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Pierre Chambon

Publications and source records attributed to Pierre Chambon.

At least 55 records · Page 3Linked to original sources
PubMed2005

PARP-1 determines specificity in a retinoid signaling pathway via direct modulation of mediator.

We show that PARP-1 is indispensable to retinoic acid receptor (RAR)-mediated transcription from the RARbeta2 promoter in a highly purified, reconstituted transcription system and that RA-inducible expression of all RARbeta isoforms is abrogated in PARP-1(-/-) cells in vivo. Importantly, PARP-1 activity was independent of its catalytic domain. PARP-1 directly interacts with RAR and Mediator. Chromatin immunoprecipitation experiments confirmed the presence of PARP-1 and Mediator on RAR-responsive promoters in vivo. Importantly, Mediator was inactive (Cdk8+) under basal conditions but was activated (Cdk8-) upon induction. However, in PARP-1(-/-) cells, Mediator was retained in its inactive state (Cdk8+) upon induction consistent with the absence of gene expression. PARP-1 became dispensable for ligand-dependent transcription in a chromatin reconstituted transcription assay when Mediator was devoid of the Cdk8 module (CRSP). PARP-1 appears to function as a specificity factor regulating the RA-induced switch of Mediator from the inactive (Cdk8+) to the active (Cdk8-) state in RAR-dependent transcription.

Animals↗
PubMed2005

Retinoic acid controls the bilateral symmetry of somite formation in the mouse embryo.

A striking characteristic of vertebrate embryos is their bilaterally symmetric body plan, which is particularly obvious at the level of the somites and their derivatives such as the vertebral column. Segmentation of the presomitic mesoderm must therefore be tightly coordinated along the left and right embryonic sides. We show that mutant mice defective for retinoic acid synthesis exhibit delayed somite formation on the right side. Asymmetric somite formation correlates with a left-right desynchronization of the segmentation clock oscillations. These data implicate retinoic acid as an endogenous signal that maintains the bilateral synchrony of mesoderm segmentation, and therefore controls bilateral symmetry, in vertebrate embryos.

Aldehyde Oxidoreductases↗
PubMed2005

Differences in gene expression between wild type and Hoxa1 knockout embryonic stem cells after retinoic acid treatment or leukemia inhibitory factor (LIF) removal.

Homeobox (Hox) genes encode a family of transcription factors that regulate embryonic patterning and organogenesis. In embryos, alterations of the normal pattern of Hox gene expression result in homeotic transformations and malformations. Disruption of the Hoxa1 gene, the most 3' member of the Hoxa cluster and a retinoic acid (RA) direct target gene, results in abnormal ossification of the skull, hindbrain, and inner ear deficiencies, and neonatal death. We have generated Hoxa1(-/-) embryonic stem (ES) cells (named Hoxa1-15) from Hoxa1(-/-) mutant blastocysts to study the Hoxa1 signaling pathway. We have characterized in detail these Hoxa1(-/-) ES cells by performing microarray analyses, and by this technique we have identified a number of putative Hoxa-1 target genes, including genes involved in bone development (e.g. Col1a1, Postn/Osf2, and the bone sialoprotein gene or BSP), genes that are expressed in the developing brain (e.g. Nnat, Wnt3a, BDNF, RhoB, and Gbx2), and genes involved in various cellular processes (e.g. M-RAS, Sox17, Cdkn2b, LamA1, Col4a1, Foxa2, Foxq1, Klf5, and Igf2). Cell proliferation assays and Northern blot analyses of a number of ES cell markers (e.g. Rex1, Oct3/4, Fgf4, and Bmp4) suggest that the Hoxa1 protein plays a role in the inhibition of cell proliferation by RA in ES cells. Additionally, Hoxa1(-/-) ES cells express high levels of various endodermal markers, including Gata4 and Dab2, and express much less Fgf5 after leukemia inhibitory factor (LIF) withdrawal. Finally, we propose a model in which the Hoxa1 protein mediates repression of endodermal differentiation while promoting expression of ectodermal and mesodermal characteristics.

Animals↗
PubMed2005

Direct crossregulation between retinoic acid receptor {beta} and Hox genes during hindbrain segmentation.

During anteroposterior (AP) patterning of the developing hindbrain, the expression borders of many transcription factors are aligned at interfaces between neural segments called rhombomeres (r). Mechanisms regulating segmental expression have been identified for Hox genes, but for other classes of AP patterning genes there is only limited information. We have analysed the murine retinoic acid receptor beta gene (Rarb) and show that it is induced prior to segmentation, by retinoic-acid (RA) signalling from the mesoderm. Induction establishes a diffuse expression border that regresses until, at later stages, it is stably maintained at the r6/r7 boundary by inputs from Hoxb4 and Hoxd4. Separate RA- and Hox-responsive enhancers mediate the two phases of Rarb expression: a regulatory mechanism remarkably similar to that of Hoxb4. By showing that Rarb is a direct transcriptional target of Hoxb4, this study identifies a new molecular link, completing a feedback circuit between Rarb, Hoxb4 and Hoxd4. We propose that the function of this circuit is to align the initially incongruent expression of multiple RA-induced genes at a single segment boundary.

Aldehyde Oxidoreductases↗
PubMed2005

Retinoid signaling competence and RARbeta-mediated gene regulation in the developing mammalian telencephalon.

To study retinoid signaling in the developing telencephalon, we transfected a retinoid reporter gene into different regions of developing telencephalon. We found that the ventral telencephalon was more competent to retinoid signaling than the dorsal telencephalon. Moreover, among all retinoic acid receptors (RARs) and retinoid X receptors (RXRs), RARbeta was strongly induced by retinoic acid in the ventral telencephalon, suggesting that RARbeta might be involved in retinoid signaling competence. The RT-PCR analysis indicated that RARbeta was selectively expressed in the developing striatum of ventral telencephalon. We then demonstrated that null mutations of RARbeta gene resulted in reduction of striatal-enriched tyrosine phosphatase (STEP) mRNA in the striatum of RARbeta-/- mutant mice. Conversely, the gain-of-function study showed that ectopic expression of RARbeta1 in the cerebral cortex enhanced STEP expression, and the effect was RARbeta-isoform specific. Our study identified RARbeta as an important molecule for transducing retinoid signals in developing ventral telencephalon.

Animals↗
PubMed2005

Contribution of cellular retinol-binding protein type 1 to retinol metabolism during mouse development.

Within cells, retinol (ROL) is bound to cytoplasmic proteins (cellular retinol-binding proteins [CRBPs]), whose proposed function is to protect it from unspecific enzymes through channeling to retinoid-metabolizing pathways. We show that, during development, ROL and retinyl ester levels are decreased in CRBP type 1 (CRBP1) -deficient embryos and fetuses by 50% and 80%, respectively. The steady state level of retinoic acid (RA) is also decreased but to a lesser extent. However, CRBP1-null fetuses do not exhibit the abnormalities characteristic of a vitamin A-deficiency syndrome. Neither CRBP1 deficiency alters the expression patterns of RA-responding genes during development, nor does CRBP1 availability modify the expression of an RA-dependent gene in primary embryonic fibroblasts treated with ROL. Therefore, CRBP1 is required in prenatal life to maintain normal amounts of ROL and to ensure its efficient storage but seems of secondary importance for RA synthesis, at least under conditions of maternal vitamin A sufficiency.

Animals↗
PubMed2005

Temporally controlled targeted somatic mutagenesis in skeletal muscles of the mouse.

To generate temporally controlled targeted somatic mutations selectively and efficiently in skeletal muscles, we established a transgenic HSA-Cre-ER(T2) mouse line in which the expression of the tamoxifen-dependent Cre-ER(T2) recombinase is under the control of a large genomic DNA segment of the human skeletal muscle alpha-actin gene, contained in a P1-derived artificial chromosome. In this transgenic line Cre-ER(T2) is selectively expressed in skeletal muscles, and Cre-ER(T2)-mediated alteration of LoxP flanked (floxed) target genes is skeletal muscle-specific and strictly tamoxifen-dependent. HSA-Cre-ER(T2) mice should be of great value to analyze gene function in skeletal muscles, and to establish animal models of human skeletal muscle disorders.

Actins↗
PubMed2005

Mouse phenogenomics: the fast track to "systems metabolism".

With the completion of the many genomes, genetics is positioned to meet physiology. In this review, we summarize the coming of "systems metabolism" in mammals through the use of the mouse, as a model system to study metabolism. Building on mouse genetics with increasingly sophisticated clinical and molecular phenotyping strategies has enabled scientists to now tackle complex biomedical questions, such as those related to the pathogenesis of the common metabolic disorders. The ultimate goal of such strategies will be to mimic human metabolism with the click of a mouse.

Animals↗
PubMed2005

Disturbed epidermal structure in mice with temporally controlled fatp4 deficiency.

So far, little is known about the physiological role of fatty acid transport protein 4 (Fatp4, Slc27a4). Mice with a targeted disruption of the Fatp4 gene display features of a human neonatally lethal restrictive dermopathy with a hyperproliferative hyperkeratosis, a disturbed epidermal barrier, a flat dermal-epidermal junction, a reduced number of pilo-sebaceous structures, and a compact dermis, demonstrating that Fatp4 is necessary for the formation of the epidermal barrier. Because Fatp4 is widely expressed, it is unclear whether intrinsic Fatp4 deficiency in the epidermis alone can cause changes in the epidermal structure or whether the abnormalities observed are secondary to the loss of Fatp4 in other organs. To evaluate the functional role of Fatp4 in the skin, we generated a mouse line with Fatp4 deficiency inducible in the epidermis. Mice with epidermal keratinocyte-specific Fatp4 deficiency developed a hyperproliferative hyperkeratosis with a disturbed epidermal barrier. These changes resemble the histological abnormalities in the epidermis of newborn mice with total Fatp4 deficiency. We conclude that Fatp4 in epidermal keratinocytes is essential for the maintenance of a normal epidermal structure.

Animals↗
PubMed2005

Retinaldehyde dehydrogenase 2 and Hoxc8 are required in the murine brachial spinal cord for the specification of Lim1+ motoneurons and the correct distribution of Islet1+ motoneurons.

Retinoic acid (RA) activity plays sequential roles during the development of the ventral spinal cord. Here, we have investigated the functions of local RA synthesis in the process of motoneuron specification and early differentiation using a conditional knockout strategy that ablates the function of the retinaldehyde dehydrogenase 2 (Raldh2) synthesizing enzyme essentially in brachial motoneurons, and later in mesenchymal cells at the base of the forelimb. Mutant (Raldh2L-/-) embryos display an early embryonic loss of a subset of Lim1+ brachial motoneurons, a mispositioning of Islet1+ neurons and inappropriate axonal projections of one of the nerves innervating extensor limb muscles, which lead to an adult forepaw neuromuscular defect. The molecular basis of the Raldh2L-/- phenotype relies in part on the deregulation of Hoxc8, which in turn regulates the RA receptor RARbeta. We further show that Hoxc8 mutant mice, which exhibit a similar congenital forepaw defect, display at embryonic stages molecular defects that phenocopy the Raldh2L-/- motoneuron abnormalities. Thus, interdependent RA signaling and Hox gene functions are required for the specification of brachial motoneurons in the mouse.

Aldehyde Oxidoreductases↗
PubMed2005

Temporally controlled targeted somatic mutagenesis in embryonic surface ectoderm and fetal epidermal keratinocytes unveils two distinct developmental functions of BRG1 in limb morphogenesis and skin barrier formation.

Animal SWI2/SNF2 protein complexes containing either the brahma (BRM) or brahma-related gene 1 (BRG1) ATPase are involved in nucleosome remodelling and may control the accessibility of sequence-specific transcription factors to DNA. In vitro studies have indicated that BRM and BRG1 could regulate the expression of distinct sets of genes. However, as mice lacking BRM are viable and fertile, BRG1 might efficiently compensate for BRM loss. By contrast, as Brg1-null fibroblasts are viable but Brg1-null embryos die during the peri-implantation stage, BRG1 might exert cell-specific functions. To further investigate the in vivo role of BRG1, we selectively ablated Brg1 in keratinocytes of the forming mouse epidermis. We show that BRG1 is selectively required for epithelial-mesenchymal interactions in limb patterning, and during keratinocyte terminal differentiation, in which BRM can partially substitute for BRG1. By contrast, neither BRM nor BRG1 are essential for the proliferation and early differentiation of keratinocytes, which may require other ATP-dependent nucleosome-remodelling complexes. Finally, we demonstrate that cell-specific targeted somatic mutations can be created at various times during the development of mouse embryos cell-specifically expressing the tamoxifen-activatable Cre-ER(T2) recombinase.

Alleles↗
PubMed2005

Targeted somatic mutagenesis in the mouse epidermis.

The efficient introduction of somatic mutations in a given gene at a given time and in specific cell types of the skin will greatly facilitate the studies of a number of genes expressed in the skin and the production of animal models for skin diseases. We describe here strategies and techniques to create spatiotemporally controlled somatic mutations of target genes in the skin using a conditional Cre/LoxP system. They are based on cell-specific expression of the chimeric Cre recombinase Cre-ERT2, whose activity is induced by antiestrogens such as Tamoxifen (Tam), and which is obtained by fusing the Cre recombinase with a mutated ligand binding domain of the human estrogen receptor ERalpha. As an example, we present ablation of the retinoid receptor RXRalpha in epidermal basal keratinocytes of adult mice.

Animals↗
PubMed2004

Specific deletion of focal adhesion kinase suppresses tumor formation and blocks malignant progression.

We have generated mice with a floxed fak allele under the control of keratin-14-driven Cre fused to a modified estrogen receptor (CreER(T2)). 4-Hydroxy-tamoxifen treatment induced fak deletion in the epidermis, and suppressed chemically induced skin tumor formation. Loss of fak induced once benign tumors had formed inhibited malignant progression. Although fak deletion was associated with reduced migration of keratinocytes in vitro, we found no effect on wound re-epithelialization in vivo. However, increased keratinocyte cell death was observed after fak deletion in vitro and in vivo. Our work provides the first experimental proof implicating FAK in tumorigenesis, and this is associated with enhanced apoptosis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2004

Opposing actions of cellular retinol-binding protein and alcohol dehydrogenase control the balance between retinol storage and degradation.

Vitamin A homoeostasis requires the gene encoding cellular retinol-binding protein-1 (Crbp1) which stimulates conversion of retinol into retinyl esters that serve as a storage form of vitamin A. The gene encoding alcohol dehydrogenase-1 (Adh1) greatly facilitates degradative metabolism of excess retinol into retinoic acid to protect against toxic effects of high dietary vitamin A. Crbp1-/-/Adh1-/- double mutant mice were generated to explore whether the stimulatory effect of CRBP1 on retinyl ester formation is due to limitation of retinol oxidation by ADH1, and whether ADH1 limits retinyl ester formation by opposing CRBP1. Compared with wild-type mice, liver retinyl ester levels were greatly reduced in Crbp1-/- mice, but Adh1-/- mice exhibited a significant increase in liver retinyl esters. Importantly, relatively normal liver retinyl ester levels were restored in Crbp1-/-/Adh1-/- mice. During vitamin A deficiency, the additional loss of Adh1 completely prevented the excessive loss of liver retinyl esters observed in Crbp1-/- mice for the first 5 weeks of deficiency and greatly minimized this loss for up to 13 weeks. Crbp1-/- mice also exhibited increased metabolism of a dose of retinol into retinoic acid, and this increased metabolism was not observed in Crbp1-/-/Adh1-/- mice. Our findings suggest that opposing actions of CRBP1 and ADH1 enable a large fraction of liver retinol to remain esterified due to CRBP1 action, while continuously allowing some retinol to be oxidized to retinoic acid by ADH1 for degradative retinoid turnover under any dietary vitamin A conditions.

Alcohol Dehydrogenase↗
PubMed2004

Association of the transcriptional corepressor TIF1beta with heterochromatin protein 1 (HP1): an essential role for progression through differentiation.

The transcriptional intermediary factor 1beta (TIF1beta) is a corepressor for KRAB-domain-containing zinc finger proteins and is believed to play essential roles in cell physiology by regulating chromatin organization at specific loci through association with chromatin remodeling and histone-modifying activities and recruitment of heterochromatin protein 1 (HP1) proteins. In this study, we have engineered a modified embryonal carcinoma F9 cell line (TIF1beta(HP1box/-)) expressing a mutated TIF1beta protein (TIF1beta(HP1box)) unable to interact with HP1 proteins. Phenotypic analysis of TIF1beta(HP1box/-) and TIF1beta(+/-) cells shows that TIF1beta-HP1 interaction is not required for differentiation of F9 cells into primitive endoderm-like (PrE) cells on retinoic acid (RA) treatment but is essential for further differentiation into parietal endoderm-like (PE) cells on addition of cAMP and for differentiation into visceral endoderm-like cells on treatment of vesicles with RA. Complementation experiments reveal that TIF1beta-HP1 interaction is essential only during a short window of time within early differentiating PrE cells to establish a selective transmittable competence to terminally differentiate on further cAMP inducing signal. Moreover, the expression of three endoderm-specific genes, GATA6, HNF4, and Dab2, is down-regulated in TIF1beta(HP1box/-) cells compared with wild-type cells during PrE differentiation. Collectively, these data demonstrate that the interaction between TIF1beta and HP1 proteins is essential for progression through differentiation by regulating the expression of endoderm differentiation master players.

Adaptor Proteins, Signal Transducing↗
PubMed2004

TIF1delta, a novel HP1-interacting member of the transcriptional intermediary factor 1 (TIF1) family expressed by elongating spermatids.

TIF1 (transcriptional intermediary factor 1) proteins are encoded by an expanding family of developmental and physiological control genes that are conserved from flies to man. These proteins are characterized by an N-terminal RING-B box-coiled-coil (RBCC) motif and a C-terminal PHD finger/bromodomain unit, and have been implicated in epigenetic mechanisms of transcriptional repression involving histone modifiers and heterochromatin-binding proteins. We describe here the isolation and functional characterization of a fourth murine TIF1 gene, TIF1delta. The predicted TIF1delta protein displays all the structural hallmarks of a bona fide TIF1 family member and resembles the other TIF1s in that it can exert a deacetylase-dependent silencing effect when tethered to a promoter region. Moreover, like TIF1alpha and TIF1beta, TIF1delta can homodimerize and contains a PXVXL motif necessary and sufficient for HP1 (heterochromatin protein 1) binding. Although TIF1alpha and TIF1beta also bind nuclear receptors and Kruppel-associated boxes specifically and respectively, TIF1delta appears to lack nuclear receptor- and Kruppel-associated box binding activity. Furthermore, TIF1delta is unique among the TIF1 family proteins in that its expression is largely restricted to the testis and confined to haploid elongating spermatids, where it associates preferentially with HP1 isotype gamma (HP1gamma) and forms discrete foci dispersed within the centromeric chromocenter and the surrounding nucleoplasm. Collectively, these data are consistent with specific, nonredundant functions for the TIF1 family members in vivo and suggest a role for TIF1delta in heterochromatin-mediated gene silencing during postmeiotic phases of spermatogenesis.

Amino Acid Sequence↗
PubMed2004

Estrogen receptor alpha signaling in inflammatory leukocytes is dispensable for 17beta-estradiol-mediated inhibition of experimental autoimmune encephalomyelitis.

Estrogen treatment has been shown to exert a protective effect on experimental autoimmune encephalomyelitis (EAE), and is under clinical trial for multiple sclerosis. Although it is commonly assumed that estrogens exert their effect by modulating immune functions, we show in this study that 17beta-estradiol (E2) treatment can inhibit mouse EAE without affecting autoantigen-specific T cell responsiveness and type 1 cytokine production. Using mutant mice in which estrogen receptor alpha (ERalpha) has been unambiguously inactivated, we found that ERalpha was responsible for the E2-mediated inhibition of EAE. We next generated irradiation bone marrow chimeras in which ERalpha expression was selectively impaired in inflammatory T lymphocytes or was limited to the radiosensitive hemopoietic compartment. Our data show that the protective effect of E2 on clinical EAE and CNS inflammation was not dependent on ERalpha signaling in inflammatory T cells. Likewise, EAE development was not prevented by E2 treatment in chimeric mice that selectively expressed ERalpha in the systemic immune compartment. In conclusion, our data demonstrate that the beneficial effect of E2 on this autoimmune disease does not involve ERalpha signaling in blood-derived inflammatory cells, and indicate that ERalpha expressed in other tissues, such as CNS-resident microglia or endothelial cells, mediates this effect.

Animals↗