Correlation of the exon/intron organization to the conserved domains of the mouse transcriptional corepressor TIF1beta

TIF1beta, a member of the transcriptional intermediary factor 1 family, has been reported to function as a corepressor for the large class of KRAB domain-containing zinc finger proteins of the Krüppel type. In this study, we report the genomic organization and nucleotide sequence of the mouse TIF1beta gene. This gene comprises 17 coding exons located within 7 kb of genomic DNA. Exon sizes vary from 37 bp (exon 10) to 901 bp (exon 1), and intron sizes range from 71 bp to 1843 bp. All introns have the conserved GT and AG dinucleotides present at the donor and acceptor sites, respectively. The functional/homology regions of the TIF1beta protein are encoded by distinct exons. The amino-terminal RING finger is encoded by two exons interrupted by a small intron. The B boxes lie within individual exons. Similarly to the RING finger, the PHD finger is encoded by two exons. Three exons constitute the carboxy-terminal bromodomain, and their position correlates well with the secondary structure elements of the domain as predicted by computer modeling. Taken together, these results will facilitate the genetic manipulation of TIF1beta for future in vivo structure-function studies

TIF1alpha: a possible link between KRAB zinc finger proteins and nuclear receptors

International audienceLigand-induced gene activation by nuclear receptors (NRs) is thought to be mediated by transcriptional intermediary factors (TIFs), that interact with their ligand-dependent AF-2 activating domain. Included in the group of the putative AF-2 TIFs identified so far is TIF1alpha, a member of a new family of proteins which contains an N-terminal RBCC (RING finger-B boxes-coiled coil) motif and a C-terminal bromodomain preceded by a PHD finger. In addition to these conserved domains present in a number of transcriptional regulatory proteins, TIF1alpha was found to contain several protein-protein interaction sites. Of these, one specifically interacts with NRs bound to their agonistic ligand and not with NR mutants that are defective in the AF-2 activity. Immediately adjacent to this 'NR box', TIF1alpha contains an interaction site for members of the chromatin organization modifier (chromo) family, HP1alpha and MOD1, which both are heterochromatinic proteins. Finally, TIF1alpha also has a binding site for KRAB silencing domains of C2H2 zinc finger proteins. TIF1beta, another member of the TIF1 gene family, has some interacting partners in common with TIF1alpha. TIF1beta can interact with HP1alpha, MOD1 and KRAB domains, but apparently not with NRs. Both TIF1alpha and TIF1beta repress transcription when fused to a DNA binding domain in transiently transfected mammalian cells. A model discussing the potential function(s) of TIF1s in the control of transcription at the level of the chromatin template will be presented

Heterochromatin formation in mammalian cells: interaction between histones and HP1 proteins

Members of the heterochromatin protein 1 (HP1) family are silencing nonhistone proteins. Here, we show that in P19 embryonal carcinoma (EC) nuclei, HP1 alpha, beta, and gamma form homo- and heteromers associated with nucleosomal core histones. In vitro, all three HP1s bind to tailed and tailless nucleosomes and specifically interact with the histone-fold of histone H3. Furthermore, HP1alpha interacts with the linker histone H1. HP1alpha binds to H3 and H1 through its chromodomain (CD) and hinge region, respectively. Interestingly, the Polycomb (Pc1/M33) CD also interacts with H3, and HP1alpha and Pc1/M33 binding to H3 is severely impaired by CD mutations known to abrogate HP1 and Polycomb silencing in Drosophila. These results define a novel function for the conserved CD and suggest that HP1 self-association and histone binding may play a crucial role in HP1-mediated heterochromatin assembly

Cell differentiation induces TIF1beta association with centromeric heterochromatin via an HP1 interaction

International audienceThe transcriptional intermediary factor 1 (TIF1) family protein TIF1beta is a corepressor for Krüppel-associated box (KRAB)-domain-containing zinc finger proteins and plays a critical role in early embryogenesis. Here, we examined TIF1beta distribution in the nucleus of mouse embryonic carcinoma F9 cells during retinoic-acid-induced primitive endodermal differentiation. Using confocal immunofluorescence microscopy, we show that, although TIF1beta is diffusely distributed throughout the nucleoplasm of undifferentiated cells, it relocates and concentrates into distinct foci of centromeric heterochromatin in differentiated cells characterized by a low proliferation rate and a well developed cytokeratin network. This relocation was not observed in isoleucine-deprived cells, which are growth arrested, or in compound RXR alpha(-/-)/RAR gamma(-/-) null mutant cells, which are resistant to RA-induced differentiation. Amino-acid substitutions in the PxVxL motif of TIF1beta, which abolish interaction with members of the heterochromatin protein 1 (HP1) family, prevent its centromeric localization in differentiated cells. Collectively, these data provide compelling evidence for a dynamic nuclear compartmentalization of TIF1beta that is regulated during cell differentiation through a mechanism that requires HP1 interaction

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

Bonus, a Drosophila homolog of TIF1 proteins, interacts with nuclear receptors and can inhibit betaFTZ-F1-dependent transcription

The Drosophila bonus (bon) gene encodes a homolog of the vertebrate TIF1 transcriptional cofactors. bon is required for male viability, molting, and numerous events in metamorphosis including leg elongation, bristle development, and pigmentation. Most of these processes are associated with genes that have been implicated in the ecdysone pathway, a nuclear hormone receptor pathway required throughout Drosophila development. Bon is associated with sites on the polytene chromosomes and can interact with numerous Drosophila nuclear receptor proteins. Bon binds via an LxxLL motif to the AF-2 activation domain present in the ligand binding domain of betaFTZ-F1 and behaves as a transcriptional inhibitor in vivo

Conserved interaction between distinct Krüppel-associated box domains and the transcriptional intermediary factor 1 beta

The Krüppel-associated box (KRAB) domain, originally identified as a 75-aa sequence present in numerous Krüppel-type zinc-finger proteins, is a potent DNA-binding-dependent transcriptional repression domain that is believed to function through interaction with the transcriptional intermediary factor 1 (TIF1) beta. On the basis of sequence comparison and phylogenetic analysis, we have recently defined three distinct subfamilies of KRAB domains. In the present study, individual members of each subfamily were tested for transcriptional repression and interaction with TIF1 beta and two other closely related family members (TIF1 alpha and TIF1 gamma). All KRAB variants were shown, (i) to repress transcription when targeted to DNA through fusion to a heterologous DNA-binding domain in mammalian cells, and (ii) to interact specifically with TIF1 beta, but not with TIF1 alpha or TIF1 gamma. Taken together, these results implicate TIF1 beta as a common transcriptional corepressor for the three distinct subfamilies of KRAB zinc-finger proteins and suggest a high degree of conservation in the molecular mechanism underlying their transcriptional repression activity

Common properties of the nuclear body protein SP100 and the TIF1alpha chromatin factor: the role of SUMO modification

This work was supported by grants from the European Community, the Association for International Cancer Research, and the Association pour la Recherche sur le Cancer.The SP100 protein, together with PML, represents a major constituent of the PML-SP100 nuclear bodies (NBs). The function of these ubiquitous subnuclear structures, whose integrity is compromised in pathological situations such as acute promyelocytic leukemia (APL) or DNA virus infection, remains poorly understood. There is little evidence for the occurrence of actual physiological processes within NBs. The two NE proteins PML and SP100 are covalently modified by the ubiquitin-related SUMO-1 modifier, and recent work indicates that this modification is critical for the regulation of NE dynamics. In exploring the functional relationships between NBs and chromatin, we have shown previously that SP100 interacts with members of the HP1 family of nonhistone chromosomal proteins and that a variant SP100 cDNA encodes a high-mobility group (HMG1/2) protein. Here we report the isolation of a further cDNA, encoding the SP100C protein, that contains the PHD-bromodomain motif characteristic of chromatin proteins. We further show that TIF1 alpha, a chromatin-associated factor with homology to both PML and SP100C, is also modified by SUMO-1. Finally, in vitro experiments indicate that SUMO modification of SP100 enhances the stability of SP100-HP1 complexes. Taken together, our results suggest an association of SP100 and its variants with the chromatin compartment and, further, indicate that SUMO modification may play a regulatory role in the functional interplay between the nuclear bodies and chromatin.Publisher PDFPeer reviewe

Morphologic evolution of eastern Paris Basin: "ancient surfaces" and Quaternary incisions

International audienceLes investigations sur l'emplacement du laboratoire souterrain de Meuse/Haute-Marne pour évaluer sa stabilité géologique ont en grande partie contribué à réviser l'évolution géomorphologique du bassin de Paris par l'étude des paléosurfaces d'altération et des processus commandant l'érosion pendant le Quaternaire. Les travaux sur le terrain (cartographie, échantillonnage) associés aux méthodes de datations (paleomagnétisme sur des altérites, l'ESR sur les terrasses alluviales et l'U/Th TIMS sur des spéléothèmes) et combinés avec la modélisation numérique, ont été essentiels dans toutes les études. Ils ont permis de clore certains débats par la caractérisation de plusieurs paléosurfaces qui étaient jusque-là attribuées au Tertiaire, par l'identification d'ensembles de formes d'érosion fluviale dans des secteurs où elles n'avaient jamais été identifiées, par la compréhension du rôle des karsts dans l'érosion de surface. Les résultats principaux peuvent être récapitulés comme suit : 1) " la surface supérieure " se compose en fait de plusieurs surfaces d'altération, bien identifiées, qui ont été formées à diverses périodes : Crétacé inférieur et début du Tertiaire ; 2) l'évolution du paysage quaternaire est conduite par les incisions des cours d'eau et le recul des cuestas, tandis que les karsts jouent un rôle significatif mais pas déterminant ; 3) la modélisation montre qu'un soulèvement tectonique doit être pris en considération pour simuler l'incision. Ces résultats sont essentiels pour l'analyse de Géoprospective: les paléosurfaces apportent une information importante sur l'évolution géodynamique régionale à long terme, l'altération continentale et son impact sur les caractéristiques géologiques de la formation, alors que l'incision par les cours d'eau donne les éléments quantitatifs sur l'évolution récente du paysage qui permettent d'estimer des évolutions plausibles du site pendant le million d'années à venir

Morphologic evolution of eastern Paris Basin: "ancient surfaces" and Quaternary incisions

International audienceLes investigations sur l'emplacement du laboratoire souterrain de Meuse/Haute-Marne pour évaluer sa stabilité géologique ont en grande partie contribué à réviser l'évolution géomorphologique du bassin de Paris par l'étude des paléosurfaces d'altération et des processus commandant l'érosion pendant le Quaternaire. Les travaux sur le terrain (cartographie, échantillonnage) associés aux méthodes de datations (paleomagnétisme sur des altérites, l'ESR sur les terrasses alluviales et l'U/Th TIMS sur des spéléothèmes) et combinés avec la modélisation numérique, ont été essentiels dans toutes les études. Ils ont permis de clore certains débats par la caractérisation de plusieurs paléosurfaces qui étaient jusque-là attribuées au Tertiaire, par l'identification d'ensembles de formes d'érosion fluviale dans des secteurs où elles n'avaient jamais été identifiées, par la compréhension du rôle des karsts dans l'érosion de surface. Les résultats principaux peuvent être récapitulés comme suit : 1) " la surface supérieure " se compose en fait de plusieurs surfaces d'altération, bien identifiées, qui ont été formées à diverses périodes : Crétacé inférieur et début du Tertiaire ; 2) l'évolution du paysage quaternaire est conduite par les incisions des cours d'eau et le recul des cuestas, tandis que les karsts jouent un rôle significatif mais pas déterminant ; 3) la modélisation montre qu'un soulèvement tectonique doit être pris en considération pour simuler l'incision. Ces résultats sont essentiels pour l'analyse de Géoprospective: les paléosurfaces apportent une information importante sur l'évolution géodynamique régionale à long terme, l'altération continentale et son impact sur les caractéristiques géologiques de la formation, alors que l'incision par les cours d'eau donne les éléments quantitatifs sur l'évolution récente du paysage qui permettent d'estimer des évolutions plausibles du site pendant le million d'années à venir