Project description:The RNA-binding protein RBM20 has been implicated in dilated cardiomyopathy (DCM), a major cause of chronic heart failure. To determine how RBM20 regulates alternative splicing, we combined transcriptome-wide CLIP-seq, RNA-seq, and quantitative proteomics in cell culture, rat, and human hearts. Our analyses revealed a distinct RBM20 RNA-recognition element in predominantly intronic binding sites and linked repression of exon splicing with RBM20-binding near 3prime- and 5prime-splice sites. Our proteomic data show RBM20 interaction with U1- and U2-snRNPs and suggests splicing repression through spliceosome stalling at complex A. Among direct RBM20 targets are several genes involved in DCM as well as new genes not previously associated with the disease process. In human failing hearts, we demonstrate that reduced expression levels of RBM20 affect alternative splicing of several direct targets, indicating that differences in RBM20 gene expression may affect cardiac function. These findings reveal a new mechanism to understand the pathogenesis of human heart failure. The provided data files for RNA-seq contain information for reads that map to human RBM20 only.
Project description:Tyrosine kinase inhibitors (TKIs), as a class of small-molecule drugs that exert anti-tumor effects by inhibiting tyrosine kinase-catalyzed phosphorylation, have been used in the treatment of various cancers. Sorafenib, as a multi-targeted TKI drug, is the first-line treatment for advanced renal cell carcinoma and unresectable hepatocellular carcinoma. However, sorafenib has repeatedly been reported to cause cardiac events in patients without a history of heart diseases during clinical use, indicating that it has cardiotoxicity. Alternative splicing of cardiac contraction-related genes happens during heart development and cardiac diseases, and is critical for heart function. However, whether alternative splicing plays a role in drug-induced cardiotoxicity remains unexplored. RBM20 is an important cardiac-specific splicing factor, mutations of which cause dilated cardiomyopathy or other cardiac dysfunctions. Rbm20 also mediates alternative splicing of genes essential for heart contraction, which is often negatively affected in drug-induced cardiotoxicity. Existing studies do not fully explain the mechanism of sorafenib cardiotoxicity, and none of the relationship between cardiotoxicity of sorafenib and alternative splicing mediated by tissue-specific splicing factors, such as Rbm20, have been reported. In order to explore whether cardiac-specific alternative splicing plays a role in sorafenib-induced cardiotoxicity, we establish both cell and animal models of cardiotoxicity, and obtain the following results: (1) By constructing a rat animal model administered with sorafenib, we find that sorafenib causes abnormal cardiac function in rats, and the genes that undergo alternative splicing in rat hearts are related to cytoskeleton of actin; (2) Alternatively spliced genes induced by sorafenib in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are enriched in sarcomere, actin filament, calcium transient regulation, mitochondria, all of which are critical for cardiac contraction. These genes are associated with dilated cardiomyopathy, hypertrophic cardiomyopathy and other cardiomyopathy; (3) Sorafenib induces a decrease in the expression of cardiac-specific splicing factor RBM20; (3) Many genes whose splicing are altered by sorafenib overlap with Rbm20 targets, indicating that sorafenib may affect alternative splicing through Rbm20; (4) Sorafenib induces pathogenic alternative splicing of FHOD3, which is a RBM20 target gene and participates in myocardial sarcomere formation. Sorafenib also affects alternative splicing of SLC25A3, which encodes a phosphate transporter on the mitochondrial inner membrane and regulates ATP synthesis; (5) Enhancing the expression of RBM20 rescues the cardiotoxicity of sorafenib by reducing apoptosis and increasing ATP levels, which is mediated by reversing the alternative splicing of FHOD3 and SLC25A3 induced by sorafenib. This paper uncovers that sorafenib reduces the expression of RBM20 to cause pathogenic alternative splicing of genes related to myocardial sarcomere and energy mechanism, resulting in abnormal myocardial function. Increasing the expression of RBM20 reverses the alternative splicing of FHOD3 and SLC25A3 associated with cardiac sarcomeres and mitochondria respectively, rescuing the cardiotoxicity of sorafenib.
Project description:Precise coordination of molecular programs and neuronal growth govern the formation, maintenance, and adaptation of neuronal circuits. RNA metabolism has emerged as a key regulatory node of neural development and nervous system pathologies. To uncover novel cell-type-specific RNA regulators, we systematically investigated expression of RNA recognition motif-containing proteins in the mouse neocortex. Surprisingly, we found RBM20, an alternative splicing regulator associated with dilated cardiomyopathy, to be expressed in cortical parvalbumin interneurons and mitral cells of the olfactory bulb. Genome-wide mapping of RBM20 target mRNAs revealed that neuronal RBM20 binds distal intronic regions. Loss of neuronal RBM20 has only modest impact on alternative splice isoforms but results in a significant reduction in an array of mature mRNAs in the neuronal cytoplasm. This phenotype is particularly pronounced for genes with long introns that encode synaptic proteins. We hypothesize that RBM20 ensures fidelity of pre-mRNA splicing by suppressing non-productive splicing events in long neuronal genes. This work highlights a common requirement of two excitable cell types, cardiomyocytes and neurons, for RBM20-dependent transcriptome regulation.
Project description:Precise coordination of molecular programs and neuronal growth govern the formation, maintenance, and adaptation of neuronal circuits. RNA metabolism has emerged as a key regulatory node of neural development and nervous system pathologies. To uncover novel cell-type-specific RNA regulators, we systematically investigated expression of RNA recognition motif-containing proteins in the mouse neocortex. Surprisingly, we found RBM20, an alternative splicing regulator associated with dilated cardiomyopathy, to be expressed in cortical parvalbumin interneurons and mitral cells of the olfactory bulb. Genome-wide mapping of RBM20 target mRNAs revealed that neuronal RBM20 binds distal intronic regions. Loss of neuronal RBM20 has only modest impact on alternative splice isoforms but results in a significant reduction in an array of mature mRNAs in the neuronal cytoplasm. This phenotype is particularly pronounced for genes with long introns that encode synaptic proteins. We hypothesize that RBM20 ensures fidelity of pre-mRNA splicing by suppressing non-productive splicing events in long neuronal genes. This work highlights a common requirement of two excitable cell types, cardiomyocytes and neurons, for RBM20-dependent transcriptome regulation.
Project description:Severe forms of dilated cardiomyopathy (DCM) are associated with point mutations in the alternative splicing regulator RBM20 that are frequently located in the arginine/serine-rich domain (RS-domain). Such mutations can cause defective splicing and cytoplasmic mislocalization, which leads to the formation of detrimental cytoplasmic granules. Successful development of personalized therapies requires identifying the direct mechanisms of pathogenic RBM20 variants. Here, we decipher the molecular mechanism of RBM20 mislocalization and its specific role in DCM pathogenesis. We demonstrate that mislocalized RBM20 variants retain their splice regulatory activity, which reveals that aberrant cellular localization drives the pathological phenotype. A genome-wide CRISPR knock-out screen combined with image-enabled cell sorting identified Transportin-3 (TNPO3) as the main nuclear importer of RBM20. We show that the direct RBM20-TNPO3 interaction involves the RS-domain, disrupted by pathogenic variants. Re-localization of pathogenic RBM20 variants to the nucleus restores alternative splicing and dissolves cytoplasmic granules in cell culture and animal models. These findings provide proof-of-principle for developing therapeutic strategies to restore RBM20’s nuclear localization in RBM20-DCM patients.
Project description:Background: Modulation of mRNA splicing acts as an important layer of gene regulation, in addition to transcriptional regulation and epigenetic modifications. RNA binding proteins (RBPs) play essential roles in mediating RNA splicing and are key regulators of heart development and function. Our previous studies demonstrated that RBPMS (RNA-binding protein with multiple splicing) regulates cardiac development through modulating mRNA splicing during embryogenesis. Here we explored the postnatal function of RBPMS in the heart. Methods: We ablated Rbpms in the heart by generating a cardiac-specific knockout mouse line (Myh6-Cre, Rbpmsfl/fl), and evaluated its cardiac functions by histology, echocardiography, and gene expression. Paired-end RNA sequencing and RT-PCR were performed to identify and validate splicing targets of RBPMS in adult mouse hearts. Proximity-dependent Biotin Identification (BioID) assay and mass spectrometry analysis were performed to identify RBPMS binding partners. We also measured contractility and calcium fluxes in isolated mouse cardiomyocytes, and contractile forces of cardiac papillary muscle. Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) were also used as a model to explore the influence of RBPMS on contractility of human cardiomyocytes. Results: he absence of Rbpms in the heart led to dilated cardiomyopathy (DCM) and heart failure, causing early death in mice. Mice with cardiac-specific knockout of Rbpms showed myocardium noncompaction with reduced cardiomyocyte number at the neonatal stage and developed DCM with pervasive myocardial fibrosis in adulthood. We found that RBPMS mediates a largely distinct RNA splicing profile in adult mouse hearts compared to neonatal hearts, indicating a stage-specific modulation of alternative RNA splicing by RBPMS. In adult hearts, RBPMS mainly influenced alternative splicing of genes associated with sarcomere structures and cardiomyocyte contraction, such as Ttn, Pdlim5 and Nexn, to generate new protein isoforms. In neonatal hearts, RBPMS influenced the splicing of cytoskeletal genes. RBMPS was associated with spliceosome factors and other RNA binding proteins that play important roles in the heart, such as RBM20 and GATA4. Importantly, we found that the absence of Rbpms caused severe cardiomyocyte contractile defects and reduced calcium sensitivity in both mouse and hiPSC-CMs. Our results demonstrated that Rbpms is crucial for postnatal cardiac function and cardiomyocyte contractility by regulating RNA alternative splicing. Conclusions: Loss of Rbpms in the heart causes reduced cardiomyocyte number and impaired cardiomyocyte contraction, leading to DCM and heart failure.
Project description:Background: Despite the prevalence and biological relevance of both signalling pathways and alternative pre-mRNA splicing, our knowledge of how intracellular signalling impacts on alternative splicing regulation remains fragmentary. We report a genome-wide analysis of changes in alternative splicing using splicing-sensitive microarrays, induced by activation of two distinct signalling pathways, insulin and wingless, in Drosophila cells in culture. Results: Alternative splicing changes induced by insulin affect more than 150 genes and more than 50 genes are regulated by wingless activation. About 40% of the genes showing changes in alternative splicing also show regulation of mRNA levels, suggesting distinct but also significantly overlapping programs of transcriptional and posttranscriptional regulation. Distinct functional sets of genes are regulated by each pathway and, remarkably, a significant overlap is observed between functional categories of genes regulated transcriptionally and at the level of alternative splicing. Functions related with carbohydrate metabolism and cellular signalling are enriched among genes regulated by insulin and wingless, respectively. Computational searches identify pathway-specific sequence motifs enriched near regulated 5â splice sites. Conclusion: Taken together, our data indicate that signalling cascades trigger pathway-specific and biologically coherent regulatory programs of alternative splicing regulation. They also reveal that alternative splicing can provide a novel molecular mechanism for cross-talk between different signalling pathways. To monitor transcriptional and alternative splicing changes induced by activation of the insulin and wingless pathways, a custom-designed microarray platform was employed featuring probes for all Drosophila genes for which different mRNA isoforms generated by alternative splicing have been described (see Blanchette M, Green RE, Brenner SE, Rio DC: Global analysis of positive and negative pre-mRNA splicing regulators in Drosophila. Genes Dev 2005, 19(11):1306-1314.). Three biological replicates of total RNA isolated after pathway activation or controls (untreated cells for insulin, control dsRNA for wingless) were purified, reverse transcribed into cDNA and labelled with Cy5 or Cy3 fluorochromes and the cDNA was hybridized to the microarray,
Project description:Alternative splicing of pre-mRNA is a prominent mechanism to generate protein diversity, yet its regulation is poorly understood. Here, we demonstrate a direct role for histone modifications in alternative splicing. We find distinctive histone modification signatures which correlate with splicing outcome in a set of human genes. Modulation of histone modifications causes splice site switching. The mechanism for histone-mediated splice site selection involves a histone mark which is read by a chromatin protein, which in turn recruits a splicing regulator. These results outline an adaptor system for reading of histone marks by the pre-mRNA splicing machinery. To obtain an estimate of how many PTB-dependent alternative splicing events are regulated by SET2/MRG15-mediated recruitment of PTB, we carried out a genomewide comparative analysis of alternative splicing in hMSC cells depleted of either SETD2, MRG15 or PTB using specific siRNAs, or mock-depleted using a control siRNA.
Project description:Ethanol’s anxiolytic actions contribute to increased consumption and the development of Alcohol Use Disorder (AUD). Our laboratory previously identified genetic loci contributing to the anxiolytic-like properties of ethanol in BXD recombinant inbred mice, derived from C57BL/6J (B6) and DBA/2J (D2) progenitor strains. That work identified Ninein (Nin) as a candidate gene underlying ethanol’s acute anxiolytic-like properties in BXD mice. Nin has a complex exonic content with known alternative splicing events that alter cellular distribution of the NIN protein. We hypothesize that strain-specific differences in Nin alternative splicing contribute to changes in Nin gene expression and B6/D2 strain differences in ethanol anxiolysis. Using quantitative reverse-transcriptase PCR to target Nin alternative splicing, we identified isoform-specific exon expression differences between B6 and D2 mice in prefrontal cortex, nucleus accumbens and amygdala. We extended this analysis using deep RNA sequencing in B6 and D2 nucleus accumbens samples and that Nin expression was significantly higher in D2 mice. Furthermore, exon utilization and alternative splicing analyses identified 8 differentially utilized exons and significant exon-skipping events between the strains, including 3 novel splicing events in the 3’ end of the Nin gene that were specific to the D2 strain. Our studies provide the first in-depth analysis of Nin alternative splicing in brain and identify a potential genetic mechanism altering Nin expression between B6 and D2 mice, thus contributing to differences in the anxiolytic-like properties of ethanol between these strains. This work contributes to our understanding of genetic differences modulating ethanol actions on anxiety that may contribute to the risk for alcohol use disorder.