VaSP: Quantification and Visualization of Variations of Splicing in Population
1. Introduction
VaSP is an R package for discovery of genome-wide variable alternative splicing events from short-read RNA-seq data and visualizations of gene splicing information for publication-quality multi-panel figures. (Warning: The visualizing function is removed due to the dependent package Sushi deprecated. If you want to use it, please change back to an older version.)
Figure 1. Overview of VaSP. (A).
The workflow and functions of VaSP. The input is an R
data object ballgown (see ?ballgown) produced by a standard
RNA-seq data analysis protocol, including mapping with HISAT, assembling
with StringTie, and collecting expression information with R package Ballgown. VaSP
calculates the Single Splicing Strength (3S) scores for all splicing
junctions in the genome (?spliceGenome) or in a particular
gene (?spliceGene), identifies genotype-specific splicing
(GSS) events (?BMfinder), and displays differential
splicing information (?splicePlot. This function is
removed). The 3S scores can be also used for other analyses, such as
differential splicing analysis or splicing QTL identification.
(B). VaSP estimates 3S scores based on junction-read
counts normalized by gene-level read coverage. In this example, VaSP
calculates the splicing scores of four introns in a gene X with two
transcript isoforms. Only the fourth intron is a full usage intron
excised by both the two isoforms and the other three are alternative
donor site (AltD) sites or Intron Retention (IntronR), respectively.
(C). Visualization of splicing information in gene
MSTRG.183 (LOC_Os01g03070), whole gene without splicing scores.
(D). Visualization of differential splicing region of
the gene MSTRG.183 with splicing score displaying. In C and D, the
y-axes are read depths and the arcs (lines between exons) indicate
exon-exon junctions (introns). The dotted arcs indicate no
junction-reads spanning the intron (3S = 0) and solid arcs indicate 3S
> 0. The transcripts labeled beginning with ‘LOC_Os’ indicate
annotated transcripts by reference genome annotation and the ones
beginning with “MSTRG” are transcripts assembled by StringTie. (Yu et al., 2021)
2. Citation
Yu, H., Du, Q., Campbell, M., Yu, B., Walia, H. and Zhang, C. (2021), Genome‐wide discovery of natural variation in pre‐mRNA splicing and prioritising causal alternative splicing to salt stress response in rice. New Phytol. https://doi.org/10.1111/nph.17189
3. Installation
Start R (>= 4.0) and run:
if (!requireNamespace("BiocManager", quietly = TRUE))
install.packages("BiocManager")
BiocManager::install("VaSP")
vignette('VaSP')If you use an older version of R (>= 3.5), enter:
4. Data input
Users need to follow the manual of R package Ballgown (https://github.com/alyssafrazee/ballgown) to create a
ballgown object as an input for the VaSP package. See
?ballgown for detailed information on creating Ballgown
objects. The object can be stored in a .RDate file by
save() . Here is an example of constructing rice.bg object
from HISAT2+StringTie output
5. Quick start
Calculate 3S (Single Splicing Strength) scores, find GSS (genotype-specific splicing) events and display the splicing information.
- Calculating 3S scores:
library(VaSP)
#> Loading required package: ballgown
#>
#> Attaching package: 'ballgown'
#> The following object is masked from 'package:base':
#>
#> structure
data(rice.bg)
?rice.bg
rice.bg
#> ballgown instance with 33 transcripts and 6 samples
score<-spliceGene(rice.bg, gene="MSTRG.183", junc.type = "score")
tail(round(score,2),2)
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 58 0 0.02 0.22 0.23 0.23 0.23
#> 59 0 0.00 0.00 0.12 0.12 0.12- Discovering GSS:
gss <- BMfinder(score, cores = 1)
#> Warning in BMfinder(score, cores = 1): sample size < 30, the result should be
#> further tested!
#> ---BMfinder: 16 features * 6 samples
#> ---Completed: a total of 4 bimodal distrubition features found!
gss
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 55 2 2 1 1 1 1
#> 57 1 1 2 2 2 2
#> 58 1 1 2 2 2 2
#> 59 1 1 1 2 2 2- Extracing intron information
gss_intron<-structure(rice.bg)$intron
(gss_intron<-gss_intron[gss_intron$id%in%rownames(gss)])
#> GRanges object with 4 ranges and 2 metadata columns:
#> seqnames ranges strand | id transcripts
#> <Rle> <IRanges> <Rle> | <integer> <character>
#> [1] Chr1 1179011-1179226 - | 55 15:16
#> [2] Chr1 1179011-1179134 - | 57 17
#> [3] Chr1 1179011-1179110 - | 58 18
#> [4] Chr1 1179011-1179106 - | 59 19
#> -------
#> seqinfo: 1 sequence from an unspecified genome; no seqlengths
range(gss_intron)
#> GRanges object with 1 range and 0 metadata columns:
#> seqnames ranges strand
#> <Rle> <IRanges> <Rle>
#> [1] Chr1 1179011-1179226 -
#> -------
#> seqinfo: 1 sequence from an unspecified genome; no seqlengths- Showing the splicing information (deprecated)
6. Functions
Currently, there are 6 functions in VaSP:
getDepth: Get read depth from a BAM file (in
bedgraph format)
getGeneinfo: Get gene informaton from a
ballgown object
spliceGene: Calculate 3S scores for one
gene
spliceGenome: Calculate genome-wide splicing
scores
BMfinder: Discover bimodal distrubition
features
splicePlot: Visualization of read coverage,
splicing information and gene information in a gene region
(deprecated)
6.1 getDepth
Get read depth from a BAM file (in bedgraph format) and return a
data.frame in bedgraph file format which can be used as input for
plotBedgraph in the SuShi package.
path <- system.file("extdata", package = "VaSP")
bam_files <- list.files(path, "*.bam$")
bam_files
#> [1] "Sample_027.bam" "Sample_102.bam" "Sample_237.bam"
depth <- getDepth(file.path(path, bam_files[1]), "Chr1", start = 1171800,
end = 1179400)
head(depth)
#> chrom start stop value
#> 1 Chr1 1171799 1171859 0
#> 2 Chr1 1171859 1171899 1
#> 3 Chr1 1171899 1171902 2
#> 4 Chr1 1171902 1171903 4
#> 5 Chr1 1171903 1171909 5
#> 6 Chr1 1171909 1171911 6
# library(Sushi)
# par(mar=c(3,5,1,1))
# plotBedgraph(depth, "Chr1", chromstart = 1171800, chromend = 1179400,yaxt = "s")
# mtext("Depth", side = 2, line = 2.5, cex = 1.2, font = 2)
# labelgenome("Chr1", 1171800, 1179400, side = 1, scipen = 20, n = 5,scale = "Kb")6.2 getGeneinfo
Get gene informaton from a ballgown object by genes or by genomic
regions and return a data.frame in bed-like file format that can be used
as input for plotGenes in the SuShi
package
unique(geneIDs(rice.bg))
#> [1] "MSTRG.177" "MSTRG.178" "MSTRG.179" "MSTRG.180" "MSTRG.181" "MSTRG.182"
#> [7] "MSTRG.183" "MSTRG.184" "MSTRG.185" "MSTRG.186"
gene_id <- c("MSTRG.181", "MSTRG.182", "MSTRG.183")
geneinfo <- getGeneinfo(genes = gene_id, rice.bg)
trans <- table(geneinfo$name) # show how many exons each transcript has
trans
#>
#> LOC_Os01g03050.1 LOC_Os01g03060.1 LOC_Os01g03060.2 LOC_Os01g03060.3
#> 5 2 3 3
#> LOC_Os01g03070.1 LOC_Os01g03070.2 MSTRG.181.1 MSTRG.182.2
#> 14 14 6 3
#> MSTRG.183.3 MSTRG.183.4 MSTRG.183.5
#> 14 14 14
# chrom = geneinfo$chrom[1]
# chromstart = min(geneinfo$start) - 1500
# chromend = max(geneinfo$stop) + 1000
# color = rep(SushiColors(2)(length(trans)), trans)
# par(mar=c(3,1,1,1))
# p<-plotGenes(geneinfo, chrom, chromstart, chromend, col = color, bheight = 0.2,
# bentline = FALSE, plotgenetype = "arrow", labeloffset = 0.5)
# labelgenome(chrom, chromstart , chromend, side = 1, n = 5, scale = "Kb")6.3 spliceGene
Calculate 3S Scores from ballgown object for a given gene. This
function can only calculate one gene. Please use function
spliceGenome to obtain genome-wide 3S scores.
rice.bg
#> ballgown instance with 33 transcripts and 6 samples
head(geneIDs(rice.bg))
#> 1 2 3 4 5 6
#> "MSTRG.177" "MSTRG.177" "MSTRG.177" "MSTRG.178" "MSTRG.178" "MSTRG.179"
score <- spliceGene(rice.bg, "MSTRG.183", junc.type = "score")
count <- spliceGene(rice.bg, "MSTRG.183", junc.type = "count")
## compare
tail(score)
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 54 1.073545 1.1034944 0.9799037 1.0581254 1.0581254 1.0581254
#> 55 1.073545 1.1034944 0.1224880 0.1594436 0.1594436 0.1594436
#> 56 0.788727 1.3148018 1.1803386 1.3190330 1.3190330 1.3190330
#> 57 0.000000 0.0000000 0.5790340 0.4058563 0.4058563 0.4058563
#> 58 0.000000 0.0234786 0.2227054 0.2319179 0.2319179 0.2319179
#> 59 0.000000 0.0000000 0.0000000 0.1159589 0.1159589 0.1159589
tail(count)
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 54 49 47 88 73 73 73
#> 55 49 47 11 11 11 11
#> 56 36 56 106 91 91 91
#> 57 0 0 52 28 28 28
#> 58 0 1 20 16 16 16
#> 59 0 0 0 8 8 8
## get intron structrue
intron <- structure(rice.bg)$intron
intron[intron$id %in% rownames(score)]
#> GRanges object with 16 ranges and 2 metadata columns:
#> seqnames ranges strand | id transcripts
#> <Rle> <IRanges> <Rle> | <integer> <character>
#> [1] Chr1 1172688-1173213 - | 43 15:19
#> [2] Chr1 1173416-1173795 - | 44 15:19
#> [3] Chr1 1173877-1173965 - | 45 15:19
#> [4] Chr1 1174170-1174670 - | 46 15:19
#> [5] Chr1 1175175-1176065 - | 48 15:19
#> ... ... ... ... . ... ...
#> [12] Chr1 1179011-1179226 - | 55 15:16
#> [13] Chr1 1174881-1174952 - | 56 16:19
#> [14] Chr1 1179011-1179134 - | 57 17
#> [15] Chr1 1179011-1179110 - | 58 18
#> [16] Chr1 1179011-1179106 - | 59 19
#> -------
#> seqinfo: 1 sequence from an unspecified genome; no seqlengths6.4 spliceGenome
Calculate 3S scores from ballgown objects for all genes and return a
list of two elements: “score’ is a matrix of intron 3S scores with
intron rows and sample columns and”intron” is a GRanges
object of intron structure.
rice.bg
#> ballgown instance with 33 transcripts and 6 samples
splice <- spliceGenome(rice.bg, gene.select = NA, intron.select = NA)
#> ---Calculate gene-level read coverage:
#> 10 genes selected.
#> ---Extract intron-level read ucount:
#> 81 introns in 9 genes selected.
names(splice)
#> [1] "score" "intron"
head(splice$score)
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 1 1.4852698 1.6132865 1.934796 1.834662 1.834662 1.834662
#> 2 1.1580070 1.5164893 1.924559 1.726741 1.726741 1.726741
#> 3 1.2838773 1.7423494 2.129300 2.309516 2.309516 2.309516
#> 4 1.8377067 1.3551606 1.904085 2.050505 2.050505 2.050505
#> 5 0.9817885 0.9679719 1.289864 1.446146 1.446146 1.446146
#> 6 1.1076589 1.1615663 1.637923 1.661988 1.661988 1.661988
splice$intron
#> GRanges object with 81 ranges and 3 metadata columns:
#> seqnames ranges strand | id transcripts gene_id
#> <Rle> <IRanges> <Rle> | <integer> <character> <character>
#> [1] Chr1 1146321-1146479 - | 1 1:2 MSTRG.177
#> [2] Chr1 1146612-1147484 - | 2 1:2 MSTRG.177
#> [3] Chr1 1147563-1148021 - | 3 1:3 MSTRG.177
#> [4] Chr1 1148200-1148268 - | 4 1:3 MSTRG.177
#> [5] Chr1 1148442-1148530 - | 5 1:3 MSTRG.177
#> ... ... ... ... . ... ... ...
#> [77] Chr1 1187243-1187436 - | 77 c(28, 29, 32) MSTRG.186
#> [78] Chr1 1189347-1190773 - | 78 29:30 MSTRG.186
#> [79] Chr1 1190863-1190978 - | 79 29:30 MSTRG.186
#> [80] Chr1 1189347-1189914 - | 80 31:33 MSTRG.186
#> [81] Chr1 1189961-1190037 - | 81 33 MSTRG.186
#> -------
#> seqinfo: 1 sequence from an unspecified genome; no seqlengths6.5 BMfinder
Find bimodal distrubition features and divide the samples into 2 groups by k-means clustering and return a matrix with feature rows and sample columns.
score <- spliceGene(rice.bg, "MSTRG.183", junc.type = "score")
score <- round(score, 2)
as <- BMfinder(score, cores = 1) # 4 bimodal distrubition features found
#> Warning in BMfinder(score, cores = 1): sample size < 30, the result should be
#> further tested!
#> ---BMfinder: 16 features * 6 samples
#> ---Completed: a total of 4 bimodal distrubition features found!
## compare
as
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 55 2 2 1 1 1 1
#> 57 1 1 2 2 2 2
#> 58 1 1 2 2 2 2
#> 59 1 1 1 2 2 2
score[rownames(score) %in% rownames(as), ]
#> Sample_027 Sample_042 Sample_102 Sample_137 Sample_237 Sample_272
#> 55 1.07 1.10 0.12 0.16 0.16 0.16
#> 57 0.00 0.00 0.58 0.41 0.41 0.41
#> 58 0.00 0.02 0.22 0.23 0.23 0.23
#> 59 0.00 0.00 0.00 0.12 0.12 0.126.6 splicePlot
Visualization of read coverage, splicing information and gene
information in a gene region. This function is a wrapper of
getDepth, getGeneinfo,
spliceGene, plotBedgraph and
plotGenes. (This function is deprecated)
samples <- paste("Sample", c("027", "102", "237"), sep = "_")
bam.dir <- system.file("extdata", package = "VaSP")
## plot the whole gene region without junction lables
splicePlot(rice.bg, samples, bam.dir, gene = "MSTRG.183", junc.text = FALSE,
bheight = 0.2)
## plot the alternative splicing region with junction splicing scores
splicePlot(rice.bg, samples, bam.dir, gene = "MSTRG.183", start = 1179000)If the bam files are provided (bam.dir is not NA), the
read depth for each sample is plotted. Otherwise
(bam.dir=NA), the conserved exons of the samples are
displayed by rectangles (an example is the figure in 4. Quick
start). And by default (junc.type = 'score',
junc.text = TRUE), the junctions (represented by arcs) are
labeled with splicing scores. You can change the argument
junc.text = FALSE to unlabel the junctions or change the
argument junc.type = 'count' to label with junction read
counts.
There are other more options to modify the plot, please see the
function ?splicePlot for details (deprecated).
7. Session Information
sessionInfo()
#> R version 4.4.2 (2024-10-31)
#> Platform: x86_64-pc-linux-gnu
#> Running under: Ubuntu 24.04.1 LTS
#>
#> Matrix products: default
#> BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3
#> LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so; LAPACK version 3.12.0
#>
#> locale:
#> [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
#> [3] LC_TIME=en_US.UTF-8 LC_COLLATE=C
#> [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
#> [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
#> [9] LC_ADDRESS=C LC_TELEPHONE=C
#> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
#>
#> time zone: Etc/UTC
#> tzcode source: system (glibc)
#>
#> attached base packages:
#> [1] stats graphics grDevices utils datasets methods base
#>
#> other attached packages:
#> [1] VaSP_1.19.0 ballgown_2.39.0 rmarkdown_2.29
#>
#> loaded via a namespace (and not attached):
#> [1] KEGGREST_1.47.0 SummarizedExperiment_1.37.0
#> [3] rjson_0.2.23 xfun_0.49
#> [5] bslib_0.8.0 Biobase_2.67.0
#> [7] lattice_0.22-6 vctrs_0.6.5
#> [9] tools_4.4.2 bitops_1.0-9
#> [11] generics_0.1.3 stats4_4.4.2
#> [13] curl_6.0.1 parallel_4.4.2
#> [15] RSQLite_2.3.8 AnnotationDbi_1.69.0
#> [17] cluster_2.1.6 blob_1.2.4
#> [19] Matrix_1.7-1 RColorBrewer_1.1-3
#> [21] S4Vectors_0.45.2 lifecycle_1.0.4
#> [23] GenomeInfoDbData_1.2.13 compiler_4.4.2
#> [25] Rsamtools_2.23.1 Biostrings_2.75.1
#> [27] statmod_1.5.0 codetools_0.2-20
#> [29] GenomeInfoDb_1.43.2 htmltools_0.5.8.1
#> [31] sys_3.4.3 buildtools_1.0.0
#> [33] sass_0.4.9 RCurl_1.98-1.16
#> [35] yaml_2.3.10 crayon_1.5.3
#> [37] jquerylib_0.1.4 BiocParallel_1.41.0
#> [39] cachem_1.1.0 DelayedArray_0.33.2
#> [41] limma_3.63.2 abind_1.4-8
#> [43] nlme_3.1-166 sva_3.55.0
#> [45] genefilter_1.89.0 locfit_1.5-9.10
#> [47] digest_0.6.37 restfulr_0.0.15
#> [49] maketools_1.3.1 splines_4.4.2
#> [51] fastmap_1.2.0 grid_4.4.2
#> [53] cli_3.6.3 SparseArray_1.7.2
#> [55] S4Arrays_1.7.1 survival_3.7-0
#> [57] XML_3.99-0.17 edgeR_4.5.0
#> [59] UCSC.utils_1.3.0 bit64_4.5.2
#> [61] XVector_0.47.0 httr_1.4.7
#> [63] matrixStats_1.4.1 bit_4.5.0
#> [65] png_0.1-8 memoise_2.0.1
#> [67] evaluate_1.0.1 knitr_1.49
#> [69] GenomicRanges_1.59.1 IRanges_2.41.1
#> [71] BiocIO_1.17.1 mgcv_1.9-1
#> [73] rtracklayer_1.67.0 rlang_1.1.4
#> [75] DBI_1.2.3 xtable_1.8-4
#> [77] BiocGenerics_0.53.3 annotate_1.85.0
#> [79] jsonlite_1.8.9 R6_2.5.1
#> [81] MatrixGenerics_1.19.0 GenomicAlignments_1.43.0
#> [83] zlibbioc_1.52.0