Isoform-resolved transcriptome of the human preimplantation embryo [PacBio]
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE190547 | GEO | 2023/09/26
REPOSITORIES: GEO
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Project description:Human preimplantation development is a complex process involving extensive remodeling of gene expression. However, the preimplantation embryo transcriptome has only been annotated using short-read sequencing, which fails to capture full-length mRNAs and associated isoform diversity. We present a novel human embryo transcriptome using integrated long- and short-read RNA sequencing data. Our analysis reveals a total of 110,212 novel isoforms transcribed from known genes containing either a novel combination of known splice sites or at least one novel splice site, and 17,964 isoforms transcribed from completely novel genes located either in antisense direction of known genes or in intergenic space.
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Project description:The aim of this study was to obtain a landscape of alternative splicing (AS) in human hepatocellular carcinoma (HCC). We applied hybrid sequencing by integrating Pacbio long-read and Illumina short-read RNA sequencing data from 8 patient-derived HCC cell lines, and used an immortalized hepatocyte cell line as reference. This study revealed features of annotated and novel splice variants in HCC cells, including transcript length, AS type and protein changes. We also identified novel isoforms and tumor specific isoforms, which may represent potential biomarkers and targets for therapeutic development.
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Project description:U2AF1 S34F is one of the most recurrent splicing factor mutations in lung adenocarcinoma (ADC) and has been shown to cause transcriptome-wide pre-mRNA splicing alterations. While U2AF1 S34F-associated splicing alterations have been described, the fate of affected mRNA isoforms remains largely unexplored. To better understand the impact U2AF1 S34F has on isoform fate and function, we conducted high-throughput long-read cDNA sequencing from isogenic human bronchial epithelial cells with and without U2AF1 S34F mutation. We find that nearly 75% (49,366) of our long-read constructed multi-exon isoforms do not overlap GENCODE or short-read assembled isoforms, a large proportion of which (12,397) are due to novel junction connectivity rather than novel splice site usage. We find 198 transcript isoforms with significant expression and usage changes relative to wild-type, some of which were not assembled by short-reads. We find an enrichment of isoforms from immune related genes are down regulated in the presence of U2Af1 S34F, none of which are observed to have splicing changes detected from long-read data. Finally, we reveal that isoforms likely targeted by nonsense-mediated decay are largely downregulated in U2AF1 S34F cells, suggesting that the impact of observed isoform changes may alter the translational output of affected genes. Altogether, our data builds on previous work by providing a higher resolution transcriptome snapshot of full-length isoform alterations associated with U2AF1 S34F in HBEC3kt cells.
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Project description:The generation of distinct messenger RNA isoforms through alternative splicing and alternative 3' end formation influences the expression and function of genes, often in a cell-type specific manner. Here, we quantitatively assess the regulatory relationships between transcription initiation and co-transcriptional processing steps, particularly 3' end formation. Applying multiple long-read-sequencing approaches to obtain an assembly accurately representing even the longest mRNA isoforms from end-to-end, we quantify mRNA isoform choice in Drosophila and human tissues, including the transcriptionally complex nervous system. We find that in Drosophila brains as well as in human cerebral organoids, 3' end site choice is globally influenced by the site of transcription start. We define a subset of TSSs, “dominant promoters” that impose a transcriptional constraint to predetermine splice and polyadenylation variants, which are characterized by specific epigenetic signatures. In vivo deletion or overexpression of dominant promoters disrupted the 3' end expression landscape. Our study demonstrates the crucial impact of transcription initiation site choice on the regulation of transcript diversity and tissue identity.
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Project description:The human HIF3A gene undergoes extensive alternative splicing resulting in seven known isoforms. The short splice variant, HIF-3alpha4, is an inhibitor of the hypoxia response driven by HIF-1 and HIF-2. The role of the long isoforms remains unclear. We used cDNA microarray to study the overall impact of HIF3A knock-down by transfecting Hep3B cells with siRNA targeting a region shared by all splice variants under 1 % hypoxia.
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Project description:Alternative splicing is widely acknowledged to be a crucial regulator of gene expression and is a key contributor to both normal developmental processes and disease states. While cost-effective and accurate for quantification, short-read RNA-seq lacks the ability to resolve full-length transcript isoforms despite increasingly sophisticated computational methods. Long-read sequencing platforms such as Pacific Biosciences (PacBio) and Oxford Nanopore (ONT) bypass the transcript reconstruction challenges of short-reads. Here we describe TALON, the ENCODE4 pipeline for analyzing PacBio cDNA and ONT direct-RNA transcriptomes. We apply TALON to three human ENCODE Tier 1 cell lines and show that while both technologies perform well at full-transcript discovery and quantification, each one displayed distinct artifacts. We further apply TALON to mouse cortical and hippocampal transcriptomes and find that a substantial proportion of neuronal genes have more reads associated with novel isoforms than with annotated ones. These data show that TALON is a technology-agnostic long-read transcriptome discovery and quantification pipeline capable of tracking both known and novel transcript models, as well as their expression levels, across datasets for both simple studies and in larger projects. These properties will enable TALON users to move beyond the limitations of short-read data to perform isoform discovery and quantification in a uniform manner on existing and future long-read platforms.
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Project description:Genome-wide association studies (GWASs) have revealed thousands of associations in many complex traits and diseases. Previous studies suggest that a subset of associations are due to alterations in splicing; however, interpreting the effects of splicing on protein isoforms is hindered by limitations in defining full-length transcript isoforms using short-read RNA-seq data. Long-read RNA-seq represents a powerful approach to define and quantify transcript isoforms. In this study, we developed a novel approach that integrates information from GWAS, splicing QTL (sQTL), and PacBio long-read RNA-seq in a disease relevant model to infer the effects of sQTL on the ultimate protein isoform products they encode. Such information enables identification of genes potentially responsible for GWAS associations. As a proof-of-concept, we generated deep coverage (N=~22 million full-length reads) PacBio long-read RNAseq data on human fetal osteoblasts (hFOBs), a cell-line of relevance to the regulation of bone mineral density (BMD). We identified 68,326 protein-coding isoforms, including 17,375 (25%) which were novel. Next, we used Bayesian colocalization to identify 1,863 sQTLs from the Genotype-Tissue Expression (GTEx) project in 732 protein-coding genes which colocalized with BMD associations (H4PP > 0.75). A total of 836 junctions with colocalizing sQTLs in 459 (of the 732) genes were expressed in hFOB long-read RNA-seq data. With these data, we formulated hypotheses regarding the potential mechanism of action of each sQTL. For example, we identified 7 junctions with colocalizing sQTLs (maximum H4PP = 0.98-0.99) in TPM2 for splice junctions between two nearly mutually exclusive exons, and two different transcript termination sites, making it impossible to interpret without long-read RNA-seq data. siRNA mediated knockdown in hFOBs showed two TPM2 isoforms with opposing effects on mineralization. Our results suggest that splicing is a major mechanism underlying GWAS associations and long-read proteogenomics data is critical to precisely define the protein isoforms that are produced from splicing alterations.
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