Project description:The Drosophila polyadenosine RNA binding protein Nab2, which is orthologous to a human protein lost in a form of inherited intellectual disability, controls axon projection, locomotion, and memory. Here we define an unexpectedly specific role for Nab2 in regulating splicing of ~150 exons/introns in the head transcriptome and link the most prominent of these, female retention of a male-specific exon in the sex determination factor Sex-lethal (Sxl), to a role in m6A-dependent mRNA splicing. Genetic evidence indicates that aberrant Sxl splicing underlies multiple phenotypes in Nab2 mutant females. At a molecular level, Nab2 associates with Sxl pre-mRNA and ensures proper female-specific splicing by preventing m6A hypermethylation by Mettl3 methyltransferase. Consistent with these results, reducing Mettl3 expression rescues developmental, behavioral and neuroanatomical phenotypes in Nab2 mutants. Overall these data identify Nab2 as a required regulator of m6A-regulated Sxl splicing and imply a broader link between Nab2 and Mettl3-regulated brain RNAs.
Project description:Stem cells need to balance self-renewal and differentiation for correct tissue development and homeostasis. Defects in this balance can lead to developmental defects or tumor formation. In recent years, mRNA splicing has emerged as one important mechanism regulating cell fate decisions. Here we address the role of the evolutionary conserved splicing co-factor Barricade (Barc)/CUS2/Tat-SF1 in Drosophila neural stem cell (neuroblast) lineage formation. We show that Barc is required for the generation of neurons during Drosophila brain development by ensuring correct neural progenitor proliferation and differentiation. Barc associates with components of the U2 small nuclear ribonucleic proteins (snRNP), and its depletion causes alternative splicing in form of intron retention in a subset of genes. Using bioinformatics analysis and a cell culture based splicing assay, we found that Barc dependent introns share three major traits: they are short, GC rich and have weak 3’ splice sites. Our results show that Barc, together with the U2snRNP, plays an important role in regulating neural stem cell lineage progression during brain development and facilitates correct splicing of a subset of introns.
Project description:Nab2 encodes a polyadenosine RNA-binding protein (RBP) with broad roles in post-transcriptional regulation, including in RNA export, poly(A) tail length control, and mRNA splicing, and loss of its human ortholog ZC3H14 gives rise to a form of autosomal recessive intellectual disability. Understanding of Nab2/ZC3H14 function in metazoan nervous systems is limited, in part, because no comprehensive identification of metazoan-Nab2-associated RNA transcripts has yet been conducted. Moreover, many Nab2/ZC3H14 functional protein partnerships likely remain unidentified. Here we present evidence that Drosophila melanogaster Nab2 interacts with the RBP Ataxin-2 (Atx2), a neuronal translational regulator, and implicate these proteins in coordinate regulation of neuronal morphology and adult viability. We then present the first high-throughput identifications of RNAs associating with Nab2 and Atx2 in Drosophila brain neurons using an RNA immunoprecipitation-sequencing (RIP-Seq) approach. Critically, the RNA interactomes of each RBP overlap. The identities of shared associated transcripts (e.g. drk, me31B, stai) and of transcripts specific to Nab2 or Atx2 (e.g. Arpc2, tea, respectively) promise insight into the neuronal functions of and interactions between each RBP. Significantly, we find Nab2 exhibits high specificity in its RNA associations in neurons in vivo, associating with only a fraction of all polyadenylated RNAs. These Nab2-associated RNAs are overrepresented for internal A-rich motifs, suggesting such sequences may partially mediate Nab2 target selection. Taken together, these data demonstrate 1)Nab2 opposingly regulates neuronal morphology and shares associated neuronal RNAs with Atx2 and 2)Drosophila Nab2 associates with a more specific subset of polyadenylated mRNAs than its polyadenosine affinity alone may suggest.
Project description:To determine the prevalence of cotranscriptional splicing in Drosophila, we sequenced nascent RNA transcripts from Drosophila S2 cells as well as from Drosophila heads. 87% of introns assayed manifest more than 50% cotranscriptional splicing. The remaining 13% are cotranscriptionally spliced poorly, or slowly, with ~3% being almost completely retained in nascent pre-mRNA. Although individual introns showed slight but statistically significant differences in splicing efficiency, similar global levels of splicing were seen from both sources. Importantly, introns with low cotranscriptional splicing efficiencies are present in the same primary transcript with efficiently spliced introns, indicating that splicing is intron-specific. The analysis also indicates that cotranscriptional splicing is less efficient for first introns, longer introns and introns annotated as alternative. FinallyFinally, S2 cells expressing the slow RpII215C4 mutant manifest substantially less intron retention than wild-type S2 cells. Examination of Total pA and Nascent RNA from 2 different cell populations and isolated fly heads.
Project description:In this study, we identify MBNL1 as a unique molecular vulnerability across MLL-rearranged leukemias. Through transcriptomic profiling and novel splicing analyses of MLL-rearranged leukemia cell lines following shRNA knockdown of MBNL1, we show that MBNL1 regulates alternative splicing (predominantly intron retention) of genes essential to MLL-rearranged leukemogenesis, such as DOT1L and SETD1A.
Project description:Stem cells need to balance self-renewal and differentiation for correct tissue development and homeostasis. Defects in this balance can lead to developmental defects or tumor formation. In recent years, mRNA splicing has emerged as one important mechanism regulating cell fate decisions. Here we address the role of the evolutionary conserved splicing co-factor Barricade (Barc)/CUS2/Tat-SF1 in Drosophila neural stem cell (neuroblast) lineage formation. We show that Barc is required for the generation of neurons during Drosophila brain development by ensuring correct neural progenitor proliferation and differentiation. Barc associates with components of the U2 small nuclear ribonucleic proteins (snRNP), and its depletion causes alternative splicing in form of intron retention in a subset of genes. Using bioinformatics analysis and a cell culture based splicing assay, we found that Barc dependent introns share three major traits: they are short, GC rich and have weak 3’ splice sites. Our results show that Barc, t...
Project description:Nascent RNA sequencing has recently revealed that pre-mRNA splicing can occur shortly after the intron emerges from RNA polymerase II (Pol II). Differences in co-transcriptional splicing profiles suggest regulation by cis- and/or trans-acting factors. Here we used Single Molecule Intron Tracking (SMIT) in budding yeast to identify a cohort of regulators by machine learning. One candidate, Nab2, displayed reduced co-transcriptional splicing of some pre-mRNAs when depleted. Unexpectedly, these splicing defects were attributable to readthrough transcription, which was revealed by long read sequencing of nascent RNA; individual readthrough transcripts induced by Nab2 depletion sometimes spanned multiple genes. Thus, Nab2 regulation of splicing was indirect. Moreover, unspliced transcripts displayed downstream readthrough in both control and Nab2-depleted cells, highlighting the coupling between splicing and 3′ end formation. We conclude that Nab2 is required for proper 3′ end processing, which ensures both transcription termination as well as proper splicing of downstream genes.
Project description:To determine the prevalence of cotranscriptional splicing in Drosophila, we sequenced nascent RNA transcripts from Drosophila S2 cells as well as from Drosophila heads. 87% of introns assayed manifest more than 50% cotranscriptional splicing. The remaining 13% are cotranscriptionally spliced poorly, or slowly, with ~3% being almost completely retained in nascent pre-mRNA. Although individual introns showed slight but statistically significant differences in splicing efficiency, similar global levels of splicing were seen from both sources. Importantly, introns with low cotranscriptional splicing efficiencies are present in the same primary transcript with efficiently spliced introns, indicating that splicing is intron-specific. The analysis also indicates that cotranscriptional splicing is less efficient for first introns, longer introns and introns annotated as alternative. FinallyFinally, S2 cells expressing the slow RpII215C4 mutant manifest substantially less intron retention than wild-type S2 cells.
Project description:We exploit the predictable time course of Drosophila brain development to perform a temporally coupled quantitative proteomic analysis of the pupal brain in Nab2 mutant or overexpression models, which reveals that Nab2 is required to regulate the abundance of a number of proteins with critical roles in Drosophila neurons. Pupal brains lacking Nab2 show dysregulation of proteins, such as Futsch, Turtle, Contactin, and Van Gogh, that typically function in brain morphogenesis, neuroblast proliferation, circadian sleep/wake cycle, and other neurodevelopmental processes. Overall, these data define a role for Nab2 during neurodevelopment in regulating protein abundance for a subset of the brain proteome and provide a window into the potential functions of human ZC3H14 protein.
Project description:Transcriptomic and epigenomic profiling of matched CML diagnosis/remission samples revealed a reconfiguration of gene expression and DNA methylation at remission exhibiting patterns similar to those observed in healthy individuals. In contrast, alternative splicing retains chronic phase-like abnormal patterns. Most dramatic dissimilarities between remission and healthy control samples were observed in intron retention. While reduced DNA methylation around splice sites could explain increased intron retention at diagnosis, maintenance of high intron retention levels at remission has other causes, such as reduced splicing factor expression and histone modifications.