functionalgenomics/atena
Analysis of Transposable Elements

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In functionalgenomics/atena: Analysis of Transposable Elements 

knitr::opts_chunk$set(echo = TRUE)

Downloading the data

The data used as example in the atena vignette and help pages is publicly available at the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus (accession no. GSE47006, https://www.ncbi.nlm.nih.gov/geo). This dataset was analysed in Ohtani H et al., 2013. The two selected samples are: piwi knockdown and control samples (GSM1142845 and GSM1142844). The raw data files (.fastq) were downloaded from Sequence Read Archive (SRA, https://www.ncbi.nlm.nih.gov/sra) (samples SRX278536 and SRX278535, respectively)

Alignment with BWA

The data was aligned with BWA mem using the -a option to output all found alignments for single-end, thus, including secondary alignments.

The resulting sorted BAM files (control_KD.sorted.bam and piwi_KD.sorted.bam) contain secondary alignments.

Control KD

## fetch FASTQ file
FASTQFILE=/projects_fg/TEs/OhtaniSaito13_DmGTSF1/control_KD.fastq.gz

## define where the BWA genome index is
wget http://ftp.ensembl.org/pub/release-104/fasta/drosophila_melanogaster/dna/Drosophila_melanogaster.BDGP6.32.dna.toplevel.fa.gz
GENOMEINDEX=/projects_fg/genomes/drosophila/Drosophila_melanogaster.BDGP6.32.dna.toplevel.fa.gz

## define number of threads to be used by BWA
NTHREADS=4

f=${FASTQFILE##*/}
PREFIX=${f%%.fastq.gz}

if [ ! -e BAM ] ; then mkdir -p BAM ; fi

module load BWA/0.7.17
module load SAMtools/1.7

echo $PREFIX
bwa mem -t $NTHREADS $GENOMEINDEX $FASTQFILE | \
  samtools view -b -o BAM/$PREFIX.unsorted.bam -

samtools sort BAM/$PREFIX.unsorted.bam \
  --threads 5 \
  -o BAM/$PREFIX.sorted.bam

samtools index BAM/$PREFIX.sorted.bam BAM/$PREFIX.sorted.bai

Piwi KD

## fetch FASTQ file
FASTQFILE=/projects_fg/TEs/OhtaniSaito13_DmGTSF1/piwi_KD.fastq.gz

f=${FASTQFILE##*/}
PREFIX=${f%%.fastq.gz}

if [ ! -e BAM ] ; then mkdir -p BAM ; fi

echo $PREFIX
bwa mem -t $NTHREADS $GENOMEINDEX $FASTQFILE | \
  samtools view -b -o BAM/$PREFIX.unsorted.bam -

samtools sort BAM/$PREFIX.unsorted.bam \
  --threads 5 \
  -o BAM/$PREFIX.sorted.bam

samtools index BAM/$PREFIX.sorted.bam BAM/$PREFIX.sorted.bai

Getting TE and gene annotations

Gene annotations

# Gene annotations
wget http://ftp.ensembl.org/pub/release-103/gtf/drosophila_melanogaster/Drosophila_melanogaster.BDGP6.32.103.gtf.gz

TE annotations

# TE annotations: obtained from the RepeatMasker track in UCSC genome browser
# downloaded from https://genome.ucsc.edu/cgi-bin/hgTables (BDGP Release 6 +
# ISO1 MT/dm6; group: Variation and Repeats; track: RepeatMasker; table: rmsk)
## Obtaining RepeatMasker annotations in GTF and BED format
wget https://github.com/dpryan79/ChromosomeMappings/blob/master/BDGP6_UCSC2ensembl.txt?raw=true
mv /genomics/users/bea/HERVs/drosophila_atena/BDGP6_UCSC2ensembl.txt\?raw\=true \
/genomics/users/bea/HERVs/drosophila_atena/BDGP6_UCSC2ensembl.txt

# Adding the Ensembl nomenclature to RepeatMasker annotations
ann <- read.table("
        /genomics/users/bea/HERVs/drosophila_atena/Dmelanogaster_rmsk_dm6.txt",
        header = TRUE)
chr <- read.table(
        "/genomics/users/bea/HERVs/drosophila_atena/BDGP6_UCSC2ensembl.txt")
colnames(chr) <- c("UCSC","Ensembl")
ann <- merge(ann, chr, by.y = "UCSC", by.x = "genoName")
# rRNA, simple repeat regions, low complexity regions, satellite repeats and
# artefacts will be filtered out from RepeatMasker annotations since they are
# not TEs
repClass <- c("RC", "LINE", "LTR", "DNA", "Unknown", "Other", "RNA")
ann <- ann[ann$repClass %in% repClass,]
# Creating a GRanges object with the annotations
suppressPackageStartupMessages(library(GenomicRanges))
ann_gr <- GRanges(seqnames = Rle(ann$Ensembl), 
                ranges = IRanges(start = ann$genoStart, end = ann$genoEnd),
                strand = Rle(ann$strand),
                mcols = DataFrame(ann[,11:13], 
                            name = paste(ann$repName, 1:nrow(ann), sep = "_")))
names(ann_gr) <- mcols(ann_gr)$mcols.name
colnames(mcols(ann_gr)) <- gsub(colnames(mcols(ann_gr)), 
                                pattern = "mcols.", replacement = "")
rtracklayer::export.gff2(ann_gr, con = "/genomics/users/bea/HERVs/drosophila_atena/Dmelanogaster_rmsk_dm6.gtf")

Subsampling .bam files

The resulting .bam files were subsampled to smaller files containing just a few alignments.

First .bam files were sorted by name in order to group alignments coming from the same read (the primary alignment + secondary alignments in case of multimapping reads).

samtools sort -n -@ 4 /projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/piwi_KD.sorted.bam -o piwi_KD.sortedbyname.bam -O bam
samtools sort -n -@ 4 /projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/control_KD.sorted.bam -o control_KD.sortedbyname.bam -O bam

Finding which TEs are the 20 most expressed. Also finding which reads from piwi map to tese 20 most expressed TEs:

library(Matrix)
library(Rsamtools)
library(GenomicAlignments)
library(rtracklayer)

#' @importFrom S4Vectors nLnode nRnode isSorted from to Hits
.appendHits <- function(hits1, hits2) {
    stopifnot(nRnode(hits1) == nRnode(hits2))
    stopifnot(isSorted(from(hits1)) == isSorted(from(hits2)))
    hits <- c(Hits(from=from(hits1), to=to(hits1),
                    nLnode=nLnode(hits1)+nLnode(hits2),
                    nRnode=nRnode(hits1), sort.by.query=isSorted(from(hits1))),
            Hits(from=from(hits2)+nLnode(hits1), to=to(hits2),
                    nLnode=nLnode(hits1)+nLnode(hits2),
                    nRnode=nRnode(hits2), sort.by.query=isSorted(from(hits2))))
    hits
}


te_dros <- import(
    "/genomics/users/bea/HERVs/drosophila_atena/Dmelanogaster_rmsk_dm6.gtf")
names(te_dros) <- mcols(te_dros)$ID

bampath <- "/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM"
bamfiles <- c("/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/piwi_KD.sorted.bam",
            "/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/control_KD.sorted.bam")

bfl <- BamFileList(bamfiles, yieldSize = 10000000, asMates = FALSE)
sbflags <- scanBamFlag(isUnmappedQuery=FALSE,
                        isDuplicate=FALSE,
                        isNotPassingQualityControls=FALSE)
param <- ScanBamParam(flag=sbflags)

i <- 2
bf <- bfl[[i]]
ov <- Hits(nLnode=0, nRnode=length(te_dros), sort.by.query=TRUE)
alnreadids <- character(0)
l <- 0
open(bf)
while (length(alnreads <- do.call("readGAlignments", c(list(file = bf), 
                                            list(param=param), 
                                            list(use.names=TRUE))))) {
    alnreadids <- c(alnreadids, names(alnreads))
    l <- l+1
    print(l)
    thisov <- findOverlaps(alnreads, te_dros, ignore.strand=FALSE)
    ov <- .appendHits(ov, thisov)
}
close(bf)

.buildOvAlignmentsMatrix <- function(ov, arids, rids, fidx) {
    oamat <- Matrix(FALSE, nrow=length(rids), ncol=length(fidx))
    mt1 <- match(arids[queryHits(ov)], rids)
    mt2 <- match(subjectHits(ov), fidx)
    oamat[cbind(mt1, mt2)] <- TRUE

    oamat
}

saveRDS(ov, file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_ovAllTEs.rds")
readids <- unique(alnreadids[queryHits(ov)])
tx_idx <- sort(unique(subjectHits(ov)))
ovalnmat <- .buildOvAlignmentsMatrix(ov, alnreadids, readids, tx_idx)
topreads <- readids[order(rowSums(ovalnmat),decreasing = TRUE)[1:175]]
topreads2 <- paste(topreads,"\t",sep="")
write.table(topreads2, 
            file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_topreads_piwi.txt",
            quote = FALSE, row.names = FALSE, col.names = FALSE)

ovalnmat_topreads <- ovalnmat[order(rowSums(ovalnmat), decreasing = TRUE)[1:175],]

te_dros_top20 <- te_dros[tx_idx[order(colSums(ovalnmat_topreads), decreasing = TRUE)[1:20]]]
saveRDS(te_dros_top20, 
        file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_GRangesTop20TEs_piwi.rds")

Finding which genes are the 50 most expressed:

suppressPackageStartupMessages(library(GenomicAlignments))
suppressPackageStartupMessages(library(rtracklayer))

# BAM files
bamfiles <- c("/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/piwi_KD.sorted.bam",
            "/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/control_KD.sorted.bam")
bfl <- BamFileList(bamfiles, yieldSize = 100000, asMates = FALSE)
sbflags <- scanBamFlag(isUnmappedQuery=FALSE,
                        isDuplicate=FALSE,
                        isNotPassingQualityControls=FALSE)
param <- ScanBamParam(flag=sbflags)

# Annotations
gene_dros <- import(
    "/projects_fg/genomes/drosophila/Drosophila_melanogaster.BDGP6.32.103.gtf")
gene_dros <- gene_dros[!(gene_dros$gene_biotype == "transposable_element")]
gene_dros <- gene_dros[gene_dros$type == "gene"]
names(gene_dros) <- gene_dros$gene_id

# Counting
overlap_all <- summarizeOverlaps(gene_dros, bfl, singleEnd=TRUE, 
                                param = param, ignore.strand = FALSE)
saveRDS(overlap_all, file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13gene_counts.rds")

top50_gene <- rownames(assay(overlap_all)[order(rowSums(assay(overlap_all)), 
                                                decreasing = TRUE),])[1:50]
write.table(top50_gene, 
            file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13gene_counts_top50.txt",
            quote = FALSE, row.names = FALSE, col.names = FALSE)

gene_dros_top50 <- gene_dros[top50_gene]
saveRDS(gene_dros_top50, 
        file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_GRangesTop50genes.rds")

Finding which reads from control map to the 20 most expressed TEs:

suppressPackageStartupMessages(library(GenomicAlignments))
suppressPackageStartupMessages(library(rtracklayer))

# BAM files
bamfiles <- c("/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/piwi_KD.sorted.bam",
              "/projects_fg/TEs/OhtaniSaito13_DmGTSF1/BAM/control_KD.sorted.bam")
bfl <- BamFileList(bamfiles, yieldSize = 1000000, asMates = FALSE)
sbflags <- scanBamFlag(isUnmappedQuery=FALSE,
                       isDuplicate=FALSE,
                       isNotPassingQualityControls=FALSE)
param <- ScanBamParam(flag=sbflags)

## --- Looking now for overlapping reads ---
library(Matrix)

.appendHits <- function(hits1, hits2) {
  stopifnot(nRnode(hits1) == nRnode(hits2))
  stopifnot(isSorted(from(hits1)) == isSorted(from(hits2)))
  hits <- c(Hits(from=from(hits1), to=to(hits1),
                 nLnode=nLnode(hits1)+nLnode(hits2),
                 nRnode=nRnode(hits1), sort.by.query=isSorted(from(hits1))),
            Hits(from=from(hits2)+nLnode(hits1), to=to(hits2),
                 nLnode=nLnode(hits1)+nLnode(hits2),
                 nRnode=nRnode(hits2), sort.by.query=isSorted(from(hits2))))
  hits
}

te_dros_top20 <- readRDS("/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_GRangesTop20TEs_piwi.rds")
i <- 2
bf <- bfl[[i]]
ov <- Hits(nLnode=0, nRnode=length(te_dros_top20), sort.by.query=TRUE)
alnreadids <- character(0)
l <- 1
open(bf)
while (length(alnreads <- readGAlignments(bf, param = param, use.names = TRUE))) {
  alnreadids <- c(alnreadids, names(alnreads))
  thisov <- findOverlaps(alnreads, te_dros_top20, ignore.strand=FALSE)
  ov <- .appendHits(ov, thisov)
  l <- l+1
  print(l)
}
close(bf)

readhits <- table(alnreadids[queryHits(ov)])
saveRDS(ov, 
        file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_ovTopTEs_control.rds")

topreads<- names(readhits)[order(readhits, decreasing = TRUE)][1:175]
topreads2 <- paste(topreads,"\t",sep="")

write.table(topreads2, 
            file = "/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_topreads_control.txt",
            quote = FALSE, row.names = FALSE, col.names = FALSE)

Subsampling BAM files by selecting reads based on reads ids which have been previously identified to map to the most expressed TEs.

# 175 reads correspond to a high number of alignments, which causes bam files 
# to be too large
# Reducing to 150 reads:
head -n 150 OhtaniSaito13_topreads_piwi.txt > OhtaniSaito13_topreads_piwi2.txt
mv OhtaniSaito13_topreads_piwi2.txt OhtaniSaito13_topreads_piwi.txt

head -n 150 OhtaniSaito13_topreads_control.txt > OhtaniSaito13_topreads_control2.txt
mv OhtaniSaito13_topreads_control2.txt OhtaniSaito13_topreads_control.txt


module load SAMtools

# piwi
samtools view /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD.sortedbyname.bam | grep -f /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_topreads_piwi.txt > /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled_wtheader.sort.sam

samtools view /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD.sortedbyname.bam -H > header_piwi_KD_subsampled.txt
cat header_piwi_KD_subsampled.txt /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled_wtheader.sort.sam > /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.sam

samtools sort /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.sam -o /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.bam
samtools index /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.bam /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.bai

# control
samtools view /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD.sortedbyname.bam | grep -f /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_topreads_control.txt > /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled_wtheader.sort.sam

samtools view /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD.sortedbyname.bam -H > header_control_KD_subsampled.txt
cat header_control_KD_subsampled.txt /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled_wtheader.sort.sam > /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.sam

samtools sort /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.sam -o /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.bam
samtools index /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.bam /genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.bai

Final files included in atena package:

/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.bam
/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/piwi_KD_subsampled.sort.bai
/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.bam
/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/control_KD_subsampled.sort.bai
/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_GRangesTop20TEs_piwi.rds
/genomics/users/bea/HERVs/drosophila_OhtaniSaito13_DmGTSF1/OhtaniSaito13_GRangesTop50genes.rds

Which have been renamed to:

piwi_KD.bam
piwi_KD.bai
control_KD.bam
control_KD.bai
Top20TEs.rds
Top50genes.rds

Adding 10 top expressed TEs according to the ERVmap method ERVmap did not provide any overlap for Top20TEs.rds. This is due to the fact that the alignments which caused these 20 TEs to be the most expressed are mainly secondary alignments of multi-mapping reads. Since ERVmap does not count secondary alignments, 0 overlaps are found for these 20 TEs in ERVmap. For this reason, the following approach was carried out in order to include 10 more TEs in the annotations. These 10 TEs were selected by looking where the primary alignments of the subsampled BAM files mapped to. 

tefile <- "Dmelanogaster_rmsk_dm6.gtf"
te_dros <- import(tefile)

alnreads <- do.call(readfun, c(list(file = bf),
                                list(param=param), 
                                list(strandMode=empar@strandMode)[strand_arg],
                                list(use.names=(!avsoas || avgene))))
ovall <- findOverlaps(te_dros, alnreads)
tes <- countQueryHits(ovall)
te_dros[order(tes, decreasing = TRUE)][1:10]
teall <- c(TE_annot, te_dros[order(tes, decreasing = TRUE)][1:10])
colnames(mcols(teall))[2] <- "feature_type"
saveRDS(teall, 
    file = "bioc-devel/ERVs/OhtaniSaito13_subsampled_for_atena/Top30TEs.rds")

# Finally, 2 duplicated TEs were removed creating the final object Top28TEs.rds

Adding seqinfo data

TE_annot <- readRDS(file = "Top28TEs.rds")
gene_annot <- readRDS(file =  "Top50genes.rds")

suppressPackageStartupMessages(library(BSgenome.Dmelanogaster.UCSC.dm6))
suppressPackageStartupMessages(library(GenomeInfoDb))
seqlevelsStyle(gene_annot) <- "UCSC"
seqlevelsStyle(TE_annot) <- "UCSC"

seqlevels(gene_annot, 
          pruning.mode="coarse") <- seqlevels(BSgenome.Dmelanogaster.UCSC.dm6)

seqlevels(TE_annot, 
          pruning.mode="coarse") <- seqlevels(BSgenome.Dmelanogaster.UCSC.dm6)

seqlengths(gene_annot) <- seqlengths(BSgenome.Dmelanogaster.UCSC.dm6)
seqlengths(TE_annot) <- seqlengths(BSgenome.Dmelanogaster.UCSC.dm6)

saveRDS(TE_annot, file = "Top28TEs.rds")
saveRDS(gene_annot, file = "Top50genes.rds")


functionalgenomics/atena documentation built on Nov. 4, 2024, 7:33 p.m.

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