---
title: "DegNorm: an R package for degradation normalization for RNA-seq data"
author: "Bin Xiong, Ji-Ping Wang"
date: "`r Sys.Date()`"
output:
rmarkdown::html_document:
highlight: pygments
toc: true
fig_width: 5
vignette: >
%\VignetteIndexEntry{DegNorm}
%\VignetteEngine{knitr::rmarkdown}
%\VignetteEncoding{UTF-8}
---
**Maintainer**: Ji-Ping Wang, <<jzwang@northwestern.edu>>
([**Python package download**](https://nustatbioinfo.github.io/DegNorm/))**
```{r setup, include = FALSE}
library(DegNorm)
knitr::opts_chunk$set(
collapse = TRUE,
comment = "#>"
)
library(knitr)
knit_hooks$set(optipng = hook_optipng)
```
**Reference**:
Xiong, B., Yang, Y., Fineis, F. Wang, J.-P., DegNorm: normalization of
generalized transcript degradation improves accuracy in RNA-seq analysis,
Genome Biology, 2019,20:75
# What is DegNorm?
DegNorm, short for **Deg**radation **Norm**alization, is a bioinformatics
pipeline designed to correct for bias due to the heterogeneous patterns of
transcript degradation in RNA-seq data. DegNorm
helps improve the accuracy of the differential expression analysis by
accounting for this degradation.
In practice, RNA samples are often more-or-less degraded, and the degradation
severity is not only sample-specific, but gene-specific as well. It is known
that longer genes tend to degrade faster than shorter ones. As such,
commonplace global degradation normalization approaches that impose a
single normalization factor on all genes within a sample can be ineffective
in correcting for RNA degradation bias.
# DegNorm pipline available formats
We've developed an R package and an indepedent Python package
([download](https://nustatbioinfo.github.io/DegNorm/)),
both of which allow to run the entire pipeline from the RNA-seq alignment
(.bam) files.
# Install DegNorm R package
```{r,eval=FALSE}
if(!requireNamespace("BiocManager", quietly = TRUE))
install.packages("BiocManager")
BiocManager::install("DegNorm")
```
# DegNorm main features
DegNorm R package contains two major functions: (1) processing the RNA-seq
alignment file (.bam) to calculate the coverage; and (2) using a core algorithm
written in RcppArmadillo to perform rank-one over-approximation on converage
matrices for each gene to estimate the degramation index (DI) score for each
gene within each sample.
DegNorm outputs DI scores together with degradation-normalized read counts
(based on DI scores). It also provides supplementary functions for
visualization of degradation at both gene and sample level. The following
diagram illustrates the flow of DegNorm pipeline.
{width=60%}
The following vignette is intended to provide example codes for running
DegNorm R package. It presumes that you have successfully installed
DegNorm package. We illustrate below how to: 1) calculate the read coverage
curves for all genes within all samples, and 2) perform degradation
normalization on coverage curves. Either step is computing intensive.
Dependent upon the number of samples and the sequencing depth, the total
computing time may last a few hours. DegNorm utilizes
the parallel computing functionality of R and automatically detects the number
of cores on your computer to run jobs in parallel. Due to the large size
of bam file and limited computing power of personal computer, we recommend
users to run it in servers or computing clusters.
## 1. Compute coverage score based on alignment .bam files
#### Set up input file: .bam and .gtf files.
```{r}
## specify bam_files from RNA-seq, you should replace it by your own bam files
bam_file_list=list.files(path=system.file("extdata",package="DegNorm"),
pattern=".bam$",full.names=TRUE)
```
The three bam files were subsetted from a specific region of chorosome 21 from
the origianl bam for package size limitation. Original files can be found from
the included reference above.
```{r}
## gtf_file you used for RNA-seq alignment, replace it by your own gtf file
gtf_file=list.files(path=system.file("extdata",package="DegNorm"),
pattern=".gtf$",full.names=TRUE)
```
#### Run main function to create read coverage matrix and read counts
```{r,eval=TRUE}
## calculate the read coverage score for all genes of all samples
coverage_res_chr21_sub=read_coverage_batch(bam_file_list, gtf_file,cores=2)
```
`cores` argument specifies the number of cores to use. Users should
try to use as many as possible cores to maximize the computing efficiency.
```{r,eval=FALSE}
## save the coverage results
save(coverage_res_chr21_sub,file="coverage_res_chr21_sub.Rda")
```
Function `read_coverage_batch` returns the coverage matrices as a list,
one per gene, and a dataframe for read counts, each row for one gene and
each column for one sample.
```{r}
data("coverage_res_chr21")
## summarize the coverage results
summary_CoverageClass(coverage_res_chr21)
```
```{r}
## extract coverage scores and counts from coverage_res
coverage_matrix=coverage_res_chr21$coverage
counts=coverage_res_chr21$counts
```
## 2. DegNorm core algorithm
Run degnorm core algorithm for degradation normalization. DegNorm purpose
is for differential expression analysis. Thus genes with extremely low read
counts from all samples are filtered out. The current filtering criterion is
that if more than half of the samples have less than 5 read count, that gene
will not be considered in the degnorm algorithm. In the following example, I
am using downsamling to save time below (default). Alternatively you can set
down_sampling = 0, which takes longer time.
If `down_samplin= 1`, read coverage scores are binned with size by `grid_size`
for baseline selection to achieve better efficiency. The default `grid_size` is
10 bp. We recommend to use a `grid_size` less than 50 bp. `iteration` specifies
the big loop in DegNorm algorithm and 5 is usually sufficient. `loop` specifies
the iteration number in the matrix factorization over-approximation.
```{r,eval=TRUE}
res_DegNorm_chr21 = degnorm(read_coverage = coverage_res_chr21[[1]],
counts = coverage_res_chr21[[2]],
iteration = 5,
down_sampling = 1,
grid_size=10,
loop = 100,
cores=2)
```
If `down_sampling= 0`, then the argument `grid_size` is ignored.
```{r,eval=FALSE}
## save the DegNorm results
save(res_DegNorm_chr21,file="res_DegNorm_chr21.Rda")
```
Function `degnorm` returns a list of multiple objects. counts_normed is the
one with degradation normalized read counts for you to input DeSeq or EdgeR
for DE analysis.
```{r}
data("res_DegNorm_chr21")
```
```{r}
## summary of the DegNorm output
summary_DegNormClass(res_DegNorm_chr21)
```
The difference of number of genes between `res_DegNorm` and `coverage_res`
is 207 (339-132). The 207 genes were filtered out from `degnorm` degradation
normalization because less than half of the samples (3) have more than 5
read count.
```{r}
## extrac normalized read counts
counts_normed=res_DegNorm_chr21$counts_normed
```
## 3. Plot functions in DegNorm
DegNorm provides four plot functions for visualization of degradation and
sample quality diagnosis.
* plot_coverage
* plot_corr
* plot_heatmap
* plot_boxplot
#### -- Plot the before-/after-degradation coverage curves
```{r,fig.width=6,fig.height=5,message=FALSE,eval=TRUE}
##gene named "SOD1"
plot_coverage(gene_name="SOD1", coverage_output=coverage_res_chr21,
degnorm_output=res_DegNorm_chr21,group=c(0,1,1))
```
#### -- Boxplot of the degradation index(DI) scores
```{r,fig.width=6,fig.height=5,message=FALSE,warning=FALSE,eval=TRUE}
plot_boxplot(DI=res_DegNorm_chr21$DI)
```
#### -- Heatmap plot of the degradation index(DI) scores
```{r,fig.width=6,fig.height=5,message=FALSE,eval=TRUE}
plot_heatmap(DI=res_DegNorm_chr21$DI)
```
#### -- Correlation matrix plot of degradation index(DI) scores
```{r,fig.width=6,fig.height=5,message=FALSE,warning=FALSE,eval=TRUE}
plot_corr(DI=res_DegNorm_chr21$DI)
```
# Session info
```{r sessionInfo}
sessionInfo()
```