Long terminal repeat (LTR) retrotransposons account for approximately 10% of mouse and 8% of human genomes and may play a role in modifying gene expression. Many species harbor retrotransposon families encompassing both autonomous and non-autonomous members. Specifically, the mouse Early Transposon (ETn) family members lack all retroviral genes but are transcriptionally and retrotranspositionally active, causing over 20 known insertional germline mutations. ETns owe their retrotransposition potential to proteins encoded by structurally intact MusD retrotransposons with whom they share LTRs. ETn elements are transcribed at a much higher level than MusD retrotransposons in embryos and undifferentiated cells, suggesting their evasion of host restriction mechanisms. However, mechanisms responsible for the replicative success of non-autonomous retrotransposon subfamilies over their coding-competent relatives are poorly understood. In the first stage of my research, I analyzed regulatory sequences in an ETn LTR responsible for its high promoter activity in the undifferentiated cell line P19. I found that three GC-boxes that may function as Sp1/Sp3 binding sites act synergistically and are indispensable for undifferentiated cell-specific promoter activity of the LTR. Sp1 binding partners may be responsible for the restricted ETn expression. Moreover, I have shown that unlike many retroviruses, ETn elements possess multiple transcription initiation sites and that they have amplified via intracellular retrotransposition in the P19 teratocarcinoma cell line. In the next step of my research, I performed analysis of epigenetic mechanisms as a means of ERV suppression. Specifically, I showed that in embryonic stem cells, autonomous MusD retrotransposons are epigenetically suppressed to a greater degree than non-autonomous ETn retrotransposons, illustrated by a higher level of DNA methylation and a lower level of active histone modifications. I hypothesize that MusD elements may be silenced by DNA methylation and repressive chromatin spreading into the LTR from the CpG-rich internal retroviral sequence absent in ETn elements. I propose that internal structure largely devoid of high CG content enables ETn elements to evade host-imposed transcriptional repression, contributing to their high mutagenic activity in the mouse germline. / Medicine, Faculty of / Medical Genetics, Department of / Graduate

Au cours de la dernière décennie, les avancées du séquençage à haut débit ont permis de caractériser un grand nombre d’ARN non codant et d’établir l’existence de transcrits “antisens” pour de nombreux gènes chez les mammifères. Cependant leur rôle dans le contrôle de l’expression des gènes “sens” auxquels ils sont associés est encore très mal connu. Mes travaux ont porté sur la caractérisation de certains aspects du mécanisme d’action des longs ARN non codants. Ils reposent sur le développement d’une approche de constructions indicatrices fluorescentes dont l’expression est suivie par cytométrie en flux en présence ou non d’ARN “antisens”. Cette approche a le potentiel de mettre en évidence une régulation même si elle n’est présente que dans une sous population cellulaire. Une première série d’expériences a été réalisée en expression transitoire pour bénéficier d’un contexte chromatinien simplifié. Mais dans ce cas les silencing observés sont aussi actifs sur une construction contrôle, indiquant la mise en place d’une réponse non spécifique de séquence qui évoque la réponse de type interféron. Cependant, l’expression globale des gènes cellulaire n’est pas significativement affectée, indiquant une certaine spécificité de la réponse. Parmi les voies testées ni la kinase PKR, ni la RNaseL ou la voie de l’interférence par l’ARN ne peuvent rendre compte du silencing observé. Une des caractéristiques de cette régulation est qu’elle n’affecte pas les gènes intégrés au génome mais uniquement les gènes exprimés à partir d’une construction épisomale ce qui évoque des caractéristiques souhaitables pour un mécanisme antiviral. Cependant l’ampleur de cette réponse non spécifique empêche toute étude plus approfondie d’un mécanisme spécifique s’il existe. Mes travaux se sont alors portés sur l’étude de ces mêmes constructions en clone stable dans deux contextes différents pour l’expression de l’ARN antisens ; en cis ou en trans. Dans le cas de l’expression en trans, un ARN antisens sans séquence régulatrice particulière ne permet pas la mise en place d’un silencing. Cette observation est en accord avec le faible nombre de longs ARN antisens connus pour agir en trans dans la nature. Par contre l’expression en cis d’un ARN antisens peut conduire à un silencing spécifique. Cette organisation dans laquelle les gènes « sens » et « antisens » sont situés sur le même fragment d’ADN correspond à celle majoritairement observée pour les longs ARNs antisens dans la nature (cisNAT, cis Natural Antisense Transcripts). Cependant, mes travaux montrent que le silencing observé n’est pas stable dans le temps et disparaît dès lors que la transcription antisens cesse, indiquant l’absence d’une mémoire épigénétique. Un tel mode de régulation est compatible avec une interférence transcriptionnelle dans laquelle la transcription et non le produit ARN est la cause du silencing. Par ailleurs, j’ai observé un certain nombre de cas de co-régulation du transcrit sens et antisens ce qui traduit la possibilité d’activer en cis la transcription du gène cible par le promoteur de son ARN antisens. Ce phénomène est probablement facilité par la petite taille de nos constructions, mais cette dualité de réponse est en accord avec l’absence de corrélation (positive ou négative) entre l’expression des gènes et de leur transcrits antisens. L’ensemble de mes travaux montrent la faible capacité d’un ARN antisens à induire un silencing. L’approche développée doit donc permettre de rechercher des co-activateurs du silencing, par exemple en introduisant des sites de recrutement de complexes modificateurs de la chromatine. / During the last decade next generation sequencing has allowed the characterization of a large number of non-coding RNA and to establish that a majority of mammalian genes were also transcribed in the opposite orientation. However the functional significance of this antisense transcription is currently unclear.My work focused on the characterization of the regulatory potential of long non-coding RNA. It relied on the use of fluorescent reporter constructs, the expression of which in the presence or absence of antisense RNA is analyzed by flow cytometry. . This approach has the potential to uncover a regulation mechanism even if it takes place only in a subpopulation of cells.A first series of experiments has been realized by transient expression assays in order to benefit from a simplified chromatin context. However in this case the silencing associated with antisense transcripts is also active on control constructs, indicating that at least part of the response is not sequence specific suggesting the involvement of an interferon-type response. However, cellular gene expression is not significantly affected indicating some level of specificity. Among the investigated pathways, neither the PKR kinase, nor RNaseL or RNA interference pathway can account for the observed silencing. One of this regulation attributes is that it does not affect genes integrated in the genome but only genes expressed from episomes, a selectivity which would seem appropriate for an antiviral mechanism. Nevertheless the extent of this non-specific response impedes any further study on a specific mechanism, if it operates.My work then focused on the study of these reporter constructs after integration in the genome, antisense RNA being expressed in cis or in trans.In the case of trans expression, an antisense RNA devoid of any specific regulatory sequence does not allow the setting of a silencing. This observation is consistent with the low number of long antisense RNA known to act in trans in nature.On the other side, the cis expression of an antisense RNA can lead to a specific silencing. This organization in which “sense” and “antisense” genes are located in the same DNA fragment matches with the ones mostly observed for long antisense RNA in nature (cisNAT, cis Natural Antisense Transcripts). However, my work shows that the observed silencing is not stable over time and the effects terminate once antisense transcription stops, which indicates the absence of an epigenetic memory. This mode of regulation is compatible with a transcriptional interference in which transcription – and not its RNA product - is causing the silencing. Besides, I observed a certain number of sense and antisense transcript co-regulation cases highlighting the possibility to activate the transcription of the target gene by the promoter of its antisense RNA. This phenomenon is probably facilitated by the small size of our constructs, but this duality of response is in agreement with the lack of correlation (either positive or negative) between the expression of genes and their antisense transcripts.This study shows the limited capacity of an antisense RNA to induce a silencing. The developed approach should allow the search for silencing co-activators, for instance by introducing chromatin remodeling complexes recruitment sites.

This thesis is focused on the ARP2/3 complex, which is a de novo actin cytoskeleton nucleator. This highly conserved complex is composed of seven subunits and regulates branching of actin filaments at a constant angle of 70 degrees. In plant and animal cells ARP2/3 is involved in various processes, which are connected with the initiation of actin polymerization; for example it participates in determining the direction and speed of cell growth and the movement of vesicles and organelles within the cell. The mutation of individual subunits is lethal for animal cells, but in plants, these mutants have only mild symptoms such as distorted trichomes or changes in epidermal cells. The aim of the presented work was to study the function of the ARP2/3 complex by the method of partial silencing of subunits using RNA interference. Specifically, it was the ARPC1 subunit of Arabidopsis thaliana and the ARPC2 subunit studied on the cellular model, the tobacco BY-2 cell line. Experimental work involved the creation of DNA constructs for induction of silencing, transformation of plant material, silencing rate analysis, and phenotype tracking in selected lines. Although lines with reduced transcript levels of the given ARP2/3 complex subunit were found, no phenotypic changes were observed in these lines. Key words...

This thesis explores the legacy of the Herero-Nama genocide that occurred in 1904 to 1908 by examining the descendant’s narrative in contrast to the preeminent state narrative. I investigate both these narratives from the emic perspective of the Herero people in Namibia, who today are a minority group. By following the narrative, I discover the fundamental emplotments and multidimensionality in the genocide narrative imperative which are tribal democracy, nationhood and ancestral land. My informants imply that the genocide is a neglected and buried memory in contemporary Namibia, and I apply theoretical concepts such as Werbner’s immediate memory and anti-memory, but also Trouillot’s notion of silencing to understand in what way the state narrative is being amplified by the ruling government, subsequently silencing the genocide. At the same time, I also want to see how the genocide narrative is being maintained in a milieu of silencing forces. The genocide is still a sensitive topic among the descendants who feel that the dignity of their ancestors has been tarnished throughout the 20th century. In Herero religion ancestor spirits hold an utterly pivotal role as mediators between the living and god.

The Drosophila genome is thought to have five recA like proteins: Rad51B, Rad51C, Rad51D, XRCC2 and XRCC3. In Drosophila Rad51/SpnA, XRCC3/SpnB, and Rad51 C/SpnD participate in homologous recombination repair. The function of DmRad51 D and DmXRCC2 are unknown. The goal of this project was to elucidate the function ofXRCC2 in Drosophila. RNA interference allowed us to knockdown the function XRCC2 and its possible binding partner Rad51D. It was seen the knocking down the function of either XRCC2 or Rad51D does not affect the viability of the fly. However, drug treatment data does not allow us to make any conclusions about how the knockdown ofXRCC2 affects the viability of the fly. RNA in-situ hybridization shows highly intricate and complex branching patterns for XRCC2, which resembles the embryonic tracheal system. Lastly, XRCC2 was purified to generate an antibody made to recognize the XRCC2 protein will help localize the XRCC2 protein in future studies as well as determine protein-protein interactions with XRCC2.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13073号 / 論農博第2843号 / 新制||農||1046(附属図書館) / 学位論文||H29||N5029(農学部図書室) / 33224 / 京都大学大学院農学研究科農学専攻 / (主査)教授 北島 宣, 教授 土井 元章, 教授 田尾 龍太郎 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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Recent advances in plant genetic engineering offer substantial benefits to farmers throughout the world. Genetic research has identified many exogenous genes that could considerably decrease production costs through transgene-mediated resistance to insect, viral, fungal and bacterial pathogens. Potato can be produced from true potato seed (TPS) through a sexual polyploidization step, known as 4x-2x hybridization. Little is known regarding the stability of transgenes through sexual polyploidization in potato, although studies have associated ploidy elevation with transgene silencing in plants such as Arabidopsis thaliana. In the present study, potato was transformed with two different transgenes, cry3Aa and PVYo cp, and transgene expression was analyzed through 4x-2x hybridization. Transgene introgression did not affect fertility or agronomic performance (tuber set, average tuber weight, total tuber yield) of the resulting 4x-2x hybrids; however, reduced seed germination was observed for several transgenic lines in an in vitro study. Ploidy elevation did not affect a highly expressed single copy cry3Aa transgene, simplex or duplex, transmitted through pollen to 4x-2x hybrids. By contrast, multiple copies of cry3Aa triggered significant transgene silencing in diploids and silencing was further pronounced upon pollen transmission to 4x-2x hybrids. Crosses between two, single insert plants demonstrated additional evidence that multiple cry3Aa transgenes resulted in reduced expression, as well as provided evidence for maternal effects on expression of the cry3Aa transgene. Finally, Cry3Aa expression levels of progeny derived from low expressing, multiple copy 4x-2x hybrids indicated that reduction of transgene number in progeny, through meiotic segregation, could increase Cry3Aa expression. The results suggest that 4x-2x hybridization using single copy, male parents can result in high expressing, transgenic 4x-2x hybrids while segregating for a low frequency of non-transgenic hybrids that create a "refuge" to inhibit development of resistance to transgenes in pest populations. / Ph. D.