Biology subjects

Burge, C. B.

Publications and source records attributed to Burge, C. B..

15 recordsLinked to original sources

bioRxiv2024

KATMAP: Inferring splicing factor activity and regulatory targets from knockdown data

Typical RNAseq experiments uncover hundreds of splicing changes, reflecting underlying changes in splicing factor (SF) activity. Understanding transcriptomic variation in terms of SF activity requires elucidating the rules by which each SF impacts splicing. Here we present an interpretable regression model, KATMAP, which models splicing changes transcriptome-wide in terms of changes in SF binding and resulting altered regulation. The regulatory principles KATMAP learns generalize to predict the SFs regulation at individual exons, with potential for design of splice-switching antisense oligonucleotides and inference of the displaced factor. We also discover cooperative splicing regulation by QKI and RFBOX proteins. KATMAP interprets RNAseq data by uncovering the factors responsible for transcriptomic changes, distinguishing direct SF targets from indirect effect, and infers relevant SFs from clinical RNAseq data.

bioinformatics↗

bioRxiv2024

Understanding species-specific and conserved RNA-protein interactions in vivo and in vitro

While evolution is often considered from a DNA- and protein-centric view, RNA-based regulation can also impact gene expression and protein sequences. Here we examined interspecies differences in RNA-protein interactions using the conserved neuronal RNA binding protein, Unkempt (UNK) as model. We find that roughly half of mRNAs bound in human are also bound in mouse. Unexpectedly, even when transcript-level binding was conserved across species differential motif usage was prevalent. To understand the biochemical basis of UNK-RNA interactions, we reconstituted the human and mouse UNK-RNA interactomes using a high-throughput biochemical assay. We uncover detailed features driving binding, show that in vivo patterns are captured in vitro, find that highly conserved sites are the strongest bound, and associate binding strength with downstream regulation. Furthermore, subtle sequence differences surrounding motifs are key determinants of species-specific binding. We highlight the complex features driving protein-RNA interactions and how these evolve to confer species-specific regulation.

evolutionary biology↗

bioRxiv2023

Regulatory features aid interpretation of 3'UTR variants

Our ability to determine the clinical impact of variants in 3 untranslated regions (UTRs) of genes remains poor. We provide a thorough analysis of 3UTR variants from several datasets. Variants in putative regulatory elements including RNA-binding protein motifs, eCLIP peaks, and microRNA sites are up to 16 times more likely than other variants to have gene expression and phenotype associations. Heterozygous variants in regulatory motifs result in allele-specific protein binding in cell lines and allele-specific gene expression differences in population studies. In addition, variants in shared regions of alternatively polyadenylated isoforms and those proximal to polyA sites are more likely to affect gene expression and phenotype. Finally, pathogenic 3UTR variants in ClinVar are 20 times more likely than benign variants to fall in a regulatory site. We incorporated these findings into RegVar, a software tool that interprets regulatory elements and annotations for any 3UTR variant, and predicts whether the variant is likely to affect gene expression or phenotype. This tool will help prioritize variants for experimental studies and identify pathogenic variants in patients.

genomics↗

bioRxiv2022

Human LUC7 proteins impact splicing of two major subclasses of 5' splice sites

Mutation or deletion of the U1 snRNP-associated factor LUC7L2 is associated with myeloid neoplasms, and knockout of LUC7L2 alters cellular metabolism. Here, we uncover that members of the LUC7 protein family differentially regulate two major classes of 5 splice sites (5SS) and broadly regulate mRNA splicing in both human cell lines and leukemias with LUC7L2 copy number variation. We describe distinctive 5SS features of exons impacted by the three human LUC7 paralogs: LUC7L2 and LUC7L enhance splicing of "right-handed" 5SS with stronger consensus matching on the intron side of the near-invariant /GU, while LUC7L3 enhances splicing of "left-handed" 5SS with stronger consensus matching upstream of the /GU. We validated our model of sequence-specific 5SS regulation both by mutating splice sites and swapping domains between human LUC7 proteins. Evolutionary analysis indicates that the LUC7L2/LUC7L3 subfamilies diverged before the divergence of animals and plants. Analysis of Arabidopsis thaliana mutants confirmed that plant LUC7 orthologs possess specificity similar to their human counterparts, indicating that 5SS regulation by LUC7 proteins is deeply conserved.

molecular biology↗

bioRxiv2022

Quantifying negative selection in human 3' UTRs uncovers constrained targets of RNA-binding proteins

Many non-coding variants associated with phenotypes occur in 3 untranslated regions (3 UTRs) and may affect interactions with RNA-binding proteins (RBPs) to regulate post-transcriptional gene expression. However, identifying functional 3 UTR variants has proven difficult. We used allele frequencies from the Genome Aggregation Database (gnomAD) to identify classes of 3 UTR variants under strong negative selection in humans. We developed intergenic mutability-adjusted proportion singleton (iMAPS), a generalized measure related to MAPS, to quantify negative selection in non-coding regions. This approach, in conjunction with in vitro and in vivo binding data, identifies precise RBP binding sites, miRNA target sites, and polyadenylation signals (PASs) under strong selection. For each class of sites, we identified thousands of gnomAD variants under selection comparable to missense coding variants, and found that sites in core 3 UTR regions upstream of the most-used PAS are under strongest selection. Together, this work improves our understanding of selection on human genes and validates approaches for interpreting genetic variants in human 3 UTRs.

evolutionary biology↗

bioRxiv2022

Splicing quality control mediated by DHX15 and itsG-patch activator, SUGP1

Pre-mRNA splicing is surveilled at different stages by quality control (QC) mechanisms. The leukemia-associated DExH-box family helicase hDHX15/scPrp43, is known to disassemble spliceosomes after splicing. Here, using rapid protein depletion and analysis of nascent and mature RNA to enrich for direct effects, we identified a widespread splicing QC function for DHX15 in human cells, consistent with recent in vitro studies. We found that suboptimal introns with weak splice sites, multiple branch points, and cryptic introns are repressed by DHX15, suggesting a general role in promoting splicing fidelity. We identified SUGP1 as a G-patch factor that activates DHX15s splicing QC function. This interaction is dependent on both DHX15s ATPase activity and on SUGP1s ULM domain. Together, our results support a model in which DHX15 plays a major role in splicing QC when recruited and activated by SUGP1.

molecular biology↗

bioRxiv2021

Sensory nerves enhance triple-negative breast cancer migration and metastasis via the axon guidance molecule PlexinB3

In breast cancer, nerve presence has been correlated with more invasive disease and worse prognosis, yet the mechanisms by which different types of peripheral nerves drive tumor progression remain poorly understood. In this study, we identified sensory nerves as more abundant in human triple-negative breast cancer (TNBC) tumors. Coinjection of sensory neurons isolated from the dorsal root ganglia (DRG) of adult female mice with human TNBC cells in immunocompromised mice increased the number of lung metastases. Direct in vitro co-culture of human TNBC cells with the dorsal root ganglia (DRG) of adult female mice revealed that TNBC cells adhere to sensory neuron fibers leading to an increase in migration speed. Species-specific RNA sequencing revealed that co-culture of TNBC cells with sensory nerves upregulates the expression of genes associated with cell migration and adhesion in cancer cells. We demonstrate that the axon guidance molecule Plexin B3 mediates cancer cell adhesion to and migration on sensory nerves. Together, our results identify a novel mechanism by which nerves contribute to breast cancer migration and metastasis by inducing a shift in TNBC cell gene expression and support the rationale for disrupting neuron-cancer cell interactions to target metastasis. SignificanceThe presence of nerves in breast tumors has been associated with poor outcome. Understanding the mechanisms by which nerves contribute to tumor progression could help identify novel strategies to target metastatic disease.

cancer biology↗

bioRxiv2019

Secondary motifs enable concentration-dependent regulation by Rbfox family proteins

The Rbfox family of splicing factors regulate alternative splicing during animal development and in disease, impacting thousands of exons in the maturing brain, heart, and muscle. Rbfox proteins have long been known to bind to the RNA sequence GCAUG with high affinity, but just half of Rbfox CLIP peaks contain a GCAUG motif. We incubated recombinant RBFOX2 with over 60,000 transcriptomic sequences to reveal significant binding to several moderate-affinity, non-GCAYG sites at a physiologically relevant range of RBFOX concentrations. We find that many of these "secondary motifs" bind Rbfox robustly in vivo and that several together can exert regulation comparable to a GCAUG in a trichromatic splicing reporter assay. Furthermore, secondary motifs regulate RNA splicing in neuronal development and in neuronal subtypes where cellular Rbfox concentrations are highest, enabling a second wave of splicing changes as Rbfox levels increase.

biochemistry↗

bioRxiv2019

Exon-mediated activation of transcription starts

The processing of transcripts from mammalian genes often occurs near in time and space to their transcription. Here we describe a phenomenon we call exon-mediated activation of transcription starts (EMATS) that affects thousands of mammalian genes in which the splicing of internal exons impacts the spectrum of promoters used and expression level of the host gene. We observed that evolutionary gain of new internal exons is associated with gain of new TSSs nearby and increased gene expression. Inhibiting exon splicing reduced transcription from nearby promoters. Conversely, creation of new splice sites and enable splicing of new exons activated transcription from cryptic promoters. The strongest effects were associated with weak promoters located proximal and upstream of efficiently spliced exons. Together, our findings support a model in which splicing factors recruit transcription machinery locally to influence TSS choice, and identify exon gain, loss and regulatory change as major contributors to the evolution of alternative promoters and altered gene expression in mammals.

genomics↗

bioRxiv2018

Widespread PERK-dependent repression of ER targets in response to ER stress

The UPR (Unfolded Protein Response) is a well-orchestrated response to ER protein folding and processing overload, integrating both transcriptional and translational outputs. Its three arms in mammalian cells, the PERK translational response arm, together with the ATF6 and IRE1-XBP1-mediated transcriptional arms, have been thoroughly investigated.\n\nUsing ribosome footprint profiling, we performed a deep characterization of gene expression programs involved in the early and late ER stress responses, within WT or PERK -/- Mouse Embryonic Fibroblasts (MEFs). We found that both repression and activation gene expression programs, affecting hundreds of genes, are significantly hampered in the absence of PERK. Specifically, PERK -/- cells do not show global translational inhibition, nor do they specifically activate early gene expression programs upon short exposure to ER stress. Furthermore, while PERK -/- cells do activate/repress late ER-stress response genes, the response is substantially weaker. Importantly, we highlight a widespread PERK-dependent repression gene expression program, consisting of ER targeted proteins, including transmembrane proteins, glycoproteins, and proteins with disulfide bonds. This phenomenon occurs in various different cell types, and has a major translational regulatory component. Moreover, we revealed a novel interplay between PERK and the XBP1-ATF6 arms of the UPR, whereby PERK attenuates the expression of a specific subset of XBP1-ATF6 targets, further illuminating the complexity of the integrated ER stress response.

molecular biology↗

bioRxiv2018

Allele-specific binding of RNA-binding proteins reveals functional genetic variants in the RNA

Allele-specific protein-RNA binding is an essential aspect that may reveal functional genetic variants influencing RNA processing and gene expression phenotypes. Recently, genome-wide detection of in vivo binding sites of RNA binding proteins (RBPs) is greatly facilitated by the enhanced UV crosslinking and immunoprecipitation (eCLIP) protocol. Hundreds of eCLIP-Seq data sets were generated from HepG2 and K562 cells during the ENCODE3 phase. These data afford a valuable opportunity to examine allele-specific binding (ASB) of RBPs. To this end, we developed a new computational algorithm, called BEAPR (Binding Estimation of Allele-specific Protein-RNA interaction). In identifying statistically significant ASB sites, BEAPR takes into account UV cross-linking induced sequence propensity and technical variations between replicated experiments. Using simulated data and actual eCLIP-Seq data, we show that BEAPR largely outperforms often-used methods Chi-Squared test and Fishers Exact test. Importantly, BEAPR overcomes the inherent over-dispersion problem of the other methods. Complemented by experimental validations, we demonstrate that ASB events are significantly associated with genetic regulation of splicing and mRNA abundance, supporting the usage of this method to pinpoint functional genetic variants in post-transcriptional gene regulation. Many variants with ASB patterns of RBPs were found as genetic variants with cancer or other disease relevance. About 38% of ASB variants were in linkage disequilibrium with single nucleotide polymorphisms from genome-wide association studies. Overall, our results suggest that BEAPR is an effective method to reveal ASB patterns in eCLIP and can inform functional interpretation of disease-related genetic variants.

bioinformatics↗

bioRxiv2018

Numerous recursive sites contribute to accuracy of splicing of long introns in flies

Recursive splicing, a process by which a single intron is removed from pre-mRNA transcripts in multiple distinct segments, has been observed in a small subset of Drosophila melanogaster introns. However, detection of recursive splicing requires observation of splicing intermediates which are inherently unstable, making it difficult to study. Here we developed new computational approaches to identify recursively spliced introns and applied them, in combination with existing methods, to nascent RNA sequencing data from Drosophila S2 cells. These approaches identified hundreds of novel sites of recursive splicing, expanding the catalog of recursively spliced fly introns by 4-fold. Recursive sites occur in most very long (> 40 kb) fly introns, including many genes involved in morphogenesis and development, and tend to occur near the midpoints of introns. Suggesting a possible function for recursive splicing, we observe that fly introns with recursive sites are spliced more accurately than comparably sized non-recursive introns.

genomics↗

bioRxiv2017

Sequence, Structure and Context Preferences of Human RNA Binding Proteins

Production of functional cellular RNAs involves multiple processing and regulatory steps principally mediated by RNA binding proteins (RBPs). Here we present the affinity landscapes of 78 human RBPs using an unbiased assay that determines the sequence, structure, and context preferences of an RBP in vitro from deep sequencing of bound RNAs. Analyses of these data revealed several interesting patterns, including unexpectedly low diversity of RNA motifs, implying frequent convergent evolution of binding specificity toward a relatively small set of RNA motifs, many with low compositional complexity. Offsetting this trend, we observed extensive preferences for contextual features outside of core RNA motifs, including spaced \"bipartite\" motifs, biased flanking nucleotide context, and bias away from or towards RNA structure. These contextual features are likely to enable targeting of distinct subsets of transcripts by different RBPs that recognize the same core motif. Our results enable construction of \"RNA maps\" of RBP activity without requiring crosslinking-based assays, and provide unprecedented depth of information on the interaction of RBPs with RNA.

biochemistry↗

bioRxiv2017

A Large-Scale Binding and Functional Map of Human RNA Binding Proteins

Genomes encompass all the information necessary to specify the development and function of an organism. In addition to genes, genomes also contain a myriad of functional elements that control various steps in gene expression. A major class of these elements function only when transcribed into RNA as they serve as the binding sites for RNA binding proteins (RBPs), which act to control post-transcriptional processes including splicing, cleavage and polyadenylation, RNA editing, RNA localization, stability, and translation. Despite the importance of these functional RNA elements encoded in the genome, they have been much less studied than genes and DNA elements. Here, we describe the mapping and characterization of RNA elements recognized by a large collection of human RBPs in K562 and HepG2 cells. These data expand the catalog of functional elements encoded in the human genome by addition of a large set of elements that function at the RNA level through interaction with RBPs.\n\nHighlightsO_LI223 eCLIP datasets for 150 RBPs reveal a wide variety of in vivo RNA target classes.\nC_LIO_LI472 knockdown/RNA-seq profiles of 263 RBPs reveal factor-responsive targets and integration with eCLIP indicates RNA expression and splicing regulatory patterns.\nC_LIO_LI78 RNA Bind-N-Seq profiles of in vitro binding motifs reveal links between in vitro and in vivo binding and indicate that eCLIP peaks that contain in vitro motifs are more strongly associated with regulation.\nC_LIO_LI274 maps of RBP subcellular localization by immunofluorescence indicate widespread organelle-specific RNA processing regulation.\nC_LIO_LI63 ChIP-seq profiles of DNA association suggest broad interconnectivity between chromatin association and RNA processing.\nC_LI

genomics↗

bioRxiv2017

Intron Length and Recursive Sites are Major Determinants of Splicing Efficiency in Flies

Production of most eukaryotic mRNAs requires splicing of introns from pre-mRNA. The splicing reaction requires definition of splice sites, which are initially recognized in either intron-spanning (\"intron definition\") or exon-spanning (\"exon definition\") pairs. To understand how exon and intron length and splice site recognition mode impact splicing, we measured splicing rates genome-wide in Drosophila, using metabolic labeling/RNA sequencing and new mathematical models to estimate rates. We found that the modal intron length range of 60-70 nt represents a local maximum of splicing rates, but that much longer exon-defined introns are spliced even faster and more accurately. Surprisingly, we observed low variation in splicing rates across introns in the same gene, suggesting the presence of gene-level influences, and we identified multiple gene level variables associated with splicing rate. Together our data suggest that developmental and stress response genes may have preferentially evolved exon definition in order to enhance rates of splicing.

genomics↗