New connections between splicing and human disease

B-cell immune deficiency in twin sisters expands the phenotype of MOPDI

Microcephalic osteodysplastic primordial dwarfism type I (MOPDI) is a very rare and severe autosomal recessive disorder characterized by marked intrauterine growth retardation, skeletal dysplasia, microcephaly and brain malformations. MOPDI is caused by biallelic mutations in RNU4ATAC, a non-coding gene involved in U12-type splicing of 1% of the introns in the genome, which are recognized by their specific splicing consensus sequences. Here, we describe a unique observation of immunodeficiency in twin sisters with mild MOPDI, who harbor a novel n.108_126del mutation, encompassing part of the U4atac snRNA 3' stem-loop and Sm protein binding site, and the previously reported n.111G>A mutation. Interestingly, both twin sisters show mild B-cell anomalies, including low naive B-cell counts and increased memory B-cell and plasmablasts counts, suggesting partial and transitory blockage of B-cell maturation and/or excessive activation of naive B-cells. Hence, the localization of a mutation in stem II of U4atac snRNA, as observed in another RNU4ATAC-opathy with immunodeficiency, that is, Roifman syndrome (RFMN), is not required for the occurrence of an immune deficiency. Finally, we emphasize the importance of considering immunodeficiency in MOPDI management to reduce the risk of serious infectious episodes.

Minor Spliceosomal 65K/RNPC3 Interacts with ANKRD11 and Mediates HDAC3-Regulated Histone Deacetylation and Transcription

RNA splicing is crucial in the multilayer regulatory networks for gene expression, making functional interactions with DNA- and other RNA-processing machineries in the nucleus. However, these established couplings are all major spliceosome-related; whether the minor spliceosome is involved remains unclear. Here, through affinity purification using Drosophila lysates, an interaction is identified between the minor spliceosomal 65K/RNPC3 and ANKRD11, a cofactor of histone deacetylase 3 (HDAC3). Using a CRISPR/Cas9 system, Deletion strains are constructed and found that both Dm65KΔ/Δ and Dmankrd11Δ/Δ mutants have reduced histone deacetylation at Lys9 of histone H3 (H3K9) and Lys5 of histone H4 (H4K5) in their heads, exhibiting various neural-related defects. The 65K-ANKRD11 interaction is also conserved in human cells, and the HsANKRD11 middle-uncharacterized domain mediates Hs65K association with HDAC3. Cleavage under targets and tagmentation (CUT&Tag) assays revealed that HsANKRD11 is a bridging factor, which facilitates the synergistic common chromatin-binding of HDAC3 and Hs65K. Knockdown (KD) of HsANKRD11 simultaneously decreased their common binding, resulting in reduced deacetylation of nearby H3K9. Ultimately, this study demonstrates that expression changes of many genes caused by HsANKRD11-KD are due to the decreased common chromatin-binding of HDAC3 and Hs65K and subsequently reduced deacetylation of H3K9, illustrating a novel and conserved coupling mechanism that links the histone deacetylation with minor spliceosome for the regulation of gene expression.

Alternative splicing and related RNA binding proteins in human health and disease

Alternative splicing (AS) serves as a pivotal mechanism in transcriptional regulation, engendering transcript diversity, and modifications in protein structure and functionality. Across varying tissues, developmental stages, or under specific conditions, AS gives rise to distinct splice isoforms. This implies that these isoforms possess unique temporal and spatial roles, thereby associating AS with standard biological activities and diseases. Among these, AS-related RNA-binding proteins (RBPs) play an instrumental role in regulating alternative splicing events. Under physiological conditions, the diversity of proteins mediated by AS influences the structure, function, interaction, and localization of proteins, thereby participating in the differentiation and development of an array of tissues and organs. Under pathological conditions, alterations in AS are linked with various diseases, particularly cancer. These changes can lead to modifications in gene splicing patterns, culminating in changes or loss of protein functionality. For instance, in cancer, abnormalities in AS and RBPs may result in aberrant expression of cancer-associated genes, thereby promoting the onset and progression of tumors. AS and RBPs are also associated with numerous neurodegenerative diseases and autoimmune diseases. Consequently, the study of AS across different tissues holds significant value. This review provides a detailed account of the recent advancements in the study of alternative splicing and AS-related RNA-binding proteins in tissue development and diseases, which aids in deepening the understanding of gene expression complexity and offers new insights and methodologies for precision medicine.

Deletions of singular U1 snRNA gene significantly interfere with transcription and 3'-end mRNA formation

Small nuclear RNAs (snRNAs) are structural and functional cores of the spliceosome. In metazoan genomes, each snRNA has multiple copies/variants, up to hundreds in mammals. However, the expressions and functions of each copy/variant in one organism have not been systematically studied. Focus on U1 snRNA genes, we investigated all five copies in Drosophila melanogaster using two series of constructed strains. Analyses of transgenic flies that each have a U1 promoter-driven gfp revealed that U1:21D is the major and ubiquitously expressed copy, and the other four copies have specificities in developmental stages and tissues. Mutant strains that each have a precisely deleted copy of U1-gene exhibited various extents of defects in fly morphology or mobility, especially deletion of U1:82Eb. Interestingly, splicing was changed at limited levels in the deletion strains, while large amounts of differentially-expressed genes and alternative polyadenylation events were identified, showing preferences in the down-regulation of genes with 1-2 introns and selection of proximal sites for 3'-end polyadenylation. In vitro assays suggested that Drosophila U1 variants pulled down fewer SmD2 proteins compared to the canonical U1. This study demonstrates that all five U1-genes in Drosophila have physiological functions in development and play regulatory roles in transcription and 3'-end formation.

Alternative splicing events and function in the tumor microenvironment: New opportunities and challenges

Alternative splicing controls gene expression at the transcriptional level, producing structurally and functionally distinct protein heterodimers. Aberrant alternative splicing greatly affects cell development and plays an important role in the invasion and metastasis of many types of cancer. Recently, it has been shown that alternative splicing can alter the tumor microenvironment and regulate processes such as remodeling, immunity, and inflammation in the tumor microenvironment. However, there is no comprehensive literature review of the complex relationship between alternative splicing and the tumor microenvironment. Therefore, this review aims to collect all the latest data on this topic and provide a new perspective on the therapeutic and potential prognostic markers of cancer.

Case control study: G-allele of rs4244165 in JAK1 gene correlated with high-level brief psychiatric rating scale in bipolar patients

Bipolar disorder (BD) is a chronic and clinically complex disease, characterized by pathological disturbances in mood and energy. Cytokines can access the brain and their signaling pathways affect brain functions, such as neurotransmitter metabolism, neuroendocrine function, neural/synaptic plasticity, and mood neural circuitry. JAK 1 is the most common phosphorylation protein combined with the tyrosine kinase cytokine receptors; therefore, we investigated the association between the Janus family kinase 1 (JAK1) gene polymorphisms (rs2780895, rs4244165, and rs17127024) and susceptibility to BD. The case study population included 93 patients diagnosed with BD and 112 healthy controls, selected from the central coastal region of Tunisia. Polymerase chain reaction-restriction fragment length polymorphism was used to investigate these 3 JAK1 polymorphisms. We compared the sociodemographic and clinical parameters of 3 genotypes of this single nucleotide polymorphisms rs2780895, rs4244165, and rs17127024 of the JAK1 gene. The frequencies of the 3 genotypes were similar in the patient and control groups. One-way analysis of variance revealed a significant variation in rs4244165. After hospitalization, the average of the brief psychiatric rating scale score was significantly higher for the wild-type GG genotype than that for the double-mutation TT genotype (31.23% vs 22.85%, P = .043). The least significant difference post hoc test also showed a significant difference between the GG and TT genotypes at both hospital admission (P = .001) and after hospitalization (P = .012), with the GG genotype being associated with a higher brief psychiatric rating scale score. Haplotypic analysis revealed that the wild-type haplotype with the highest frequency (46.62%) was CTG. Our results showed no association between the 3 studied positions and bipolar disorder. However, the G-allele of rs4244165 in JAK1 is associated with the highest level of the brief psychiatric rating scale in patients with bipolar disorder. The JAK/signal transducer and activator of transcription pathway is an interesting therapeutic route that requires further investigations. Studying their regulatory regions can provide a clearer picture of all the interactions involved in the regulation of genetic expression in response to treatment.

The MSH2 c.793-1G>A variant disrupts normal splicing and is associated with Lynch syndrome

Instruction

Lynch syndrome (LS) is the most common inherited cancer predisposition disorder of colorectal cancer (CRC) which is associated with pathogenic variants in 4 mismatch repair (MMR) genes. Here, we reported a multi-generation Chinese family clinically diagnosed with LS.

Methods

To identify the underlying pathogenic gene variants, 30 whole blood samples and 4 colorectal cancer tissue samples and their clinical data were obtained from this four-generation family. Microsatellite instability-high (MSI) testing, immunohistochemistry (IHC), and Whole-Exome Sequencing (WES) were performed to identify the MMR/MSI and the underlying gene variants. The minigene splicing assay and in vitro splicing assay were used to explore the function of this variant.

Results

MSI-H and dMMR was revealed by the MSI testing and IHC, Whole-Exome Sequencing (WES) in 3 patients successfully identified a splicing variant (c.793-1G>A) in intron 4 of MSH2. Sanger sequencing validated the WES results, and all the "healthy" individuals carrying the variant have been identified in the family by PCR. Bioinformatics analysis and in vitro minigene assay showed that the pathogenic variant affected the splicing process of MSH2 gene to generate 2 kinds defective transcription products, and consequently reduced the expression of MSH2 protein. The mutation carriers were later recommended for colonoscopy and other important cancer diagnostic inspections every 1-2 years because they both have a higher risk of LS.

Discussion

We found a pathogenic splicing variant (rs863225397, c.793-1G>A) of MSH2 gene, and furtherly confirmed that this mutation plays an important role in LS patients of this pedigree based on the vitro study. Our study indicates that one splicing mutation in the MSH2 gene (c.793-1G>A) causes LS and highlights the importance of LS gene testing.

A Novel Homozygous Splice Site Variant in AIMP1 Gene Causing Hypomyelinating Leukodystrophy: Case Report and Review of the Literature

BACKGROUND

 Biallelic pathogenic variants in AIMP1 gene cause hypomyelinating leukodystrophy type 3, a severe neurodegenerative disorder with early onset characterized by microcephaly, axial hypotonia, epilepsy, spasticity, and developmental delay.

METHODS

 Clinical exome sequence was performed on patient's DNA and Sanger sequencing was used to confirm the candidate variant. To better characterize the effect of the genetic variant, functional analysis based on Sanger sequencing of the proband's complementary DNA (cDNA) was performed.

RESULTS

 We report a case of 2-year-old girl with microcephaly, significant global developmental delay, refractory epilepsy, flaccid paralysis, hypomyelination, leukodystrophy, and cerebral atrophy on brain magnetic resonance imaging (MRI). Clinical exome sequencing revealed a novel splice site variant c.603 + 1G > A in homozygosity in the AIMP1 gene. Studies on patient's cDNA showed that the variant disrupts the canonical donor splice site of intron 5, with the recognition of a cryptic splice site within exon 5, leading to the skipping of the last 24 nucleotides of this exon together with the flanking intron. This alteration is predicted to cause an in-frame deletion of eight amino acids (p.Val194_Gln201del) belonging to the tRNA-biding domain of the protein.

CONCLUSION

 To the best of our knowledge, this is the first report of a splice site variant in the AIMP1 gene causing hypomyelinating leukodystrophy. The description of this patient not only expands the mutational spectrum of AIMP1 but also provides deeper insights on genotype-phenotype correlation by comparing the clinical features of our patient with previously reported affected individuals.

Splicing accuracy varies across human introns, tissues and age

Alternative splicing impacts most multi-exonic human genes. Inaccuracies during this process may have an important role in ageing and disease. Here, we investigated mis-splicing using RNA-sequencing data from ~14K control samples and 42 human body sites, focusing on split reads partially mapping to known transcripts in annotation. We show that mis-splicing occurs at different rates across introns and tissues and that these splicing inaccuracies are primarily affected by the abundance of core components of the spliceosome assembly and its regulators. Using publicly available data on short-hairpin RNA-knockdowns of numerous spliceosomal components and related regulators, we found support for the importance of RNA-binding proteins in mis-splicing. We also demonstrated that age is positively correlated with mis-splicing, and it affects genes implicated in neurodegenerative diseases. This in-depth characterisation of mis-splicing can have important implications for our understanding of the role of splicing inaccuracies in human disease and the interpretation of long-read RNA-sequencing data.

Expression of the Ovine Gene and the Relationship Between Its Polymorphism and Feed Efficiency Traits

In the mutton industry, feed efficiency traits have the greatest influence on the economic benefits of sheep raised in housing conditions. In this study, quantitative real-time PCR (qRT-PCR), Sanger sequencing, and KASPar methods were used to detect the expression levels of the B cell scaffold protein with ankyrin repeats 1 (BANK1) gene and the relationship between its polymorphism and feed efficiency traits in Hu sheep. The qRT-PCR results showed that the BANK1 gene was extensively expressed in 10 tissues and it was expressed at remarkably higher levels in lymph than in other tissues (p < 0.05). Then, the polymorphism locus, g.93888 A > T, was detected in intron 4 of the BANK1 gene and proved to be remarkably associated with feed efficiency traits (p < 0.05). Hence, the BANK1 gene can be used as a candidate gene for improving the feed efficiency of Hu sheep and this locus could be used as a potential molecular marker for breeding high-feed efficiency sheep in future breeding efforts.

A presumed missense variant in the U2AF2 gene causes exon skipping in neurodevelopmental diseases

U2 small nuclear RNA auxiliary factor 2 (U2AF2) is an indispensable pre-mRNA splicing factor in the early process of splicing. Recently, U2AF2 was reported as a novel candidate gene associated with neurodevelopmental disorders. Herein, we report a patient with a novel presumed heterozygous missense variant in the U2AF2 gene (c.603G>T), who has a similar clinical phenotype as the patient reported before, including epilepsy, intellectual disability, language delay, microcephaly, and hypoplastic corpus callosum. We reviewed the phenotypic and genetic spectrum of patients with U2AF2-related neurological diseases, both newly diagnosed and previously reported. To investigate the possible pathogenesis, EBV-immortalized lymphoblastoid cells were derived from the peripheral blood obtained from the patient and control groups. Furthermore, according to the results of WB, RT-PCR, Q-PCR, and cDNA sequencing of RT-PCR products, the presumed missense variant c.603G>T caused exon 6 skipping in the U2AF2 mRNA transcript and led to a truncated protein (p.E163_E201del). Cell Counting Kit-8 (CCK-8) and cell cycle detection demonstrated that the variant c.603G>T inhibited the proliferation of patient lymphocyte cells compared with the control group. This study is aimed at expanding the phenotypic and genetic spectrum of U2AF2-related neurodevelopmental diseases and investigating the potential effects. This is the first report of the possible pathogenesis of a U2AF2 gene pathogenic variant in a patient with neurodevelopmental diseases and shows that a novel presumed missense variant in the U2AF2 gene causes exon skipping.

Non-ubiquitous expression of core spliceosomal protein SmB/B' in chick and mouse embryos

BACKGROUND

Although splicing is an integral part of the expression of many genes in our body, genetic syndromes with spliceosomal defects affect only specific tissues. To help understand the mechanism, we investigated the expression pattern of a core protein of the major spliceosome, SmB/B' (Small Nuclear Ribonucleoprotein Polypeptides B/B'), which is encoded by SNRPB. Loss-of-function mutations of SNRPB in humans cause cerebro-costo-mandibular syndrome (CCMS) characterized by rib gaps, micrognathia, cleft palate, and scoliosis. Our expression analysis focused on the affected structures as well as non-affected tissues, using chick and mouse embryos as model animals.

RESULTS

Embryos at young stages (gastrula) showed ubiquitous expression of SmB/B'. However, the level and pattern of expression became tissue-specific as differentiation proceeded. The regions relating to CCMS phenotypes such as cartilages of ribs and vertebrae and palatal mesenchyme express SmB/B' in the nucleus sporadically. However, cartilages that are not affected in CCMS also showed similar expressions. Another spliceosomal gene, SNRNP200, which mutations cause retinitis pigmentosa, was also prominently expressed in cartilages in addition to the retina.

CONCLUSION

The expression of SmB/B' is spatiotemporally regulated during embryogenesis despite the ubiquitous requirement of the spliceosome, however, the expression pattern is not strictly correlated with the phenotype presentation.

Genome-wide mapping of protein-DNA damage interaction by PADD-seq

Protein-DNA damage interactions are critical for understanding the mechanism of DNA repair and damage response. However, due to the relatively random distributions of UV-induced damage and other DNA bulky adducts, it is challenging to measure the interactions between proteins and these lesions across the genome. To address this issue, we developed a new method named Protein-Associated DNA Damage Sequencing (PADD-seq) that uses Damage-seq to detect damage distribution in chromatin immunoprecipitation-enriched DNA fragments. It is possible to delineate genome-wide protein-DNA damage interactions at base resolution with this strategy. Using PADD-seq, we observed that RNA polymerase II (Pol II) was blocked by UV-induced damage on template strands, and the interaction declined within 2 h in transcription-coupled repair-proficient cells. On the other hand, Pol II was clearly restrained at damage sites in the absence of the transcription-repair coupling factor CSB during the same time course. Furthermore, we used PADD-seq to examine local changes in H3 acetylation at lysine 9 (H3K9ac) around cisplatin-induced damage, demonstrating the method's broad utility. In conclusion, this new method provides a powerful tool for monitoring the dynamics of protein-DNA damage interaction at the genomic level, and it encourages comprehensive research into DNA repair and damage response.

Mutations in the non-coding RNU4ATAC gene affect the homeostasis and function of the Integrator complex

Various genetic diseases associated with microcephaly and developmental defects are due to pathogenic variants in the U4atac small nuclear RNA (snRNA), a component of the minor spliceosome essential for the removal of U12-type introns from eukaryotic mRNAs. While it has been shown that a few RNU4ATAC mutations result in impaired binding of essential protein components, the molecular defects of the vast majority of variants are still unknown. Here, we used lymphoblastoid cells derived from RNU4ATAC compound heterozygous (g.108_126del;g.111G>A) twin patients with MOPD1 phenotypes to analyze the molecular consequences of the mutations on small nuclear ribonucleoproteins (snRNPs) formation and on splicing. We found that the U4atac108_126del mutant is unstable and that the U4atac111G>A mutant as well as the minor di- and tri-snRNPs are present at reduced levels. Our results also reveal the existence of 3'-extended snRNA transcripts in patients' cells. Moreover, we show that the mutant cells have alterations in splicing of INTS7 and INTS10 minor introns, contain lower levels of the INTS7 and INTS10 proteins and display changes in the assembly of Integrator subunits. Altogether, our results show that compound heterozygous g.108_126del;g.111G>A mutations induce splicing defects and affect the homeostasis and function of the Integrator complex.

Roles of minor spliceosome in intron recognition and the convergence with the better understood major spliceosome

Catalyzed by spliceosomes in the nucleus, RNA splicing removes intronic sequences from precursor RNAs in eukaryotes to generate mature RNA, which also significantly increases proteome complexity and fine-tunes gene expression. Most metazoans have two coexisting spliceosomes; the major spliceosome, which removes >99.5% of introns, and the minor spliceosome, which removes far fewer introns (only 770 at present have been predicted in the human genome). Both spliceosomes are large and dynamic machineries, each consisting of five small nuclear RNAs (snRNAs) and more than 100 proteins. However, the dynamic assembly, catalysis, and protein composition of the minor spliceosome are still poorly understood. With different splicing signals, minor introns are rare and usually distributed alone and flanked by major introns in genes, raising questions of how they are recognized by the minor spliceosome and how their processing deals with the splicing of neighboring major introns. Due to large numbers of introns and close similarities between the two machinery, cooperative, and competitive recognition by the two spliceosomes has been investigated. Functionally, many minor-intron-containing genes are evolutionarily conserved and essential. Mutations in the minor spliceosome exhibit a variety of developmental defects in plants and animals and are linked to numerous human diseases. Here, we review recent progress in the understanding of minor splicing, compare currently known components of the two spliceosomes, survey minor introns in a wide range of organisms, discuss cooperation and competition of the two spliceosomes in splicing of minor-intron-containing genes, and contributions of minor splicing mutations in development and diseases. This article is categorized under: RNA Processing > Processing of Small RNAs RNA Processing > Splicing Mechanisms RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry.

An intron mutation of HNF1A causes abnormal splicing and impairs its activity as a transcription factor

Mutations in HNF1A are associated with Maturity Onset Diabetes of the Young type 3 (MODY3) and most of them are in the coding region. Herein, we identified an intron mutation at the 6th nucleotide upstream of the end of intron 7 of HNF1A, named IVS7-6G > A, in a patient with early-onset diabetes. The "minigene" assay showed that IVS7-6G > A produced two aberrant mRNA variants translating into two truncated proteins: L502S fs* and G437A fs*, both affecting HNF1A transactivation domain (TAD). To determine functional consequences of IVS7-6G > A mutation, we made plasmids encoding truncated HNF1A containing different portions of HNF1A TAD and found that the TAD of HNF1A is important not only for its regulatory activities, but also for its nuclearization, and the residues 282-501 was more essential than 502-631. Our data suggested IVS7-6G > A impaired HNF1A splicing and may contribute to the pathogenesis of MODY3.

Pervasive misannotation of microexons that are evolutionarily conserved and crucial for gene function in plants

It is challenging to identify the smallest microexons (≤15-nt) due to their small size. Consequently, these microexons are often misannotated or missed entirely during genome annotation. Here, we develop a pipeline to accurately identify 2,398 small microexons in 10 diverse plant species using 990 RNA-seq datasets, and most of them have not been annotated in the reference genomes. Analysis reveals that microexons tend to have increased detained flanking introns that require post-transcriptional splicing after polyadenylation. Examination of 45 conserved microexon clusters demonstrates that microexons and associated gene structures can be traced back to the origin of land plants. Based on these clusters, we develop an algorithm to genome-wide model coding microexons in 132 plants and find that microexons provide a strong phylogenetic signal for plant organismal relationships. Microexon modeling reveals diverse evolutionary trajectories, involving microexon gain and loss and alternative splicing. Our work provides a comprehensive view of microexons in plants.

The small size (≤15-nt) of micorexons poses difficulties for genome annotation and identification using standard RNA sequence mapping approaches. Here, the authors develop computational pipelines to discover and predict microexons in plants and reveal diverse evolutionary trajectories via genomewide microexon modeling.

Non-canonical splice junction processing increases the diversity of RBFOX2 splicing isoforms

The underlying mechanisms of splicing regulation through non-canonical splice junction processing remain largely unknown. Here, we identified two RBFOX2 splicing isoforms by alternative 3' splice site selection of exon 9; the non-canonical splice junction processed RBFOX2 transcript (RBFOX2-N.C.) was expressed by the selection of the 3' splice GG acceptor sequence. The cytoplasmic localization of RBFOX2-C., a canonical splice junction-processed RBFOX2 transcript, was different from that of RBFOX2-N.C., which showed nuclear localization. In addition, we confirmed that RBFOX2-C. showed a significantly stronger localization into stress granules than RBFOX2-N.C. upon sodium arsenite treatment. Next, we investigated the importance of non-canonical 3' splice GG sequence selection of specific cis-regulatory elements using minigene constructs of the RBFOX2 gene. We found that the non-canonical 3' splice GG sequence and suboptimal branch point site adjacent region were critical for RBFOX2-N.C. expression through a non-canonical 3' splice selection. Our results suggest a regulatory mechanism for the non-canonical 3' splice selection in the RBFOX2 gene, providing a basis for studies related to the regulation of alternative pre-mRNA splicing through non-canonical splice junction processing.

Pathogenic variants in RNPC3 are associated with hypopituitarism and primary ovarian insufficiency

PURPOSE

We aimed to investigate the molecular basis underlying a novel phenotype including hypopituitarism associated with primary ovarian insufficiency.

METHODS

We used next-generation sequencing to identify variants in all pedigrees. Expression of Rnpc3/RNPC3 was analyzed by in situ hybridization on murine/human embryonic sections. CRISPR/Cas9 was used to generate mice carrying the p.Leu483Phe pathogenic variant in the conserved murine Rnpc3 RRM2 domain.

RESULTS

We described 15 patients from 9 pedigrees with biallelic pathogenic variants in RNPC3, encoding a specific protein component of the minor spliceosome, which is associated with a hypopituitary phenotype, including severe growth hormone (GH) deficiency, hypoprolactinemia, variable thyrotropin (also known as thyroid-stimulating hormone) deficiency, and anterior pituitary hypoplasia. Primary ovarian insufficiency was diagnosed in 8 of 9 affected females, whereas males had normal gonadal function. In addition, 2 affected males displayed normal growth when off GH treatment despite severe biochemical GH deficiency. In both mouse and human embryos, Rnpc3/RNPC3 was expressed in the developing forebrain, including the hypothalamus and Rathke's pouch. Female Rnpc3 mutant mice displayed a reduction in pituitary GH content but with no reproductive impairment in young mice. Male mice exhibited no obvious phenotype.

CONCLUSION

Our findings suggest novel insights into the role of RNPC3 in female-specific gonadal function and emphasize a critical role for the minor spliceosome in pituitary and ovarian development and function.

Comprehensive characterization of 11 prognostic alternative splicing events in ovarian cancer interacted with the immune microenvironment

Alternative splicing (AS) events play a crucial role in the tumorigenesis and progression of cancer. Transcriptome data and Percent Spliced In (PSI) values of ovarian cancer patients were downloaded from TCGA database and TCGA SpliceSeq. Totally we identified 1472 AS events that were associated with survival of ovarian serous cystadenocarcinoma (OC) and exon skipping (ES) was the most important type. Univariate and multivariate Cox regression analysis were performed to identify survival-associated AS events and developed the prognostic model based on 11-AS events. The immune cells and different response to cytotoxic T lymphocyte associated antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) blockers in low-risk and high-risk group of OC patients were analyzed. Ten kinds of immune cells were found up-regulated in low-risk group. Activated B cell, natural killer T cell, natural killer cell and regulatory T cell were associated with survival of OC. The patients in low-risk group had good response to CTLA-4 and PD-1 blockers treatment. Moreover, a regulatory network was established according to the correlation between AS events and splicing factors (SFs). The present study provided valuable insights into the underlying mechanisms of OC. AS events that were correlated with the immune system might be potential therapeutic targets.

RNA metabolism and links to inflammatory regulation and disease

Inflammation is vital to protect the host against foreign organism invasion and cellular damage. It requires tight and concise gene expression for regulation of pro- and anti-inflammatory gene expression in immune cells. Dysregulated immune responses caused by gene mutations and errors in post-transcriptional regulation can lead to chronic inflammatory diseases and cancer. The mechanisms underlying post-transcriptional gene expression regulation include mRNA splicing, mRNA export, mRNA localisation, mRNA stability, RNA/protein interaction, and post-translational events such as protein stability and modification. The majority of studies to date have focused on transcriptional control pathways. However, post-transcriptional regulation of mRNA in eukaryotes is equally important and related information is lacking. In this review, we will focus on the mechanisms involved in the pre-mRNA splicing events, mRNA surveillance, RNA degradation pathways, disorders or symptoms caused by mutations or errors in post-transcriptional regulation during innate immunity especially toll-like receptor mediated pathways.

Phylogeny and conservation of plant U2A/U2A', a core splicing component in U2 spliceosomal complex

This study systematically identifies 112 U2A genes from 80 plant species by combinatory bioinformatics analysis, which is important for understanding their phylogenetic history, expression profiles and for predicting specific functions. In eukaryotes, a pre-mRNA can generate multiple transcripts by removing certain introns and joining corresponding exons, thus greatly expanding the transcriptome and proteome diversity. The spliceosome is a mega-Dalton ribonucleoprotein (RNP) complex that is essential for the process of splicing. In spliceosome components, the U2 small nuclear ribonucleoprotein (U2 snRNP) forms the pre-spliceosome by association with the branch site. An essential component that promotes U2 snRNP assembly, named U2A, has been extensively identified in humans, yeast and nematodes. However, studies examining U2A genes in plants are scarce. In this study, we performed a comprehensive analysis and identified a total of 112 U2A genes from 80 plant species representing dicots, monocots, mosses and algae. Comparisons of the gene structures, protein domains, and expression patterns of 112 U2A genes indicated that the conserved functions were likely retained by plant U2A genes and important for responses to internal and external stimuli. In addition, analysis of alternative transcripts and splice sites of U2A genes indicated that the fifth intron contained a conserved alternative splicing event that might be important for its molecular function. Our work provides a general understanding of this splicing factor family in terms of genes and proteins, and it will serve as a fundamental resource that will contribute to further mechanistic characterization in plants.

Impact of Alternative Splicing Variants on Liver Cancer Biology

Simple Summary

Among the top ten deadly solid tumors are the two most frequent liver cancers, hepatocellular carcinoma, and intrahepatic cholangiocarcinoma, whose development and malignancy are favored by multifactorial conditions, which include aberrant maturation of pre-mRNA due to abnormalities in either the machinery involved in the splicing, i.e., the spliceosome and associated factors, or the nucleotide sequences of essential sites for the exon recognition process. As a consequence of cancer-associated aberrant splicing in hepatocytes- and cholangiocytes-derived cancer cells, abnormal proteins are synthesized. They contribute to the dysregulated proliferation and eventually transformation of these cells to phenotypes with enhanced invasiveness, migration, and multidrug resistance, which contributes to the poor prognosis that characterizes these liver cancers.

Abstract

The two most frequent primary cancers affecting the liver, whose incidence is growing worldwide, are hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which are among the five most lethal solid tumors with meager 5-year survival rates. The common difficulty in most cases to reach an early diagnosis, the aggressive invasiveness of both tumors, and the lack of favorable response to pharmacotherapy, either classical chemotherapy or modern targeted therapy, account for the poor outcome of these patients. Alternative splicing (AS) during pre-mRNA maturation results in changes that might affect proteins involved in different aspects of cancer biology, such as cell cycle dysregulation, cytoskeleton disorganization, migration, and adhesion, which favors carcinogenesis, tumor promotion, and progression, allowing cancer cells to escape from pharmacological treatments. Reasons accounting for cancer-associated aberrant splicing include mutations that create or disrupt splicing sites or splicing enhancers or silencers, abnormal expression of splicing factors, and impaired signaling pathways affecting the activity of the splicing machinery. Here we have reviewed the available information regarding the impact of AS on liver carcinogenesis and the development of malignant characteristics of HCC and iCCA, whose understanding is required to develop novel therapeutical approaches aimed at manipulating the phenotype of cancer cells.

Impact of alternative splicing on mechanisms of resistance to anticancer drugs

A shared characteristic of many tumors is the lack of response to anticancer drugs. Multiple mechanisms of pharmacoresistance (MPRs) are involved in permitting cancer cells to overcome the effect of these agents. Pharmacoresistance can be primary (intrinsic) or secondary (acquired), i.e., triggered or enhanced in response to the treatment. Moreover, MPRs usually result in the lack of sensitivity to several agents, which accounts for diverse multidrug-resistant (MDR) phenotypes. MPRs are based on the dynamic expression of more than one hundred genes, constituting the so-called resistome. Alternative splicing (AS) during pre-mRNA maturation results in changes affecting proteins involved in the resistome. The resulting splicing variants (SVs) reduce the efficacy of anticancer drugs by lowering the intracellular levels of active agents, altering molecular targets, enhancing both DNA repair ability and defensive mechanism of tumors, inducing changes in the balance between pro-survival and pro-apoptosis signals, modifying interactions with the tumor microenvironment, and favoring malignant phenotypic transitions. Reasons accounting for cancer-associated aberrant splicing include mutations that create or disrupt splicing sites or splicing enhancers or silencers, abnormal expression of splicing factors, and impaired signaling pathways affecting the activity of the splicing machinery. Here we have reviewed the impact of AS on MPR in cancer cells.

Epigenetic interplay between methylation and miRNA in bladder cancer: focus on isoform expression

BACKGROUND

Various epigenetic factors are responsible for the non-genetic regulation on gene expression. The epigenetically dysregulated oncogenes or tumor suppressors by miRNA and/or DNA methylation are often observed in cancer cells. Each of these epigenetic regulators has been studied well in cancer progressions; however, their mutual regulatory relationship in cancer still remains unclear. In this study, we propose an integrative framework to systematically investigate epigenetic interactions between miRNA and methylation at the alternatively spliced mRNA level in bladder cancer. Each of these epigenetic regulators has been studied well in cancer progressions; however, their mutual regulatory relationship in cancer still remains unclear.

RESULTS

The integrative analyses yielded 136 significant combinations (methylation, miRNA and isoform). Further, overall survival analysis on the 136 combinations based on methylation and miRNA, high and low expression groups resulted in 13 combinations associated with survival. Additionally, different interaction patterns were examined.

CONCLUSIONS

Our study provides a higher resolution of molecular insight into the crosstalk between two epigenetic factors, DNA methylation and miRNA. Given the importance of epigenetic interactions and alternative splicing in cancer, it is timely to identify and understand the underlying mechanisms based on epigenetic markers and their interactions in cancer, leading to alternative splicing with primary functional impact.

Molecular and genomic landscapes in secondary & therapy related acute myeloid leukemia

Acute myeloid leukemia (AML) is a complex, aggressive myeloid neoplasm characterized by frequent somatic mutations that influence different functional categories' genes, resulting in maturational arrest and clonal expansion. AML can arise de novo (dn-AML) or can be secondary AML (s-AML) refers to a leukemic process which may arise from an antecedent hematologic disorder (AHD-AML), mostly from a myelodysplastic syndrome (MDS) or myeloproliferative neoplasm (MPN) or can be the result of an antecedent cytotoxic chemotherapy or radiation therapy (therapy-related AML, t-AML). Clinical and biological features in secondary and therapy-related AML are distinct from de novo AML. Secondary and therapy-related AML occurs mainly in the elderly population and responds worse to therapy with higher relapse rates due to resistance to cytotoxic chemotherapy. Over the last decade, advances in molecular genetics have disclosed the sub-clonal architecture of secondary and therapy-related AML. Recent investigations have revealed that cytogenetic abnormalities and underlying genetic aberrations (mutations) are likely to be significant factors dictating prognosis and critical impacts on treatment outcome. Secondary and therapy-related AML have a poorer outcome with adverse cytogenetic abnormalities and higher recurrences of unfavorable mutations compared to de novo AML. In this review, we present an overview of the clinical features of secondary and therapy-related AML and address the function of genetic mutations implicated in the pathogenesis of secondary leukemia. Detailed knowledge of the pathogenetic mechanisms gives an overview of new prognostic markers, including targetable mutations that will presumably lead to the designing and developing novel molecular targeted therapies for secondary and therapy-related AML. Despite significant advances in knowing the genetic aspect of secondary and therapy-related AML, its influence on the disease's pathophysiology, standard treatment prospects have not significantly evolved during the past three decades. Thus, we conclude this review by summarizing the modern and developing treatment strategies in secondary and therapy-related acute myeloid leukemia.

Human spliceosomal snRNA sequence variants generate variant spliceosomes

Human pre-mRNA splicing is primarily catalyzed by the major spliceosome, comprising five small nuclear ribonucleoprotein complexes, U1, U2, U4, U5, and U6 snRNPs, each of which contains the corresponding U-rich snRNA. These snRNAs are encoded by large gene families exhibiting significant sequence variation, but it remains unknown if most human snRNA genes are untranscribed pseudogenes or produce variant snRNAs with the potential to differentially influence splicing. Since gene duplication and variation are powerful mechanisms of evolutionary adaptation, we sought to address this knowledge gap by systematically profiling human U1, U2, U4, and U5 snRNA variant gene transcripts. We identified 55 transcripts that are detectably expressed in human cells, 38 of which incorporate into snRNPs and spliceosomes in 293T cells. All U1 snRNA variants are more than 1000-fold less abundant in spliceosomes than the canonical U1, whereas at least 1% of spliceosomes contain a variant of U2 or U4. In contrast, eight U5 snRNA sequence variants occupy spliceosomes at levels of 1% to 46%. Furthermore, snRNA variants display distinct expression patterns across five human cell lines and adult and fetal tissues. Different RNA degradation rates contribute to the diverse steady state levels of snRNA variants. Our findings suggest that variant spliceosomes containing noncanonical snRNAs may contribute to different tissue- and cell-type-specific alternative splicing patterns.

Variants in LSM7 impair LSM complexes assembly, neurodevelopment in zebrafish and may be associated with an ultra-rare neurological disease

Leukodystrophies, genetic neurodevelopmental and/or neurodegenerative disorders of cerebral white matter, result from impaired myelin homeostasis and metabolism. Numerous genes have been implicated in these heterogeneous disorders; however, many individuals remain without a molecular diagnosis. Using whole-exome sequencing, biallelic variants in LSM7 were uncovered in two unrelated individuals, one with a leukodystrophy and the other who died in utero. LSM7 is part of the two principle LSM protein complexes in eukaryotes, namely LSM1-7 and LSM2-8. Here, we investigate the molecular and functional outcomes of these LSM7 biallelic variants in vitro and in vivo. Affinity purification-mass spectrometry of the LSM7 variants showed defects in the assembly of both LSM complexes. Lsm7 knockdown in zebrafish led to central nervous system defects, including impaired oligodendrocyte development and motor behavior. Our findings demonstrate that variants in LSM7 cause misassembly of the LSM complexes, impair neurodevelopment of the zebrafish, and may be implicated in human disease. The identification of more affected individuals is needed before the molecular mechanisms of mRNA decay and splicing regulation are added to the categories of biological dysfunctions implicated in leukodystrophies, neurodevelopmental and/or neurodegenerative diseases.

Biallelic variants in RNU12 cause CDAGS syndrome

CDAGS Syndrome is a rare congenital disorder characterized by Craniosynostosis, Delayed closure of the fontanelles, cranial defects, clavicular hypoplasia, Anal and Genitourinary malformations, and Skin manifestations. We performed whole exome and Sanger sequencing to identify the underlying molecular cause in five patients with CDAGS syndrome from four distinct families. Whole exome sequencing revealed biallelic rare variants that disrupt highly conserved nucleotides within the RNU12 gene. RNU12 encodes a small nuclear RNA that is a component of the minor spliceosome and is essential for minor intron splicing. Targeted sequencing confirmed allele segregation within the four families. All five patients shared the same rare mutation NC_000022.10:g.43011402C>T, which alters a highly conserved nucleotide within the precursor U12 snRNA 3' extension. Each of them also carried a rare variant on the other allele that either disrupts the secondary structure or the Sm binding site of the RNU12 snRNA. Whole transcriptome sequencing analysis of lymphoblastoid cells identified 120 differentially expressed genes, and differential alternative splicing analysis indicated there was an enrichment of alternative splicing events in the patient. These findings provide evidence of the involvement of RNU12 in craniosynostosis, anal and genitourinary patterning, and cutaneous disease.

Gene Architecture Facilitates Intron-Mediated Enhancement of Transcription

Introns impact several vital aspects of eukaryotic organisms like proteomic plasticity, genomic stability, stress response and gene expression. A role for introns in the regulation of gene expression at the level of transcription has been known for more than thirty years. The molecular basis underlying the phenomenon, however, is still not entirely clear. An important clue came from studies performed in budding yeast that indicate that the presence of an intron within a gene results in formation of a multi-looped gene architecture. When looping is defective, these interactions are abolished, and there is no enhancement of transcription despite normal splicing. In this review, we highlight several potential mechanisms through which looping interactions may enhance transcription. The promoter-5′ splice site interaction can facilitate initiation of transcription, the terminator-3′ splice site interaction can enable efficient termination of transcription, while the promoter-terminator interaction can enhance promoter directionality and expedite reinitiation of transcription. Like yeast, mammalian genes also exhibit an intragenic interaction of the promoter with the gene body, especially exons. Such promoter-exon interactions may be responsible for splicing-dependent transcriptional regulation. Thus, the splicing-facilitated changes in gene architecture may play a critical role in regulation of transcription in yeast as well as in higher eukaryotes.

RNA Sequence and Structure Determinants of Pol III Transcriptional Termination in Human Cells

The precise mechanism of transcription termination of the eukaryotic RNA polymerase III (Pol III) has been a subject of considerable debate. Although previous studies have clearly shown that multiple uracils at the end of RNA transcripts are required for Pol III termination, the effects of upstream RNA secondary structure in the nascent transcript on transcriptional termination is still unclear. To address this, we developed an in cellulo Pol III transcription termination assay using the recently developed Tornado-Corn RNA aptamer system to create a Pol III-transcribed RNA that produces a detectable fluorescent signal when transcribed in human cells. To study the effects of RNA sequence and structure on Pol III termination, we systematically varied the sequence context upstream of the aptamer and identified sequence characteristics that enhance or diminish termination. For transcription from Pol III type 3 promoters, we found that only poly-U tracts longer than the average length found in the human genome efficiently terminate Pol III transcription without RNA secondary structure elements. We observed that RNA secondary structure elements placed in proximity to shorter poly-U tracts induced termination, and RNA secondary structure by itself was not sufficient to induce termination. For Pol III type 2 promoters, we found that the shorter poly-U tract lengths of 4 uracils were sufficient to induce termination. These findings demonstrate a key role for sequence and structural elements within Pol III-transcribed nascent RNA for efficient transcription termination, and demonstrate a generalizable assay for characterizing Pol III transcription in human cells.

Breast Cancer and the Other Non-Coding RNAs

Breast cancer is very heterogenous and the most common gynaecological cancer, with various factors affecting its development. While its impact on human lives and national health budgets is still rising in almost all global areas, many molecular mechanisms affecting its onset and development remain unclear. Conventional treatments still prove inadequate in some aspects, and appropriate molecular therapeutic targets are required for improved outcomes. Recent scientific interest has therefore focused on the non-coding RNAs roles in tumour development and their potential as therapeutic targets. These RNAs comprise the majority of the human transcript and their broad action mechanisms range from gene silencing to chromatin remodelling. Many non-coding RNAs also have altered expression in breast cancer cell lines and tissues, and this is often connected with increased proliferation, a degraded extracellular environment, and higher endothelial to mesenchymal transition. Herein, we summarise the known abnormalities in the function and expression of long non-coding RNAs, Piwi interacting RNAs, small nucleolar RNAs and small nuclear RNAs in breast cancer, and how these abnormalities affect the development of this deadly disease. Finally, the use of RNA interference to suppress breast cancer growth is summarised.

C20orf204, a hepatocellular carcinoma-specific protein interacts with nucleolin and promotes cell proliferation

In most human cancers, a large number of proteins with driver mutations are involved in tumor development, implying that multiple fine tuners are involved in cancer formation and/or maintenance. A useful strategy for cancer therapy may therefore be to target multiple cancer type-specific fine tuners. Furthermore, genome-wide association studies of tumor samples have identified a large number of long noncoding (lnc)RNA associated with various types of tumor. In this context we have previously found that C20orf204 (a splice variant of Linc00176) RNA contains a 189 amino acid (AA) long open reading frame (C20orf204-189AA) that is expressed predominantly in hepatocellular carcinoma (HCC). We report here that a protein, C20orf204-189AA, was detected in the nucleus of 14 out of 20 primary HCC, but not in control livers. Strikingly, overexpression of C20orf204-189AA enhanced cell proliferation and ribosomal RNA transcription. C20orf204-189AA is co-localized, and interacted with nucleolin via the C-terminal and with ribosomal RNA via the N-terminal domain. Furthermore, the expression of C20orf204-189AA upregulates the protein level of nucleolin. Nucleolin and C20orf204 mRNA levels in HCC are correlated with tumor differentiation grade and patient survival, suggesting that C20orf204-189AA is a cancer type-specific fine tuner in some HCC that presents itself for potential targeting therapy and cancer biomarker. Thus, cancer cells exhibit remarkable transcriptome alterations partly by adopting cancer-specific splicing isoforms of noncoding RNAs and may participate in tumor development.

Identification of Deep-Intronic Splice Mutations in a Large Cohort of Patients With Inherited Retinal Diseases

High throughput sequencing technologies have revolutionized the identification of mutations responsible for a diverse set of Mendelian disorders, including inherited retinal disorders (IRDs). However, the causal mutations remain elusive for a significant proportion of patients. This may be partially due to pathogenic mutations located in non-coding regions, which are largely missed by capture sequencing targeting the coding regions. The advent of whole-genome sequencing (WGS) allows us to systematically detect non-coding variations. However, the interpretation of these variations remains a significant bottleneck. In this study, we investigated the contribution of deep-intronic splice variants to IRDs. WGS was performed for a cohort of 571 IRD patients who lack a confident molecular diagnosis, and potential deep intronic variants that affect proper splicing were identified using SpliceAI. A total of six deleterious deep intronic variants were identified in eight patients. An in vitro minigene system was applied to further validate the effect of these variants on the splicing pattern of the associated genes. The prediction scores assigned to splice-site disruption positively correlated with the impact of mutations on splicing, as those with lower prediction scores demonstrated partial splicing. Through this study, we estimated the contribution of deep-intronic splice mutations to unassigned IRD patients and leveraged in silico and in vitro methods to establish a framework for prioritizing deep intronic variant candidates for mechanistic and functional analyses.

Novel Intronic Mutations Introduce Pseudoexons in DMD That Cause Muscular Dystrophy in Patients

Background: Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are two subtypes of muscular dystrophy diseases caused by pathogenic mutations in the DMD gene. Until now, more than 4,600 disease-causing mutations in DMD have been reported. However, only 33 mutations were deep intronic, cases with this type of mutations were limited. Methods: In this study, we used a combination of complementary DNA (cDNA) and target DNA sequencing analysis in addition to conventional whole-exome sequencing (WES). Results: Three novel hemizygous mutations IVS11 + 17811C > G (c.1331 + 17811C > G), IVS21 + 3252A > G (c.2803 + 3252A > G) and IVS40 + 362A > G (c.5739 + 362A > G) were identified in DMD patients, while a reported hemizygous mutation IVS62-285A > G (c.9225-285A > G) was found in the BMD patient. These DMD mutations lead to pseudoexon insertions, causing the generation of truncated and dysfunctional dystrophin. Conclusion: This study defines three novel and one reported intronic mutations, which can result in DMD/BMD. We also emphasize the need to combine WES and cDNA-based methods to detect the variant in the very large DMD gene in which the mutational spectrum is complex.

Quantitative analysis of the splice variants expressed by the major hepatitis B virus genotypes

Hepatitis B virus (HBV) is a major human pathogen that causes liver diseases. The main HBV RNAs are unspliced transcripts that encode the key viral proteins. Recent studies have shown that some of the HBV spliced transcript isoforms are predictive of liver cancer, yet the roles of these spliced transcripts remain elusive. Furthermore, there are nine major HBV genotypes common in different regions of the world, these genotypes may express different spliced transcript isoforms. To systematically study the HBV splice variants, we transfected human hepatoma cells, Huh7, with four HBV genotypes (A2, B2, C2 and D3), followed by deep RNA-sequencing. We found that 13-28 % of HBV RNAs were splice variants, which were reproducibly detected across independent biological replicates. These comprised 6 novel and 10 previously identified splice variants. In particular, a novel, singly spliced transcript was detected in genotypes A2 and D3 at high levels. The biological relevance of these splice variants was supported by their identification in HBV-positive liver biopsy and serum samples, and in HBV-infected primary human hepatocytes. Interestingly the levels of HBV splice variants varied across the genotypes, but the spliced pregenomic RNA SP1 and SP9 were the two most abundant splice variants. Counterintuitively, these singly spliced SP1 and SP9 variants had a suboptimal 5' splice site, supporting the idea that splicing of HBV RNAs is tightly controlled by the viral post-transcriptional regulatory RNA element.

Identification and validation of critical alternative splicing events and splicing factors in gastric cancer progression

Gene expression and alternative splicing (AS) interact in complex ways to regulate biological process which is associated with cancer development. Here, by integrated analysis of gene expression and AS events, we aimed to identify the hub AS events and splicing factors relevant in gastric cancer development (GC). RNA‐seq data, clinical data and AS events of 348 GC samples were obtained from the TCGA and TCGASpliceSeq databases. Cox univariable and multivariable analyses, KEGG and GO pathway analyses were performed to identify hub AS events and splicing factor/spliceosome genes, which were further validated in 53 GCs. By bioinformatics methods, we found that gene AS event‐ and gene expression‐mediated GC progression shared the same mechanisms, such as PI3K/AKT pathway, but the involved genes were different. Though expression of 17 hub AS events were confirmed in 53 GC tissues, only 10 AS events in seven genes were identified as critical candidates related to GC progression, notably the AS events (Exon Skip) in CLSTN1 and SEC16A. Expression of these AS events in GC correlated with activation of the PI3K/AKT pathway. Genes with AS events associated with clinical parameters and prognosis were different from the genes whose mRNA levels were related to clinical parameters and prognosis. Besides, we further revealed that QKI and NOVA1 were the crucial splicing factors regulating expression of AS events in GC, but not spliceosome genes. Our integrated analysis revealed hub AS events in GC development, which might be the potential therapeutic targets for GC.

The biological function and clinical significance of SF3B1 mutations in cancer

Spliceosome mutations have become the most interesting mutations detected in human cancer in recent years. The spliceosome, a large, dynamic multimegadalton small nuclear ribonucleoprotein composed of small nuclear RNAs associated with proteins, is responsible for removing introns from precursor mRNA (premRNA) and generating mature, spliced mRNAs. SF3B1 is the largest subunit of the spliceosome factor 3b (SF3B) complex, which is a core component of spliceosomes. Recurrent somatic mutations in SF3B1 have been detected in human cancers, including hematological malignancies and solid tumors, and indicated to be related to patient prognosis. This review summarizes the research progress of SF3B1 mutations in cancer, including SF3B1 mutations in the HEAT domain, the multiple roles and aberrant splicing events of SF3B1 mutations in the pathogenesis of tumors, and changes in mutated cancer cells regarding sensitivity to SF3B small-molecule inhibitors. In addition, the potential of SF3B1 or its mutations to serve as biomarkers or therapeutic targets in cancer is discussed. The accumulated knowledge about SF3B1 mutations in cancer provides critical insight into the integral role the SF3B1 protein plays in mRNA splicing and suggests new targets for anticancer therapy.

RT-PCR analysis of mRNA revealed the splice-altering effect of rare intronic variants in monogenic disorders

BACKGROUND

Variants perturbing the normal splicing of pre-mRNA can lead to human diseases. The splice-altering effect and eventual consequence on gene function was sometimes uncertain and hinders a definitive molecular diagnosis.

METHODS

The impact of four rare intronic variants on splicing was analyzed through reverse transcription - polymerase chain reaction (RT-PCR) analysis of mRNA derived from the peripheral blood of patients. The results were compared with in-silico prediction. Potential implication on molecular diagnosis was discussed.

RESULTS

Four rare intronic variants of SLC9A6, DLG3, GAA, and OCRL were identified in patients with suspected disorders, respectively. Although these four variants were all predicted to alter splicing by in-silico tools, RT-PCR analysis of mRNA derived from peripheral blood showed these variants affected splicing in different ways: c.899+3_899+6del of SLC9A6 resulted in one-exon skipping and an out-of-frame transcript; c.905-2A > G of DLG3 resulted in a mix of in-frame transcripts; c.1195-11T > A of GAA resulted in the in-frame insertion of nine nucleotides; c.723-2A > C of OCRL resulted in one-exon skipping and in-frame deletion of 102 nucleotides. The consequence revealed by mRNA analysis is essential for accurate interpretation of pathogenicity.

CONCLUSION

Four intronic variants all caused aberrant mRNA splicing. For intronic variants with uncertain impact on splicing, mRNA analysis is helpful for ascertainment of alternative splicing and accurate interpretation of pathogenicity.

BANDITS: Bayesian differential splicing accounting for sample-to-sample variability and mapping uncertainty

Alternative splicing is a biological process during gene expression that allows a single gene to code for multiple proteins. However, splicing patterns can be altered in some conditions or diseases. Here, we present BANDITS, a R/Bioconductor package to perform differential splicing, at both gene and transcript level, based on RNA-seq data. BANDITS uses a Bayesian hierarchical structure to explicitly model the variability between samples and treats the transcript allocation of reads as latent variables. We perform an extensive benchmark across both simulated and experimental RNA-seq datasets, where BANDITS has extremely favourable performance with respect to the competitors considered.

Targeted sequencing of FH-deficient uterine leiomyomas reveals biallelic inactivating somatic fumarase variants and allows characterization of missense variants

Uterine leiomyomas (ULs) constitute a considerable health burden in the general female population. The fumarate hydratase (FH) deficient subtype is found in up to 1.6% and can occur in hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome. We sequenced 13 FH deficient ULs from a previous immunohistochemical screen using a targeted panel and identified biallelic FH variants in all. In eight, we found an FH point mutation (two truncating, six missense) with evidence for loss of the second allele. Variant allele-frequencies in all cases with a point mutation pointed to somatic variants. Spatial clustering of the identified missense variants in the lyase domain indicated altered fumarase oligomerization with subsequent degradation as explanation for the observed FH deficiency. Biallelic FH deletions in five tumors confirm the importance of copy number loss as mutational mechanism. By curating all pathogenic FH variants and calculating their population frequency, we estimate a carrier frequency of up to 1/2,563. Comparing with the prevalence of FH deficient ULs, we conclude that most are sporadic and estimate 2.7-13.9% of females with an FH deficient UL to carry a germline FH variant. Further prospective tumor/normal sequencing studies are needed to develop a reliable screening strategy for HLRCC in women with ULs.

PRPF31 reduction causes mis-splicing of the phototransduction genes in human organotypic retinal culture

PRPF31 is ubiquitously expressed splicing factor and has an essential role in the pre-mRNA splicing in all tissues. However, it is not clear how reduced expression of this general splicing factor leads to retinal restricted disease, retinitis pigmentosa (RP). In this study, we used RNA interference and RNA-sequencing to mimic the PRPF31 haploinsufficiency in human organotypic retinal cultures (HORCs). We examined the effects of PRPF31 deficiency on splicing by analyzing the differential exon usages (DEUs) and intron retentions of the retinal transcriptome. Our results revealed that the PRPF31 deficiency causes mis-splicing of genes involved in RNA processing (PRPF3, PRPF8, PRPF4, and PRPF19) and phototransduction (RHO, ROM1, FSCN2, GNAT2, and GNAT1) in the retina in the PRPF31 reduced samples. Mis-splicing of genes implicated in phototransduction was associated with photoreceptor degeneration observed in RP patients. Our data revealed that PRPF31 deficiency leads to the mis-splicing of a distinct subset of pre-mRNAs with a widespread effect on phototransduction and RNA processing.

New insights into minor splicing-a transcriptomic analysis of cells derived from TALS patients

Minor intron splicing plays a central role in human embryonic development and survival. Indeed, biallelic mutations in RNU4ATAC, transcribed into the minor spliceosomal U4atac snRNA, are responsible for three rare autosomal recessive multimalformation disorders named Taybi-Linder (TALS/MOPD1), Roifman (RFMN), and Lowry-Wood (LWS) syndromes, which associate numerous overlapping signs of varying severity. Although RNA-seq experiments have been conducted on a few RFMN patient cells, none have been performed in TALS, and more generally no in-depth transcriptomic analysis of the ∼700 human genes containing a minor (U12-type) intron had been published as yet. We thus sequenced RNA from cells derived from five skin, three amniotic fluid, and one blood biosamples obtained from seven unrelated TALS cases and from age- and sex-matched controls. This allowed us to describe for the first time the mRNA expression and splicing profile of genes containing U12-type introns, in the context of a functional minor spliceosome. Concerning RNU4ATAC-mutated patients, we show that as expected, they display distinct U12-type intron splicing profiles compared to controls, but that rather unexpectedly mRNA expression levels are mostly unchanged. Furthermore, although U12-type intron missplicing concerns most of the expressed U12 genes, the level of U12-type intron retention is surprisingly low in fibroblasts and amniocytes, and much more pronounced in blood cells. Interestingly, we found several occurrences of introns that can be spliced using either U2, U12, or a combination of both types of splice site consensus sequences, with a shift towards splicing using preferentially U2 sites in TALS patients' cells compared to controls.

Determining the prognostic significance of alternative splicing events in soft tissue sarcoma using data from The Cancer Genome Atlas

BACKGROUND

Surgery, adjuvant chemotherapy, and radiotherapy are the primary treatment options for soft tissue sarcomas (STSs). However, identifying ways to improve the prognosis of patients with STS remains a considerable challenge. Evidence shows that the dysregulation of alternative splicing (AS) events is involved in tumor pathogenesis and progression. The present study objective was to identify survival-associated AS events that could serve as prognostic biomarkers and potentially serve as tumor-selective STS drug targets.

METHODS

STS-specific 'percent spliced in' (PSI) values for splicing events in 206 STS samples were downloaded from The Cancer Genome Atlas SpliceSeq^® database. Prognostic analyses were performed on seven types of AS events to determine their prognostic value in STS patients, for which prediction models were constructed with the risk score formula [Formula: see text]. Prediction models were also constructed to determine the prognostic value of AS events, and Spearman's rank correlation coefficients were calculated to determine the degree of correlation between splicing factor expression and the PSI values.

RESULTS

A total 10,439 events were found to significantly correlate with patient survival rates. The area under the time-dependent receiver operating characteristic curve for the prognostic predictor of STS overall survival was 0.826. Notably, the splicing events of certain STS key genes were significantly associated with STS 2-year overall survival in the present study, including exon skip (ES) events in MDM2 and EWSR1, alternate terminator events in CDKN2A and HMGA2 for dedifferentiated liposarcoma, ES in MDM2 and alternate promoter events in CDKN2A for leiomyosarcoma, and ES in EWSR1 for undifferentiated pleomorphic sarcoma. Moreover, splicing correlation networks between AS events and splicing factors revealed that almost all of the AS events showed negatively correlations with the expression of splicing factors.

CONCLUSION

An in-depth analysis of alternative RNA splicing could provide new insights into the mechanisms of STS oncogenesis and the potential for novel approaches to this type of cancer therapy.

Human PRPF40B regulates hundreds of alternative splicing targets and represses a hypoxia expression signature

Altered splicing contributes to the pathogenesis of human blood disorders including myelodysplastic syndromes (MDS) and leukemias. Here we characterize the transcriptomic regulation of PRPF40B, which is a splicing factor mutated in a small fraction of MDS patients. We generated a full PRPF40B knockout (KO) in the K562 cell line by CRISPR/Cas9 technology and rescued its levels by transient overexpression of wild-type (WT), P383L or P540S MDS alleles. Using RNA sequencing, we identified hundreds of differentially expressed genes and alternative splicing (AS) events in the KO that are rescued by WT PRPF40B, with a majority also rescued by MDS alleles, pointing to mild effects of these mutations. Among the PRPF40B-regulated AS events, we found a net increase in exon inclusion in the KO, suggesting that this splicing factor primarily acts as a repressor. PRPF40B-regulated splicing events are likely cotranscriptional, affecting exons with A-rich downstream intronic motifs and weak splice sites especially for 5' splice sites, consistent with its PRP40 yeast ortholog being part of the U1 small nuclear ribonucleoprotein. Loss of PRPF40B in K562 induces a KLF1 transcriptional signature, with genes involved in iron metabolism and mainly hypoxia, including related pathways like cholesterol biosynthesis and Akt/MAPK signaling. A cancer database analysis revealed that PRPF40B is lowly expressed in acute myeloid leukemia, whereas its paralog PRPF40A expression is high as opposed to solid tumors. Furthermore, these factors negatively or positively correlated with hypoxia regulator HIF1A, respectively. Our data suggest a PRPF40B role in repressing hypoxia in myeloid cells, and that its low expression might contribute to leukemogenesis.

Programmable mutually exclusive alternative splicing for generating RNA and protein diversity

Alternative splicing performs a central role in expanding genomic coding capacity and proteomic diversity. However, programming of splicing patterns in engineered biological systems remains underused. Synthetic approaches thus far have predominantly focused on controlling expression of a single protein through alternative splicing. Here, we describe a modular and extensible platform for regulating four programmable exons that undergo a mutually exclusive alternative splicing event to generate multiple functionally-distinct proteins. We present an intron framework that enforces the mutual exclusivity of two internal exons and demonstrate a graded series of consensus sequence elements of varying strengths that set the ratio of two mutually exclusive isoforms. We apply this framework to program the DNA-binding domains of modular transcription factors to differentially control downstream gene activation. This splicing platform advances an approach for generating diverse isoforms and can ultimately be applied to program modular proteins and increase coding capacity of synthetic biological systems.

Multiplexed primer extension sequencing: A targeted RNA-seq method that enables high-precision quantitation of mRNA splicing isoforms and rare pre-mRNA splicing intermediates

The study of pre-mRNA splicing has been greatly aided by the advent of RNA sequencing (RNA-seq), which enables the genome-wide detection of discrete splice isoforms. Quantification of these splice isoforms requires analysis of splicing informative sequencing reads, those that unambiguously map to a single splice isoform, including exon-intron spanning alignments corresponding to retained introns, as well as exon-exon junction spanning alignments corresponding to either canonically- or alternatively-spliced isoforms. Because most RNA-seq experiments are designed to produce sequencing alignments that uniformly cover the entirety of transcripts, only a comparatively small number of splicing informative alignments are generated for any given splice site, leading to a decreased ability to detect and/or robustly quantify many splice isoforms. To address this problem, we have recently described a method termed Multiplexed Primer Extension sequencing, or MPE-seq, which uses pools of reverse transcription primers to target sequencing to user selected loci. By targeting reverse transcription to pre-mRNA splice junctions, this approach enables a dramatic enrichment in the fraction of splicing informative alignments generated per splicing event, yielding an increase in both the precision with which splicing efficiency can be measured, and in the detection of splice isoforms including rare splicing intermediates. Here we provide a brief review of the shortcomings associated with RNA-seq that drove our development of MPE-seq, as well as a detailed protocol for implementation of MPE-seq.

Alteration of SF3B1 and SRSF2 Genes in Myelodysplastic Syndromes Patients in Upper Northern Thailand

Background:

The frequency and pattern of mutation in SF3B1 and SRSF2 RNA splicing machinery genes were found to vary among myelodysplastic syndrome (MDS) patients in different populations. There have been less reports of incidence of these gene mutations in Thailand especially in upper northern Thailand. This study therefore had aims to investigate the frequency and pattern of mutation in mutational hotspot of SF3B1 and SRSF2 genes among MDS patients in upper northern Thailand and to investigate the clinical features associated with the mutations.

Methods:

Fifty-five MDS patients who underwent treatment at Maharaj Nakorn Chiang Mai Hospital participated in this study. The detection of SF3B1 and SRSF2 hotspot mutations was carried out using polymerase chain reaction followed by Sanger sequencing. In addition, clinical features of individual patients with these gene mutations were also investigated.

Results:

SF3B1 mutations (SF3B1^mut) were found in 9 patients (16.4%) including E622D (1/9), R625C (1/9), H662Q (1/9), K700E (5/9), and Q699H co-mutation with K700E (1/9). SRSF2 mutations (SRSF2^mut) were found in 4 patients (7.3%) which included P95H (3/4) and P95L (1/4). The SF3B1^mut was associated with lower hemoglobin levels (p = 0.023) and higher platelet counts (p = 0.047) when compared with MDS patients without SF3B1^mut, while SRSF2^mut tended to occur in patients with a higher percentage of bone marrow blasts (p = 0.074).

Conclusion:

The findings confirmed the difference in frequency of SF3B1 and SRSF2 mutations among different populations. Specifically, we found a co-mutation of Q699H and K700E that has not been previously reported in MDS patients in the COSMIC database. It was also found that SF3B1^mut was strongly associated with low hemoglobin level, and high platelet counts whereas SRSF2^mut was mostly clustered in MDS with excess blasts subsequently increasing the probability of progression to acute myeloid leukemia.

PHD finger protein 5A promoted lung adenocarcinoma progression via alternative splicing

Alternative splicing (AS) and the regulation of AS by splicing factors play critical roles in cancer. Plant homeodomain (PHD)–finger domain protein PHF5A, a critical splicing factor involved in AS, has been demonstrated to play an oncogenic role in glioblastoma multiforme and breast cancer, but its biological function in lung cancer remains unclear. In the present study, we systematically analyzed the biological function and clinical relevance of PHF5A in non–small cell lung cancer (NSCLC). We found that PHF5A was significantly upregulated in NSCLC tumors compared with normal tissues in both TCGA data set and tissue microarrays. Upregulation of PHF5A was negatively correlated to the overall survival (OS) of lung adenocarcinoma (LUAD) patients. Loss‐of‐function and gain‐of‐function experiments confirmed that PHF5A functioned as an oncoprotein by promoting LUAD cell proliferation, migration and invasion, inducing G0/G1 cell cycle progression and inhibiting cisplatin–induced apoptosis. RNA–seq analysis identified many essential genes whose AS was dysregulated by PHF5A, including cell cycle–associated genes such as SKP2, CHEK2, ATR and apoptosis–associated genes such as API5 and BCL2L13. Additionally, pladienolide, a small molecular inhibitor of PHF5A, inhibited LUAD cell proliferation in a dose–dependent manner and induced AS changes similar to PHF5A knockdown. In conclusion, we validated that PHF5A played an oncogenic role via AS in LUAD and suggested that PHF5A might serve as a potential drug target with a promising anticancer therapeutic effect.