Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “RNA-Induced Silencing Complex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2003

RNAi: an ever-growing puzzle.

In recent years, sequence-specific gene silencing has been an area of increasing focus, both because of its interesting biology and because of its power as an experimental tool. A growing understanding of one such phenomenon, RNA interference (RNAi), has provided clues that many homology-dependent gene-silencing mechanisms share a common trigger, double-stranded RNA. Recent findings that RNAi and related pathways are involved not only in the response to exogenous pathogenic and endogenous parasitic nucleic acids but also in basic cellular processes, such as gene regulation and heterochromatin formation, have further fueled interest in this rapidly expanding field.

Animals↗
PubMed2000

A global profile of germline gene expression in C. elegans.

We used DNA microarrays to profile gene expression patterns in the C. elegans germline and identified 1416 germline-enriched transcripts that define three groups. The sperm-enriched group contains an unusually large number of protein kinases and phosphatases. The oocyte-enriched group includes potentially new components of embryonic signaling pathways. The germline-intrinsic group, defined as genes expressed similarly in germlines making only sperm or only oocytes, contains a family of piwi-related genes that may be important for stem cell proliferation. Finally, examination of the chromosomal location of germline transcripts revealed that sperm-enriched and germline-intrinsic genes are nearly absent from the X chromosome, but oocyte-enriched genes are not.

Animals↗
PubMed2001

Yb modulates the divisions of both germline and somatic stem cells through piwi- and hh-mediated mechanisms in the Drosophila ovary.

The coordinated division of distinctive types of stem cells within an organ is crucial for organogenesis and homeostasis. Here we show genetic interactions among fs(1)Yb (Yb), piwi, and hedgehog (hh) that regulate the division of both germline stem cells (GSCs) and somatic stem cells (SSCs), the two constituent stem cell populations of the Drosophila ovary. Yb is required for both GSC and SSC divisions; loss of Yb function eliminates GSCs and reduces SSC division, while Yb overexpression increases GSC number and causes SSC overproliferation. We also show that Yb acts via the piwi- and hh-mediated signaling pathways that emanate from the same signaling cells to control GSC and SSC division, respectively. hh signaling also has a minor effect in GSC division.

Animals↗
PubMed2002

RNAi related mechanisms affect both transcriptional and posttranscriptional transgene silencing in Drosophila.

Two types of transgene silencing were found for the Alcohol dehydrogenase (Adh) transcription unit. Transcriptional gene silencing (TGS) is Polycomb dependent and occurs when Adh is driven by the white eye color gene promoter. Full-length Adh transgenes are silenced posttranscriptionally at high copy number or by a pulsed increase over a threshold. The posttranscriptional gene silencing (PTGS) exhibits molecular hallmarks typical of RNA interference (RNAi), including the production of 21--25 bp length sense and antisense RNAs homologous to the silenced RNA. Mutations in piwi, which belongs to a gene family with members required for RNAi, block PTGS and one aspect of TGS, indicating a connection between the two types of silencing.

ATP-Binding Cassette Transporters↗
PubMed2002

Ziwi, the zebrafish homologue of the Drosophila piwi: co-localization with vasa at the embryonic genital ridge and gonad-specific expression in the adults.

PIWI regulates the proliferation and maintenance of germline stem cells in diverse organisms. The full-length 3.26 kb ziwi cDNA, the zebrafish homologue of piwi of Drosophila, encodes a putative protein of 858 amino acids. ZIWI is 65% homologous with the mouse and human PIWI, but only 38 and 33% with Caenorhabditis elegans and Drosophila PIWI, respectively. In adult zebrafish, ziwi is expressed exclusively in the gonads. In embryos and fry, its expression is detectable initially during segmentation and persisted for at least 4 weeks post hatching. During neurogenesis and organogenesis, its expression was detected in the CNS and fin buds. Starting from 24 hpf and later on, ziwi transcripts were found in the genital ridge.

Amino Acid Sequence↗
PubMed2002

Molecular characterization of hiwi, a human member of the piwi gene family whose overexpression is correlated to seminomas.

The piwi family genes are highly conserved during evolution and play essential roles in stem cell self-renewal, gametogenesis, and RNA interference in diverse organisms ranging from Drosophila melanogaster and C. elegans to Arabidopsis. Here we report the molecular characterization of hiwi, a human member of the piwi gene family. hiwi maps to the long arm of chromosome 12, band 12q24.33, a genomic region that displays genetic linkage to the development of testicular germ cell tumors of adolescents and adults (TGCTs), i.e., seminomas and nonseminomas. In addition, gain of this chromosomal region has been found in some TGCTs. hiwi encodes a 3.6 kb mRNA that is expressed abundantly in the adult testis. It encodes a highly basic 861-amino-acid protein that shares significant homology throughout its entire length with other members of the PIWI family proteins in Drosophila, C. elegans and mammals. In normal human testes, hiwi is specifically expressed in germline cells, with its expression detectable in spermatocytes and round spermatids during spermatogenesis. No expresssion was observed in testicular tumors of somatic origin, such as Sertoli cell and Leydig cell tumors. Enhanced expression was found in 12 out of 19 sampled testicular seminomas-tumors originating from embryonic germ cells with retention of germ cell phenotype. In contrast, no enhanced expression was detected in 10 nonseminomas-testicular tumors that originate from the same precursor cells as seminomas yet have lost their germ cell characteristics. Finally, no enhanced expression was detected in four spermatocytic seminomas-testicular tumors that most likely originate from germ cells capable of partial meiosis. Thus, hiwi is specifically expressed in both normal and malignant spermatogenic cells in a maturation stage-dependent pattern, in which it might function in germ cell proliferation.

Amino Acid Sequence↗
PubMed2002

ARGONAUTE1 is required for efficient RNA interference in Drosophila embryos.

Double-stranded RNA (dsRNA) triggers homology-dependent posttranscriptional gene interference (RNAi) in a diverse range of eukaryotic organisms, in a process mechanistically related to viral and transgene-mediated cosuppression. RNAi is characterized by the conversion of long dsRNA into approximately 21-25-nt small interfering RNAs (siRNA) that guide the degradation of homologous mRNA. Many of the genes required for siRNA production and target mRNA degradation are widely conserved. Notably, members of the Argonaute-like gene family from Arabidopsis, Caenorhabditis elegans, Drosophila, and Neurospora have been genetically and/or biochemically identified as components of the RNAi/cosuppression pathway. We show here that mutations in the Drosophila Argonaute1 (AGO1) gene suppress RNAi in embryos. This defect corresponds to a reduced ability to degrade mRNA in response to dsRNA in vitro. Furthermore, AGO1 is not required for siRNA production in vitro nor can the introduction of siRNA bypass AGO1 mutants in vivo. These data suggest that AGO1 functions downstream of siRNA production.

ATP-Binding Cassette Transporters↗
PubMed2002

Fragile X-related protein and VIG associate with the RNA interference machinery.

RNA interference (RNAi) is a flexible gene silencing mechanism that responds to double-stranded RNA by suppressing homologous genes. Here, we report the characterization of RNAi effector complexes (RISCs) that contain small interfering RNAs and microRNAs (miRNAs). We identify two putative RNA-binding proteins, the Drosophila homolog of the fragile X mental retardation protein (FMRP), dFXR, and VIG (Vasa intronic gene), through their association with RISC. FMRP, the product of the human fragile X locus, regulates the expression of numerous mRNAs via an unknown mechanism. The possibility that dFXR, and potentially FMRP, use, at least in part, an RNAi-related mechanism for target recognition suggests a potentially important link between RNAi and human disease.

Amino Acid Sequence↗
PubMed1998

A novel class of evolutionarily conserved genes defined by piwi are essential for stem cell self-renewal.

Germ-line stem cells (GSCs) serve as the source for gametogenesis in diverse organisms. We cloned and characterized the Drosophila piwi gene and showed that it is required for the asymmetric division of GSCs to produce and maintain a daughter GSC but is not essential for the further differentiation of the committed daughter cell. Genetic mosaic and RNA in situ analyses suggest that piwi expression in adjacent somatic cells regulates GSC division. piwi encodes a highly basic novel protein, well conserved during evolution. We isolated piwi homologs in Caenorhabditis elegans and humans and also identified Arabidopsis piwi-like genes known to be required for meristem cell maintenance. Decreasing C. elegans piwi expression reduces the proliferation of GSC-equivalent cells. Thus, piwi represents a novel class of genes required for GSC division in diverse organisms.

Amino Acid Sequence↗
PubMed2002

hpRNA-mediated targeting of the Arabidopsis FAD2 gene gives highly efficient and stable silencing.

The endogenous Delta 12-desaturase gene (FAD2) in Arabidopsis was targeted for silencing using seed-specific cosuppression (CS), hairpin (HP) RNA (hpRNA), and intron-spliced HP (iHP) constructs. The iHP construct, incorporating the 120-bp 3'-untranslated region of the FAD2 gene, gave the highest degree of silencing. In some iHP lines Delta 12-desaturase activity was reduced to levels as low as those in the null fad2-1 mutant, and every primary transformant showed a pronounced reduction in FAD2 activity. One highly silenced iHP line was propagated for five generations and showed no reversion or diminution in its degree of silencing. About 75% of plants transformed with the HP construct, targeting the FAD2 coding region, gave dramatically reduced Delta 12-desaturase activity, whereas approximately 50% of plants transformed with the CS construct, containing the same coding region sequence, showed silencing at a much less profound level. In all three types of constructs, the degree of silencing was increased when the transgenes were homozygous, but this was much more pronounced for the CS constructs. All three types of construct could give a single locus that was capable of effective silencing, but in the one such CS line where this was the case, the locus had a complex insertion pattern. This is consistent with the concept that posttranscriptional gene silencing is induced by double-stranded, or self-complementary, RNA that is formed in cases of CS by complex insertion patterns at a single locus and that the most effective way of generating profoundly silenced plants is by the use of constructs that encode hpRNAs. Furthermore, these results demonstrate for the first time, to our knowledge, that iHP constructs targeted against an endogenous seed-expressed gene are clearly able to generate phenotypic changes that are inherited stably over several generations, making this approach a reliable technique for genetic modification of seed quality and possibly other traits in agricultural plants.

Arabidopsis↗
PubMed2003

RNA target sequences promote spreading of RNA silencing.

It is generally recognized that a silencing-inducing locus can efficiently reduce the expression of genes that give rise to transcripts partially homologous to those produced by the silencing-inducing locus (primary targets). Interestingly, the expression of genes that produce transcripts without homology to the silencing-inducing locus (secondary targets) can also be decreased dramatically via transitive RNA silencing. This phenomenon requires primary target RNAs that contain sequences homologous to secondary target RNAs. Sequences upstream from the region homologous to the silencing inducer in the primary target transcripts give rise to approximately 22-nucleotide small RNAs, coinciding with the region homologous to the secondary target. The presence of these small RNAs corresponds with reduced expression of the secondary target whose transcripts are not homologous to the silencing inducer. The data suggest that in transgenic plants, targets of RNA silencing are involved in the expansion of the pool of functional small interfering RNAs. Furthermore, methylation of target genes in sequences without homology to the initial silencing inducer indicates not only that RNA silencing can expand across target RNAs but also that methylation can spread along target genes.

DNA Methylation↗
PubMed2002

Spreading of RNA targeting and DNA methylation in RNA silencing requires transcription of the target gene and a putative RNA-dependent RNA polymerase.

RNA silencing is a sequence-specific RNA degradation process that follows the recognition of double-stranded RNA. Here, we show that virus vectors carrying parts of a green fluorescent protein (GFP) transgene targeted RNA silencing in Nicotiana benthamiana and Arabidopsis against the entire GFP RNA. These results indicate that there was spreading of RNA targeting from the initiator region into the adjacent 5' and 3' regions of the target gene. Spreading was accompanied by methylation of the corresponding GFP DNA. It also was dependent on transcription of the transgene and on the putative RNA-dependent RNA polymerase, SDE1/SGS2. These findings indicate that SDE1/SGS2 produces double-stranded RNA using the target RNA as a template. RNA silencing of ribulose-1,5-bisphosphate carboxylase/oxygenase and phytoene desaturase was not associated with the spreading of RNA targeting or DNA methylation, indicating that these endogenous RNAs are not templates for SDE1/SGS2.

Arabidopsis↗
PubMed2002

A microRNA in a multiple-turnover RNAi enzyme complex.

In animals, the double-stranded RNA-specific endonuclease Dicer produces two classes of functionally distinct, tiny RNAs: microRNAs (miRNAs) and small interfering RNAs (siRNAs). miRNAs regulate mRNA translation, whereas siRNAs direct RNA destruction via the RNA interference (RNAi) pathway. Here we show that, in human cell extracts, the miRNA let-7 naturally enters the RNAi pathway, which suggests that only the degree of complementarity between a miRNA and its RNA target determines its function. Human let-7 is a component of a previously identified, miRNA-containing ribonucleoprotein particle, which we show is an RNAi enzyme complex. Each let-7-containing complex directs multiple rounds of RNA cleavage, which explains the remarkable efficiency of the RNAi pathway in human cells.

Adenosine Triphosphate↗