processes. Its nuclear receptors (TR) are transcription factors. Methyl dioxygenase ten-eleven translocation protein 3 (TET3) is characterized here as a TR coregulator. It stabilizes and promotes TR chromatin association in a dioxygenase-independent manner, thus increasing the sensitivity of the cell to T3. Mutations in TR cause the resistance to thyroid hormone syndrome (RTH) symptom, the severity of which varies with the particular mutation. Only some mutated TR can be stabilized by TET3. The availability of TET3 is therefore a parameter modulating TR activity, and its differential interaction with mutated TR might explain different severity of RTH. Furthermore, TET3 is likely to function as a general coregulator for nuclear receptors, as it enhances chromatin association of additional members of this superfamily.
Thyroid hormone receptor β (TRβ) dysfunction leads to deafness in humans and mice. Deafness in TR... more Thyroid hormone receptor β (TRβ) dysfunction leads to deafness in humans and mice. Deafness in TRβ−/−mutant mice has been attributed to TRβ-mediated control of voltage- and Ca2+-activated K+(BK) channel expression in inner hair cells (IHCs). However, normal hearing in young constitutive BKα−/−mutants contradicts this hypothesis. Here, we show that mice with hair cell-specific deletion of TRβ after postnatal day 11 (P11) have a delay in BKα expression but normal hearing, indicating that the origin of hearing loss in TRβ−/−mutant mice manifested before P11. Analyzing the phenotype of IHCs in constitutive TRβ−/−mice, we found normal Ca2+current amplitudes, exocytosis, and shape of compound action potential waveforms. In contrast, reduced distortion product otoacoustic emissions and cochlear microphonics associated with an abnormal structure of the tectorial membrane and enhanced tectorin levels suggest that disturbed mechanical performance is the primary cause of deafness resulting fro...
Proceedings of the National Academy of Sciences, 2002
Thyroid hormone (3,5,3′-triiodo- l -thyronine or T3) exerts a pleiotropic activity during central... more Thyroid hormone (3,5,3′-triiodo- l -thyronine or T3) exerts a pleiotropic activity during central nervous system development. Hypothyroidism during the fetal and postnatal life results in an irreversible mental retardation syndrome. At the cellular level, T3 is known to act on neuronal and glial lineages and to control cell proliferation, apoptosis, migration, and differentiation. Oligodendrocyte precursor cells (OPC) found at birth in the optic nerves are self-renewing cells that normally differentiate during the first 3 weeks of rodent postnatal life into postmitotic myelinating oligodendrocytes. In vitro , the addition of T3 to OPC is sufficient to trigger their terminal differentiation. The present analysis of T3 receptor knockout mice reveals that the absence of all T3 receptor results in the persistence of OPC proliferation in adult optic nerves, in a default in myelination, and sometimes in the degeneration of the retinal ganglion neurons. Thus, T3 signaling is necessary in v...
The thyroid hormone receptor-coding locus, c-erbAα, generates several mRNAs originating from a si... more The thyroid hormone receptor-coding locus, c-erbAα, generates several mRNAs originating from a single primary transcript that undergoes alternative splicing. We have identified for the first time two new transcripts, called TRΔα1 and TRΔα2[ mRNA for isoform α1 and α2 of the T3 receptor (TR), respectively], whose transcription is initiated from an internal promoter located within intron 7 of the c-erbAα gene. These two new transcripts exhibit tissue-specific patterns of expression in the mouse. These two patterns are in sharp contrast with the expression patterns of the full-length transcripts generated from the c-erbAα locus. TRΔα1 and TRΔα2 mRNAs encode N-terminally truncated isoforms of T3Rα1 and T3Rα2, respectively. The protein product of TRΔα1 antagonizes the transcriptional activation elicited by T3 and retinoic acid. This protein inhibits the ligand-induced activating functions of T3Rα1 and 9-cis-retinoic acid receptor-α but does not affect the retinoic acid-dependent activati...
We produced transgenic mice expressing the sheep prion protein to obtain a sensitive model for sh... more We produced transgenic mice expressing the sheep prion protein to obtain a sensitive model for sheep spongiform encephalopathies (scrapie). The complete open reading frame, with alanine, arginine, and glutamine at susceptibility codons 136, 154, and 171, respectively, was inserted downstream from the neuron-specific enolase promoter. A mouse line, Tg(OvPrP4), devoid of the murine PrP gene, was obtained by crossing with PrP knockout mice. Tg(OvPrP4) mice were shown to selectively express sheep PrP in their brains, as demonstrated in mRNA and protein analysis. We showed that these mice were susceptible to infection by sheep scrapie following intracerebral inoculation with two natural sheep scrapie isolates, as demonstrated not only by the occurrence of neurological signs but also by the presence of the spongiform changes and abnormal prion protein accumulation in their brains. Mean times to death of 238 and 290 days were observed with these isolates, but the clinical course of the dis...
HAL (Le Centre pour la Communication Scientifique Directe), 2004
Thyroid hormones are involved in the regulation of many physiological processes and regulate gene... more Thyroid hormones are involved in the regulation of many physiological processes and regulate gene transcription by binding to their nuclear receptors TRalpha and TRbeta. In the absence of triiodothyronine (T3), the unliganded receptors (aporeceptors) do bind DNA and repress the transcription of target genes. The role of thyroid hormone aporeceptors as repressors was observed in hypothyroid adult mice, but its physiological relevance in nonpathological hypothyroid conditions remained to be determined. Here we show that, in the normal mouse fetus, TRalpha aporeceptors repress heart rate as well as the expression of TRbeta and several genes encoding ion channels involved in cardiac contractile activity. Right after birth, when T3 concentration sharply increases, liganded TRalpha (holoreceptors) turn on the expression of some of these same genes concomitantly with heart rate increase. These data describe a physiological situation under which conversion of TRalpha from apo-receptors into holo-receptors, upon changes in T3 availability, plays a determinant role in a developmental process.
HAL (Le Centre pour la Communication Scientifique Directe), 2007
Thyroid hormones act directly on transcription by binding to TRalpha1, TRbeta1, and TRbeta2 nucle... more Thyroid hormones act directly on transcription by binding to TRalpha1, TRbeta1, and TRbeta2 nuclear receptors, regulating many aspects of postnatal development and homeostasis. To analyze precisely the implication of the widely expressed TRalpha1 isoform in this pleiotropic action, we have generated transgenic mice with a point mutation in the TRalpha1 coding sequence, which is expressed only after CRE/loxP-mediated DNA recombination. The amino acid change prevents interaction between TRalpha1 and histone acetyltransferase coactivators and the release of corepressors. Early expression of this dominant-negative receptor deeply affects postnatal development and adult homeostasis, recapitulating many aspects of congenital and adult hypothyroidism, except in tissues and cells where TRbeta1 and TRbeta2 are predominantly expressed. Both respective abundance and intrinsic properties of TRalpha1 and TRbeta1/2 seem to govern specificity of action.
Thyroid hormones act directly on transcription by binding to TR1, TRb1, TRb2 nuclear receptors, ... more Thyroid hormones act directly on transcription by binding to TR1, TRb1, TRb2 nuclear receptors, regulating many aspects of post-natal development and homeostasis. To precisely analyze the implication of the widely expressed TR1 isoform in this pleiotropic action, we have generated transgenic mice with a point mutation in the TR1 coding sequence, which is expressed only after CRE/loxP mediated DNA recombination. The amino-acid change prevents interaction between TR1 and histone acetyltransferase coactivators and the release of corepressors. Early expression of this dominant-negative receptor deeply affects post-natal development and adult homeostasis, recapitulating many aspects of congenital and adult hypothyroidism, except in tissues and cells where TRb1 and TRb2 are predominantly expressed. Both respective abundance and intrinsic properties of TRa1 and TRb1/2 seems to govern specificity of action.
The International journal of developmental biology, 1994
A new procedure, virofection, designed to stabilize the expression of transfected DNA has been de... more A new procedure, virofection, designed to stabilize the expression of transfected DNA has been developed. It exploits the capacity of retroviruses to integrate their genome into the chromosomes of host cells. The co-transfection of two plasmids, one carrying the genome of a defective retrovirus vector, the other one encoding all the retroviral proteins, results in a transient production of infectious virus particles. These particles can infect the neighboring cells and this leads to the stable integration of the vector genome. This procedure is time-saving and appears to be quite efficient. When applied to chicken embryonic fibroblasts cultured in vitro, it resulted in the stable expression of the lacZ gene in more than 30% of the cells, and did not induce chronic viremia. Stable lacZ expression was also achieved in chicken embryos in ovo. Virofection appears to be a promising and generally applicable method for implementing stable, safe and efficient gene transfer in vitro and in v...
Proceedings of the National Academy of Sciences, 2017
Significance Thyroid hormone (T3) controls both developmental and physiological processes. Its nu... more Significance Thyroid hormone (T3) controls both developmental and physiological processes. Its nuclear receptors (TR) are transcription factors. Methyl dioxygenase ten-eleven translocation protein 3 (TET3) is characterized here as a TR coregulator. It stabilizes and promotes TR chromatin association in a dioxygenase-independent manner, thus increasing the sensitivity of the cell to T3. Mutations in TR cause the resistance to thyroid hormone syndrome (RTH) symptom, the severity of which varies with the particular mutation. Only some mutated TR can be stabilized by TET3. The availability of TET3 is therefore a parameter modulating TR activity, and its differential interaction with mutated TR might explain different severity of RTH. Furthermore, TET3 is likely to function as a general coregulator for nuclear receptors, as it enhances chromatin association of additional members of this superfamily.
Thyroid hormone receptor β (TRβ) dysfunction leads to deafness in humans and mice. Deafness in TR... more Thyroid hormone receptor β (TRβ) dysfunction leads to deafness in humans and mice. Deafness in TRβ−/−mutant mice has been attributed to TRβ-mediated control of voltage- and Ca2+-activated K+(BK) channel expression in inner hair cells (IHCs). However, normal hearing in young constitutive BKα−/−mutants contradicts this hypothesis. Here, we show that mice with hair cell-specific deletion of TRβ after postnatal day 11 (P11) have a delay in BKα expression but normal hearing, indicating that the origin of hearing loss in TRβ−/−mutant mice manifested before P11. Analyzing the phenotype of IHCs in constitutive TRβ−/−mice, we found normal Ca2+current amplitudes, exocytosis, and shape of compound action potential waveforms. In contrast, reduced distortion product otoacoustic emissions and cochlear microphonics associated with an abnormal structure of the tectorial membrane and enhanced tectorin levels suggest that disturbed mechanical performance is the primary cause of deafness resulting fro...
Proceedings of the National Academy of Sciences, 2002
Thyroid hormone (3,5,3′-triiodo- l -thyronine or T3) exerts a pleiotropic activity during central... more Thyroid hormone (3,5,3′-triiodo- l -thyronine or T3) exerts a pleiotropic activity during central nervous system development. Hypothyroidism during the fetal and postnatal life results in an irreversible mental retardation syndrome. At the cellular level, T3 is known to act on neuronal and glial lineages and to control cell proliferation, apoptosis, migration, and differentiation. Oligodendrocyte precursor cells (OPC) found at birth in the optic nerves are self-renewing cells that normally differentiate during the first 3 weeks of rodent postnatal life into postmitotic myelinating oligodendrocytes. In vitro , the addition of T3 to OPC is sufficient to trigger their terminal differentiation. The present analysis of T3 receptor knockout mice reveals that the absence of all T3 receptor results in the persistence of OPC proliferation in adult optic nerves, in a default in myelination, and sometimes in the degeneration of the retinal ganglion neurons. Thus, T3 signaling is necessary in v...
The thyroid hormone receptor-coding locus, c-erbAα, generates several mRNAs originating from a si... more The thyroid hormone receptor-coding locus, c-erbAα, generates several mRNAs originating from a single primary transcript that undergoes alternative splicing. We have identified for the first time two new transcripts, called TRΔα1 and TRΔα2[ mRNA for isoform α1 and α2 of the T3 receptor (TR), respectively], whose transcription is initiated from an internal promoter located within intron 7 of the c-erbAα gene. These two new transcripts exhibit tissue-specific patterns of expression in the mouse. These two patterns are in sharp contrast with the expression patterns of the full-length transcripts generated from the c-erbAα locus. TRΔα1 and TRΔα2 mRNAs encode N-terminally truncated isoforms of T3Rα1 and T3Rα2, respectively. The protein product of TRΔα1 antagonizes the transcriptional activation elicited by T3 and retinoic acid. This protein inhibits the ligand-induced activating functions of T3Rα1 and 9-cis-retinoic acid receptor-α but does not affect the retinoic acid-dependent activati...
We produced transgenic mice expressing the sheep prion protein to obtain a sensitive model for sh... more We produced transgenic mice expressing the sheep prion protein to obtain a sensitive model for sheep spongiform encephalopathies (scrapie). The complete open reading frame, with alanine, arginine, and glutamine at susceptibility codons 136, 154, and 171, respectively, was inserted downstream from the neuron-specific enolase promoter. A mouse line, Tg(OvPrP4), devoid of the murine PrP gene, was obtained by crossing with PrP knockout mice. Tg(OvPrP4) mice were shown to selectively express sheep PrP in their brains, as demonstrated in mRNA and protein analysis. We showed that these mice were susceptible to infection by sheep scrapie following intracerebral inoculation with two natural sheep scrapie isolates, as demonstrated not only by the occurrence of neurological signs but also by the presence of the spongiform changes and abnormal prion protein accumulation in their brains. Mean times to death of 238 and 290 days were observed with these isolates, but the clinical course of the dis...
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Papers by Jacques Samarut