Project description:<p>RNA-Seq is an effective method to study the transcriptome, but specialized methods are required to identify 5' ends of transcripts. Several published strategies exist for this specific purpose, but their relative merits have not been systematically analyzed. Here, we directly compare the performance of six such methods - testing five with cellular RNA as well as a novel spike-in RNA assay that helps address interpretation challenges that arise from uncertainties in annotation or RNA processing. Using a single human RNA sample, we constructed and sequenced 18 libraries with these methods and one standard, control RNA-Seq library. We find that the CAGE method performed best for mRNA and that most of its unannotated peaks are supported by evidence from other genomic methods. We then applied CAGE to eight brain-related samples and revealed sample-specific transcription start site (TSS) usage as well as a transcriptome-wide shift in TSS usage between fetal and adult brain.</p>
Project description:Eukaryotes have evolved multiple ATP-dependent chromatin remodelers to shape the nucleosome landscape. We recently uncovered an evolutionarily conserved SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeler complex in plants reminiscent of the mammalian BAF subclass, which specifically incorporates the MINUSCULE (MINU) catalytic subunits and the TRIPLE PHD FINGERS (TPF) signature subunits. Here we report experimental evidence that establishes the functional relevance of TPF proteins for the complex activity. Our results show that depletion of TPF triggers similar pleiotropic phenotypes and molecular defects to those found in minu mutants. Moreover, we report the genomic location of MINU2 and TPF proteins as representative members of the plant BAF-like complex and their impact on nucleosome positioning and transcription. These analyses unravel the binding of the complex to thousands of expressed genes where it modulates the position of the +1 nucleosome. These targets tend to produce 5´-shifted transcripts in the tpf and minu mutants pointing to the participation of the complex in alternative transcriptional start site (TSS) usage. Interestingly, there is a remarkable correlation between +1 nucleosome shift and upstream TSS usage suggesting their functional connection. In summary, this study unravels the function of a plant SWI/SNF complex involved in +1 nucleosome positioning and alternative TSS usage.
Project description:Role of alternative transcription start sites in muscle growth and development remains largely undetermined. Our WTSS-seq (whole transcriptome start site sequencing) approach to capture 5'-end of RNAs clearly revealed alternative transcription start events responsible for increased muscle mass in AMPK α2 knockout mice.
Project description:Gene isoforms are mRNAs produced from the same locus, but that differ in their transcription start sites, protein coding DNA sequences, and/or untranslated regions. Consequently, different isoforms of the same gene can have altered gene function or even serve different biological functions. Conventional RNA-Seq strategies cannot accurately distinguish expression levels between distinct isoforms, and differences in gene expression studies almost always report total gene expression. However, increasing evidence indicates that differences in isoform usage may be important for the regulation of biological functions and for development of diseases such as cancer. Here, we aimed to define whether gene isoforms are subjected to differential regulation and expression by characterizing 24-hour rhythms in polyadenylation site (PAS) usage over the course of the day in the mouse liver. Conventional RNA-Seq experiments have shown that 15-30% of genes in the mouse liver are rhythmically expressed, and it is assumed that the comprising isoforms are expressed in a similar pattern. By performing 3‟-end mRNA-Seq and using stringent criteria for defining differential rhythmic expression, we show that 15% of the genes with more than one PAS exhibit differential rhythmic expression. In particular, many genes known to be rhythmic in the mouse liver harbor at least one constitutively expressed isoform, while several hundred genes characterized as arrhythmically expressed also exhibit a rhythmic isoform. Analysis of PAS usage in nuclear mRNA and single-cell data reveals that the vast majority of isoform-specific regulation does not involve post-transcriptional regulation (e.g., miRNA targeting, RNA half-life) or cell subtype-specific differences in expression. Finally, characterization of PAS usage in Bmal1-/- mice revealed that co-transcriptional regulation plays a large role in the expression of specific gene isoforms. Taken together, our results indicate that gene isoforms can be differentially regulated, and imply that gene isoforms can behave as distinct transcriptional units. Furthermore, our data suggest that conventional RNA-Seq strategies are not the most appropriate choice for detecting changes in gene isoform expression.
Project description:Transcription Start Site analysis in Mouse Ter119+ erythroid cells Strand Specific Paired end NanoCage analysis of Total RNA from Mouse Ter119+ erythroid cells