Spatio-temporal requirements for transposable element piRNA-mediated silencing during Drosophila oogenesis

International audienceDuring Drosophila oogenesis, transposable element (TE) repression involves the Piwi-interacting RNA (piRNA) pathway which ensures genome integrity for the next generation. We developed a transgenic model to study repression of the Idefix retrotrans-poson in the germline. Using a candidate gene KD-approach, we identified differences in the spatio-temporal requirements of the piRNA pathway components for piRNA-mediated silencing. Some of them (Aub, Vasa, Spn-E) are necessary in very early stages of oogenesis within the germarium and appear to be less important for efficient TE silencing thereafter. Others (Piwi, Ago3, Mael) are required at all stages of oogenesis. Moreover, during early oogenesis, in the dividing cysts within the germarium, Idefix anti-sense transgenes escape host control, and this is associated with very low piwi expression. Silencing of P-element-based transgenes is also strongly weakened in these cysts. This region, termed the 'Piwiless pocket' or Pilp, may ensure that new TE insertions occur and are transmitted to the next generation, thereby contributing to genome dynamics. In contrast, piRNA-mediated silencing is strong in germline stem cells in which TE mobilization is tightly repressed ensuring the continued production of viable germline cysts

Functional Characteristics of a Highly Specific Integrase Encoded by an LTR-Retrotransposon

Background: The retroviral Integrase protein catalyzes the insertion of linear viral DNA into host cell DNA. Although different retroviruses have been shown to target distinctive chromosomal regions, few of them display a site-specific integration. ZAM, a retroelement from Drosophila melanogaster very similar in structure and replication cycle to mammalian retroviruses is highly site-specific. Indeed, ZAM copies target the genomic 59-CGCGCg-39 consensus-sequences. To enlighten the determinants of this high integration specificity, we investigated the functional properties of its integrase protein denoted ZAM-IN. Principal Findings: Here we show that ZAM-IN displays the property to nick DNA molecules in vitro. This endonuclease activity targets specific sequences that are present in a 388 bp fragment taken from the white locus and known to be a genomic ZAM integration site in vivo. Furthermore, ZAM-IN displays the unusual property to directly bind specific genomic DNA sequences. Two specific and independent sites are recognized within the 388 bp fragment of the white locus: the CGCGCg sequence and a closely apposed site different in sequence. Conclusion: This study strongly argues that the intrinsic properties of ZAM-IN, ie its binding properties and its endonuclease activity, play an important part in ZAM integration specificity. Its ability to select two binding sites and to nick the DNA molecule reminds the strategy used by some site-specific recombination enzymes and forms the basis for site-specifi

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Epigenetics and transgenerational inheritance

International audienceA report on the ‘Non-coding RNA, epigenetics and transgenerational inheritance’ meeting, Churchill College, Cambridge, UK, 11-12 April 2013

Rhino breaks the deadlock in Drosophila testis

International audienceIn the early 2000s, Aravin and colleagues discovered, in the Drosophila melanogaster testis, a new class of small regulatory RNAs initially named repeat-associated small interfering RNA (rasiRNAs). rasiRNAs were first described as regulating a protein-coding gene. They are derived from the Suppressor of Stellate [Su(Ste)] locus located on the Y chromosome and were shown to target the X-linked Stellate repeated genes by sequence complementarity. Stellate genes encode proteins with homology to the regulatory β subunit of the protein kinase CK2. Stellate repression occurs during male gametogenesis and is essential for male fertility. These small RNAs were renamed as PIWI-interacting RNAs (pAU : Pleasenotethat}piRNAs}hasbeendefineda iRNAs); they are 23 to 29 nucleotides (nAU : Pleasenotethat}nt}hasbeendefinedas}nucleotides}inthesentence}ThesesmallRNAswererenamed t) long and bind to proteins of the PIWI family. Accordingly, piRNA pathway mutants are sterile, and they contain crystalline aggregates of Stellate-coded protein [1]. piRNAs were then discovered in mammals and in most other animal germ cells [2]. Nowadays, we know that piRNAs are mainly devoted to protecting the genome from active mobile genetic elements in the metazoan germline. In D. melanogaster, both sexes depend on a functional piRNA pathway for their fertility. Our understanding of piRNA biogenesis and function comes predominantly from studies of the female Drosophila germline, but the male's piRNA pathway remains poorly understood. Previously, studies reported that many proteins involved in the female piRNA pathway are also required for male fertility and Stellate silencing in the testis, supporting the conservation of piRNA pathway machinery in both sexes [3]. While Aub is expressed broadly from germline stem cells (GSCs) to primary spermatocytes, Ago3 and PIWI were detected only in mitotically dividing germline cells (GSCs and spermatogonia), indicating stage-specific modulations of the piRNA pathway [4-6] (Fig 1A). The 2 most active piRNA clusters in the testis are dual strand: Su(Ste) genes and AT-chX [5,7,8]. Interestingly, Aravin's team have recently defined novel piRNA clusters in D. melanogaster spermatogenesis and show piRNAs adaptation, dependent on sex-specific expression of transposons [8]. Dualstrand piRNA clusters generally lack promoters, and their expression depends on the Rhino-Deadlock-Cutoff (RDC) complex that licenses noncanonical transcription. The RDC is anchored to H3K9me3-marked chromatin via Rhino's chromodomain. This process involves 5 0-end protection of nascent RNAs and suppression of transcription termination [9]. Importantly, since fertility in male Rhino mutants was not compromised and stellate crystals were absent, RDC function in spermatogenesis was neglected [10]. In this issue of PLOS Genetics, Chen and colleagues explored whether piRNA loci in the D. melanogaster testis use the same RDC noncanonical transcription mechanism as in the female germline [11]. Unexpectedly, a detailed examination of male fertility by sperm exhaustion assays revealed germline defects and subfertility in RDC mutant males. A careful spatiotemporal analysis showed that the RDC complex is not ovary specific. RDC assembled also in early spermatogenesis to regulate piRNA cluster expression required for an efficient transposable element (TAU : Pleasenotethat}TE}hasbeendefinedas}transposableelement}inthesentence}RDCassem E) silencing in the testis. Like in ovaries, they observed that RDC marks all dua

Construction d’une formation en ligne à visée accessible et participative pour le développement des compétences des acteurs de l’inclusion sociale des personnes handicapées

International audienceLa convention des Nations unies relative aux droits des personnes handicapées (CDPH, ONU, 2006) se confronte à des réalités, notamment le manque d'accès à la formation des personnes handicapées, qui en limitent son application. Le projet ParticipaTIC, porté par le GIFFOCH, a comme objectif de concevoir une plateforme numérique à visée accessible dans le but de déve-lopper les compétences des personnes handicapées à exercer leur droit et ainsi favoriser leur inclusion sociale. Au terme des trois années de conception et de réalisation de ce projet, une réfl exion est proposée portant sur la démarche pé-dagogique et sociale qui a été adoptée pour favoriser la participation sociale des personnes handicapées. Abstract.-Th e United Nations Convention on the Rights of Persons with Disabilities (CRPD, UN, 2006) addresses the real issues limiting their implementation , notably the lack of access to training for disabled people. Th e Par-ticipaTIC project, led by the GIFFOCH, is aimed at designing an accessible digital platform in order to develop the skills of people with disabilities with respect to exercising their rights and thus favouring their social inclusion. Th e three-year design and implementation of this project having come to an end, we wish to review the pedagogical and social approach which was adopted in order to promote the social participation of persons with disabilities

flam piRNA precursors channel from the nucleus to the cytoplasm in a temporally regulated manner along Drosophila oogenesis

International audiencePIWI-interacting RNAs (piRNAs) are the effectors of transposable element silencing in the reproductive apparatus. In Drosophila ovarian somatic cells, piRNAs arise from long RNA precursors presumably processed within cytoplasmic Yb-bodies

The Intricate Evolutionary Balance between Transposable Elements and Their Host: Who Will Kick at Goal and Convert the Next Try?

International audienceTransposable elements (TEs) are mobile DNA sequences that can jump from one genomic locus to another and that have colonized the genomes of all living organisms. TE mobilization and accumulation are an important source of genomic innovations that greatly contribute to the host species evolution. To ensure their maintenance and amplification, TE transposition must occur in the germ cell genome. As TE transposition is also a major threat to genome integrity, the outcome of TE mobility in germ cell genomes could be highly dangerous because such mutations are inheritable. Thus, organisms have developed specialized strategies to protect the genome integrity from TE transposition, particularly in germ cells. Such effective TE silencing, together with ongoing mutations and negative selection, should result in the complete elimination of functional TEs from genomes. However, TEs have developed efficient strategies for their maintenance and spreading in populations, particularly by using horizontal transfer to invade the genome of novel species. Here, we discuss how TEs manage to bypass the host’s silencing machineries to propagate in its genome and how hosts engage in a fightback against TE invasion and propagation. This shows how TEs and their hosts have been evolving together to achieve a fine balance between transposition and repression