Potential Splicing Research Articles

Predicting splicing patterns from the transcription factor binding sites in the promoter with deep learning

BackgroundAlternative splicing is a pivotal mechanism of post-transcriptional modification that contributes to the transcriptome plasticity and proteome diversity in metazoan cells. Although many splicing regulations around the exon/intron regions are known, the relationship between promoter-bound transcription factors and the downstream alternative splicing largely remains unexplored.ResultsIn this study, we present computational approaches to unravel the regulatory relationship between promoter-bound transcription factor binding sites (TFBSs) and the splicing patterns. We curated a fine dataset that includes DNase I hypersensitive site sequencing and transcriptomes across fifteen human tissues from ENCODE. Specifically, we proposed different representations of TF binding context and splicing patterns to examine the associations between the promoter and downstream splicing events. While machine learning models demonstrated potential in predicting splicing patterns based on TFBS occupancies, the limitations in the generalization of predicting the splicing forms of singleton genes across diverse tissues was observed with carefully examination using different cross-validation methods. We further investigated the association between alterations in individual TFBS at promoters and shifts in exon splicing efficiency. Our results demonstrate that the convolutional neural network (CNN) models, trained on TF binding changes in the promoters, can predict the changes in splicing patterns. Furthermore, a systemic in silico substitutions analysis on the CNN models highlighted several potential splicing regulators. Notably, using empirical validation using K562 CTCFL shRNA knock-down data, we showed the significant role of CTCFL in splicing regulation.ConclusionIn conclusion, our finding highlights the potential role of promoter-bound TFBSs in influencing the regulation of downstream splicing patterns and provides insights for discovering alternative splicing regulations.

Association of Genetically Predicted Skipping of COL4A4 Exon 27 with Hematuria and Albuminuria.

Hematuria is an established sign of glomerular disease and can be associated with kidney failure, but there has been limited scientific study of this trait. Here, we combined genetic data from the UK Biobank with predicted gene expression and splicing from GTEx kidney cortex samples (n = 65) in a transcriptome-wide association study (TWAS) to identify additional potential biological mechanisms influencing hematuria. The TWAS using kidney cortex identified significant associations for 5 genes in terms of expression and 3 significant splicing events. Notably, we identified an association between the skipping of COL4A4 exon 27, which is genetically predicted by intronic rs11898094 (minor allele frequency 13%), and hematuria. Association between this variant was also found with urinary albumin excretion. We found independent evidence supporting the same variant predicting this skipping event in glomeruli-derived mRNA transcriptomics data (n = 245) from NEPTUNE. The functional significance of loss of exon 27 was demonstrated using the split NanoLuc-based α3α4α5(IV) heterotrimer assay, in which type IV collagen heterotrimer formation was quantified by luminescence. The causal splicing variant for this skipping event is yet to be identified. In summary, by integrating multiple data types, we identify a potential splicing event associated with hematuria and albuminuria.

Unveiling axolotl transcriptome for tissue regeneration with high-resolution annotation via long-read sequencing

Axolotls are known for their remarkable regeneration ability. Exploring their transcriptome provides insight into regenerative mechanisms. However, the current annotation of the axolotl transcriptome is limited, leaving the role of unannotated transcripts in regeneration unknown. To discourse this challenge, we exploited long-read sequencing technology, which enables direct observation of full-length RNA transcripts, greatly enhancing the coverage and accuracy of axolotl transcriptome annotation. By utilizing this method, we identified 222 novel gene loci and 4775 novel transcripts, which were quantified using short-read sequencing data. Through the inclusive analysis, we discovered novel homologs, potential functional proteins, noncoding RNAs, and alternative splicing events in key regeneration pathways. In particular, we identified novel transcripts with high protein-coding potential implicated in cell cycle regulation and musculoskeletal development, and regeneration were identified. Interestingly, alternative splice variants were also detected across diverse pathways critical to regeneration. This specifies that these novel transcripts potentially play vital roles underpinning the robust regenerative capacities of axolotls. Single-cell transcriptomic analysis further revealed these isoforms to predominantly exist in axolotl limb chondrocytes and mature tissue cell populations. Overall, the findings significantly advanced consideration of the axolotl transcriptome and provided a new perspective for understanding the mechanisms of regenerative abilities of axolotls.

Identification of alternative splicing regulatory patterns and characteristic splicing factors in heart failure using RNA-seq data and machine learning

Heart failure (HF) represents the advanced stage of several cardiovascular disorders. This study aimed to build an alternative splicing regulatory network and identify potential splicing factors involved in HF utilizing RNA-seq data and machine learning algorithms. We performed bioinformatics analysis on RNA-seq datasets containing samples from HF patients and normal individuals to obtain gene expression matrices and identify differently regulated alternative splicing events in HF. By calculating percent spliced-in (PSI) value, we identified 4055 abnormal alternative splicing events of 3142 genes in HF. These genes were significantly enriched in PPAR signaling, regulation of actin cytoskeleton, and muscle contraction. Interestingly, based on abnormal alternative splicing events, two distinct clusters of HF patients with distinct molecular mechanisms and pathways were identified using unsupervised clustering. Additionally, we built a regulatory network consisting of heart failure-related alternative splicing and splicing factors. Subsequently, we identify 203 HF specific pairs between splicing factors and alternative splicing events. Four splicing factors (RBM5, ZRANB2, HnRNPF, and HnRNPA0) were found using LASSO and SVM-RFE algorithms, their expression patterns were confirmed in two other microarray datasets. Our study clarifies involvement of splicing factors and alternative splicing events in HF by thoroughly analyzing RNA-seq data with machine learning methods. The findings may advance our understanding of the regulatory systems underlying biological processes associated with heart failure by providing candidates for further investigation and markers for diagnostic and therapeutic purposes.

Significance of utilizing in silico structural analysis and phenotypic data to characterize phenylalanine hydroxylase variants: A PAH landscape

Phenylketonuria (PKU) is a genetic disorder caused by variations in the phenylalanine hydroxylase (PAH) gene. Among the 3369 reported PAH variants, 33.7% are missense alterations. Unfortunately, 30% of these missense variants are classified as variants of unknown significance (VUS), posing challenges for genetic risk assessment. In our study, we focused on analyzing 836 missense PAH variants following the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines specified by ClinGen PAH Variant Curation Expert Panel (VCEP) criteria. We utilized and compared variant annotator tools like Franklin and Varsome, conducted 3D structural analysis of PAH, and examined active and regulatory site hotspots. In addition, we assessed potential splicing effect of apparent missense variants. By evaluating phenotype data from 22962 PKU patients, our aim was to reassess the pathogenicity of missense variants. Our comprehensive approach successfully reclassified 309 VUSs out of 836 missense variants as likely pathogenic or pathogenic (37%), upgraded 370 likely pathogenic variants to pathogenic, and reclassified one previously considered likely benign variant as likely pathogenic. Phenotypic information was available for 636 missense variants, with 441 undergoing 3D structural analysis and active site hotspot identification for 180 variants. After our analysis, only 6% of missense variants were classified as VUSs, and three of them (c.23A>C/p.Asn8Thr, c.59_60delinsCC/p.Gln20Pro, and c.278A >T/p.Asn93Ile) may be influenced by abnormal splicing. Moreover, a pathogenic variant (c.168G>T/p.Glu56Asp) was identified to have a risk exceeding 98% for modifications of the consensus splice site, with high scores indicating a donor loss of 0.94.The integration of ACMG/AMP guidelines with in silico structural analysis and phenotypic data significantly reduced the number of missense VUSs, providing a strong basis for genetic counseling and emphasizing the importance of metabolic phenotype information in variant curation. This study also sheds light on the current landscape of PAH variants.

Surface PD-1 expression in T cells is suppressed by HNRNPK through an exonic splicing silencer on exon 3.

Immunotherapy targeting programmed cell death 1 (PDCD1 or PD-1) and its ligands has shown remarkable promise and the regulation mechanism of PD-1 expression has received arising attention in recent years. PDCD1 exon 3 encodes the transmembrane domain and the deletion of exon 3 produces a soluble protein isoform of PD-1 (sPD-1), which can enhance immune response by competing with full-length PD-1 protein (flPD-1 or surface PD-1) on T cell surface. However, the mechanism of PDCD1 exon 3 skipping is unclear. The online SpliceAid program and minigene expression system were used to analyze potential splicing factors involved in the splicing event of PDCD1 exon 3. The potential binding motifs of heterogeneous nuclear ribonucleoprotein K (HNRNPK) on exon 3 predicted by SpliceAid were mutated by site-directed mutagenesis technology, which were further verified by pulldown assay. Antisense oligonucleotides (ASOs) targeting the exonic splicing silencer (ESS) on PDCD1 exon 3 were synthesized and screened to suppress the skipping of exon 3. The alternative splicing of PDCD1 exon 3 was analyzed by semiquantitative reverse transcription PCR. Western blot and flow cytometry were performed to detect the surface PD-1 expression in T cells. HNRNPK was screened as a key splicing factor that promoted PDCD1 exon 3 skipping, causing a decrease in flPD-1 expression on T cell membrane and an increase in sPD-1 expression. Mechanically, a key ESS has been identified on exon 3 and can be bound by HNRNPK protein to promote exon 3 skipping. Blocking the interaction between ESS and HNRNPK with an ASO significantly reduced exon 3 skipping. Importantly, HNRNPK can promote exon 3 skipping of mouse Pdcd1 gene as well. Our study revealed a novel evolutionarily conserved regulatory mechanism of PD-1 expression. The splicing factor HNRNPK markedly promoted PDCD1 exon 3 skipping by binding to the ESS on PDCD1 exon 3, resulting in decreased expression of flPD-1 and increased expression of sPD-1 in T cells.

Identification of deleterious variants in nine polycystic kidney disease affected families

Polycystic kidney disease (PKD) is common genetic renal disorder. In present study, we performed WES to identify pathogenic variant in nine families including 26 patients with PKD and 19 unaffected members. The eight pathogenic variants were identified in known PKD associated genes including PKD1 (n = 6), PKD2 (n = 1), and OFD1 (n = 1) in eight families. There is one missense, one stopgain, two non-frameshifts, two canonical splicing variants, three frameshift variants and one potential non-canonical splicing variant (NCSV) in 8 families. The six variants were novel variants and not reported in ClinVar database. In addition, the compound heterozygous variants in PKHD1 were identified including one frameshift variants (PKHD1: NM_138694.4, c.9841del, p.S3281Lfs*4) and one non-canonical splicing variant (PKHD1: NM_138694.4, c.6332 + 40A > G) which were defined as deleterious variant by four splicing prediction tools (CADD-splice, SpliceAI, Spliceogen, Squirl). We used the minigene method to validate whether the prioritized potential NSCVs disrupt the typical mRNA splicing process and found abnormally larger PCR production of minigene carrying potential NCSV comparing to wild-type minigene. Sanger sequencing confirmed the 39-bp insertion of intron 38 between exon 38 and exon 39, which results in non-frameshift and 13 amino acid insertions. In conclusion, our study expands the variant spectrum and highlight the important role of non-canonical splicing variant in PKD.

Study of prognostic splicing factors in cancer using machine learning approaches.

Splicing factors (SFs) are the major RNA-binding proteins (RBPs) and key molecules that regulate the splicing of mRNA molecules through binding to mRNAs. The expression of splicing factors is frequently deregulated in different cancer types, causing the generation of oncogenic proteins involved in cancer hallmarks. In this study, we investigated the genes that encode RNA-binding proteins and identified potential splicing factors that contribute to the aberrant splicing applying a random forest classification model. The result suggested 56 splicing factors were related to the prognosis of 13 cancers, two SF complexes in liver hepatocellular carcinoma, and one SF complex in esophageal carcinoma. Further systematic bioinformatics studies on these cancer prognostic splicing factors and their related alternative splicing events revealed the potential regulations in a cancer-specific manner. Our analysis found high ILF2-ILF3 expression correlates with poor prognosis in LIHC through alternative splicing. These findings emphasize the importance of SFs as potential indicators for prognosis or targets for therapeutic interventions. Their roles in cancer exhibit complexity and are contingent upon the specific context in which they operate. This recognition further underscores the need for a comprehensive understanding and exploration of the role of SFs in different types of cancer, paving the way for their potential utilization in prognostic assessments and the development of targeted therapies.

Reclassifying BRCA1 c.4358-2A > G and BRCA2 c.475 + 5G > C variants from “Uncertain Significance” to “Pathogenic” based on minigene assays and clinical evidence

BackgroundPathogenic variants in BRCA genes play a crucial role in the pathogenesis of ovarian cancer. Intronic variants of uncertain significance (VUS) may contribute to pathogenicity by affecting splicing. Currently, the significance of many intronic variants in BRCA has not been clarified, impacting patient treatment strategies and the management of familial cases.MethodA retrospective study was conducted to analyze BRCA intronic VUS in a cohort of 707 unrelated ovarian cancer patients at a single institution from 2018 to 2023. Three splicing predictors were employed to analyze detected intronic VUS. Variants predicted to have splicing alterations were selected for further validation through minigene assays. Patient and familial investigations were conducted to comprehend cancer incidence within pedigrees and the application of poly (ADP-ribose) polymerase inhibitors (PARPi) by the patients. In accordance with the guidelines of the American College of Medical Genetics and Genomics (ACMG), the intronic VUS were reclassified based on minigene assay results and clinical evidence.ResultApproximately 9.8% (69/707) of patients were identified as carriers of 67 different VUS in BRCA1/2, with four intronic variants accounting for 6% (4/67) of all VUS. Splicing predictors indicated potential splicing alterations in splicing for BRCA1 c.4358-2A>G and BRCA2 c.475+5G>C variants. Minigene assays utilizing the pSPL3 exon trapping vector revealed that these variants induced changes in splicing sites and frameshift, resulting in premature termination of translation (p. Ala1453Glyfs and p. Pro143Glyfs). According to ACMG guidelines, BRCA1 c.4358-2A>G and BRCA2 c.475+5G>C were reclassified as pathogenic variants. Pedigree investigations were conducted on patients with BRCA1 c.4358-2A>G variant, and the detailed utilization of PARPi provided valuable insights into research on PARPi resistance.ConclusionTwo intronic VUS were reclassified as pathogenic variants. A precise classification of variants is crucial for the effective treatment and management of both patients and healthy carriers.

The importance of having a relevant model system to investigate splicing modulation in the retina: The unforeseen cases of the intronic variants in RPE65 and IMPG2 genes

Inherited retinal diseases (IRDs) are clinically and genetically heterogeneous disorders that can be caused by pathogenic variants in one of the more than 270 genes associated with IRDs. Among them, mutations in RPE65 can lead to Leber congenital amaurosis (LCA) whereas mutations in IMPG2 to vitelliform macular dystrophy (VMD).During my talk, I will provide evidence of the importance of employing the right cellular models to identify disease mechanism(s) and eventually evaluate suitable treatments. For this, I will highlight two intriguing examples of potential splicing defects studied by our group. Such defects are attractive for splicing modulation therapies using antisense oligonucleotides (AONs), a group of versatile molecules that can alter splicing by interacting with the target sequence(s) at pre‐mRNA level. Thus, characterizing the effect of a variant at the RNA level is instrumental to assess the applicability of AON‐based therapeutic intervention.We explored the effect of the homozygous variant c.11 + 5G>A in RPE65 and a heterozygous complex allele consisting of c.3023‐15T>A and c.3023G>A (p.(Gly1008Asp)) in IMPG2. In silico predictions suggested that these variants lead to a splicing defect. To assess the pathogenic effect of these variants, splice reporter assays using midigenes were conducted in HEK293T cells. Initial results pointed towards a 124‐nt exon elongation for the RPE65 variant and an in‐frame deletion of 48‐nt at the beginning of exon 15 for the complex allele in IMPG2.To validate these results, blood cells from the patients harbouring these defects were reprogrammed to induced pluripotent stem cells (iPSCs). Subsequently, iPSCs were differentiated to the retinal cells in which these genes are endogenously expressed. For RPE65, iPSCs were differentiated into retinal pigment epithelium (RPE) cells (>90 days differentiation) or, for IMPG2, into photoreceptor precursor cells (PPCs, 30 days differentiation). For the RPE65 variant, a cell specific effect was observed: while a clear exon elongation was observed in the midigene system, in RPE, the expression of the gene was highly reduced. In addition, no protein was detected and the patient‐derived cells showed differences compared to the control line. For IMPG2, the 48‐nt deletion was detected in a lower percentage in patient‐derived PPCs compared to the levels observed in the midigene system. However, aberrantly spliced IMPG2 transcripts were highly elevated in patient‐derived PPCs in comparison to control PPCs.Overall, our work shows the importance of having the right cellular context to determine the effect of genetic variants on splicing in the retina.

Whole genome sequencing in families with oligodontia.

Tooth agenesis (TA) is among the most common malformations in humans. Although several causative mutations have been described, the genetic cause often remains elusive. Here, we test whether whole genome sequencing (WGS) could bridge this diagnostic gap. In four families with TA, we assessed the dental phenotype using the Tooth Agenesis Code after intraoral examination and radiographic and photographic documentation. We performed WGS of index patients and subsequent segregation analysis. We identified two variants of uncertain significance (a potential splice variant in PTH1R, and a 2.1 kb deletion abrogating a non-coding element in FGF7) and three pathogenic variants: a novel frameshift in the final exon of PITX2, a novel deletion in PAX9, and a known nonsense variant in WNT10A. Notably, the FGF7 variant was found in the patient, also featuring the WNT10A variant. While mutations in PITX2 are known to cause Axenfeld-Rieger syndrome 1 (ARS1) predominantly featuring ocular findings, accompanied by dental malformations, we found the PITX2 frameshift in a family with predominantly dental and varying ocular findings. Severe TA predicts a genetic cause identifiable by WGS. Final exon PITX2 frameshifts can cause a predominantly dental form of ARS1.

Neuronal stimulation‐regulated RNA splicing defects in tauopathies are corrected by treatment with a p75 NTR modulator

AbstractBackgroundLong‐term maintenance of synaptic adaptations, assessed by long‐term potentiation (LTP), relies on gene induction, and can be impaired by pathological forms of tau protein in Alzheimer’s disease and related dementias (ADRD). We have previously shown that alterations in activity‐dependent gene expression profiles present in tauopathy mice are normalized by LM11A‐31 (C31), a small molecule p75 neurotrophin receptor (NTR) signaling modulator. However, altered gene expression levels represent only part of the complexity of the activity‐regulated transcriptional program. Since neuronal stimulation regulates alternative splicing of a number of activity‐regulated transcripts, and its disruption is associated with dysfunctional changes in ADRD, we aim to identify potential alternative splicing events related to tau‐mediated synaptic dysfunction and whether such alterations are influenced by treatment with a p75 NTR modulator.MethodPS19 (P301S) and wildtype mice were treated with vehicle (Veh) or C31 by oral gavage at 6 months of age for 3 consecutive months. Gene translation‐ and protein synthesis‐dependent synaptic plasticity was induced by applying three events of theta burst stimulation (TBS). RNA sequencing on stimulated [(+) TBS] slices was used to generate activity‐related profiles of alternative splicing events at the isoform level.ResultWe identified axon guidance, glutamatergic synapse, long‐term potentiation and calcium signaling KEGG pathways among the top significant pathways with isoforms down‐regulated in (+) TBS PS19 relative to (+) WT slices. This isoform downregulation was substantially mitigated in (+) TBS slices from PS19 mice treated with C31 (see figure). For example, CACNA1H‐202, a splice‐variant that encodes a voltage‐gated calcium channel protein required for proper synaptic function, is found among the splice variants down‐regulated in Veh and up‐regulated in C31‐treated (+) TBS PS19 slices. Conversely, Prickle2‐204 isoform, associated with the formation of glutamatergic synapses, is up‐regulated in Veh and down‐regulated in C31‐treated (+) TBS PS19 slices. Currently, we are validating and examining the roles of these key C31‐modulated isoforms in neuronal function and synaptic strength as candidate molecular mechanisms involved in activity‐related effects contributing to tau‐induced neurodegeneration.ConclusionWe identified neuronal activity‐related mRNA isoform modulation by C31, indicating that p75NTR signaling might influence alternative splicing events that compromise synapse function in ADRD.

Patterns of Gene Expression, Splicing, and Allele-Specific Expression Vary among Macular Tissues and Clinical Stages of Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is a leading cause of blindness, and elucidating its underlying disease mechanisms is vital to the development of appropriate therapeutics. We identified differentially expressed genes (DEGs) and differentially spliced genes (DSGs) across the clinical stages of AMD in disease-affected tissue, the macular retina pigment epithelium (RPE)/choroid and the macular neural retina within the same eye. We utilized 27 deeply phenotyped donor eyes (recovered within a 6 h postmortem interval time) from Caucasian donors (60-94 years) using a standardized published protocol. Significant findings were then validated in an independent set of well-characterized donor eyes (n = 85). There was limited overlap between DEGs and DSGs, suggesting distinct mechanisms at play in AMD pathophysiology. A greater number of previously reported AMD loci overlapped with DSGs compared to DEGs between disease states, and no DEG overlap with previously reported loci was found in the macular retina between disease states. Additionally, we explored allele-specific expression (ASE) in coding regions of previously reported AMD risk loci, uncovering a significant imbalance in C3 rs2230199 and CFH rs1061170 in the macular RPE/choroid for normal eyes and intermediate AMD (iAMD), and for CFH rs1061147 in the macular RPE/choroid for normal eyes and iAMD, and separately neovascular AMD (NEO). Only significant DEGs/DSGs from the macular RPE/choroid were found to overlap between disease states. STAT1, validated between the iAMD vs. normal comparison, and AGTPBP1, BBS5, CERKL, FGFBP2, KIFC3, RORα, and ZNF292, validated between the NEO vs. normal comparison, revealed an intricate regulatory network with transcription factors and miRNAs identifying potential upstream and downstream regulators. Findings regarding the complement genes C3 and CFH suggest that coding variants at these loci may influence AMD development via an imbalance of gene expression in a tissue-specific manner. Our study provides crucial insights into the multifaceted genomic underpinnings of AMD (i.e., tissue-specific gene expression changes, potential splice variation, and allelic imbalance), which may open new avenues for AMD diagnostics and therapies specific to iAMD and NEO.

A Novel Splice Site Mutation in the FBN2 Gene in a Chinese Family with Congenital Contractural Arachnodactyly

Congenital contractural arachnodactyly (CCA) is a rare connective tissue disorder characterized by arachnodactyly, multiple joint contractures, progressive kyphoscoliosis, pectus deformity and abnormal crumpled ears. FBN2 is the only gene currently known to be associated with CCA. In this study, we report on a prenatal case presented with skeletal, cardiac and spinal malformations. And his father had elongated limbs, contractures of the proximal interphalangeal joints, high myopia and scoliosis. We conducted whole exome sequencing (WES) on the fetus-parental trio and a heterozygous variant (hg19 chr5:127,673,685, c.3598 + 4A > G, NM_001999.4) in intron 27 of the FBN2 gene was successfully identified, inherited from the father. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to evaluate the potential splicing effect of this variant, which confirmed that the variant caused a deletion of exon 27 (126 bp) by disrupting the splice-donor site and destroyed the 17th calcium-binding epidermal growth factor-like (cbEGF) domain. Our research not only finds the etiology of the disease in affected individuals and expands the mutation spectrum of FBN2 gene, but also provides genetic counseling and fertility guidance for this family.

Population-specific and cross-ancestry genome-wide association study identifies shared genetic architecture and 6 new risk loci including CAMK2D associated for Brugada syndrome

Abstract Introduction The Brugada syndrome (BrS) is an inherited arrhythmia characterized by coved-type ST-segment elevation in the right precordial leads and an increased risk for sudden cardiac death. Genome-wide association studies (GWAS) of BrS, mainly performed in European ancestry, have illustrated its complex genetic architecture as an polygenic disease besides a monogenic trait due to mutations in the major responsible cardiac sodium channel gene SCN5A. Clinical manifestations of BrS including the disease prevalence and the incidence of sudden death are known to be variable between Asian and European populations, however, its underlying mechanisms are largely unknown. Objectives We aimed to identify novel BrS-associated loci and to assess ancestry-dependent genetic heterogeneity that may underlie the variable clinical manifestations of BrS patients across different populations. Methods We performed a genome-wide meta-analysis of BrS in the Japanese ancestry (940 cases and 1,634 controls), followed by a cross-ancestry meta-analysis of Japanese and European GWAS (total of 3,760 cases and 11,635 controls) to identify novel risk loci and compared the allelic effects between two ancestries. We characterized the novel loci based on fine-mapping of potential causal variants, and expression and splicing quantitative trait associations using the Genotype-Tissue Expression (GTEx) database. Results The Japanese-specific genome-wide meta-analysis identified a novel association signal near the ZSCAN20 (lead variant, rs2336244; P=1.0E-08) besides previously reported 4 association signals at the SCN5A-SCN10A and HEY2 loci. Cross-ancestry genome-wide meta-analysis identified 17 association signals including 6 novel loci. The effect directions were consistent for 94.1% of the variants (16 of 17; P for sign test = 0.00027) and their allelic effects were highly correlated across ancestries (Pearson’s R=0.91 [P=2.9E-07]). The genetic risk score (GRS) derived from European-ancestry GWAS of BrS was significantly associated with the risk of BrS in the Japanese populations (odds ratio, 2.12 [95% confidence interval, 1.94–2.31]; P=1.2E-61), suggesting the shared genetic architecture across ancestries. The functional characterization of the 6 novel loci showed that one lead SNP on CAMK2D promotes an alternative splicing resulting in an isoform switch of calmodulin kinase II that favors up-regulation of the pro-inflammatory isoform δ9 and down-regulation of the pro-survival isoform δ3. Conclusions Our results identified 6 novel susceptible loci associated with BrS and revealed shared genetic architecture across ancestries.GWAS Manhattan plotShared genetic architecture

Reclassification of variants of tumor suppressor genes based on Sanger RNA sequencing without NMD inhibition.

Introduction: RNA sequence analysis can be effectively used to identify aberrant splicing, and tumor suppressor genes are adequate targets considering their loss-of-function mechanisms. Sanger sequencing is the simplest method for RNA sequence analysis; however, because of its insufficient sensitivity in cases with nonsense-mediated mRNA decay (NMD), the use of cultured specimens with NMD inhibition has been recommended, hindering its wide adoption. Method: The results of Sanger sequencing of peripheral blood RNA without NMD inhibition performed on potential splicing variants of tumor suppressor genes were retrospectively reviewed. For negative cases, in which no change was identified in the transcript, the possibility of false negativity caused by NMD was assessed through a review of the up-to-date literature. Results: Eleven potential splice variants of various tumor suppressor genes were reviewed. Six variants were classified as pathogenic or likely pathogenic based on the nullifying effect identified by Sanger RNA sequencing. Four variants remained as variants of uncertain significance because of identified in-frame changes or normal expression of both alleles. The result of one variant was suspected to be a false negative caused by NMD after reviewing a recent study that reported the same variant as causing a nullifying effect on the affected transcript. Conclusion: Although RNA changes found in the majority of cases were expected to undergo NMD by canonical rules, most cases (10/11) were interpretable by Sanger RNA sequencing without NMD inhibition due to incomplete NMD efficiency or allele-specific expression despite highly efficient NMD.

Mapping the splicing landscape of the human immune system.

Most human genes code for more than one transcript. Different ratios of transcripts of the same gene can be found in different cell types or states, indicating differential use of transcription start sites or differential splicing. Such differential transcript use (DTUs) events provide an additional layer of regulation and protein diversity. With the exceptions of PTPRC and CIITA, there are very few reported cases of DTU events in the immune system. To rigorously map DTUs between different human immune cell types, we leveraged four publicly available RNA sequencing datasets. We identified 282 DTU events between five human healthy immune cell types that appear in at least two datasets. The patterns of the DTU events were mostly cell-type-specific or lineage-specific, in the context of the five cell types tested. DTUs correlated with the expression pattern of potential regulators, namely, splicing factors and transcription factors. Of the several immune related conditions studied, only sepsis affected the splicing of more than a few genes and only in innate immune cells. Taken together, we map the DTUs landscape in human peripheral blood immune cell types, and present hundreds of genes whose transcript use changes between cell types or upon activation.

Intronic position +9 and −9 are potentially splicing sites boundary from intronic variants analysis of whole exome sequencing data

Whole exome sequencing (WES) can also detect some intronic variants, which may affect splicing and gene expression, but how to use these intronic variants, and the characteristics about them has not been reported. This study aims to reveal the characteristics of intronic variant in WES data, to further improve the clinical diagnostic value of WES. A total of 269 WES data was analyzed, 688,778 raw variants were called, among these 367,469 intronic variants were in intronic regions flanking exons which was upstream/downstream region of the exon (default is 200 bps). Contrary to expectation, the number of intronic variants with quality control (QC) passed was the lowest at the +2 and −2 positions but not at the +1 and −1 positions. The plausible explanation was that the former had the worst effect on trans-splicing, whereas the latter did not completely abolish splicing. And surprisingly, the number of intronic variants that passed QC was the highest at the +9 and −9 positions, indicating a potential splicing site boundary. The proportion of variants which could not pass QC filtering (false variants) in the intronic regions flanking exons generally accord with “S”-shaped curve. At +5 and −5 positions, the number of variants predicted damaging by software was most. This was also the position at which many pathogenic variants had been reported in recent years. Our study revealed the characteristics of intronic variant in WES data for the first time, we found the +9 and −9 positions might be a potentially splicing sites boundary and +5 and −5 positions were potentially important sites affecting splicing or gene expression, the +2 and −2 positions seem more important splicing site than +1 and −1 positions, and we found variants in intronic regions flanking exons over ± 50 bps may be unreliable. This result can help researchers find more useful variants and demonstrate that WES data is valuable for intronic variants analysis.

Identification of Significant RNA-Binding Proteins in the Process of CD44 Splicing Using the Boosted Beta Regression Algorithm.

The expression of RNA-binding proteins and their interaction with the spliced pre-mRNA are the key factors in determining the final isoform profile. Transmembrane protein CD44 is involved in differentiation, invasion, motility, growth and survival of tumor cells, and is also a commonly accepted marker of cancer stem cells and epithelial-mesenchymal transition. However, the functions of the isoforms of this protein differ significantly. In this paper, we developed a method based on the boosted beta regression algorithm for identification of the significant RNA-binding proteins in the splicing process by modeling the isoform ratio. The application of this method to the analysis of CD44 splicing in colorectal cancer cells revealed 20 significant RNA-binding proteins. Many of them were previously shown as EMT regulators, but for the first time presented as potential CD44 splicing factors.

IDENTIFICATION OF SIGNIFICANT RNA-BINDING PROTEINS IN THE PROCESS OF CD44 SPLICING USING THE BOOSTED BETA REGRESSION ALGORITHM

The expression of RNA-binding proteins and their interaction with the spliced pre-mRNA are the key factors in determining the final isoform profile. Transmembrane protein CD44 is involved in differentiation, invasion, motility, growth and survival of tumor cells, and is also a commonly accepted marker of cancer stem cells and epithelial-mesenchymal transition. However, the functions of the isoforms of this protein differ significantly. In this paper, we developed a method based on the boosted beta regression algorithm for identification of the significant RNA-binding proteins in the splicing process by modeling the isoform ratio. The application of this method to the analysis of CD44 splicing in colorectal cancer cells revealed 20 significant RNA-binding proteins. Many of them were previously shown as EMT regulators, but for the first time presented as potential CD44 splicing factors.