Global ETD Search

41	Functional study of miRNA-mRNA interactions in malaria mosquito An. gambiae Fu, Xiaonan 02 July 2018 (has links) Female adults of many mosquito species possess distinct physiological features adapting to blood feeding for successful reproduction. The disease pathogens that are transmitted by mosquitoes have evolved to take advantages of the indispensable blood feedings to complete their transmission cycles and to survive attacks from the mosquito's innate immune system. Normal egg development and mosquito immunity are tightly controlled by tissue- and stage-specific gene expression and coordinated by many signal molecules in the mosquito. Understanding gene regulation affecting mosquito reproduction and malaria parasites infection is of paramount importance for developing novel malaria control strategies. A growing body of evidence indicates that microRNAs (miRNAs) are involved in egg maturation and immune reactions against invading pathogens in mosquitoes. However, the molecular mechanisms by which specific miRNAs selectively modulate reproduction and the survival of pathogens are largely unknown. The miRNA-induced gene-silencing pathway in mosquitoes was mostly extrapolated from the studies of flies. To explore the dynamics of miRNAs in reproduction, I used small RNAs sequencing to monitor miRNAs expression and their association with Argonaute 1 (Ago1) and Argonaute 2 (Ago2) in the malaria mosquito Anopheles gambiae (An. gambiae) during the 72-h period immediately after blood feeding. I found the abundance and Ago loading of most of the mature miRNAs were relatively stable after blood ingestion. However, miRNAs of the miR-309/286/2944 cluster were considerably upregulated after blood feeding. I confirmed that miR-309 is essential for normal egg development by depletion of endogenous miR-309 with a specific antagomir. In addition, my results showed that the Ago association of some miRNAs was not proportional to their cellular abundance implying additional regulation at miRNA integration. To investigate the functional roles of miRNAs and define context-dependent miRNA-mRNA interactions during the reproductive process, I have applied an innovative experimental approach to study miRNA-mRNA interactome. CLEAR (covalent ligation of endogenous Argonaute-bound RNAs)-CLIP can generate miRNA-mRNA chimeras from UV-irradiation stabilized Ago-miRNA-mRNA complex. My results have defined tens of thousands of miRNA-mRNA interactions in mosquitoes, including novel targets for mosquito-specific miRNAs. Verification of the predicted interactions using mRNA-seq, ribosome-profiling, and luciferase reporter assay revealed a reliable miRNA-mRNA interaction network. Based on the detected interactions, I refined the paring rules for mosquito miRNAs and illustrated the dynamic pairing between different regions of miRNAs with their targets in vivo. The miRNA-mRNA interactions were compared using this approach at multiple time points before and after blood feeding. Importantly, this study showed that the interactions were dynamic and enriched in genes that are involved in metabolisms, supporting the proposed functions of miRNAs in coordinating the gene regulation in mosquito reproduction. Plasmodium falciparum (P. falciparum) is a major human malaria parasite. To understand the functions of miRNAs in the mosquito resistance to Plasmodium infection, we analyzed the miRNA-mRNA interactions after female mosquitoes taking a P. falciparum-infected blood meal or an uninfected blood meal. Comparison of the interactions revealed enhanced miRNA-mRNA interactions after P. falciparum infection involving a group of immunity-related genes. In summary, this study has provided a systematic view and significantly advanced our understanding of the miRNA functions in mosquito reproduction and P. falciparum infection. / PHD microRNA Argonaute CLEAR-CLIP CLIP-seq mRNA-seq Ribo-seq RISC miR-309 let-7 kr-h1 SIX4 oogenesis metabolism dynamics Plasmodium falciparum malaria Anopheles gambiae
42	Interactome of TNRC6 W-motifs and their conserved Role in miRNA-mediated silencing Mauri, Marta 15 December 2017 (has links) MicroRNAs (miRNAs) sind kurze nicht-kodierende RNAs, die auf posttranskriptionaler Ebene die Genexpression hemmen. Dafür bilden miRNAs Ribonukleoprotein-Komplexe, deren Kernbestandteile aller Bilateria Argonaute (AGO) und GW182 /TNRC6 Proteine sind. GW182 / TNRC6-Proteine rekrutieren CCR4-NOT-Deadenylasen über kurze Tryptophan-reiche Motive (W-Motive), welche additiv wirken und fördern so die translationale Repression und den Abbau von Ziel-mRNAs. Um mehr über die Mechanismen der miRNA-abhängigen Genrepression zu erfahren, habe ich W-Motiv-abhängige Interaktionspartner humaner TNRC6C Proteine bestimmt. Hierzu habe ich, mithilfe von quantitativer Massenspektrometrie, das Interaktom von wildtyp TNRC6C Proteinen mit dem von TNRC6C Proteinen, deren W-Motive mutiert wurden, verglichen. Neben bekannten Interaktionspartnern, wie Untereinheiten des CCR4-NOT Komplexes, habe ich Komponenten von Clathrin-Vesikeln (CCVs), Stoffwechsel assoziierte Enzyme, mitochondriale Proteine, RNA Helikasen, Kinasen und Phosphatasen mit potentiellen Funktionen in der miRNA-assoziierten Repression identifiziert. Die im ersten Teil dieser Studie vorgestellten Ergebnisse legen nahe, dass CCVs die Speicherung oder das Recycling von TNRC6 und AGO Proteinen vermitteln können und somit das miRNA-Silencing modulieren. Der zweite Teil dieser Studie befasst sich mit der Konservierung von miRNA vermitteltem Gen-Silencing in Cnidaria (Nematostella vectensis), welche sich vor 600 Millionen Jahren von der Ahnenreihe der Metazoa abspalteten. Hier zeige ich anhand humaner Zellen, dass Nematostella GW182, ähnlich wie in Bilateria, von AGO rekrutiert wird und nachfolgend in der Repression der mRNA fungiert, was darauf hinweist, dass dieser Mechanismus der miRNA-vermittelten Geninhibition bereits in den letzten gemeinsamen Vorfahren von Cnidaria und Bilateria aktiv war. / MicroRNAs (miRNAs) are short non-coding RNAs that act as post-transcriptional repressors of gene expression. To function miRNAs are assembled in ribonucleoprotein complexes, whose core components in bilaterian animals are Argonaute (AGO) and GW182/TNRC6 proteins. GW182/TNRC6 proteins additively recruit CCR4-NOT deadenylases via short tryptophan-containing motifs (W-motifs), thereby promoting translational repression and the decay of target mRNAs. To gain deeper insights into the mechanisms of miRNA silencing I determined the W-motif-specific interactome of human TNRC6C proteins. Using Stable Isotope Labeling by Amino acids in Cell Culture (SILAC) coupled to affinity purification and Mass Spectrometry (MS) I identified proteins enriched with wild type TNRC6C as compared to two mutants with disrupted W-motifs. Besides known functional interactors, such as subunits of the CCR4-NOT complex, I identified several components of clathrin-coated vesicles (CCVs), metabolic enzymes, mitochondrial proteins, RNA helicases, kinases, and phosphatases with potential functional roles in miRNA-mediated repression. The results presented in the first part of this thesis indicate that CCVs may mediate the storage or recycling of TNRC6 and AGO proteins, thus modulating miRNA silencing. The second part of the thesis addressed the conservation of the mechanisms of miRNA silencing via W-motifs in the cnidarian Nematostella vectensis, separated by 600 million years from other Metazoa. Using cultured human cells, I showed that similarly to bilaterians, GW182 in Nematostella is recruited to the miRNA repression complex via interaction with AGO proteins, and functions downstream to repress mRNA, indicating that this mechanism of miRNA-mediated silencing was already active in the last common ancestor of Cnidaria and Bilateria. miRNA Inhibitionsmechanismus Argonaute Proteine TNRC6/GW182 Proteine W-motiven Clathrin-Vesikeln (CCVs) Evolution Cnidaria Nematostella GW182 miRNA silencing Argonaute proteins TNRC6/GW182 proteins W-motifs Evolution Cnidaria Nematostella GW182 Clathrin-coated vesicles (CCVs) 570 Biologie WG 1900 WD 5355 ddc:570
43	Small RNAs and Argonautes Provide a Paternal Epigenetic Memory of Germline Gene Expression to Promote Thermotolerant Male Fertility: A Dissertation Conine, Colin C. 26 September 2014 (has links) During each life cycle, gametes must preserve and pass on both genetic and epigenetic information, making the germline both immortal and totipotent. In the male germline the dramatic morphological transformation of a germ cell through meiosis, into a sperm competent for fertilization, while retaining this information is an incredible example of cellular differentiation. This process of spermatogenesis is inherently thermosensitive in numerous metazoa ranging from worms to man. Here, I describe the role of two redundant AGO-class paralogs, ALG-3/4, and their small RNA cofactors, in promoting thermotolerant male fertility in Caenorhabditis elegans. alg-3/4 double mutants exhibit temperature dependent sterility resulting from defective spermiogenesis, the postmeiotic differentiation of haploid spermatids into spermatozoa competent for fertilization. The essential Argonaute CSR-1 functions with ALG-3/4 to positively regulate target genes required for spermiogenesis by promoting transcription via a small RNA positive feedback loop. Our findings suggest that ALG-3/4 functions during spermatogenesis to amplify a small-RNA signal loaded into CSR-1 to maintain transcriptionally active chromatin at genes required for spermiogenesis and to provide an epigenetic memory of male-specific gene expression. CSR-1, which is abundant in mature sperm, appears to transmit this memory to offspring. Surprisingly, in addition to small RNAs targeting male-specific genes, we show that males also harbor an extensive repertoire of CSR-1 small RNAs targeting oogenesis-specific mRNAs. The ALG-3/4 small RNA pathway also initiates silencing small RNA signals loaded into WAGO vii Argonautes, which function to posttranscripitonally silence their target mRNAs. Silencing WAGO/small RNA-complexes are present in sperm and presumably transmitted to offspring upon fertilization. Together these findings suggest that C. elegans sperm transmit not only the genome but also epigenetic activating and silencing signals in the form of Argonaute/small-RNA complexes, constituting a memory of gene expression in preceding generations. Argonaute Proteins Caenorhabditis elegans Genetic Epigenesis Fertility Germ Cells Messenger RNA Spermatogenesis Temperature Thermosensing Dissertations, UMMS Epigenesis, Genetic RNA, Messenger Cell Biology Cellular and Molecular Physiology Developmental Biology Genetics Molecular Biology
44	Using Experimental and Computational Strategies to Understand the Biogenesis of microRNAs and piRNAs: A Dissertation Han, Bo W. 24 July 2015 (has links) Small RNAs are single-stranded, 18–36 nucleotide RNAs that can be categorized as miRNA, siRNA, and piRNA. miRNA are expressed ubiquitously in tissues and at particular developmental stages. They fine-tune gene expression by regulating the stability and translation of mRNAs. piRNAs are mainly expressed in the animal gonads and their major function is repressing transposable elements to ensure the faithful transfer of genetic information from generation to generation. My thesis research focused on the biogenesis of miRNAs and piRNAs using both experimental and computational strategies. The biogenesis of miRNAs involves sequential processing of their precursors by the RNase III enzymes Drosha and Dicer to generate miRNA/miRNA* duplexes, which are subsequently loaded into Argonaute proteins to form the RNA-induced silencing complex (RISC). We discovered that, after assembled into Ago1, more than a quarter of Drosophila miRNAs undergo 3′ end trimming by the 3′-to-5′ exoribonuclease Nibbler. Such trimming occurs after removal of the miRNA* strand from pre-RISC and may be the final step in RISC assembly, ultimately enhancing target messenger RNA repression. Moreover, by developing a specialized Burrow-Wheeler Transform based short reads aligner, we discovered that in the absence of Nibbler a subgroup of miRNAs undergoes increased tailing—non-templated nucleotide addition to their 3′ ends, which are usually associated with miRNA degradation. Therefore, the 3′ trimming by Nibbler might increase miRNA stability by protecting them from degradation. In Drosophila germ line, piRNAs associate with three PIWI-clade Argonaute proteins, Piwi, Aub, and Ago3. piRNAs bound by Aub and Ago3 are generated by reciprocal cleavages of sense and antisense transposon transcripts (a.k.a., the “Ping-Pong” cycle), which amplifies piRNA abundance and degrades transposon transcripts in the cytoplasm. On the other hand, Piwi and its associated piRNA repress the transcription of transposons in the nucleus. We discovered that Aub- and Ago3-mediated transposon RNA cleavage not only generates piRNAs bound to each other, but also produces substrates for the endonuclease Zucchini, which processively cleaves those substrates in a periodicity of ~26 nt and generates piRNAs that predominantly load into Piwi. Without Aub or Ago3, the abundance of Piwi-bound piRNAs drops and transcriptional silencing is compromised. Our discovery revises the current model of piRNA biogenesis. Small Interfering RNA Ribonuclease III Drosophila RNA Cleavage Messenger RNA Argonaute Proteins MicroRNAs Dissertations, UMMS RNA, Small Interfering RNA, Messenger Biochemistry Computational Biology Genetics and Genomics
45	Unveiling Molecular Mechanisms of piRNA Pathway from Small Signals in Big Data: A Dissertation Wang, Wei 01 October 2015 (has links) PIWI-interacting RNAs (piRNA) are a group of 23–35 nucleotide (nt) short RNAs that protect animal gonads from transposon activities. In Drosophila germ line, piRNAs can be categorized into two different categories— primary and secondary piRNAs— based on their origins. Primary piRNAs, generated from transcripts of specific genomic regions called piRNA clusters, which are enriched in transposon fragments that are unlikely to retain transposition activity. The transcription and maturation of primary piRNAs from those cluster transcripts are poorly understood. After being produced, a group of primary piRNAs associates Piwi proteins and directs them to repress transposons at the transcriptional level in the nucleus. Other than their direct role in repressing transposons, primary piRNAs can also initiate the production of secondary piRNA. piRNAs with such function are loaded in a second PIWI protein named Aubergine (Aub). Similar to Piwi, Aub is guided by piRNAs to identify its targets through base-pairing. Differently, Aub functions in the cytoplasm by cleaving transposon mRNAs. The 5' cleavage products are not degraded but loaded into the third PIWI protein Argonaute3 (Ago3). It is believed that an unidentified nuclease trims the 3' ends of those cleavage products to 23–29 nt, becoming mature piRNAs remained in Ago3. Such piRNAs whose 5' ends are generated by another PIWI protein are named secondary piRNAs. Intriguingly, secondary piRNAs loaded into Ago3 also cleave transposon mRNA or piRNA cluster transcripts and produce more secondary piRNAs loaded into Aub. This reciprocal feed-forward loop, named the “Ping-Pong cycle”, amplified piRNA abundance. By dissecting and analyzing data from large-scale deep sequencing of piRNAs and transposon transcripts, my dissertation research elucidates the biogenesis of germline piRNAs in Drosophila. How primary piRNAs are processed into mature piRNAs remains enigmatic. I discover that primary piRNA signal on the genome display a fixed periodicity of ~26 nt. Such phasing depends on Zucchini, Armitage and some other primary piRNA pathway components. Further analysis suggests that secondary piRNAs bound to Ago3 can initiate phased primary piRNA production from cleaved transposon RNAs. The first ~26 nt becomes a secondary piRNA that bind Aub while the subsequent piRNAs bind Piwi, allowing piRNAs to spread beyond the site of RNA cleavage. This discovery adds sequence diversity to the piRNA pool, allowing adaptation to changes in transposon sequence. We further find that most Piwi-associated piRNAs are generated from the cleavage products of Ago3, instead of being processed from piRNA cluster transcripts as the previous model suggests. The cardinal function of Ago3 is to produce antisense piRNAs that direct transcriptional silencing by Piwi, rather to make piRNAs that guide post-transcriptional silencing by Aub. Although Ago3 slicing is required to efficiently trigger phased piRNA production, an alternative, slicing-independent pathway suffices to generate Piwi-bound piRNAs that repress transcription of a subset of transposon families. The alternative pathway may help flies silence newly acquired transposons for which they lack extensively complementary piRNAs. The Ping-Pong model depicts that first ten nucleotides of Aub-bound piRNAs are complementary to the first ten nt of Ago3-bound piRNAs. Supporting this view, piRNAs bound to Aub typically begin with Uridine (1U), while piRNAs bound to Ago3 often have adenine at position 10 (10A). Furthermore, the majority of Ping-Pong piRNAs form this 1U:10A pair. The Ping-Pong model proposes that the 10A is a consequence of 1U. By statistically quantifying those target piRNAs not paired to g1U, we discover that 10A is not directly caused by 1U. Instead, fly Aub as well as its homologs, Siwi in silkmoth and MILI in mice, have an intrinsic preference for adenine at the t1 position of their target RNAs. On the other hand, this t1A (and g10A after loading) piRNA directly give rise to 1U piRNA in the next Ping-Pong cycle, maximizing the affinity between piRNAs and PIWI proteins. Small Interfering RNA Argonaute Proteins RNA Interference Drosophila Proteins High-Throughput Nucleotide Sequencing DNA Transposable Elements Dissertations, UMMS RNA, Small Interfering High-Throughput Nucleotide Sequencing Biochemistry Bioinformatics Computational Biology Molecular Biology Molecular Genetics
46	GEMINIVIRUSES AS MODELS TO STUDY THE ESTABLISHMENT AND MAINTENANCE OF DNA METHYLATION Jackel, Jamie Nicole 23 August 2013 (has links) No description available. Molecular Biology Plant Biology Virology RNA polymerase IV RNA polymerase V DNA methylation histone methylation geminivirus DRB proteins Dicer-like proteins Argonaute proteins silencing suppressor AL2 L2 Adenosine Kinase methyl cycle
47	Micro RNA-Mediated regulation of the full-length and truncated isoforms of human neurotrophic tyrosine kinase receptor type 3 (NTRK 3) Guidi, Mònica 13 January 2009 (has links) Neurotrophins and their receptors are key molecules in the development of thenervous system. Neurotrophin-3 binds preferentially to its high-affinity receptorNTRK3, which exists in two major isoforms in humans, the full-length kinaseactiveform (150 kDa) and a truncated non-catalytic form (50 kDa). The twovariants show different 3'UTR regions, indicating that they might be differentiallyregulated at the post-transcriptional level. In this work we explore howmicroRNAs take part in the regulation of full-length and truncated NTRK3,demonstrating that the two isoforms are targeted by different sets of microRNAs.We analyze the physiological consequences of the overexpression of some of theregulating microRNAs in human neuroblastoma cells. Finally, we providepreliminary evidence for a possible involvement of miR-124 - a microRNA with noputative target site in either NTRK3 isoform - in the control of the alternativespicing of NTRK3 through the downregulation of the splicing repressor PTBP1. / Las neurotrofinas y sus receptores constituyen una familia de factores crucialespara el desarrollo del sistema nervioso. La neurotrofina 3 ejerce su funciónprincipalmente a través de una unión de gran afinidad al receptor NTRK3, del cualse conocen dos isoformas principales, una larga de 150KDa con actividad de tipotirosina kinasa y una truncada de 50KDa sin dicha actividad. Estas dos isoformasno comparten la misma región 3'UTR, lo que sugiere la existencia de unaregulación postranscripcional diferente. En el presente trabajo se ha exploradocomo los microRNAs intervienen en la regulación de NTRK3, demostrando que lasdos isoformas son reguladas por diferentes miRNAs. Se han analizado lasconsecuencias fisiológicas de la sobrexpresión de dichos microRNAs utilizandocélulas de neuroblastoma. Finalmente, se ha estudiado la posible implicación delmicroRNA miR-124 en el control del splicing alternativo de NTRK3 a través de laregulación de represor de splicing PTBP1. RISC complex retinoic acid renilla luciferase real-time quantitative PCR PTBP1 pri-miRNA pre-miRNA post-transcriptional regulation piRNA PicTar pGL4.13 PCR P-body p75NTR overexpression NTRK3 NTRK2 NTRK1 non-coding RNAs NGF neurotrophin neurotrophic signaling neuronal differentiation neurodevelopment neuroblastoma nervous system mRNA miRNA target prediction miRNA profiling miRNA mimic miRNA microarray miRNA inhibitor miRanda microRNA microarray luciferase assay Ingenuity Pathway Analysis (IPA) heLa cells gene silencing gene regulation full-length isoform (FL-NTRK3) firefly luciferase ERK disease dicer cancer development BDNF argonaute alternative splicing 3'UTR RNAhybrid RT-PCR SH-SY5Y cells siRNA standard error synaptic plasticity target validation TargetScan transfection translational repression TrkA TrkB TrkC truncated isoform (TR-NTRK3) tyrosine kinase (TK) western blot 575 61

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