Biology subjects

Calvo-Roitberg, E.

Publications and source records attributed to Calvo-Roitberg, E..

8 recordsLinked to original sources

bioRxiv2026

Formation of an RNA-mediated nuclear compartment

Mammalian nuclei are spatially compartmentalized so that active and inactive segments of the genome occupy separate sub-nuclear neighborhoods. Compartments are often found in association with nuclear structures such as the nuclear lamina, nucleoli, and nuclear speckles (speckles), suggesting links between them. The molecular mechanisms by which compartments form remain largely unknown. Speckles are nuclear bodies that contain high concentrations of RNA splicing factors and associated chromatin has a high density of highly expressed genes. Combining liquid chromatin Hi-C to quantify chromatin interaction lifetimes genome-wide, immunofluorescence, fluorescence in situ hybridization, live cell imaging, and nascent transcript analysis, we have determined the biophysical and molecular basis of the speckle-associated chromosomal compartment. We find that genomic regions making up this compartment are stably glued together. Surprisingly, removal of speckles by rapid depletion of SON and SRRM2 that form the structural scaffold of these bodies shows that this stable association is not dependent on the speckle itself. Instead, we find that RNA molecules are the molecular glue that forms the biophysical basis of the speckle chromatin compartment. Based on observations that promoters and enhancers are also engaged in stable long-lived chromatin interactions that are independent of RNA, we propose a pathway for formation of the speckle chromosomal compartment: Initial stable clustering of promoters and enhancers is followed by production of (nascent) RNA. The exceptionally high density of GC-rich RNA emerging from speckle-associated loci forms a glue that holds these loci together and facilitates recruitment of speckle components. The result is a structurally stable nuclear compartment that facilitates efficient splicing.

genomics↗

bioRxiv2025

CRYPTID-exon: streamlined detection of cryptic exons from RNA-seq data

Cryptic splicing has emerged as a pervasive feature of mammalian gene expression, with recent studies uncovering thousands of previously unannotated splice sites. Despite its prevalence, the functional consequences of this hidden layer of splicing remain largely unknown due to challenges in identifying the exact exonic regions introduced into mRNA transcripts. Here, we introduce a novel computational approach, CRYPTID-exon, that accurately predicts exon boundaries by modeling RNA-seq read coverage around empirically derived splice sites. We use CRYPTID-exon to identify and characterize thousands of cryptic exons in nascent and mature RNA from human cells. Additionally, we demonstrate that CRYPTID-exon is well powered to identify exons that are sensitive to translation-mediated degradation processes. Finally, given the growing interest in leveraging cryptic exons to modulate gene expression levels, we use our approach to identify cryptic exons in disease-relevant genes. We see that targeting these cryptic exons with splice-switching antisense oligonucleotides (ASOs) can alter gene expression and splicing patterns of the parent genes. Our study provides a framework to systematically identify and characterize cryptic exons, which will enable downstream insights into their impact on mRNA stability and translation.

genomics↗

bioRxiv2025

SPARK: in silico simulations for benchmarking nascent RNA sequencing experiments

Nascent RNA sequencing offers profound insights into transcriptional dynamics, yet there are substantial challenges to analyzing these data. The development of proper computational tools necessitates realistic benchmarking datasets that reflect biological variability and technical biases. We present simulated pre-mRNA and RNA kinetics (SPARK), a versatile in silico framework for generating reads across nascent RNA sequencing approaches. SPARK simulates the process of transcription -- allowing for variable elongation rates and pausing events -- and key experimental features. SPARK provides a comprehensive platform for computational development and benchmarking in nascent RNA genomics.

genomics↗

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

Challenges in identifying mRNA transcript starts and ends from long-read sequencing data

Long-read sequencing (LRS) technologies have the potential to revolutionize scientific discoveries in RNA biology, especially by enabling the comprehensive identification and quantification of full length mRNA isoforms. However, inherently high error rates make the analysis of long-read sequencing data challenging. While these error rates have been characterized for sequence and splice site identification, it is still unclear how accurately LRS reads represent transcript start and end sites. Here, we systematically assess the variability and accuracy of mRNA terminal ends identified by LRS reads across multiple sequencing platforms. We find substantial inconsistencies in both the start and end coordinates of LRS reads spanning a gene, such that LRS reads often fail to accurately recapitulate annotated or empirically derived terminal ends of mRNA molecules. To address this challenge, we introduce an approach to condition reads based on empirically derived terminal ends and identified a subset of reads that are more likely to represent full-length transcripts. Our approach can improve transcriptome analyses by enhancing the fidelity of transcript terminal end identification, but may result in lower power to quantify genes or discover novel isoforms. Thus, it is necessary to be cautious when selecting sequencing approaches and/or interpreting data from long-read RNA sequencing.

bioinformatics↗

bioRxiv2023

Genome-wide kinetic profiling of pre-mRNA 3' end cleavage

Cleavage and polyadenylation is necessary for the formation of mature mRNA molecules. The rate at which this process occurs can determine the temporal availability of mRNA for subsequent function throughout the cell and is likely tightly regulated. Despite advances in high-throughput approaches for global kinetic profiling of RNA maturation, genome-wide 3 end cleavage rates have never been measured. Here, we describe a novel approach to estimate the rates of cleavage, using metabolic labeling of nascent RNA, high-throughput sequencing, and mathematical modeling. Using in-silico simulations of nascent RNA-seq data, we show that our approach can accurately and precisely estimate cleavage half-lives for both constitutive and alternative sites. We find that 3 end cleavage is fast on average, with half-lives under a minute, but highly variable across individual sites. Rapid cleavage is promoted by the presence of canonical sequence elements and an increased density of polyadenylation signals near a cleavage site. Finally, we find that cleavage rates are associated with the localization of RNA Polymerase II at the end of a gene and faster cleavage leads to quicker degradation of downstream read-through RNA. Our findings shed light on the features important for efficient 3 end cleavage and the regulation of transcription termination.

genomics↗

bioRxiv2022

High-throughput analysis of ANRIL circRNA isoforms in human pancreatic islets

The antisense non-coding RNA in the INK locus (ANRIL) is a hotspot for genetic variants associated with cardiometabolic disease. We recently found increased ANRIL abundance in human pancreatic islets from donors with certain Type II Diabetes (T2D) risk-SNPs, including a T2D risk-SNP located within ANRIL exon 2 associated with beta cell proliferation. Recent studies have found that expression of circular species of ANRIL is linked to the regulation of cardiovascular phenotypes. Less is known about how the abundance of circular ANRIL may influence T2D phenotypes. Herein, we sequence circular RNA in pancreatic islets to characterize circular isoforms of ANRIL. We identify highly expressed circular ANRIL isoforms whose expression is correlated across dozens of individuals and characterize ANRIL splice sites that are commonly involved in back-splicing. We find that samples with the T2D risk allele in ANRIL exon 2 had higher ratios of circular to linear ANRIL compared to protective-allele carriers, and that higher circular:linear ANRIL was associated with decreased beta cell proliferation. Our study points to a combined involvement of both linear and circular ANRIL species in T2D phenotypes and opens the door for future studies of the molecular mechanisms by which ANRIL impacts cellular function in pancreatic islets.

genomics↗

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↗