Imprinted MicroRNA Gene Clusters in the Evolution, Development, and Functions of Mammalian Placenta

In mammals, the expression of a subset of microRNA (miRNA) genes is governed by genomic imprinting, an epigenetic mechanism that confers monoallelic expression in a parent-of-origin manner. Three evolutionarily distinct genomic intervals contain the vast majority of imprinted miRNA genes: the rodent-specific, paternally expressed C2MC located in intron 10 of the Sfmbt2 gene, the primate-specific, paternally expressed C19MC positioned at human Chr.19q13.4 and the eutherian-specific, maternally expressed miRNAs embedded within the imprinted Dlk1-Dio3 domains at human 14q32 (also named C14MC in humans). Interestingly, these imprinted miRNA genes form large clusters composed of many related gene copies that are co-expressed with a marked, or even exclusive, localization in the placenta. Here, we summarize our knowledge on the evolutionary, molecular, and physiological relevance of these epigenetically-regulated, recently-evolved miRNAs, by focusing on their roles in placentation and possibly also in pregnancy diseases (e.g., preeclampsia, intrauterine growth restriction, preterm birth)

Rôle du Segment d'entrée interne des ribosomes dans la neurovirulence du Poliovirus (corrélation entre les propriétés biologiques et la structure de l'ARN)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Bornavirus

International audienc

Analyse du transport intracellulaire du bornavirus

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Bornavirus et cellules cibles : une amitié presque sincère

International audienceViruses have to meet the challenge to cope with the limited capacity of renewal of neuronal cells in order to allow their replication and persistence in the central nervous system (CNS). Accordingly, many neurotropic viruses establish latency to optimize their maintenance in the CNS. Bornaviruses have evolved a different and original strategy to persist in neurons, which involves an active replication without associated cytopathic effect. Despite their small genomes and limited number of proteins, bornaviruses hijack multiple signaling pathways, leading to escape from immune surveillance or protection of cells against apoptosis. Long term persistence has even led to integration of genome elements within the host cell genome, leading to "fossil bornaviruses" in a wide range of vertebrate species. Hence, bornaviruses represent the ideal host-cell adaptation example and can thus be considered as the "best enemy" for its hosts.Se répliquer et persister au sein du système nerveux central (SNC) présente de nombreuses contraintes pour les virus, étant donnée la faible capacité de renouvellement des neurones. De ce fait, beaucoup de virus neurotropes entrent dans une phase de latence et persistent ainsi efficacement. Les bornavirus ont développé une stratégie différente et originale de persistance dans les neurones, au sein desquels ils se répliquent activement sans entraîner d'effet cytopathique. En dépit du petit nombre de protéines qu'ils expriment, les bornavirus détournent de multiples voies de signalisation cellulaires, leur permettant d'échapper à la réponse immune de l'hôte ou de conférer une résistance cellulaire à l'apoptose. La persistance à long terme du bornavirus conduit même parfois à l'intégration d'éléments de son génome dans le génome cellulaire et des « bornavirus fossiles » sont ainsi retrouvés dans un très grand nombre de génomes de vertébrés. Les bornavirus sont donc un exemple d'adaptation parfaite entre un virus et sa cellule cible, faisant d'eux les « meilleurs ennemis » de leurs hôte

Poliovirus Internal Ribosome Entry Segment Structure Alterations That Specifically Affect Function in Neuronal Cells: Molecular Genetic Analysis

Translation of poliovirus RNA is driven by an internal ribosome entry segment (IRES) present in the 5′ noncoding region of the genomic RNA. This IRES is structured into several domains, including domain V, which contains a large lateral bulge-loop whose predicted secondary structure is unclear. The primary sequence of this bulge-loop is strongly conserved within enteroviruses and rhinoviruses: it encompasses two GNAA motifs which could participate in intrabulge base pairing or (in one case) could be presented as a GNRA tetraloop. We have begun to address the question of the significance of the sequence conservation observed among enterovirus reference strains and field isolates by using a comprehensive site-directed mutagenesis program targeted to these two GNAA motifs. Mutants were analyzed functionally in terms of (i) viability and growth kinetics in both HeLa and neuronal cell lines, (ii) structural analyses by biochemical probing of the RNA, and (iii) translation initiation efficiencies in vitro in rabbit reticulocyte lysates supplemented with HeLa or neuronal cell extracts. Phenotypic analyses showed that only viruses with both GNAA motifs destroyed were significantly affected in their growth capacities, which correlated with in vitro translation defects. The phenotypic defects were strongly exacerbated in neuronal cells, where a temperature-sensitive phenotype could be revealed at between 37 and 39.5°C. Biochemical probing of mutated domain V, compared to the wild type, demonstrated that such mutations lead to significant structural perturbations. Interestingly, revertant viruses possessed compensatory mutations which were distant from the primary mutations in terms of sequence and secondary structure, suggesting that intradomain tertiary interactions could exist within domain V of the IRES

Effects of vaccine strain mutations in domain V of the internal ribosome entry segment compared in the wild type poliovirus type 1 context.

Initiation of poliovirus (PV) protein synthesis is governed by an internal ribosome entry segment structured into several domains including domain V, which is accepted to be important in PV neurovirulence because it harbors an attenuating mutation in each of the vaccine strains developed by A. Sabin. To better understand how these single point mutations exert their effects, we placed each of them into the same genomic context, that of PV type 1. Only the mutation equivalent to the Sabin type 3 strain mutation resulted in significantly reduced viral growth both in HeLa and neuroblastoma cells. This correlated with poor translation efficiency in vitro and could be explained by a structural perturbation of the domain V of the internal ribosome entry segment, as evidenced by RNA melting experiments. We demonstrated that reduced cell death observed during infection by this mutant is due to the absence of inhibition of host cell translation. We confirmed that this shut-off is correlated principally with cleavage of eIF4GII and not eIF4GI and that this cleavage is significantly impaired in the case of the defective mutant. These data support the previously reported conclusion that the 2A protease has markedly different affinities for the two eIF4G isoforms

Heterodimerization with Jun Family Members Regulates c-Fos Nucleocytoplasmic Traffic

International audienc

Heterodimerization with different Jun proteins controls c-Fos intranuclear dynamics and distribution.

International audienceThe c-Fos proto-oncogenic transcription factor defines a multigene family controlling many processes both at the cell and the whole organism level. To bind to its target AP-1/TRE or CRE DNA sequences in gene promoters and exert its transcriptional part, c-Fos must heterodimerize with other bZip proteins, its best studied partners being the Jun proteins (c-Jun, JunB and JunD). c-Fos expression is regulated at many transcriptional and post-transcriptional levels. Yet, little is known on how its localization is dynamically regulated in the cell. We have investigated here its intranuclear mobility using FRAP-, genetic- and biochemical approaches. Whereas monomeric c-Fos is highly mobile and distributed evenly with nucleolar exclusion in the nucleus, heterodimerization with c-Jun entails intranuclear redistribution and dramatic reduction in mobility of c-Fos due to predominant association with the nuclear matrix independently of any binding to AP-1/TRE or CRE sequences. In contrast to c-Jun, dimerization with JunB does not detectably affect c-Fos mobility. However, dimerization with JunB affects intranuclear distribution with significant differences in the localization of c-Fos:c-Jun and c-Fos:JunB dimers. Moreover, c-Jun and JunB exert comparable effects on another Fos family member, Fra-1. Thus, we report a novel regulation, i.e. differentially regulated intranuclear mobility and distribution of Fos proteins by their Jun partners, and suggest the existence of intranuclear storage sites for latent c-Fos:c-Jun AP-1 complexes. This may affect the numerous physiopathological functions these transcription factors control