RNA-Seq pipeline

Snakemake workflow for general purpose RNA-Seq library annotation developed by the Zavolan lab.

Reads are processed, aligned, quantified and analyzed with state-of-the-art tools to give meaningful initial insights into various aspects of an RNA-Seq library while cutting down on hands-on time for bioinformaticians.

The scheme below is a visual representation of an example run of the workflow:

Installation

Installing Singularity

For improved reproducibility and reusability of the workflow, as well as an easy means to run it on a high performance computing (HPC) cluster managed, e.g., by Slurm, each individual step of the workflow runs in its own container. Specifically, containers are created out of Singularity images built for each software used within the workflow. As a consequence, running this workflow has very few individual dependencies. It does, however, require that Singularity be installed. See the links below for installation instructions for the most up-to-date (as of writing) as well as for the tested version (2.6.1) of Singularity:

• Singularity v3.5
• Singularity v2.6

Setting up a Snakemake virtual environment

In addition to Singularity, Snakemake needs to be installed. We strongly recommended to do so via a virtual environment. Here we describe the steps necessary to set up such a virtual environment with a recent version (v4.4+) of the conda package manager. If you prefer to use another solution, such as virtualenv, adapt the steps according to the specific instructions of your preferred solution.

If you do not have conda installed for Python3, we recommend to install the minimal version (Python and package manager) Miniconda (see the link for installation instructions). Be sure to select the correct version for your operating system and ensure that you select the Python 3 option.

To create and activate the environment, run:

conda create -n rnaseq_pipeline \
    -c bioconda \
    -c conda-forge \
    snakemake=5.10.0
conda activate rnaseq_pipeline

Cloning the repository

Traverse to the desired path on your file system, then clone the repository and move into it with:

git clone ssh://git@git.scicore.unibas.ch:2222/zavolan_group/pipelines/rnaseqpipeline.git
cd rnaseqpipeline

All installation requirements should now be met with.

Testing the installation

We have prepared several tests to check the integrity of the workflow. The most important one lets you execute the workflow on a small set of example input files.

Run workflow on local machine

Execute the following command to run the test workflow on your local machine:

bash tests/test_integration_workflow/test.local.sh

Run workflow via Slurm

Execute the following command to run the test workflow on a Slurm-managed HPC.

bash tests/test_integration_workflow/test.local.sh

NOTE: Depending on the configuration of your Slurm installation or if using a different workflow manager, you may need to adapt file cluster.json and the arguments to options --config and --cores in file test.slurm.sh, both located in directory tests/test_integration_workflow. Consult the manual of your workload manager as well as the section of the Snakemake manual dealing with cluster execution.

Running the workflow on your own samples

1. Assuming that you are currently inside the repository's root directory, create a directory for your workflow run and traverse inside it with:

   mkdir runs/my_run
   cd runs/my_run

2. Create empty sample table, workflow configuration and, if necessary, cluster configuration files:

   touch samples.tsv
   touch config.yaml
   touch cluster.json

3. Use your editor of choice to manually populate these files with appropriate values. Have a look at the examples in the tests/ directory to see what the files should look like, specifically:

   • samples.tsv
   • config.yaml
   • cluster.json

4. Create a runner script. Pick one of the following choices for either local or cluster execution. Before execution of the respective command, you must replace the data directory placeholders in the argument to the --singularity-args option with a comma-separated list of all directories containing input data files (samples and any annoation files etc) required for your run.

   Runner script for local execution:

   cat << "EOF" > run.sh
   #!/bin/bash
   mkdir -p logs/local_log
   snakemake \
       --snakefile="../../snakemake/Snakefile" \
       --configfile="config.yaml" \
       --cores=4 \
       --printshellcmds \
       --rerun-incomplete \
       --use-singularity \
       --singularity-args="--bind <data_dir_1>,<data_dir_2>,<data_dir_n>"
   EOF

   OR

   Runner script for Slurm cluster exection (note that you may need to modify the arguments to --cluster and --cores depending on your HPC and workload manager configuration):

   cat << "EOF" > run.sh
   #!/bin/bash
   mkdir -p logs/cluster_log
   snakemake \
       --snakefile="../../snakemake/Snakefile" \
       --configfile="config.yaml" \
       --cluster-config="cluster.json" \
       --cluster="sbatch --cpus-per-task={cluster.threads} --mem={cluster.mem} --qos={cluster.queue} --time={cluster.time} --job-name={cluster.name} -o {cluster.out} -p scicore" \
       --cores=256 \
       --printshellcmds \
       --rerun-incomplete \
       --use-singularity \
       --singularity-args="--bind <data_dir_1>,<data_dir_2>,<data_dir_n>"
   EOF

5. Start your workflow run:

   bash run.sh

Configuring workflow runs via LabKey tables

Our lab stores metadata for sequencing samples in a locally deployed LabKey instance. This repository provides two scripts that give programmatic access to the LabKey data table and convert it to the corresponding workflow inputs (samples.tsv and config.yaml), respectively. As such, these scripts largely automate step 3. of the above instructions. However, as these scripts were specifically for the needs of our lab, they are likely not portable or, at least, will require considerable modification for other setups (e.g., different LabKey table structure).

NOTE: All of the below steps assume that your current working directory is the repository's root directory.

1. The scripts have additional dependencies that can be installed with:

   pip install -r scripts/requirements.txt

2. In order to gain programmatic access to LabKey via its API, a credential file is required. Create it with the following command after replacing the placeholder values with your real credentials (talk to your LabKey manager if you do not have these):

   cat << EOF | ( umask 0377; cat >> ${HOME}/.netrc; )
   machine <remote-instance-of-labkey-server>  
   login <user-email>
   password <user-password>  
   EOF

3. Run the LabKey API client script:

   python scripts/labkey_api.py <project_name> <labkey_table_nane>

   NOTE: Right now the script only prints a pandas data frame representation of the LabKey table on the screen and manually needs to be saved to a file for the next step. Ultimately the script will produce either a file in table format or will be merged with the following script.

4. Generate the workflow configuration with the following command, after replacing the placeholders with the appropriate values:

   python scripts scripts/labkey_to_snakemake.py \
       --input_table=<labkey_output_table> \
       --input_dict="scripts/input_dict.tsv" \
       --config_file="runs/my_run/config.yaml" \
       --samples_table="runs/my_run/samples.tsv" \
       --genomes_path=<path_to_annotation_files>

Additional information

The metadata field names in the LabKey instance and those in the parameters in the Snakemake workflow have different names. A mapping between LabKey field identifiers and Snakemake parameters is listed below: