Biology subjects

Fiszbein, A.

Publications and source records attributed to Fiszbein, A..

10 recordsLinked to original sources

bioRxiv2026

SRSF1 regulates polyadenylation site selection independently of and through coordination with U1 snRNP

Proper polyadenylation site (PAS) selection is critical for RNA isoform determination. Core spliceosomal components, including U1 snRNP, regulate PAS choice, but whether they work with other splicing factors in this role remains unclear. Here, we establish that the splicing factor SRSF1 regulates 3'-end selection through complementary mechanisms with varying degrees of independence from U1 snRNP. Within 3 UTRs, largely independent of U1 snRNP, SRSF1 binds RNA near proximal PASs and promotes their usage. Congruent with this observation, breast cancer tumors with altered SRSF1 levels display shifted 3'-end selection. At PASs modulated by both SRSF1 and U1 snRNP, SRSF1 acts on sites through U1 snRNP-mediated Pol II interactions. Consistent with co-transcriptional regulation, SRSF1 reduces the Pol II elongation index and transcription readthrough. Together, our results reveal that SRSF1 shapes RNA isoform determination beyond its canonical role in splicing, through a combination of direct RNA binding and U1 snRNP-dependent co-transcriptional coordination.

molecular biology↗

bioRxiv2025

An SMN2 splicing-correcting antisense oligonucleotide promotes gene looping

We have previously proposed a combined therapy for spinal muscular atrophy based on the upregulation of exon 7 (E7) inclusion into SMN2 mRNA by the antisense oligonucleotide nusinersen (ASO1) together with histone deacetylase inhibitors (HDACi). Using a CRISPR/deadCas-based strategy, we show here that targeting histone acetylation at the SMN2 E7 region duplicates the HDACi effect, which overcomes pleiotropic effects. Most noticeably, targeted acetylation at the E7 region causes acetylation and activation of the 30-kbp-distant promoter. Since E7 and the nusinersen target site map near the SMN2 gene 3'-end, this cross-talk between the two ends of the gene prompted us to use chromosome conformation analysis (3C) to find that ASO1 promotes gene looping. This unpredicted property of ASOs in modulating chromatin 3D configuration depends on cohesin, CTCF, cleavage/polyadenylation factors and a canonical poly(A) signal, and causes promoter activation at a long distance, which expands the therapeutic potential of splicing-correcting ASOs.

molecular biology↗

bioRxiv2025

SpliceImpactR maps alternative RNA processing events driving protein functional diversity

Alternative RNA processing is a key regulator of gene expression, driving transcript and proteomic diversity essential for cell function. However, the precise impacts of different alternative RNA processing events on protein function remain poorly understood. Here, we introduce SpliceImpactR, an open-source tool that systematically identifies RNA isoform switches--including alternative first and last exons, exon skipping, intron retention, hybrid exons, and splice site variation--across the human transcriptome, and predicts their impact on encoded proteins. We find that intron retention and hybrid exons frequently alter the coding potential of transcripts. Strikingly, when both isoforms remain protein-coding, 87% of alternative RNA processing events result in substantial changes to the protein sequence. Among these, alternative last exons drive the largest changes, frequently disrupting protein-protein interactions. Across human tissues, alternative first exons drive the largest relative changes in proteins, often resulting in tissue-specific protein domains. Notably, frameshifts introduced by alternative splicing are often rescued by co-regulated alternative downstream exons, suggesting a buffering mechanism in isoform regulation. Moreover, we show that alternative splicing exhibits gradual, tissue-specific variation, rather than binary on/off behavior, enabling conserved regulation of protein domains across tissues. Together, our results provide a proteome-wide view of splicing regulation, uncovering widespread, context-dependent impacts of alternative splicing on the human proteome.

bioinformatics↗

bioRxiv2024

Biosurfer for systematic tracking of regulatory mechanisms leading to protein isoform diversity

Long-read RNA sequencing has shed light on transcriptomic complexity, but questions remain about the functionality of downstream protein products. We introduce Biosurfer, a computational approach for comparing protein isoforms, while systematically tracking the transcriptional, splicing, and translational variations that underlie differences in the sequences of the protein products. Using Biosurfer, we analyzed the differences in 32,799 pairs of GENCODE annotated protein isoforms, finding a majority (70%) of variable N-termini are due to the alternative transcription start sites, while only 9% arise from 5 UTR alternative splicing. Biosurfers detailed tracking of nucleotide-to-residue relationships helped reveal an uncommonly tracked source of single amino acid residue changes arising from the codon splits at junctions. For 17% of internal sequence changes, such split codon patterns lead to single residue differences, termed "ragged codons". Of variable C-termini, 72% involve splice- or intron retention-induced reading frameshifts. We found an unusual pattern of reading frame changes, in which the first frameshift is closely followed by a distinct second frameshift that restores the original frame, which we term a "snapback" frameshift. We analyzed long read RNA-seq-predicted proteome of a human cell line and found similar trends as compared to our GENCODE analysis, with the exception of a higher proportion of isoforms predicted to undergo nonsense-mediated decay. Biosurfers comprehensive characterization of long-read RNA-seq datasets should accelerate insights of the functional role of protein isoforms, providing mechanistic explanation of the origins of the proteomic diversity driven by the alternative splicing. Biosurfer is available as a Python package at https://github.com/sheynkman-lab/biosurfer.

genomics↗

bioRxiv2024

A large-scale cancer-specific protein-DNA interaction network

Cancer development and progression are generally associated with dysregulation of gene expression, often resulting from changes in transcription factor (TF) sequence or expression. Identifying key TFs involved in cancer gene regulation provides a framework for potential new therapeutics. This study presents a large-scale cancer gene TF-DNA interaction network as well as an extensive promoter clone resource for future studies. Most highly connected TFs do not show a preference for binding to promoters of genes associated with either good or poor cancer prognosis, suggesting that emerging strategies aimed at shifting gene expression balance between these two prognostic groups may be inherently complex. However, we identified potential for oncogene targeted therapeutics, with half of the tested oncogenes being potentially repressed by influencing specific activator or bifunctional TFs. Finally, we investigate the role of intrinsically disordered regions within the key cancer-related TF estrogen receptor [a] (ESR1) on DNA binding and transcriptional activity, and found that these regions can have complex trade-offs in TF function. Altogether, our study not only broadens our knowledge of TFs involved in the cancer gene regulatory network but also provides a valuable resource for future studies, laying a foundation for potential therapeutic strategies targeting TFs in cancer.

systems biology↗

bioRxiv2024

mRNA initiation and termination are spatially coordinated

The expression of a precise mRNA transcriptome is crucial for establishing cell identity and function, with dozens of alternative isoforms produced for a single gene sequence. The regulation of mRNA isoform usage occurs by the coordination of co-transcriptional mRNA processing mechanisms across a gene. Decisions involved in mRNA initiation and termination underlie the largest extent of mRNA isoform diversity, but little is known about any relationships between decisions at both ends of mRNA molecules. Here, we systematically profile the joint usage of mRNA transcription start sites (TSSs) and polyadenylation sites (PASs) across tissues and species. Using both short and long read RNA-seq data, we observe that mRNAs preferentially using upstream TSSs also tend to use upstream PASs, and congruently, the usage of downstream sites is similarly paired. This observation suggests that mRNA 5 end choice may directly influence mRNA 3 ends. Our results suggest a novel "Positional Initiation-Termination Axis" (PITA), in which the usage of alternative terminal sites are coupled based on the order in which they appear in the genome. PITA isoforms are more likely to encode alternative protein domains and use conserved sites. PITA is strongly associated with the length of genomic features, such that PITA is enriched in longer genes with more area devoted to regions that regulate alternative 5 or 3 ends. Strikingly, we found that PITA genes are more likely than non-PITA genes to have multiple, overlapping chromatin structural domains related to pairing of ordinally coupled start and end sites. In turn, PITA coupling is also associated with fast RNA Polymerase II (RNAPII) trafficking across these long gene regions. Our findings indicate that a combination of spatial and kinetic mechanisms couple transcription initiation and mRNA 3 end decisions based on ordinal position to define the expression mRNA isoforms.

genomics↗

bioRxiv2023

evopython: a Python package for feature-focused, comparative genomic data exploration

MotivationSoftware such as LiftOver allows for the intra- and inter-species conversion of genomic coordinates between genome assemblies, but this coordinate-centric workflow is naive to sequence alterations underling the conversion. For instance, it does not clarify the location of any insertions or deletions that might have occurred. ResultsTo facilitate inter-species, sequence-based analyses, we developed evopython, a simple, object-oriented Python package that enables the sequence-aware resolution of genomic coordinates directly from pairwise and multiple whole-genome alignment data. The output is a Python dictionary storing all information relevant to the alignment: the participating species names, the position of the alignment in each species genome assembly, and the aligned sequences. Availability and implementationThe source code and documentation are available at https://github.com/fiszbein-lab/evopython. Contactanafisz@bu.edu

bioinformatics↗

bioRxiv2022

Splicing-dependent transcriptional activation

Transcription and splicing are intrinsically coupled. Transcription dynamics regulate splicing, and splicing feeds back to transcription initiation to jointly determine gene expression profiles. A recently described phenomenon called exon-mediated activation of transcription starts (EMATS) shows that splicing of internal exons can regulate transcription initiation and activate cryptic promoters. Here, we present the first complete catalog of human EMATS genes that have a weak alternative promoter located upstream and proximate to an efficiently spliced internal skipped exon. We found that EMATS genes are associated with Mendelian genetic diseases --specifically intellectual development disorders, cardiomyopathy, and immunodeficiency-- and provide a list of EMATS genes with pathological variants. EMATS was originally described as a natural mechanism used during evolution to fine-tune gene expression through punctual genomic mutations that affect splicing. Here, we show that EMATS can be used to manipulate gene expression with therapeutic purposes. We constructed stable cell lines expressing a splicing reporter based on the alternative splicing of exon 7 of SMN2 gene under the regulation of different promoters. Using a small molecule (Risdiplam) and an antisense oligonucleotide (ASO) modeled after Spinraza, we promoted the inclusion of SMN2 exon 7 which triggered an increase in gene expression up to 40-folds by activating transcription initiation. We observed the strongest effects in reporters under the regulation of weak human promoters, where the highest drug doses dramatically increased exon inclusion. Overall, our findings present evidence to develop the first therapeutic strategy to use EMATS to activate gene expression using small molecules and ASOs that affect splicing.

molecular biology↗

bioRxiv2021

Widespread occurrence of hybrid internal-terminal exons in human transcriptomes

Alternative RNA processing is a major mechanism for diversifying the human transcriptome. Messenger RNA isoform differences are predominantly driven by alternative first exons, cassette internal exons and alternative last exons. Despite the importance of classifying exons to understand isoform structure, there is a lack of tools to look at isoform-specific exon usage using RNA-sequencing data. We recently observed that alternative transcription start sites often arise near annotated internal exons, creating "hybrid" exons that can be used as both first or internal exons. To investigate the creation of hybrid exons, we built the HIT (Hybrid-Internal-Terminal) exon pipeline that systematically classifies exons depending on their isoform-specific usage. Using a combination of junction reads coverage and probabilistic modeling, the HIT index identified thousands of hybrid first-internal and internal-last exons that were previously misclassified. Hybrid exons are enriched in long genes with at least ten internal exons, have longer flanking introns and strong splice sites. The usage of hybrid exons varies considerably across human tissues, but they are predominantly used in brain, testis and colon cells. Notably, genes involved in RNA splicing have the highest fraction of intra-tissue hybrid exons. Further, we found more than 100,000 inter-tissue hybrid exons that changed from internal to terminal exons across tissues. By developing the first method that can classify exons according to their isoform contexts, our findings demonstrate the existence of hybrid exons, expand the repertoire of tissue-specific terminal exons and uncover unexpected complexities of the human transcriptome.

bioinformatics↗

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↗