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[Fertilization: the spermatic nucleus unlocked by an ultra-specialized thioredoxin].

Author(s) : Horard B, Loppin B,
Journal : Med Sci (Paris)

A helical bundle in the N-terminal domain of the BLM helicase mediates dimer and potentially hexamer formation.

Author(s) : Shi J, Chen W, Zhang B, Fan S, Ai X, Liu N, Rety S, Xi X,
Journal : J Biol Chem
Helicases play a critical role in processes such as replication or recombinationby unwinding double-stranded DNA; mutations of these genes can therefore have devastating biological consequences. In humans, mutations in genes of three members of the RecQ family helicases (blm, wrn, and recq4) give rise to three strikingly distinctive clinical phenotypes: Bloom syndrome, Werner syndrome, andRothmund-Thomson syndrome, respectively. However, the molecular basis for these varying phenotypic outcomes is unclear, in part because a full mechanistic description of helicase activity is lacking. Because the helicase core domains are highly conserved, it has been postulated that functional differences among family members might be explained by significant differences in the N-terminal domains, but these domains are poorly characterized. To help fill this gap, we now describe bioinformatics, biochemical, and structural data for three vertebrate BLM proteins. We pair high resolution crystal structures with SAXS analysis to describe an internal, highly conserved sequence we term the dimerization helical bundle in N-terminal domain (DHBN). We show that, despite the N-terminal domain being loosely structured and potentially lacking a definedthree-dimensional structure in general, the DHBN exists as a dimeric structure required for higher order oligomer assembly. Interestingly, the unwinding amplitude and rate decrease as BLM is assembled from dimer into hexamer, and also, the stable DHBN dimer can be dissociated upon ATP hydrolysis. Thus, the structural and biochemical characterizations of N-terminal domains will provide new insights into how the N-terminal domain affects the structural and functional organization of the full BLM molecule.

An miRNA-DNMT1 Axis Is Involved in Azacitidine Resistance and Predicts Survival in Higher-Risk Myelodysplastic Syndrome and Low Blast Count Acute Myeloid Leukemia.

Author(s) : Solly F, Koering C, Mohamed A, Maucort-Boulch D, Robert G, Auberger P, Flandrin-Gresta P, Ades L, Fenaux P, Kosmider O, Tavernier-Tardy E, Cornillon J, Guyotat D, Campos L, Mortreux F, Wattel E,
Journal : Clin Cancer Res
Purpose: Azacitidine inhibits DNA methyltransferases, including DNMT1, and is currently the standard of care for patients with higher-risk myelodysplastic syndrome (HRMDS) or low blast count acute myeloid leukemia (AML).Experimental Design: The expression of 754 miRNAs was compared in azacitidine-resistant and azacitidine-sensitive myelodysplastic syndrome cells. We investigated the role of differentially expressed miRNAs on DNMT1 expression and azacitidine resistance in vitro We next evaluated anti-DNMT1 miRNA expression in pretreatment bone marrow samples derived from 75 patients treated with azacitidine for HRMDS or AML.Results: Seven miRNAs, including 5 that in silico targeted the DNMT1 3' UTR,were repressed in azacitidine-resistant cells in which DNMT1 protein levels weresignificantly higher. Ectopic anti-DNMT1 miRNA expression decreased DNMT1 expression and increased azacitidine sensitivity, whereas specific inhibition ofendogenous anti-DNMT1 miRNAs increased DNMT1 expression and triggered azacitidine resistance. In patients treated with azacitidine, decreased expression of anti-DNMT1 miRNAs was associated with poor outcome. miR-126* had the strongest prognostic impact. Patients with miR-126*low myelodysplastic syndrome had significantly lower response rates (P = 0.04) and higher relapse rates (P = 0.03), as well as shorter progression-free (PFS; P = 0.004) and overall survival(OS; P = 0.004). Multivariate analysis showed that age, miR-126* expression, andrevised International Prognostic Scoring System risk independently predicted PFSand OS. In 15 patient samples collected over time, decreased miRNA expression levels were associated with secondary resistance.Conclusions: A decreased expression of anti-DNMT1 miRNAs might account for azacitidine resistance in HRMDS and AML, and measuring miRNA expression before and during treatment might help predict primary or secondary azacitidine resistance. Clin Cancer Res; 23(12); 3025-34. (c)2016 AACR.

An miRNA-DNMT1 Axis Is Involved in Azacitidine Resistance and Predicts Survival in Higher-Risk Myelodysplastic Syndrome and Low Blast Count Acute Myeloid Leukemia

Author(s) : Solly F, Koering C, Mohamed A, Maucort-Boulch D, Robert G, Auberger P, Flandrin-Gresta P, Ad?s L, Fenaux P, Kosmider O, Tavernier-Tardy E, Cornillon J, Guyotat D, Campos L, Mortreux F, Wattel E,
Journal : Clin Cancer Res

Coupling 1D modifications and 3D nuclear organization: data, models and function.

Author(s) : Jost D, Vaillant C, Meister P,
Journal : Curr Opin Cell Biol
Over the past decade, advances in molecular methods have strikingly improved theresolution at which nuclear genome folding can be analyzed. This revealed a wealth of conserved features organizing the one dimensional DNA molecule into tridimensional nuclear domains. In this review, we briefly summarize the main findings and highlight how models based on polymer physics shed light on the principles underlying the formation of these domains. Finally, we discuss the mechanistic similarities allowing self-organization of these structures and the functional importance of these in the maintenance of transcriptional programs.

Eicosapentaenoic acid modulates the synergistic action of CREB1 and ID/E2A family members in the rat pup brain and mouse embryonic stem cells.

Author(s) : Rossi M, Spichty M, Attorri L, Distante C, Nervi C, Salvati S, Vitelli L,
Journal : Biochim Biophys Acta
The aim of this study was to investigate the molecular mechanism by which eicosapentaenoic acid (EPA) may exert neuroprotective effects through an "EPA-cyclic AMP response element-binding protein (CREB)" signaling pathway. The current study reveals that EPA modulates the exquisite interplay of interaction of CREB1 with the inhibitor of DNA binding (ID) and E2A family members, thereby delivering mechanistic insights into specific neural differentiation program. Inthis scenario, our work provides evidence for the capability of CREB1 to sequester ID:E2A family members in brain tissues and neural differentiating mouse embryonic stem cells (mESCs) through formation of a [CREB1]2:ID2:E47 tetrameric complex.In essence, the molecular function of CREB1 is to dynamically regulate the location-specific assembly or disassembly of basic-helix-loop-helix (bHLH):HLH protein complexes to mediate the activation of neural/glial target genes. Together, these findings support the one-to-many binding mechanism of CREB1 and indicate that EPA treatment potentiates the integration of CREB dependent signaling with HLH/bHLH transcriptional network, adding specificity tothe CREB1-mediated gene regulation during neural/glial differentiation. Our current research on the EPA-CREB axis could reveal new molecular targets for treating neurogenerative disease.

Escherichia coli DNA polymerase I can disrupt G-quadruplex structures during DNA replication.

Author(s) : Teng F, Hou X, Fan S, Rety S, Dou S, Xi X,
Journal : FEBS J
Non-canonical four-stranded G-quadruplex (G4) DNA structures can form in G-rich sequences that are widely distributed throughout the genome. The presence of G4 structures can impair DNA replication by hindering the progress of replicative polymerases (Pols), and failure to resolve these structures can lead to genetic instability. In the present study, we combined different approaches to address the question of whether and how Escherichia coli Pol I resolves G4 obstacles during DNA replication and/or repair. We found that E. coli Pol I-catalyzed DNA synthesis could be arrested by G4 structures at low protein concentrations and the degree of inhibition was strongly dependent on the stability of the G4 structures. Interestingly, at high protein concentrations, E. coli Pol I was able to overcome some kinds of G4 obstacles without the involvement of other molecules and could achieve complete replication of G4 DNA. Mechanistic studies suggested that multiple Pol I proteins might be implicated in G4 unfolding, and the disruption of G4 structures requires energy derived from dNTP hydrolysis. The present work not only reveals an unrealized function of E. coli Pol I, but also presents a possible mechanism by which G4 structures can be resolved during DNA replication and/or repair in E. coli.

Fatty acid transport protein 1 regulates retinoid metabolism and photoreceptor development in mouse retina.

Author(s) : Cubizolle A, Guillou L, Mollereau B, Hamel C, Brabet P,
Journal : PLoS One
In retinal pigment epithelium (RPE), RPE65 catalyzes the isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol in the visual cycle and controls the rhodopsin regeneration rate. However, the mechanisms by which theseprocesses are regulated are still unclear. Fatty Acid Transport Protein 1 (FATP1) is involved in fatty acid uptake and lipid metabolism in a variety of cell types. FATP1 co-localizes with RPE65 in RPE and inhibits its isomerase activity in vitro. Here, we further investigated the role of FATP1 in the visual cycle usingtransgenic mice that overexpress human FATP1 specifically in the RPE (hFATP1TG mice). The mice displayed no delay in the kinetics of regeneration of the visualchromophore 11-cis-retinal after photobleaching and had no defects in light sensitivity. However, the total retinoid content was higher in the hFATP1TG micethan in wild type mice, and the transgenic mice also displayed an age-related accumulation (up to 40%) of all-trans-retinal and retinyl esters that was not observed in control mice. Consistent with these results, hFATP1TG mice were moresusceptible to light-induced photoreceptor degeneration. hFATP1 overexpression also induced an ~3.5-fold increase in retinosome autofluorescence, as measured by two-photon microscopy. Interestingly, hFATP1TG retina contained ~25% more photoreceptor cells and ~35% longer outer segments than wild type mice, revealing a non-cell-autonomous effect of hFATP1 expressed in the RPE. These data are the first to show that FATP1-mediated fatty acid uptake in the RPE controls both retinoid metabolism in the outer retina and photoreceptor development.

Functional link between DEAH/RHA helicase Prp43 activation and ATP base binding.

Author(s) : Robert-Paganin J, Halladjian M, Blaud M, Lebaron S, Delbos L, Chardon F, Capeyrou R, Humbert O, Henry Y, Henras A, Rety S, Leulliot N,
Journal : Nucleic Acids Res
The DEAH box helicase Prp43 is a bifunctional enzyme from the DEAH/RHA helicase family required both for the maturation of ribosomes and for lariat intron release during splicing. It interacts with G-patch domain containing proteins which activate the enzymatic activity of Prp43 in vitro by an unknown mechanism.In this work, we show that the activation by G-patch domains is linked to the unique nucleotide binding mode of this helicase family. The base of the ATP molecule is stacked between two residues, R159 of the RecA1 domain (R-motif) andF357 of the RecA2 domain (F-motif). Using Prp43 F357A mutants or pyrimidine nucleotides, we show that the lack of stacking of the nucleotide base to the F-motif decouples the NTPase and helicase activities of Prp43. In contrast the R159A mutant (R-motif) showed reduced ATPase and helicase activities. We show that the Prp43 R-motif mutant induces the same phenotype as the absence of the G-patch protein Gno1, strongly suggesting that the processing defects observed in the absence of Gno1 result from a failure to activate the Prp43 helicase. Overall we propose that the stacking between the R- and F-motifs and the nucleotide baseis important for the activity and regulation of this helicase family.

Genome evolution is driven by gene expression-generated biophysical constraints through RNA-directed genetic variation: A hypothesis

Author(s) : Auboeuf D,
Journal : Bioessays

Genomic regions controlling shape variation in the first upper molar of the house mouse.

Author(s) : Pallares L, Ledevin R, Pantalacci S, Turner L, Steingrimsson E, Renaud S,
Journal : Elife
Numerous loci of large effect have been shown to underlie phenotypic variation between species. However, loci with subtle effects are presumably more frequently involved in microevolutionary processes but have rarely been discovered. We explore the genetic basis of shape variation in the first upper molar of hybrid mice between Mus musculus musculus and M. m. domesticus. We performed the first genome-wide association study for molar shape and used 3D surface morphometrics to quantify subtle variation between individuals. We show that many loci of small effect underlie phenotypic variation, and identify five genomic regions associated with tooth shape; one region contained the gene microphthalmia-associated transcription factor Mitf that has previously been associated with tooth malformations. Using a panel of five mutant laboratory strains, we show the effect of the Mitf gene on tooth shape. This is the first report of a gene causing subtle but consistent variation in tooth shape resembling variation in nature.

HBZ-mediated shift of JunD from growth suppressor to tumor promoter in leukemic cells by inhibition of ribosomal protein S25 expression.

Author(s) : Terol M, Gazon H, Lemasson I, Duc-Dodon M, Barbeau B, Cesaire R, Mesnard J, Peloponese J,
Journal : Leukemia
Human T-cell leukemia virus type 1 (HTLV-1) basic-leucine zipper (bZIP) factor (HBZ) is a key player in proliferation and transformation of HTLV-1-infected cells, thus contributing to adult T-cell leukemia (ATL) development. HBZ deregulates gene expression within the host cell by interacting with several cellular partners. Through its C-terminal ZIP domain, HBZ is able to contact andactivate JunD, a transcription factor of the AP-1 family. JunD mRNA is intronless but can generate two protein isoforms by alternative translation initiation: JunD full-length and Delta JunD, an N-terminal truncated form unresponsive to the tumor suppressor menin. Using various cell lines and primary T-lymphocytes, we show that after serum deprivation HBZ induces the expression of Delta JunD isoform. We demonstrate that, unlike JunD, Delta JunD induces proliferation and transformation of cells. To decipher the mechanisms for Delta JunD production, we looked into the translational machinery and observed that HBZ induces nuclear retention of RPS25 mRNA and loss of RPS25 protein expression, a component of thesmall ribosomal subunit. Therefore, HBZ bypasses translational control of JunD uORF and favors the expression of Delta JunD. In conclusion, we provide strong evidences that HBZ induces Delta JunD expression through alteration of the cellular translational machinery and that the truncated isoform Delta JunD has acentral role in the oncogenic process leading to ATL.Leukemia advance online publication, 24 March 2017; doi:10.1038/leu.2017.74.

HTLV-1-induced leukotriene B4 secretion by T cells promotes T cell recruitment and virus propagation.

Author(s) : Percher F, Curis C, Peres E, Artesi M, Rosewick N, Jeannin P, Gessain A, Gout O, Mahieux R, Ceccaldi P, Van den Broeke A, Duc Dodon M, Afonso P,
Journal : Nat Commun
The human T-lymphotropic virus type 1 (HTLV-1) is efficiently transmitted through cellular contacts. While the molecular mechanisms of viral cell-to-cell propagation have been extensively studied in vitro, those facilitating the encounter between infected and target cells remain unknown. In this study, we demonstrate that HTLV-1-infected CD4 T cells secrete a potent chemoattractant, leukotriene B4 (LTB4). LTB4 secretion is dependent on Tax-induced transactivation of the pla2g4c gene, which encodes the cytosolic phospholipase A2 gamma. Inhibition of LTB4 secretion or LTB4 receptor knockdown on target cells reduces T-cell recruitment, cellular contact formation and virus propagation in vitro. Finally, blocking the synthesis of LTB4 in a humanized mouse model of HTLV-1 infection significantly reduces proviral load. This results from a decrease in the number of infected clones while their expansion is not impaired. This study shows the critical role of LTB4 secretion in HTLV-1 transmission both in vitro and in vivo.

IC-Finder: inferring robustly the hierarchical organization of chromatin folding.

Author(s) : Haddad N, Vaillant C, Jost D,
Journal : Nucleic Acids Res
The spatial organization of the genome plays a crucial role in the regulation ofgene expression. Recent experimental techniques like Hi-C have emphasized the segmentation of genomes into interaction compartments that constitute conserved functional domains participating in the maintenance of a proper cell identity. Here, we propose a novel method, IC-Finder, to identify interaction compartments(IC) from experimental Hi-C maps. IC-Finder is based on a hierarchical clustering approach that we adapted to account for the polymeric nature of chromatin. Basedon a benchmark of realistic in silico Hi-C maps, we show that IC-Finder is one of the best methods in terms of reliability and is the most efficient numerically. IC-Finder proposes two original options: a probabilistic description of the inferred compartments and the possibility to explore the various hierarchies of chromatin organization. Applying the method to experimental data in fly and human, we show how the predicted segmentation may depend on the normalization scheme and how 3D compartmentalization is tightly associated with epigenomic information. IC-Finder provides a robust and generic 'all-in-one' tool to uncover the general principles of 3D chromatin folding and their influence on gene regulation. The software is available at

Identification of Nascent Memory CD8 T Cells and Modeling of Their Ontogeny.

Author(s) : Crauste F, Mafille J, Boucinha L, Djebali S, Gandrillon O, Marvel J, Arpin C,
Journal : Cell Syst
Primary immune responses generate short-term effectors and long-term protective memory cells. The delineation of the genealogy linking naive, effector, and memory cells has been complicated by the lack of phenotypes discriminating effector from memory differentiation stages. Using transcriptomics and phenotypic analyses, we identify Bcl2 and Mki67 as a marker combination that enables the tracking of nascent memory cells within the effector phase. We then use a formalapproach based on mathematical models describing the dynamics of population sizeevolution to test potential progeny links and demonstrate that most cells followa linear naive-->early effector-->late effector-->memory pathway. Moreover, our mathematical model allows long-term prediction of memory cell numbers from a fewearly experimental measurements. Our work thus provides a phenotypic means to identify effector and memory cells, as well as a mathematical framework to investigate their genealogy and to predict the outcome of immunization regimens in terms of memory cell numbers generated.

Identification of protein features encoded by alternative exons using Exon Ontology.

Author(s) : Tranchevent L, Aube F, Dulaurier L, Benoit-Pilven C, Rey A, Poret A, Chautard E, Mortada H, Desmet F, Chakrama F, Moreno-Garcia M, Goillot E, Janczarski S, Mortreux F, Bourgeois C, Auboeuf D,
Journal : Genome Res
Transcriptomic genome-wide analyses demonstrate massive variation of alternativesplicing in many physiological and pathological situations. One major challenge is now to establish the biological contribution of alternative splicing variation in physiological- or pathological-associated cellular phenotypes. Toward this end, we developed a computational approach, named "Exon Ontology," based on terms corresponding to well-characterized protein features organized in an ontology tree. Exon Ontology is conceptually similar to Gene Ontology-based approaches but focuses on exon-encoded protein features instead of gene level functional annotations. Exon Ontology describes the protein features encoded by a selected list of exons and looks for potential Exon Ontology term enrichment. By applyingthis strategy to exons that are differentially spliced between epithelial and mesenchymal cells and after extensive experimental validation, we demonstrate that Exon Ontology provides support to discover specific protein features regulated by alternative splicing. We also show that Exon Ontology helps to unravel biological processes that depend on suites of coregulated alternative exons, as we uncovered a role of epithelial cell-enriched splicing factors in the AKT signaling pathway and of mesenchymal cell-enriched splicing factors in driving splicing events impacting on autophagy. Freely available on the web, Exon Ontology is the first computational resource that allows getting a quick insightinto the protein features encoded by alternative exons and investigating whethercoregulated exons contain the same biological information.

Identification of protein features encoded by alternative exons using Exon Ontology

Author(s) : Tranchevent L, Aub? F, Dulaurier L, Benoit-Pilven C, Rey A, Poret A, Chautard E, Mortada H, Desmet F, Chakrama F, Moreno-Garcia M, Goillot E, Janczarski S, Mortreux F, Bourgeois C, Auboeuf D,
Journal : Genome Res

Inferring gene regulatory networks from single-cell data: a mechanistic approach

Author(s) : Herbach U, Bonnaffoux A, Espinasse T, Gandrillon O,
Journal : BMC Syst Biol

Integrated time-lapse and single-cell transcription studies highlight the variable and dynamic nature of human hematopoietic cell fate commitment

Author(s) : Moussy A, Cosette J, Parmentier R, da Silva C, Corre G, Richard A, Gandrillon O, Stockholm D, ldi A,
Journal : PLoS Biol

Maternal age generates phenotypic variation in Caenorhabditis elegans.

Author(s) : Perez M, Francesconi M, Hidalgo-Carcedo C, Lehner B,
Journal : Nature
Genetically identical individuals that grow in the same environment often show substantial phenotypic variation within populations of organisms as diverse as bacteria, nematodes, rodents and humans. With some exceptions, the causes are poorly understood. Here we show that isogenic Caenorhabditis elegans nematodes vary in their size at hatching, speed of development, growth rate, starvation resistance, fecundity, and also in the rate of development of their germline relative to that of somatic tissues. We show that the primary cause of this variation is the age of an individual's mother, with the progeny of young mothers exhibiting several phenotypic impairments. We identify age-dependent changes in the maternal provisioning of the lipoprotein complex vitellogenin to embryos as the molecular mechanism that underlies the variation in multiple traits throughout the life of an animal. The production of sub-optimal progeny by youngmothers may reflect a trade-off between the competing fitness traits of a short generation time and the survival and fecundity of the progeny.

Mechanical constraint from growing jaw facilitates mammalian dental diversity.

Author(s) : Renvoise E, Kavanagh K, Lazzari V, Hakkinen T, Rice R, Pantalacci S, Salazar-Ciudad I, Jernvall J,
Journal : Proc Natl Acad Sci U S A
Much of the basic information about individual organ development comes from studies using model species. Whereas conservation of gene regulatory networks across higher taxa supports generalizations made from a limited number of species, generality of mechanistic inferences remains to be tested in tissue culture systems. Here, using mammalian tooth explants cultured in isolation, we investigate self-regulation of patterning by comparing developing molars of the mouse, the model species of mammalian research, and the bank vole. A distinct patterning difference between the vole and the mouse molars is the alternate cusp offset present in the vole. Analyses of both species using 3D reconstructions ofdeveloping molars and jaws, computational modeling of cusp patterning, and toothexplants cultured with small braces show that correct cusp offset requires constraints on the lateral expansion of the developing tooth. Vole molars cultured without the braces lose their cusp offset, and mouse molars cultured with the braces develop a cusp offset. Our results suggest that cusp offset, which changes frequently in mammalian evolution, is more dependent on the 3D support of the developing jaw than other aspects of tooth shape. This jaw-tooth integration of a specific aspect of the tooth phenotype indicates that organs may outsource specific aspects of their morphology to be regulated by adjacent body parts or organs. Comparative studies of morphologically different species are needed to infer the principles of organogenesis.

microRNAs stimulate translation initiation mediated by HCV-like IRESes.

Author(s) : Mengardi C, Limousin T, Ricci E, Soto-Rifo R, Decimo D, Ohlmann T,
Journal : Nucleic Acids Res
MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression by recognizing and hybridizing to a specific sequence generally located in the 3 untranslated region (UTR) of targeted mRNAs. miRNA-induced inhibition of translation occurs during the initiation step, most probably at the level of ribosome scanning. In this process, the RNA-induced silencing complex interacts both with PABP and the 43S pre-initiation complex to disrupt scanning of the 40Sribosome. However, in some specific cases, miRNAs can stimulate translation. Although the mechanism of miRNA-mediated upregulation is unknown, it appears that the poly(A) tail and the lack of availability of the TNRC6 proteins are amongst major determinants. The genomic RNA of the Hepatitis C Virus is uncapped, non-polyadenylated and harbors a peculiar internal ribosome entry site (IRES) that binds the ribosome directly to the AUG codon. Thus, we have exploited the unique properties of the HCV IRES and other related IRESes (HCV-like) to study how translation initiation can be modulated by miRNAs on these elements. Here, we report that miRNA binding to the 3 UTR can stimulate translation of a reporter gene given that its expression is driven by an HCV-like IRES and that it lacks apoly(A) tail at its 3 extremity.

Multi-invasions are recombination byproducts that induce chromosomal rearrangements

Author(s) : Piazza A, Wright W, Heyer W,
Journal : Cell
Inaccurate repair of broken chromosomes generates structural variants that can fuel evolution and inflict pathology. We describe a novel rearrangement mechanism in which translocation between intact chromosomes is induced by a lesion on a third chromosome. This multi-invasion-induced rearrangement (MIR) stems from a homologous recombination byproduct, where a broken DNA end simultaneously invades two intact donors. No homology is required between the donors, and the intervening sequence from the invading molecule is inserted at the translocation site. MIR is stimulated by increasing homology length and spatial proximity of the donors, and depends on the overlapping activities of the structure-selective endonucleases Mus81-Mms4, Slx1-Slx4, and Yen1. Conversely, the 3’-flap nuclease Rad1-Rad10 and enzymes known to disrupt recombination intermediates (Sgs1-Top3-Rmi1, Srs2 and Mph1) inhibit MIR. Resolution of MIR intermediates propagates secondary chromosome breaks that frequently cause additional rearrangements. MIR features have implications for the formation of simple and complex rearrangements underlying human pathologies.

Nerve Growth Factor Signaling from Membrane Microdomains to the Nucleus: Differential Regulation by Caveolins.

Author(s) : Spencer A, Yu L, Guili V, Reynaud F, Ding Y, Ma J, Jullien J, Koubi D, Gauthier E, Cluet D, Falk J, Castellani V, Yuan C, Rudkin B,
Journal : Int J Mol Sci
Membrane microdomains or "lipid rafts" have emerged as essential functional modules of the cell, critical for the regulation of growth factor receptor-mediated responses. Herein we describe the dichotomy between caveolin-1and caveolin-2, structural and regulatory components of microdomains, in modulating proliferation and differentiation. Caveolin-2 potentiates while caveolin-1 inhibits nerve growth factor (NGF) signaling and subsequent cell differentiation. Caveolin-2 does not appear to impair NGF receptor trafficking but elicits prolonged and stronger activation of MAPK (mitogen-activated proteinkinase), Rsk2 (ribosomal protein S6 kinase 2), and CREB (cAMP response element binding protein). In contrast, caveolin-1 does not alter initiation of the NGF signaling pathway activation; rather, it acts, at least in part, by sequesteringthe cognate receptors, TrkA and p75NTR, at the plasma membrane, together with the phosphorylated form of the downstream effector Rsk2, which ultimately prevents CREB phosphorylation. The non-phosphorylatable caveolin-1 serine 80 mutant (S80V), no longer inhibits TrkA trafficking or subsequent CREB phosphorylation. MC192, a monoclonal antibody towards p75NTR that does not block NGF binding, prevents exit of both NGF receptors (TrkA and p75NTR) from lipid rafts. The results presented herein underline the role of caveolin and receptor signaling complex interplay in the context of neuronal development and tumorigenesis.

Non-Canonical G-quadruplexes cause the hCEB1 minisatellite instability in Saccharomyces cerevisiae

Author(s) : Piazza A, Cui X, Adrian M, Samazan F, Heddi B, Phan A, Nicolas A,
Journal : Elife
G-quadruplexes (G4) are polymorphic four-stranded structures formed by certain G-rich nucleic acids in vitro, but the sequence and structural features dictating their formation and function in vivo remains uncertain. Here we report a structure-function analysis of the complex hCEB1 G4-forming sequence. We isolated four G4 conformations in vitro, all of which bear unusual structural features: Form 1 bears a V-shaped loop and a snapback guanine; Form 2 contains a terminal G-triad; Form 3 bears a zero-nucleotide loop; and Form 4 is a zero-nucleotide loop monomer or an interlocked dimer. In vivo, Form 1 and Form 2 differently account for 2/3rd of the genomic instability of hCEB1 in two G4-stabilizing conditions. Form 3 and an unidentified form contribute to the remaining instability, while Form 4 has no detectable effect. This work underscores the structural polymorphisms originated from a single highly G-rich sequence and demonstrates the existence of non-canonical G4s in cells, thus broadening the definition of G4-forming sequences.

p53-dependent programmed necrosis controls germ cell homeostasis during spermatogenesis.

Author(s) : Napoletano F, Gibert B, Yacobi-Sharon K, Vincent S, Favrot C, Mehlen P, Girard V, Teil M, Chatelain G, Walter L, Arama E, Mollereau B,
Journal : PLoS Genet
The importance of regulated necrosis in pathologies such as cerebral stroke and myocardial infarction is now fully recognized. However, the physiological relevance of regulated necrosis remains unclear. Here, we report a conserved role for p53 in regulating necrosis in Drosophila and mammalian spermatogenesis. We found that Drosophila p53 is required for the programmed necrosis that occurs spontaneously in mitotic germ cells during spermatogenesis. This form of necrosis involved an atypical function of the initiator caspase Dronc/Caspase 9, independent of its catalytic activity. Prevention of p53-dependent necrosis resulted in testicular hyperplasia, which was reversed by restoring necrosis in spermatogonia. In mouse testes, p53 was required for heat-induced germ cell necrosis, indicating that regulation of necrosis is a primordial function of p53conserved from invertebrates to vertebrates. Drosophila and mouse spermatogenesis will thus be useful models to identify inducers of necrosis to treat cancers that are refractory to apoptosis.

Perspectives: Using polymer modeling to understand the formation and function of nuclear compartments

Author(s) : Haddad N, Jost D, Vaillant C,
Journal : Chromosome Research

Recombination, meiotic expression and human codon usage.

Author(s) : Pouyet F, Mouchiroud D, Duret L, Semon M,
Journal : Elife
Synonymous codon usage (SCU) varies widely among human genes. In particular, genes involved in different functional categories display a distinct codon usage, which was interpreted as evidence that SCU is adaptively constrained to optimizetranslation efficiency in distinct cellular states. We demonstrate here that SCUis not driven by constraints on tRNA abundance, but by large-scale variation in GC-content, caused by meiotic recombination, via the non-adaptive process of GC-biased gene conversion (gBGC). Expression in meiotic cells is associated witha strong decrease in recombination within genes. Differences in SCU among functional categories reflect differences in levels of meiotic transcription, which is linked to variation in recombination and therefore in gBGC. Overall, the gBGC model explains 70% of the variance in SCU among genes. We argue that the strong heterogeneity of SCU induced by gBGC in mammalian genomes precludes any optimization of the tRNA pool to the demand in codon usage.