In animal gonads, 23-30nt long PIWI interacting RNAs (piRNAs) guarantee genome integrity by guiding the sequence specific silencing of selfish genetic elements such as transposons. Two major branches of piRNA biogenesis, namely primary processing and ping-pong amplification, feed into the PIWI clade of Argonaute proteins. Despite our conceptual understanding of piRNA biogenesis, major gaps exist in the mechanistic understanding of the underlying molecular processes as well as in the knowledge of the involved players. Here, we demonstrate an essential role for the female sterility gene shutdown in the piRNA pathway. Shutdown, an evolutionarily conserved co-chaperone of the immunophilin class is the first piRNA biogenesis factor that is essential for all primary and secondary piRNA populations in Drosophila. Based on these findings, we define distinct groups of piRNA biogenesis factors and reveal the core concept of how PIWI family proteins are hard-wired into piRNA biogenesis processes. Overall design: small-RNA libraries from 2 control samples and 7 knock-down samples of D. mel. ovaries and 2 small-RNA profiles from Piwi IP and Aub IP from OSCs.
The cochaperone shutdown defines a group of biogenesis factors essential for all piRNA populations in Drosophila.
Specimen part, SubjectView Samples
These investigations studied the fundamentals of how plants perceive gravity and develop in microgravity. It informs how gene regulation is altered by spaceflight conditions.
Comparative transcriptomics indicate changes in cell wall organization and stress response in seedlings during spaceflight.
Specimen partView Samples
Limitation for amino acids is thought to regulate translation in mammalian cells primarily by signaling through the kinases mTORC1 and GCN2. We find that limitation for the amino acid arginine causes a selective loss of tRNA charging, which regulates translation through ribosome pausing at two of six arginine codons. Interestingly, limitation for leucine, an essential and abundant amino acid in protein, results in little or no ribosome pausing. Chemical and genetic perturbation of mTORC1 and GCN2 signaling revealed that their robust response to leucine limitation prevents ribosome pausing, while an insufficient response to arginine limitation led to loss of arginine tRNA charging and ribosome pausing. Codon-specific ribosome pausing decreased protein production and triggered premature ribosome termination without significantly reducing mRNA levels. Together, our results suggest that amino acids which are not optimally sensed by the mTORC1 and GCN2 pathways still regulate translation through an evolutionarily conserved mechanism based on synonymous codon usage. Overall design: Ribosome profiling was performed in HEK293T, HCT116, or HeLa cells during limitation for leucine or arginine for 3 or 6 hours to determine the effect of limiting single amino acid levels of ribosome elongation kinetics at the cognate codons. The same cell lines grown in nutrient-rich conditions were used as a control. These experiments were repeated in HEK293T cells with 250 nM Torin1, in cells stably expressing a flag-tagged wild-type or Q99L mutant RagB-GTPase or hrGFP, and in a GCN2 knockout cell line to determine the role of the mTORC1 and GCN2 pathways.
Translational Control through Differential Ribosome Pausing during Amino Acid Limitation in Mammalian Cells.
Cell line, SubjectView Samples
Cerebral palsy is primarily an upper motor neuron disease that results in a spectrum of progressive movement disorders. Secondary to the neurological lesion, muscles from patients with cerebral palsy are often spastic and form debilitating contractures that limit range of motion and joint function. With no genetic component, the pathology of skeletal muscle in cerebral palsy is a response to aberrant neurological input in ways that are not fully understood. This study was designed to gain further understanding of the skeletal muscle response to cerebral palsy using microarrays and correlating the transcriptional data with functional measures. Hamstring biopsies from gracilis and semitendinosus muscles were obtained from a cohort of patients with cerebral palsy (n=10) and typically developing patients (n=10) undergoing surgery. Affymetrix HG-U133A 2.0 chips (n=40) were used and expression data was verified for 6 transcripts using quantitative real-time PCR, as well as for two genes not on the microarray. Chips were clustered based on their expression and those from patients with cerebral palsy clustered separately. Significant genes were determined conservatively based on the overlap of three summarization algorithms (n=1,398). Significantly altered genes were analyzed for over-representation among gene ontologies, transcription factors, pathways, microRNA and muscle specific networks. These results centered on an increase in extracellular matrix expression in cerebral palsy as well as a decrease in metabolism and ubiquitin ligase activity. The increase in extracellular matrix products was correlated with mechanical measures demonstrating the importance in disability. These data lay a framework for further studies and novel therapies.
Transcriptional abnormalities of hamstring muscle contractures in children with cerebral palsy.
Sex, Age, Disease, SubjectView Samples
We describe a novel quantitative cDNA expression profiling strategy, involving amplification of the majority of mouse transcriptome using a defined set of 44 heptamer primers. The amplification protocol allows for efficient amplification from as low as 50pg of mRNA and did not alter the expression of the transcripts even with 200 fold dilution of the minimum requirement of the starting material (10ng of mRNA) for standard RNA-seq protocols. We implemented our methodology on embryological lineage segregation, achieved by graded activation of Activin A/TGFß signaling in mouse embryonic stem cells (mESCs). The fold changes in transcript expression were in excellent agreement with quantitative RT-PCR and we observed a dynamic range spanning more than five orders of magnitude in RNA concentration with a reliable estimation of low abundant transcripts. Our transcriptome data identified key lineage markers, while the high sensitivity showed that novel lineage specific transcripts anticipate the differentiation of specific cell types. We compared our strategy with Std. RNA-seq (Mortazavi et al. 2008) and SMART-seq (Ramsköld et al. 2012). We also showed potential of our methodology to suppress the representation of highly expressing ribosomal transcripts. Overall design: Sequencing was performed on day 4 differentiating mouse ESCs treated for two days with 3 different dosages of Activin A (3ng/mL, 15ng/mL and 100ng/mL). The cells were also treated with SB-431542. Serial dilutions of mRNA derived Activin A(3ng/mL) samples were used to detemine the minimum amount of mRNA required to construct relaible sequencing library. SMARTseq libraries were prepared for both Activin A(3ng/mL) and Activin A(100ng/mL) samples. Three Different primer sets were designed to suppress the representaiton of Ribosomal transcripts.
Quantitative transcriptomics using designed primer-based amplification.
Specimen part, TreatmentView Samples
Transcriptomics data obtained from limiting amounts of mRNA is often noisy, providing primarily qualitative changes in transcript expressions. So far, technical variations arising out of the library preparation protocols have not been adequately characterized at reduced levels of mRNA. Here, we generated sequencing libraries from limiting amounts of mRNA using three amplification-based methods, viz. Smart-seq, DP-seq and CEL-seq, and demonstrated significant technical variations in these libraries. Reduction in mRNA levels led to inefficient amplification of the majority of low to moderately expressed transcripts. Furthermore, stochasticity in primer hybridization and/or enzyme incorporation was magnified during the amplification step resulting in significant distortions in fold changes of the transcripts. Consequently, the majority of the differentially expressed transcripts identified were either high-expressed and/or exhibited high fold changes. High technical variations, which were sequencing depth independent, ultimately masked subtle biological differences mandating the development of improved amplification-based strategies for quantitative transcriptomics from limiting amounts of mRNA. Overall design: Sequencing libraries were prepared from serial dilutions of mRNA, ranging from 1 ng to 25 pg, using three amplification-based methods, viz. Smart-seq, DP-seq and CEL-seq. The mRNA was derived from an in vitro model of lineage segregation achieved by modulating TGF beta signaling pathway in differentiating mouse embryonic stem cells.
Technical variations in low-input RNA-seq methodologies.
Specimen part, SubjectView Samples
Hypoxia plays a key pathogenic role in the outcome of many pathologic conditions. To elucidate how organisms successfully adapt to hypoxia, a population of Drosophila melanogaster was generated, through an iterative selection process, that is able to complete its lifecycle at 4% O2, a level lethal to the starting parental population. Transcriptomic analysis of flies adapted for >200 generations was performed to identify pathways and processes that contribute to the adapted phenotype, comparing gene expression of three developmental stages with generation-matched control flies. A third group was included, hypoxia-adapted flies reverted to 21% O2 for five generations, to address the relative contributions of genetics and hypoxic environment to the gene expression differences. We identified the largest number of expression differences in 0.5-3 hr post-eclosion adult flies that were hypoxia-adapted and maintained in 4% O2, and found evidence that changes in Wnt signaling contribute to hypoxia tolerance in flies.
Wnt pathway activation increases hypoxia tolerance during development.
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In this study, we confirmed that transformed dedifferentiated astrocytes and neurons acquired a stem/progenitor cell state, although they still retained gene expression memory from their parental cell-type. Transcriptional network analysis on transformed cells revealed up-regulation of genes involved in three signaling pathways: Wnt signaling, cell cycle and focal adhesion with the gene Spp1, also known as osteopontin (OPN) serving as a key node connecting these three pathways. Inhibition of OPN blocked the formation of aggregated neurospheres, affected the proliferative capacity of transformed cell-types and reduced the expression levels of neural stem cell markers. Specific inhibition of OPN in murine glioma tumors prolonged mice survival. We conclude that OPN is an important player in dedifferentiation of cells during tumor formation, hence its inhibition can be a therapeutic target for glioblastoma. Overall design: Cortical neurons and astrocytes were derived from 11 days old SynapsinI-Cre and GFAP-Cre mice, respectively. The cells were cultured in their respective media to maintain their identity. These cells were then transduced with HRas-shp53 lentivirus with a transduction efficiency of >90%. The transduced neurons and astrocytes were later switched to neural stem cell media devoid of serum and supplemented with FGF-2 (NSC media). Within one week, these cells became proliferative and aggregated to form free-floating neurospheres. These cells, hereinafter referred to as NSynR53 and AGR53, respectively, were later harvested and mRNA collected for sequencing library generation using DP-seq. To assess the regression of these cells to an undifferentiated state along the differentiation axis, enriched populations of mESC and NSC were also grown in vitro and mRNA obtained from these cells were subjected to sequencing library preparation.
Identification of therapeutic targets for glioblastoma by network analysis.
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This study demonstrates that siRNA off-targets (e.g. 3'UTR off-targets), can be significantly reduced when cells are treated with a relatively low dose of siRNA (e.g. 1nM) that is sufficient to effectively silence the intended target.
siRNA off-target effects can be reduced at concentrations that match their individual potency.
Cell lineView Samples
Fusarium head blight (FHB) is a major disease of cereal crops caused by the fungus Fusarium graminearum (Fg). FHB affects the flowering heads (or spikes) and developing seeds. This study compare the gene expression profile in wheat spikelets (spk 2) inoculated with either water (mock treatment) or a pathogenic strain of Fusarium graminearum (WT); spikelets 2 were inoculated 24 hrs after a neighbour spikelet (spk 0) was treated with either water or F. graminerum mutant strain Tri6 or NoxAB. Spikelets 2 were sampled 8 and 24 hrs after the second treatment.
Components of priming-induced resistance to Fusarium head blight in wheat revealed by two distinct mutants of Fusarium graminearum.
Specimen partView Samples