Mapping and modeling the genomic basis of differential RNA isoform expression at single-cell resolution with LR-Split-seq
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ABSTRACT: The rise in throughput and quality of long-read sequencing should allow unambiguous identification of full-length transcript isoforms. However, its application to single-cell RNA-seq has been limited by throughput and expense. Here we develop and characterize long-read Split-seq (LR-Split-seq), which uses combinatorial barcoding to sequence single cells with long reads. Applied to the C2C12 myogenic system, LR-split-seq associates isoforms to cell types with relative economy and design flexibility. We find widespread evidence of changing isoform expression during differentiation including alternative transcription start sites (TSS) and/or alternative internal exon usage. LR-Split-seq provides an affordable method for identifying cluster-specific isoforms in single cells.
Project description:In this work, we generated a MHCC97H proteome datasets by In-gel digestion on Orbitrap Fusion Lumos. We systematically compared RNC-seq and Ribo-seq in the context of proteome identification, especially when identifying protein isoforms from AS. We also demonstrated that the single-molecule long read sequencing technique identified thousands of new splice variants and guided the MS identifications of new protein isoforms.
Project description:Long-read proteogenomic data was used to create sample-matched protein database for WTC11 sample. This includes many potential alternative protein isoforms (major and minor isoforms) per gene. The IS-PRM method called Tomahto was tested versus DDA to demonstrate improved coverage of isoform-specific peptides. We called this overall method of long-read RNA informed Tomahto targeting LRP-IS-PRM and used it for protein-level evidence of multiple isoforms derived from alternative splicing.
Project description:Long-read proteogenomic data was used to create sample-matched protein database for WTC11 sample. This includes many potential alternative protein isoforms (major and minor isoforms) per gene. The IS-PRM method called Tomahto was tested versus DDA to demonstrate improved coverage of isoform-specific peptides. We called this overall method of long-read RNA informed Tomahto targeting LRP-IS-PRM and used it for protein-level evidence of multiple isoforms derived from alternative splicing.
Project description:Alternative splicing (AS) isoforms create numerous proteoforms, expanding the complexity of the genome. Highly similar sequences, incomplete reference databases and the insufficient sequence coverage of mass spectrometry limit the identification of AS proteoforms.In this work, we compared RNC-seq and Ribo-seq in the context of proteome identification, especially when identifying protein isoforms from AS. We also demonstrated that the single-molecule long read sequencing technique identified thousands of new splice variants and guided the MS identifications of new protein isoforms.
Project description:Alternative splicing is an essential mechanism for diversifying proteins, with different mature RNA isoforms producing different proteins with potentially distinct functions. Two major challenges in characterizing the cellular function of isoforms are the lack of both experimental methods to specifically and efficiently modulate isoform expression and computational tools for complex experimental design. To address these gaps, we developed and methodically tested a strategy which pairs the RNA-targeting CRISPR/Cas13d system with guide RNAs (gRNAs) that overlap exon-exon junctions in the mature RNA. We perform a high-throughput essentiality screen, numerous qPCR assays, and PacBio long read sequencing to affirm that our strategy works to specifically target the unique junctions of isoforms to robustly knockdown their RNA. In parallel, we provide computational tools for experimental design and screen analysis. Considering all possible splice junctions in current GENCODE annotations and our predictions of gRNA efficacy, we estimate that this strategy can target 94% of all human isoforms, including 29,238 protein-coding and 9,638 lncRNA isoforms that are specifically targetable with a gRNA spanning a unique splice junction.
Project description:Transcription and translation are intertwined processes where mRNA isoforms are crucial intermediaries. However, methodological limitations in analyzing translation at the mRNA isoform level have impaired our ability to comprehensively establish links between the full-length transcripts and the translatome. This has left gaps in our understanding of critical biological processes, regulatory mechanisms, and disease progression. To address this, we develop an integrated computational and experimental framework called long-read Ribo-STAMP (LR-Ribo-STAMP). LR-Ribo-STAMP capitalizes on advancements in long-read sequencing and RNA-base editing-mediated technologies to simultaneously and scalably profile translation and transcription at both gene and mRNA isoform levels for the first time. In this report, we show agreement between gene-level translation profiles obtained with LR-Ribo-STAMP and those from previously validated short-read Ribo-STAMP data in unperturbed cells. At the mRNA isoform level, we show that LR-Ribo-STAMP successfully profiles translation in unperturbed cells and links mRNA isoforms and regulatory features, such as upstream ORFs (uORFs) and regulatory sequences, to translation measurements. We further demonstrate the method’s effectiveness in profiling disease models by profiling translation at gene and isoform levels in a triple-negative breast cancer cell line under normoxia and hypoxia. Here, we find that LR-Ribo-STAMP effectively delineates orthogonal transcriptional and translation shifts between conditions at gene and isoform levels. At the isoform level, LR-Ribo-STAMP uniquely identifies key regulatory elements and shifts in mRNA isoform transcription that correlate with changes in translational, providing an example of insight that can inform the development of novel therapeutics. Overall, LR-Ribo-STAMP is a significant advancement in translation methods and can have profound implications for basic research and clinical applications.
Project description:To explore the molecular mechanisms involved in the toxicity in the livers exposed to MC-LR at the environmental level, the hepatic transcriptome was performed. A total of 210 genes were differentially expressed (P<0.05, |fold change|≥2) in response to MC-LR exposure; among them, 143 genes were significantly upregulated, and 67 genes were downregulated. Pathway enrichment analysis identified the top biological functions associated with the genes differentially expressed in response to MC-LR exposure, which were circadian regulation of gene expression, negative regulation of glucocorticoid receptor signaling pathway, the epoxygenase P450 pathway, regulation of insulin secretion, lipid metabolic process, and cell cycle pathway.
Project description:Alternative splicing increases the diversity of transcriptomes and proteomes in metazoans. The extent to which alternative splicing is active and functional in unicellular organisms is less understood. Here we exploit a single-molecule long-read sequencing technique and develop a computational tool, SpliceHunter, to characterize the transcriptome in the meiosis of fission yeast. We reveal 17017 alternative splicing events in 19741 novel isoforms at different stages of meiosis, including antisense and read-through transcripts. Intron retention is the major type of alternative splicing, followed by “alternate intron in exon”. 887 novel transcription units are detected; 60 of the predicted proteins show homology in other species and form theoretical stable structures. We compare the dynamics of novel isoforms based on the number of supporting full-length reads with those of annotated isoforms and explore the translational capacity and quality of novel isoforms. The evaluation of these factors indicates that the majority of novel isoforms are unlikely to be both condition-specific and translatable but the possibility of functional novel isoforms is not excluded. Together, this study highlights the diversity and dynamics at the isoform level in the sexual development of fission yeast.
Project description:The expressions of piRNA in mouse sperm were altered by MC-LR-exposure or Hsp90aa1 shRNA. MC-LR could induce intergenerational toxicity.
Project description:The Plasmodium falciparum human malaria parasite genome is incompletely annotated and does not accurately represent the transcriptomic diversity of this species. To address this need, we performed long-read transcriptomic sequencing. To increase representation of mRNA isoforms expressed during intraerythrocytic stages, RNA was extracted from samples taken at time-points from synchronized cultures. 5 capped mRNA was enriched and converted to cDNA library. The cDNA libraries were sequenced on Nanopore and PacBio long-read platforms. Candidate non-redundant isoforms were annotated from each library dataset for creating a new transcript annotation catalog. Isoforms with alternative 5 ends represented the largest class of novel isoforms, although the majority of these do not seem to represent the products of alternative transcription initiation events. We suggest that most isoforms do not encode protein isoforms and instead represent RNA decay products.