Polycomb Group-Dependent, Heterochromatin Protein 1-Independent, Chromatin Structures Silence Retrotransposons in Somatic Tissues Outside Ovaries

Somatic cells are equipped with different silencing mechanisms that protect the genome against retrotransposons. In Drosophila melanogaster, a silencing pathway implicating the argonaute protein PIWI represses retrotransposons in cells surrounding the oocyte, whereas a PIWI-independent pathway is involved in other somatic tissues. Here, we show that these two silencing mechanisms result in distinct chromatin structures. Using sensor transgenes, we found that, in somatic tissues outside of the ovaries, these transgenes adopt a heterochromatic configuration implicating hypermethylation of H3K9 and K27. We identified the Polycomb repressive complexes (PRC1 and 2), but not heterochromatin protein 1 to be necessary factors for silencing. Once established, the compact structure is stably maintained through cell divisions. By contrast, in cells where the silencing is PIWI-dependent, the transgenes display an open and labile chromatin structure. Our data suggest that a post-transcriptional gene silencing (PTGS) mechanism is responsible for the repression in the ovarian somatic cells, whereas a mechanism that couples PTGS to transcriptional gene silencing operates to silence retrotransposons in the other somatic tissues

La Piñata : opéra et forme ouverte

Cette version de la thèse a été tronquée des éléments de composition originale et de certains éléments protégés par le droit d’auteur.. Une version plus complète est disponible en ligne pour les membres de la communauté de l’Université de Montréal et peut aussi être consultée dans une des bibliothèques UdeM.Cette thèse de doctorat en composition propose de cerner les étapes qui m’ont menée à la création d’un opéra à forme ouverte nommé La Piñata. La thèse est divisée en deux parties. La première explore le concept d’œuvre à forme ouverte et les différentes déclinaisons qu’il peut engendrer. Cette exploration m’amène à définir le modèle de forme ouverte auquel j’ai fait appel dans La Piñata. La deuxième partie met en lumière les rouages de mon travail de composition. J’y présente le livret de l’opéra et les stratégies compositionnelles pour le mettre en musique. J’y élabore le concept d’objet musical, pierre angulaire de la structure musicale de l’opéra. J’aborde aussi le traitement de l’écriture vocale, la composition de l’espace signifiant et la présentation de quelques clés supplémentaires pour bien saisir mon langage musical. Cette thèse ouvre donc la voie au modèle de forme ouverte de La Piñata : une structure pouvant se développer librement, à l'image d’une toile, construite par l’ajout progressif de tableaux, qui donne lieu à une constellation d'évènements, des ruptures de ton, la représentation de différents lieux et la juxtaposition de plusieurs temporalités. Finalement, nous verrons que ce projet de recherche-création m’a permis d’entrer en contact intime avec cette forme d’art particulière qu’est l’opéra, de l’étudier, de la critiquer, d’élaborer un langage personnel grâce à l’exploration de nouvelles techniques expressives et d’affermir ma position en tant qu’artiste créatrice.This doctoral dissertation aims to define the steps leading to the creation of an open form opera titled La Piñata. The dissertation is structured in two parts. The first part explores the concept of open form and the multiple practical applications it can generate. This exploration brings me to detail the open form model I used for La Piñata. The second part highlights the workings of my compositional process, presenting the libretto and the approaches I favoured to set it to music; I develop the concept of musical objet, describing my modus operandi for vocal composition, the creation of a signifying space and proposing a few additional keys to my musical language. Therefore, this doctoral project paves the way to the open form model created for La Piñata: a structure designed to be developed freely through the gradual introduction of fragments, ultimately forming a constellation of events, allowing tonal ruptures, portraying a growing number of spaces and juxtaposing temporalities. Finally, I will highlight how this research and creation project helped me forge a close connection with the specific art form that is opera and how the study and critique of this art form helped me create a personal language, leading me to explore new expressive means and strengthening my position as an artist

Assessing Interprofessional Learning during a Student Placement in an Interprofessional Rehabilitation University Clinic in Primary Healthcare in a Canadian Francophone Minority Context

Background: Interprofessional collaboration is deemed the key to quality patient care and the future for healthcare delivery models. Such a complex competency needs to be learned; as such, interprofessional education should be a key component of health professional programs. An Interprofessional Rehabilitation University Clinic was created to promote interprofessional education at the pre-licensure level. However, few resources are currently available to assess interprofessional learning; no tool (English or French) that specifically assesses interprofessional learning could be identified.Methods and Findings: A self-administered questionnaire was developed to assess interprofessional learning during a clinical placement. Using a single-group posttest-only design, this descriptive pilot project reports the results obtained with this tool for the first 15 students on placement at the Clinic. Preliminary findings suggest this tool helped demonstrate that, during placements in an interprofessional clinic, students developed some understanding of their own profession as well as of other professions. Responses showed that participants believe that interprofessional interventions are more efficient, save time, and facilitate sharing of information leading to a better comprehension of the clients’ situations. The tool suggests that students feel that an interprofessional educational experience is beneficial for clients and for themselves.Conclusions: Assessing interprofessional learning is challenging. Although the tool developed during this project is most promising, further research is warranted to increase its usefulness in assessing interprofessional learning

Protocole d’évaluation de la sécurité à domicile (PESAD) : version francophone du SAFER-HOME v.3

Les intervenants de la santé sont appelés à se prononcer sur la sécurité des aînés vivant à domicile et ils ont, à cet effet, très peu d’outils francophones à leur disposition. Le Protocole d’évaluation de la sécurité à domicile (PESAD) est issu de la traduction et de la validation transculturelle du SAFER-HOME. Le processus de validation et l’étude de la fidélité des résultats ont mis en lumière un outil intéressant et possédant de bonnes qualités métrologiques. Il permet aux intervenants francophones d’obtenir des résultats d’évaluation complets et rigoureux relativement à la sécurité à domicile des aînés francophones.Health workers are called upon to give their opinion on the safety of elderly people living at home and they have very few French-language tools at their disposal. The Protocole d’évaluation de la sécurité à domicile (PESAD) is the result of a translation and cultural validation of SAFER-HOME. The validation process and testing of the reliability of the results suggest that PESAD is an interesting and high quality measurement tool. It enables Francophone health-care workers to obtain complete and accurate evaluation results about the home safety of elderly Francophones

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

Viral particles of the endogenous retrovirus ZAM from Drosophila melanogaster use a pre-existing endosome/exosome pathway for transfer to the oocyte

BACKGROUND: Retroviruses have evolved various mechanisms to optimize their transfer to new target cells via late endosomes. Here, we analyzed the transfer of ZAM, a retroelement from Drosophila melanogaster, from ovarian follicle cells to the oocyte at stage 9–10 of oogenesis, when an active yolk transfer is occurring between these two cell types. RESULTS: Combining genetic and microscopic approaches, we show that a functional secretory apparatus is required to tether ZAM to endosomal vesicles and to direct its transport to the apical side of follicle cells. There, ZAM egress requires an intact follicular epithelium communicating with the oocyte. When gap junctions are inhibited or yolk receptors mutated, ZAM particles fail to sort out the follicle cells. CONCLUSION: Overall, our results indicate that retrotransposons do not exclusively perform intracellular replication cycles but may usurp exosomal/endosomal traffic to be routed from one cell to another

Bystander effectors of chondrosarcoma cells irradiated at different LET impair proliferation of chondrocytes

While the dose-response relationship of radiation-induced bystander effect (RIBE) is controversial at low and high linear energy transfer (LET), mechanisms and effectors of cell-to-cell communication stay unclear and highly dependent of cell type. In the present study, we investigated the capacity of chondrocytes in responding to bystander factors released by chondrosarcoma cells irradiated at different doses (0.05 to 8 Gy) with X-rays and C-ions. Following a medium transfer protocol, cell survival, proliferation and DNA damages were quantified in bystander chondrocytes. The bystander factors secreted by chondrosarcoma cells were characterized. A significant and major RIBE response was observed in chondrocyte cells (T/C-28a2) receiving conditioned medium from chondrosarcoma cells (SW1353) irradiated with 0.1 Gy of X-rays and 0.05 Gy of C-ions, resulting in cell survivals of 36% and 62%, respectively. Micronuclei induction in bystander cells was observed from the same low doses. The cell survival results obtained by clonogenic assays were confirmed using impedancemetry. The bystander activity was vanished after a heat treatment or a dilution of the conditioned media. The cytokines which are well known as bystander factors, TNF-alpha and IL-6, were increased as a function of doses and LET according to an ELISA multiplex analysis. Together, the results demonstrate that irradiated chondrosarcoma cells can communicate stress factors to non-irradiated chondrocytes, inducing a wide and specific bystander response related to both doses and LET

Chromatin domain boundary element search tool for Drosophila

Chromatin domain boundary elements prevent inappropriate interaction between distant or closely spaced regulatory elements and restrict enhancers and silencers to correct target promoters. In spite of having such a general role and expected frequent occurrence genome wide, there is no DNA sequence analysis based tool to identify boundary elements. Here, we report chromatin domain Boundary Element Search Tool (cdBEST), to identify boundary elements. cdBEST uses known recognition sequences of boundary interacting proteins and looks for ‘motif clusters’. Using cdBEST, we identified boundary sequences across 12 Drosophila species. Of the 4576 boundary sequences identified in Drosophila melanogaster genome, >170 sequences are repetitive in nature and have sequence homology to transposable elements. Analysis of such sequences across 12 Drosophila genomes showed that the occurrence of repetitive sequences in the context of boundaries is a common feature of drosophilids. We use a variety of genome organization criteria and also experimental test on a subset of the cdBEST boundaries in an enhancer-blocking assay and show that 80% of them indeed function as boundaries in vivo. These observations highlight the role of cdBEST in better understanding of chromatin domain boundaries in Drosophila and setting the stage for comparative analysis of boundaries across closely related species

Drosophila mini-white model system: new insights into positive position effects and the role of transcriptional terminators and gypsy insulator in transgene shielding

The white gene, which is responsible for eye pigmentation, is widely used to study position effects in Drosophila. As a result of insertion of P-element vectors containing mini-white without enhancers into random chromosomal sites, flies with different eye color phenotypes appear, which is usually explained by the influence of positive/negative regulatory elements located around the insertion site. We found that, in more than 70% of cases when mini-white expression was subject to positive position effects, deletion of the white promoter had no effect on eye pigmentation; in these cases, the transposon was inserted into the transcribed regions of genes. Therefore, transcription through the mini-white gene could be responsible for high levels of its expression in most of chromosomal sites. Consistently with this conclusion, transcriptional terminators proved to be efficient in protecting mini-white expression from positive position effects. On the other hand, the best characterized Drosophila gypsy insulator was poorly effective in terminating transcription and, as a consequence, only partially protected mini-white expression from these effects. Thus, to ensure maximum protection of a transgene from position effects, a perfect boundary/insulator element should combine three activities: to block enhancers, to provide a barrier between active and repressed chromatin, and to terminate transcription