Annuaire
2015
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Retinoic Acid Receptors Control Spermatogonia Cell-Fate and Induce Expression of the SALL4A Transcription Factor.
- Journal : PLoS Genet
- 2015
- All-trans retinoic acid (ATRA) is instrumental to male germ cell differentiation, but its mechanism of action remains elusive. To address this question, we have analyzed the phenotypes of mice lacking, in spermatogonia, all rexinoid receptors (RXRA, RXRB and RXRG) or all ATRA receptors (RARA, RARB and RARG). We demonstrate that the combined ablation of RXRA and RXRB in spermatogonia recapitulates the set of defects observed both upon ablation of RAR in spermatogonia. We also showthat ATRA activates RAR and RXR bound to a conserved regulatory region to increase expression of the SALL4A transcription factor in spermatogonia. Our results reveal that this major pluripotency gene is a target of ATRA signaling and that RAR/RXR heterodimers are the functional units driving its expression inspermatogonia. They add to the mechanisms through which ATRA promote expression of the KIT tyrosine kinase receptor to trigger a critical step in spermatogonia differentiation. Importantly, they indicate also that meiosis eventually occurs in the absence of a RAR/RXR pathway within germ cells and suggest that instructing this process is either ATRA-independent or requires an ATRA signal originating from Sertoli cells.
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Scaling, selection, and evolutionary dynamics of the mitotic spindle.
- Journal : Curr Biol
- 2015
- BACKGROUND: Cellular structures such as the nucleus, Golgi, centrioles, and spindle show remarkable diversity between species, but the mechanisms that produce these variations in cell biology are not known. RESULTS: Here we investigate the mechanisms that contribute to variations in morphology and dynamics of the mitotic spindle, which orchestrates chromosome segregation in all Eukaryotes and positions the division plane in many organisms. We use high-throughput imaging of the first division in nematodes to demonstrate that the measured effects of spontaneous mutations, combined with stabilizing selection on cell size, are sufficient to quantitatively explain both the levelsof within-species variation in the spindle and its diversity over approximately 100 million years of evolution. Furthermore, our finding of extensive within-species variation for the spindle demonstrates that there is not just one"wild-type" form, rather that cellular structures can exhibit a surprisingly broad diversity of naturally occurring behaviors. CONCLUSIONS: Our results arguethat natural selection acts predominantly on cell size and indirectly influencesthe spindle through the scaling of the spindle with cell size. Previous studies have shown that the spindle also scales with cell size during early development.Thus, the scaling of the spindle with cell size controls its variation over bothontogeny and phylogeny.
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Sequential pattern mining for discovering gene interactions and their contextual information from biomedical texts.
- Journal : J Biomed Semantics
- 2015
- BACKGROUND: Discovering gene interactions and their characterizations from biological text collections is a crucial issue in bioinformatics. Indeed, text collections are large and it is very difficult for biologists to fully take benefit from this amount of knowledge. Natural Language Processing (NLP) methodshave been applied to extract background knowledge from biomedical texts. Some ofexisting NLP approaches are based on handcrafted rules and thus are time consuming and often devoted to a specific corpus. Machine learning based NLP methods, give good results but generate outcomes that are not really understandable by a user. RESULTS: We take advantage of an hybridization of datamining and natural language processing to propose an original symbolic method toautomatically produce patterns conveying gene interactions and their characterizations. Therefore, our method not only allows gene interactions but also semantics information on the extracted interactions (e.g., modalities, biological contexts, interaction types) to be detected. Only limited resource isrequired: the text collection that is used as a training corpus. Our approach gives results comparable to the results given by state-of-the-art methods and iseven better for the gene interaction detection in AIMed. CONCLUSIONS: Experiments show how our approach enables to discover interactions and their characterizations. To the best of our knowledge, there is few methods that automatically extract the interactions and also associated semantics information. The extracted gene interactions from PubMed are available through a simple web interface at https://bingotexte.greyc.fr/. The software is available at https://bingo2.greyc.fr/?q=node/22.
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Short loop length and high thermal stability determine genomic instability induced by G-quadruplex-forming minisatellites
- Journal : The EMBO journal
- 2015
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Spen is required for pigment cell survival during pupal development in Drosophila.
- Journal : Dev Biol
- 2015
- Apoptosis is required during development to eliminate superfluous cells and sculpt tissues; spatial and timed control of apoptosis ensures that the necessary number of cells is eliminated at a precise time in a given tissue. The elimination of supernumerary pigment or inter-ommatidial cells (IOCs) depends oncell-cell communication and is necessary for the formation of the honeycomb-likestructure of the Drosophila eye. However, the mechanisms occurring during pupal development and controlling apoptosis of superfluous IOC in space and time remain unclear. Here, we found that split-ends (spen) is required for IOC survival at the time of removal of superfluous IOCs. Loss of spen function leads to abnormalremoval of IOCs by apoptosis. We show that spen is required non-autonomously in cone cells for the survival of IOCs by positively regulating the Spitz/EGFR pathway. We propose that Spen is an important survival factor that ensures spatial control of the apoptotic wave that is necessary for the correct patterning and formation of the Drosophila eye.
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Structure of Escherichia coli tryptophanase purified from an alkaline-stressed bacterial culture.
- Journal : Acta Crystallogr F Struct Biol Commun
- 2015
- Tryptophanase is a bacterial enzyme involved in the degradation of tryptophan toindole, pyruvate and ammonia, which are compounds that are essential for bacterial survival. Tryptophanase is often overexpressed in stressed cultures. Large amounts of endogenous tryptophanase were purified from Escherichia coli BL21 strain overexpressing another recombinant protein. Tryptophanase was crystallized in space group P6522 in the apo form without pyridoxal 5'-phosphatebound in the active site.
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Temperature-induced variation in gene expression burst size in metazoan cells.
- Journal : BMC Mol Biol
- 2015
- BACKGROUND: Gene expression is an inherently stochastic process, owing to its dynamic molecular nature. Protein amount distributions, which can be acquired bycytometry using a reporter gene, can inform about the mechanisms of the underlying microscopic molecular system. RESULTS: By using different clones of chicken erythroid progenitor cells harboring different integration sites of a CMV-driven mCherry protein, we investigated the dynamical behavior of such distributions. We show that, on short term, clone distributions can be quickly regenerated from small population samples with a high accuracy. On longer term, on the contrary, we show variations manifested by correlated fluctuation in the Mean Fluorescence Intensity. In search for a possible cause of this correlation,we demonstrate that in response to small temperature variations cells are able to adjust their gene expression rate: a modest (2 degrees C) increase in external temperature induces a significant down regulation of mean expression values, with a reverse effect observed when the temperature is decreased. Using a two-state model of gene expression we further demonstrate that temperature acts by modifying the size of transcription bursts, while the burst frequency of the investigated promoter is less systematically affected. CONCLUSIONS: For the first time, we report that transcription burst size is a key parameter for gene expression that metazoan cells from homeotherm animals can modify in response toan external thermal stimulus.
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The Bacteroides sp. 3_1_23 Pif1 protein is a multifunctional helicase.
- Journal : Nucleic Acids Res
- 2015
- ScPif1 DNA helicase is the prototypical member of a 5'-to-3' helicase superfamily conserved from bacteria to human and plays various roles in the maintenance of genomic homeostasis. While many studies have been performed with eukaryotic Pif1helicases, including yeast and human Pif1 proteins, the potential functions and biochemical properties of prokaryotic Pif1 helicases remain largely unknown. Here, we report the expression, purification and biochemical analysis of Pif1 helicase from Bacteroides sp. 3_1_23 (BsPif1). BsPif1 binds to a large panel of DNA substrates and, in particular, efficiently unwinds partial duplex DNAs with 5'-overhang, fork-like substrates, D-loop and flap-like substrates, suggesting that BsPif1 may act at stalled DNA replication forks and enhance Okazaki fragment maturation. Like its eukaryotic homologues, BsPif1 resolves R-loop structures and unwinds DNA-RNA hybrids. Furthermore, BsPif1 efficiently unfolds G-quadruplexes and disrupts nucleoprotein complexes. Altogether, these results highlight that prokaryotic Pif1 helicases may resolve common issues that arise during DNA transactions. Interestingly, we found that BsPif1 is different from yeast Pif1, but resembles more human Pif1 with regard to substrate specificity, helicase activity and mode of action. These findings are discussed in the context of the possible functions of prokaryotic Pif1 helicases in vivo.
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The complex pattern of epigenomic variation between natural yeast strains at single-nucleosome resolution.
- Journal : Epigenetics Chromatin
- 2015
- BACKGROUND: Epigenomic studies on humans and model species have revealed substantial inter-individual variation in histone modification profiles. However, the pattern of this variation has not been precisely characterized, particularlyregarding which genomic features are enriched for variability and whether distinct histone marks co-vary synergistically. Yeast allows us to investigate intra-species variation at high resolution while avoiding other sources of variation, such as cell type or subtype. RESULTS: We profiled histone marks H3K4me3, H3K9ac, H3K14ac, H4K12ac and H3K4me1 in three unrelated wild strains ofSaccharomyces cerevisiae at single-nucleosome resolution and analyzed inter-strain differences statistically. All five marks varied significantly at specific loci, but to different extents. The number of nucleosomes varying for agiven mark between two strains ranged from 20 to several thousands; +1 nucleosomes were significantly less subject to variation. Genes with highly evolvable or responsive expression showed higher variability; however, the variation pattern could not be explained by known transcriptional differences between the strains. Synergistic variation of distinct marks was not systematic,with surprising differences between functionally related H3K9ac and H3K14ac. Interestingly, H3K14ac differences that persisted through transient hyperacetylation were supported by H3K4me3 differences, suggesting stabilizationvia cross talk. CONCLUSIONS: Quantitative variation of histone marks among S. cerevisiae strains is abundant and complex. Its relation to functional characteristics is modular and seems modest, with partial association with gene expression divergences, differences between functionally related marks and partial co-variation between marks that may confer stability. Thus, the specificcontext of studies, such as which precise marks, individuals and genomic loci are investigated, is primordial in population epigenomics studies. The complexity found in this pilot survey in yeast suggests that high complexity can be anticipated among higher eukaryotes, including humans.
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The DREAM complex promotes gene body H2A.Z for target repression.
- Journal : Genes Dev
- 2015
- The DREAM (DP, Retinoblastoma [Rb]-like, E2F, and MuvB) complex controls cellular quiescence by repressing cell cycle genes, but its mechanism of action is poorlyunderstood. Here we show that Caenorhabditis elegans DREAM targets have an unusual pattern of high gene body HTZ-1/H2A.Z. In mutants of lin-35, the sole p130/Rb-like gene in C. elegans, DREAM targets have reduced gene body HTZ-1/H2A.Z and increased expression. Consistent with a repressive role for gene body H2A.Z,many DREAM targets are up-regulated in htz-1/H2A.Z mutants. Our results indicatethat the DREAM complex facilitates high gene body HTZ-1/H2A.Z, which plays a role in target gene repression.
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The intimate genetics of Drosophila fertilization.
- Journal : Open Biol
- 2015
- The union of haploid gametes at fertilization initiates the formation of the diploid zygote in sexually reproducing animals. This founding event of embryogenesis includes several fascinating cellular and nuclear processes, such as sperm-egg cellular interactions, sperm chromatin remodelling, centrosome formation or pronuclear migration. In comparison with other aspects of development, the exploration of animal fertilization at the functional level hasremained so far relatively limited, even in classical model organisms. Here, we have reviewed our current knowledge of fertilization in Drosophila melanogaster,with a special emphasis on the genes involved in the complex transformation of the fertilizing sperm nucleus into a replicated set of paternal chromosomes.
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The propagation of perturbations in rewired bacterial gene networks.
- Journal : Nat Commun
- 2015
- What happens to gene expression when you add new links to a gene regulatory network? To answer this question, we profile 85 network rewirings in E. coli. Here we report that concerted patterns of differential expression propagate fromreconnected hub genes. The rewirings link promoter regions to different transcription factor and sigma-factor genes, resulting in perturbations that span four orders of magnitude, changing up to approximately 70% of the transcriptome.Importantly, factor connectivity and promoter activity both associate with perturbation size. Perturbations from related rewirings have more similar transcription profiles and a statistical analysis reveals approximately 20 underlying states of the system, associating particular gene groups with rewiring constructs. We examine two large clusters (ribosomal and flagellar genes) in detail. These represent alternative global outcomes from different rewirings because of antagonism between these major cell states. This data set of systematically related perturbations enables reverse engineering and discovery of underlying network interactions.
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The role of spatial organization of cells in erythropoiesis.
- Journal : J Math Biol
- 2015
- Erythropoiesis, the process of red blood cell production, occurs mainly in the bone marrow. The functional unit of mammalian erythropoiesis, the erythroblasticisland, consists of a central macrophage surrounded by adherent erythroid progenitor cells (CFU-E/Pro-EBs) and their differentiating progeny, the erythroblasts. Central macrophages display on their surface or secrete various growth or inhibitory factors that influence the fate of the surrounding erythroid cells. CFU-E/Pro-EBs have three possible fates: (a) expansion of their numbers without differentiation, (b) differentiation into reticulocytes that are released into the blood, (c) death by apoptosis. CFU-E/Pro-EB fate is under the control of a complex molecular network, that is highly dependent upon environmental conditions in the erythroblastic island. In order to assess the functional role of space coupled with the complex network behavior in erythroblastic islands, wedeveloped hybrid discrete-continuous models of erythropoiesis. A model was developed in which cells are considered as individual physical objects, intracellular regulatory networks are modeled with ordinary differential equations and extracellular concentrations by partial differential equations. Weused the model to investigate the impact of an important difference between humans and mice in which mature late-stage erythroblasts produce the most Fas-ligand in humans, whereas early-stage erythroblasts produce the most Fas-ligand in mice. Although the global behaviors of the erythroblastic islands in both species were similar, differences were found, including a relatively slower response time to acute anemia in humans. Also, our modeling approach was very consistent with in vitro culture data, where the central macrophage in reconstituted erythroblastic islands has a strong impact on the dynamics of red blood cell production. The specific spatial organization of erythroblastic islands is key to the normal, stable functioning of mammalian erythropoiesis, both in vitro and in vivo. Our model of a simplified molecular network controlling cell decision provides a realistic functional unit of mammalian erythropoiesis that integrates multiple microenvironmental influences within theerythroblastic island with those of circulating regulators of erythropoiesis, such as EPO and glucocorticosteroids, that are produced at remote sites.
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TIF1gamma Suppresses Tumor Progression by Regulating Mitotic Checkpoints and Chromosomal Stability.
- Journal : Cancer Res
- 2015
- The transcription accessory factor TIF1gamma/TRIM33/RFG7/PTC7/Ectodermin functions as a tumor suppressor that promotes development and cellular differentiation. However, its precise function in cancer has been elusive. In the present study, we report that TIF1gamma inactivation causes cells to accumulate chromosomal defects, a hallmark of cancer, due to attenuations in the spindle assembly checkpoint and the post-mitotic checkpoint. TIF1gamma deficiency also caused a loss of contact growth inhibition and increased anchorage-independent growth in vitro and in vivo. Clinically, reduced TIF1gamma expression in human tumors correlated with an increased rate of genomic rearrangements. Overall, ourwork indicates that TIF1gamma exerts its tumor-suppressive functions in part by promoting chromosomal stability.
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Tinkering signaling pathways by gain and loss of protein isoforms: the case of the EDA pathway regulator EDARADD.
- Journal : BMC Evol Biol
- 2015
- BACKGROUND: Only a handful of signaling pathways are major actors of developmentand responsible for both the conservation and the diversification of animal morphologies. To explain this twofold nature, gene duplication and enhancer evolution were predominantly put forth as tinkering mechanisms whereas the evolution of alternative isoforms has been, so far, overlooked. We investigate here the role of gain and loss of isoforms using Edaradd, a gene of the Ecodysplasin pathway, implicated in morphological evolution. A previous study had suggested a scenario of isoform gain and loss with an alternative isoform (A) newly gained in mammals but secondarily lost in mouse lineage. RESULTS: For a comprehensive view of A and B Edaradd isoforms history during mammal evolution, we obtained sequences for both isoforms in representative mammals and performed in vitro translations to support functional predictions. We showed that the ancestral B isoform is well conserved, whereas the mammal-specific A isoform waslost at least 7 times independently in terminal lineages throughout mammal phylogeny. Then, to gain insights into the functional relevance of this evolutionary pattern, we compared the biological function of these isoforms: i) In cellulo promoter assays showed that they are transcribed from two alternativepromoters, only B exhibiting feedback regulation. ii) RT-PCR in various tissues and ENCODE data suggested that B isoform is systematically expressed whereas A isoform showed a more tissue-specific expression. iii) Both isoforms activated the NF-kappaB pathway in an in cellulo reporter assay, albeit at different levels and with different dynamics since A isoform exhibited feedback regulation at theprotein level. Finally, only B isoform could rescue a zebrafish edaradd knockdown. CONCLUSIONS: These results suggest that the newly evolved A isoform enables modulating EDA signaling in specific conditions and with different dynamics. We speculate that during mammal diversification, A isoform regulation may have evolved rapidly, accompanying and possibly supporting the diversity of ectodermal appendages, while B isoform may have ensured essential roles. This study makes the case to pay greater attention to mosaic loss of evolutionarily speaking "young" isoforms as an important mechanism underlying phenotypic diversity and not simply as a manifestation of neutral evolution.
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Transcriptomics of developing embryos and organs: A raising tool for evo-devo.
- Journal : J Exp Zool B Mol Dev Evol
- 2015
- Comparative transcriptomics has become an important tool for revisiting many evo-devo questions and exploring new ones, and its importance is likely to increase in the near future, partly because RNA-seq data open many new possibilities. The aim of this opinion piece is twofold. In the first section, we discuss the particularities of transcriptomic studies in evo-devo, focusing mainly on RNA-seq data. The preliminary processing steps (getting coding sequences as well as expression levels) are challenging, because many studied species do not have a sequenced genome. The next step (interpreting expression differences) is also challenging, due to several issues with interpreting expression levels in complex tissues, managing developmental stages and species heterochronies, and the problem of conceptualizing expression differences. In the second section, we discuss some past and possible future applications of transcriptomic approaches (using microarray or RNA-seq) to three major themes inevo-devo: the evolution of the developmental toolkit, the genetic and developmental basis for phenotypic changes, and the general rules of the evolution of development. We believe that conceptual and technical tools are necessary in order to fully exploit the richness of multispecies transcriptomic time-series data.
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Transforming Growth Factor beta/activin signalling induces epithelial cell flattening during Drosophila oogenesis.
- Journal : Biol Open
- 2015
- Although the regulation of epithelial morphogenesis is essential for the formation of tissues and organs in multicellular organisms, little is known about how signalling pathways control cell shape changes in space and time. In the Drosophila ovarian epithelium, the transition from a cuboidal to a squamous shape is accompanied by a wave of cell flattening and by the ordered remodelling of E-cadherin-based adherens junctions. We show that activation of the TGFbeta pathway is crucial to determine the timing, the degree and the dynamic of cell flattening. Within these cells, TGFbeta signalling controls cell-autonomously the formation of Actin filament and the localisation of activated Myosin II, indicating that internal forces are generated and used to remodel AJ and to promote cytoskeleton rearrangement. Our results also reveal that TGFbeta signalling controls Notch activity and that its functions are partly executed through Notch. Thus, we demonstrate that the cells that undergo the cuboidal-to-squamous transition produce active cell-shaping mechanisms, rather than passively flattening in response to a global force generated by the growth of the underlying cells. Thus, our work on TGFbeta signalling provides new insights into the mechanisms through which signal transduction cascades orchestrate cell shape changes to generate proper organ structure.
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Two bromodomain proteins functionally interact to recapitulate an essential BRDT-like function in Drosophila spermatocytes.
- Journal : Open Biol
- 2015
- In mammals, the testis-specific bromodomain and extra terminal (BET) protein BRDT is essential for spermatogenesis. In Drosophila, it was recently reported that the tBRD-1 protein is similarly required for male fertility. Interestingly, however, tBRD-1 has two conserved bromodomains in its N-terminus but it lacks anextra terminal (ET) domain characteristic of BET proteins. Here, using proteomics approaches to search for tBRD-1 interactors, we identified tBRD-2 as a novel testis-specific bromodomain protein. In contrast to tBRD-1, tBRD-2 contains a single bromodomain, but which is associated with an ET domain in its C-terminus.Strikingly, we show that tbrd-2 knock-out males are sterile and display aberrantmeiosis in a way highly similar to tbrd-1 mutants. Furthermore, these two factors co-localize and are interdependent in spermatocytes. We propose that Drosophila tBRD-1 and tBRD-2 associate into a functional BET complex in spermatocytes, which recapitulates the activity of the single mammalian BRDT-like protein.
Link to PubMed entry