Computational Analysis of Full-length cDNAs Reveals Frequent Coupling Between Transcriptional and Splicing Programs

High-throughput sequencing studies revealed that the majority of human and mouse multi-exon genes have multiple splice forms. High-density oligonucleotide array-based measurements have further established that many exons are expressed in a tissue-specific manner. The mechanisms underlying the tissue-dependent expression of most alternative exons remain, however, to be understood. In this study, we focus on one possible mechanism, namely the coupling of (tissue specific) transcription regulation with alternative splicing. We analyzed the FANTOM3 and H-Invitational datasets of full-length mouse and human cDNAs, respectively, and found that in transcription units with multiple start sites, the inclusion of at least 15% and possibly up to 30% of the ‘cassette’ exons correlates with the use of specific transcription start sites (TSS). The vast majority of TSS-associated exons are conserved between human and mouse, yet the conservation is weaker when compared with TSS-independent exons. Additionally, the currently available data only support a weak correlation between the probabilities of TSS association of orthologous exons. Our analysis thus suggests frequent coupling of transcriptional and splicing programs, and provides a large dataset of exons on which the molecular basis of this coupling can be further studied

A Simple Physical Model Predicts Small Exon Length Variations

One of the most common splice variations are small exon length variations caused by the use of alternative donor or acceptor splice sites that are in very close proximity on the pre-mRNA. Among these, three-nucleotide variations at so-called NAGNAG tandem acceptor sites have recently attracted considerable attention, and it has been suggested that these variations are regulated and serve to fine-tune protein forms by the addition or removal of a single amino acid. In this paper we first show that in-frame exon length variations are generally overrepresented and that this overrepresentation can be quantitatively explained by the effect of nonsense-mediated decay. Our analysis allows us to estimate that about 50% of frame-shifted coding transcripts are targeted by nonsense-mediated decay. Second, we show that a simple physical model that assumes that the splicing machinery stochastically binds to nearby splice sites in proportion to the affinities of the sites correctly predicts the relative abundances of different small length variations at both boundaries. Finally, using the same simple physical model, we show that for NAGNAG sites, the difference in affinities of the neighboring sites for the splicing machinery accurately predicts whether splicing will occur only at the first site, splicing will occur only at the second site, or three-nucleotide splice variants are likely to occur. Our analysis thus suggests that small exon length variations are the result of stochastic binding of the spliceosome at neighboring splice sites. Small exon length variations occur when there are nearby alternative splice sites that have similar affinity for the splicing machinery

Longitudinal Evaluation of an N-Ethyl-N-Nitrosourea-Created Murine Model with Normal Pressure Hydrocephalus

Normal-pressure hydrocephalus (NPH) is a neurodegenerative disorder that usually occurs late in adult life. Clinically, the cardinal features include gait disturbances, urinary incontinence, and cognitive decline.Herein we report the characterization of a novel mouse model of NPH (designated p23-ST1), created by N-ethyl-N-nitrosourea (ENU)-induced mutagenesis. The ventricular size in the brain was measured by 3-dimensional micro-magnetic resonance imaging (3D-MRI) and was found to be enlarged. Intracranial pressure was measured and was found to fall within a normal range. A histological assessment and tracer flow study revealed that the cerebral spinal fluid (CSF) pathway of p23-ST1 mice was normal without obstruction. Motor functions were assessed using a rotarod apparatus and a CatWalk gait automatic analyzer. Mutant mice showed poor rotarod performance and gait disturbances. Cognitive function was evaluated using auditory fear-conditioned responses with the mutant displaying both short- and long-term memory deficits. With an increase in urination frequency and volume, the mutant showed features of incontinence. Nissl substance staining and cell-type-specific markers were used to examine the brain pathology. These studies revealed concurrent glial activation and neuronal loss in the periventricular regions of mutant animals. In particular, chronically activated microglia were found in septal areas at a relatively young age, implying that microglial activation might contribute to the pathogenesis of NPH. These defects were transmitted in an autosomal dominant mode with reduced penetrance. Using a whole-genome scan employing 287 single-nucleotide polymorphic (SNP) markers and further refinement using six additional SNP markers and four microsatellite markers, the causative mutation was mapped to a 5.3-cM region on chromosome 4.Our results collectively demonstrate that the p23-ST1 mouse is a novel mouse model of human NPH. Clinical observations suggest that dysfunctions and alterations in the brains of patients with NPH might occur much earlier than the appearance of clinical signs. p23-ST1 mice provide a unique opportunity to characterize molecular changes and the pathogenic mechanism of NPH

A trio of unique alternative splicing patterns : the splicing of tandem NAGNAG acceptors, transcription-start-site-dependent and mutually dependent cassette exons

With the rapid increase in the volume of genomic and transcript data in mouse and human, a diverse set of alternative splicing patterns can be discovered. We have set out to explore in more depth some of these unique splicing patterns which include: i.) tandem acceptor splice sites termed ’NAGNAGs’, which cause an exon length variation of three nucleotides, ii.) the splicing of internal cassette exons, whose inclusion and exclusion are strongly associated with their transcriptional start sites, iii.) and groups of internal cassette exons that are always observed to be either included or excluded together within a transcript. We did not find much evidence of functional potential for the majority of variant acceptor splice sites carrying the NAGNAG motif and thus conclude that their abundance is due mostly to the stochastic behaviour of the spliceosome. We inferred that a large fraction (15-30%) of internal cassette exons in transcription units with multiple start sites are included and skipped in a transcription-start-site-dependent manner. We did not find that this relationship is conserved in orthologous human and mouse exons. Our first analysis has revealed several interesting trends in mutually dependent exons when compared to mutually exclusive and constitutive exons: these exons have a stronger pressure to maintain the reading frame as a group of exons rather than individually, and they generally have shorter intron lengths. Ours are the first analyses of transcription-start-site-dependent and mutually-dependent splicing. Their mechanisms remain to be further elucidated and our results provide a good starting point for future computational and experimental studies

Low detection of exon skipping in mouse genes orthologous to human genes on chromosome 22

Magister Scientiae - MSc (Biochemistry)Alternative RNA splicing is one of the leading mechanisms contributing towards transcript and protein diversity. Several alternative splicing surveys have confirmed the frequent occurrence of exon skipping in human genes. However, the occurrence of exon skipping in mouse genes has not yet been extensively examined. Recent improvements in mouse genome sequencing have permitted the current study to explore the occurrence of exon skipping in mouse genes orthologous to human genes on chromosome 22. A low number (5/72 multi-exon genes) of mouse exon-skipped genes were captured through alignments of mouse ESTs to mouse genomic contigs. Exon-skipping events in two mouse exon-skipped genes (GNB1L, SMARCB1) appear to affect biological processes such as electron and protein transport. All mouse, skipped exons were observed to have ubiquitous tissue expression. Comparison of our mouse exon-skipping events to previously detected human exon-skipping events on chromosome 22 by Hide et al.2001, has revealed that mouse and human exon-skipping events were never observed together within an orthologous gene-pair. Although the transcript identity between mouse and human orthologous transcripts were high (greater than 80% sequence identity), the exon order in these gene-pairs may be different between mouse and human orthologous genes. Main factors contributing towards the low detection of mouse exon-skipping events include the lack of mouse transcripts matching to mouse genomic sequences and the under-prediction of mouse exons. These factors resulted in a large number (112/269) of mouse transcripts lacking matches to mouse genomic contigs and nearly half (12/25) of the mouse multi-exon genes, which have matching Ensembl transcript identifiers, have under-predicted exons. The low frequency of mouse exon skipping on chromosome 22 cannot be extrapolated to represent a genome-wide estimate due to the small number of observed mouse exon-skipping events. However, when compared to a higher estimate (52/347) of exon skipping in human genes for chromosome 22 produced under similar conditions by Hide et al.2001, it is possible that our mouse exon-skipping frequency may be lower than the human frequency. Our hypothesis contradicts with a previous study by Brett et al.2002, in which the authors claim that mouse and human alternative splicing is comparable. Our conclusion that the mouse exon-skipping frequency may be lower than the human estimate remains to be tested with a larger mouse multi-exon gene set. However, the mouse exon-skipping frequency may represent the highest estimate that can be obtained given that the current number (87) of mouse genes orthologous to chromosome 22 in Ensembl (v1 30th Jan. 2002) does not deviate significantly from our total number (72) of mouse multi-exon genes. The quality of the current mouse genomic data is higher than the one utilized in this study. The capture of mouse exon-skipping events may increase as the quality and quantity of mouse genomic and transcript sequences improves.South Afric

Prenatal diagnosis of short-rib polydactyly syndrome type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3) associated with compound heterozygous mutations in DYNC2H1 in a fetus

Objective: We present the perinatal imaging findings and molecular genetic analysis in a fetus with short-rib polydactyly syndrome (SRPS) type III or short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3). Case report: A 29-year-old, primigravid woman was referred for genetic counseling at 15 weeks of gestation because of abnormal ultrasound findings of short limbs, a narrow chest and bilateral polydactyly of the hands and feet, consistent with a diagnosis of SRPS type III. Chorionic villus sampling was performed, and targeted next-generation sequencing (NGS) was applied to analyze a panel of 25 genes including CEP120, DYNC2H1, DYNC2LI1, EVC, EVC2, FGFR2, FGFR3, HOXD10, IFT122, IFT140, IFT172, IFT52, IFT80, KIAA0586, NEK1, PAPSS2, SLC26A2, SOX9, TCTEX1D2, TCTN3, TTC21B, WDR19, WDR34, WDR35 and WDR60. The NGS analysis identified novel mutations in the DYNC2H1 gene. The fetus was compound heterozygous for a missense mutation c.8077G > T (p.Asp2693Tyr) of paternal origin in DYNC2H1 and a frameshift mutation c.11741_11742delTT (p.Phe3914X) of maternal origin in DYNC2H1. The fetus had a karyotype of 46,XY, and postnatally manifested characteristic SRPS type III phenotype. Conclusion: Targeted NGS is useful in genetic diagnosis of fetal skeletal dysplasia and SRPS, and the information acquired is helpful in genetic counseling

Highly Efficient Intracellular Protein Delivery by Cationic Polyethyleneimine-Modified Gelatin Nanoparticles

Intracellular protein delivery may provide a safe and non-genome integrated strategy for targeting abnormal or specific cells for applications in cell reprogramming therapy. Thus, highly efficient intracellular functional protein delivery would be beneficial for protein drug discovery. In this study, we generated a cationic polyethyleneimine (PEI)-modified gelatin nanoparticle and evaluated its intracellular protein delivery ability in vitro and in vivo. The experimental results showed that the PEI-modified gelatin nanoparticle had a zeta potential of approximately +60 mV and the particle size was approximately 135 nm. The particle was stable at different biological pH values and temperatures and high protein loading efficiency was observed. The fluorescent image results revealed that large numbers of particles were taken up into the mammalian cells and escaped from the endosomes into the cytoplasm. In a mouse C26 cell-xenograft cancer model, particles accumulated in cancer cells. In conclusion, the PEI-modified gelatin particle may provide a biodegradable and highly efficient protein delivery system for use in regenerative medicine and cancer therapy

Proportion of In-Frame Variations at Donor and Acceptor Splice Sites That Are Located within CDS, UTR, and Noncoding Regions

<p>This figure shows the fractions of alternative splice events that lead to an in-frame shift with respect to the reference boundary at acceptor (3′) and donor (5′) splice sites of CDS, UTR, and noncoding (NC) exons. The estimated fraction is in the middle of the gray bar, with the gray bar indicating two standard errors. The dashed line shows the fraction 1/3 that would be expected by chance.</p

Proportion of Putative Donor (GT) and Acceptor (AG) Splice Sites That Are Located In-Frame Relative to the Splice Sites in CDS, UTR, and Noncoding Regions

<p>This figure shows the fraction of AG dinucleotides that occur at distance that is a multiple of three in the first 100 intronic bases upstream of acceptor (3′) splice sites of exons that show splice variation at their acceptor sites, and the fraction of GT dinucleotides that occur at a distance that is a multiple of three in the first 100 intronic bases downstream of donor (5′) splice sites of exons that show splice variations at their donor sites. Occurrences of AG or GT within the first four bases flanking the splice sites were not counted. The estimated fraction is in the middle of the gray bar, with the gray bar indicating two standard errors. The dashed line shows the fraction 1/3 that would be expected by chance.</p

Dependency of the Frequency of Alternative Splicing at NAGNAG Sites on the Relative Likelihood of the Two Putative Acceptor Sites

<p>The figure shows the fraction of all NAGNAG boundaries that splice only at the first NAG (red), only at the second NAG (green), or at both NAGs (blue) as a function of the log-likelihood difference of the first and second putative splice sites for the acceptor site WM.</p