Project description:Extensive transcriptional heterogeneity revealed by isoform profiling Application of TIF-Seq (Transcript IsoForm Sequencing) to S.cerevisiae. The method was applied to simultaneously identify the 5' capped mRNA transcription start site and the 3' polyadenylation site in different conditions: WT cells grown in glucose media [ypd, 2 biological replicates (bio) and 3 independent library preparations, technical replicates(lib)], WT cells grown in galactose media [ypgal, 4 biological replicates (bio) and 3 independent library preparations, technical replicates(lib)]. A modified protocol designed to enrich in long mRNA molecules was performed for WT cells grown in glucose media [ypd, 2 biological replicates (bio)] and in galactose media [ypgal, 2 biological replicates (bio)] conditions. Finally, control samples performed with a modified protocol designed to identify non-capped but polyadenylated molecules was performed in WT cells grown both in glucose (nypd) and galactose (nypgal) media.
Project description:Mitochondrial transcription factor A (Tfam) binds to and organizes mitochondrial DNA (mtDNA) genome into a mitochondrial nucleoid (mt-nucleoid) structure, which is necessary for mtDNA transcription and maintenance. Here, we demonstrate the mtDNA-organizing activity of mouse Tfam and its transcript isoform (Tfam(iso)), which has a smaller high-mobility group (HMG)-box1 domain, using a yeast model system that contains a deletion of the yeast homolog of mouse Tfam protein, Abf2p. When the mouse Tfam genes were introduced into the ABF2 locus of yeast genome, the corresponding mouse proteins, Tfam and Tfam(iso), can functionally replace the yeast Abf2p and support mtDNA maintenance and mitochondrial biogenesis in yeast. Growth properties, mtDNA content and mitochondrial protein levels of genes encoded in the mtDNA were comparable in the strains expressing mouse proteins and the wild-type yeast strain, indicating that the proteins have robust mtDNA-maintaining and -expressing function in yeast mitochondria. These results imply that the mtDNA-organizing activities of the mouse mt-nucleoid proteins are structurally and evolutionary conserved, thus they can maintain the mtDNA of distantly related and distinctively different species, such as yeast.
Project description:The origin of replication complex subunit ORC1 is important for DNA replication. The gene is known to encode a meiotic transcript isoform (mORC1) with an extended 5'-untranslated region (5'-UTR), which was predicted to inhibit protein translation. However, the regulatory mechanism that controls the mORC1 transcript isoform is unknown and no molecular biological evidence for a role of mORC1 in negatively regulating Orc1 protein during gametogenesis is available. By interpreting RNA profiling data obtained with growing and sporulating diploid cells, mitotic haploid cells, and a starving diploid control strain, we determined that mORC1 is a middle meiotic transcript isoform. Regulatory motif predictions and genetic experiments reveal that the activator Ndt80 and its middle sporulation element (MSE) target motif are required for the full induction of mORC1 and the divergently transcribed meiotic SMA2 locus. Furthermore, we find that the MSE-binding negative regulator Sum1 represses both mORC1 and SMA2 during mitotic growth. Finally, we demonstrate that an MSE deletion strain, which cannot induce mORC1, contains abnormally high Orc1 levels during post-meiotic stages of gametogenesis. Our results reveal the regulatory mechanism that controls mORC1, highlighting a novel developmental stage-specific role for the MSE element in bi-directional mORC1/SMA2 gene activation, and correlating mORC1 induction with declining Orc1 protein levels. Because eukaryotic genes frequently encode multiple transcripts possessing 5'-UTRs of variable length, our results are likely relevant for gene expression during development and disease in higher eukaryotes.
Project description:Alternative splicing generates differing RNA isoforms that govern phenotypic complexity of eukaryotes. Its malfunction underlies many diseases, including cancer and cardiovascular diseases. Comparative analysis of RNA isoforms at the genome-wide scale has been difficult. Here, we established an experimental and computational pipeline that accurately quantifies transcript isoforms in their entire length from cDNA sequences with a full-length isoform detection accuracy of 97.6%. We generated a searchable, quantitative human transcriptome annotation with 31,025 known and 5,740 novel transcript isoforms (http://steinmetzlab.embl.de/iBrowser/). By analyzing the isoforms in the presence of RNA Binding Motif Protein 20 (RBM20) mutations associated with aggressive dilated cardiomyopathy (DCM), we identified 121 differentially expressed transcript isoforms in 107 cardiac genes. By establishing an isoform-differential expression test, our approach revealed that 11 of these genes displayed no detectable change in overall RNA expression. However, significant differences in the expression of specific isoforms in these genes was observed. These isoform specific effects demonstrate the need of analyzing RNA isoform expression levels rather than total gene expression levels.
Project description:Static gene expression programs have been extensively characterized in stem cells and mature human cells. However, the dynamics of RNA isoform change upon cell-state transitions during cell differentiation, and the determinants and functional consequences have largely remained unclear. Here, we used an improved model for human neurogenesis in vitro that we show is amenable for systems-wide analyses of gene expression. Our multi-omics analysis reveals that the pronounced alterations in cell morphology correlate strongly with widespread changes in RNA isoform expression. Our approach identifies thousands of new RNA isoforms that are expressed at distinct stages during neurogenesis. RNA isoforms mainly arise from the alternative usage of transcription start sites and poly-adenylation sites as well as the skipping of individual exons during human neurogenesis. The transcript isoform changes can remodel the abundance and functions of protein isoforms. Finally, our study identifies a set of RNA-binding proteins as a likely determinant of differentiation stage-specific global isoform changes.