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Tumour-normal read-level methylation pattern and pseudo-bulk simulator

DOI

Read-level methylome simulator using a beta-binomial distribution.

It currently supports only two cell-type simulations (tumour and normal).

Pseudo-bulk samples with random cell-type compositions can be also simulated with the read-level methylomes.

Set-up

methylseq_simulation requires Python version > 3.6 (So far, it has been tested under Python version 3.7, 3.8 and 3.9). The dependencies are clarified in requirements.txt.

pip installation

If your environment (e.g. conda, Python venv and so on) is already activated, you can simply install the dependencies by pip install -r requirements.txt

Conda environment

Conda is a package and environment manager. It helps you with managing software dependencies independently from your local system. If you want to start conda, please find their installation guidance here.

  1. Create a new conda environment with a specific python version conda creat -n $your_env_name python=$python_version
  2. Install the dependencies by pip install -r requirements.txt

Python venv

Python also supports a virtual environment.

  1. Create a Python virtual environment by python -m venv $your_directory_path
  2. Activate the virtual environment by source $your_directory_path/bin/activate
  3. Install dependencies by pip install -r requirements.txt

Docker

Docker also provides resources to manage environment called container. We provide Dockerfile to run the simulator with the required dependencies.

  1. Build a docker container by sudo docker build -t methylseq_simulation .
  2. Run the container by sudo docker run -i -t methylseq_simulation /bin/bash
  3. You can use the command line as described in Quick start

pip error handling

If you get a version-related error message as below:

Could not find a version that satisfies the requirement numpy==1.21.4
(from versions: 1.14.5, 1.14.6, 1.15.0, 1.15.1, 1.15.2, 1.15.3, 1.15.4,
1.16.0, 1.16.1, 1.16.2, 1.16.3, 1.16.4, 1.16.5, 1.16.6, 1.17.0, 1.17.1,
1.17.2, 1.17.3, 1.17.4, 1.17.5, 1.18.0, 1.18.1, 1.18.2, 1.18.3, 1.18.4,
1.18.5, 1.19.0, 1.19.1, 1.19.2, 1.19.3, 1.19.4, 1.19.5, 1.20.0, 1.20.1,
1.20.2, 1.20.3, 1.21.0, 1.21.1, 1.21.2, 1.21.3)

You may want to upgrade your pip by pip install --upgrade pip

Input files

The simulator requires a reference genome FASTA file (such as hg19.fa) to simulate the reads. You can download various genome sequences from UCSC as a gzipped FASTA file.

If you have a specific set of regions you want to simulate reads, you can give the file name with -d option. The file must be tab-separated and include chromosome, start and end information with chr, start and end for column names.

Quick start

You can simulate read-level methylomes and pseudo-bulk samples (with --bulk option) by running main.py as below:

python main.py --help
usage: main.py [-h] -r F_REF [-d F_REGION] [-o OUTPUT_DIR] [--save_img]
               [-ng N_REGIONS] [-a A] [-b B] [-nr N_READS] [-k K_MER]
               [-l LEN_READ] [--seed SEED] [--bulk] [-nb N_BULKS] [-s STD]

optional arguments:
  -h, --help            show this help message and exit
  -r F_REF, --f_ref F_REF
                        .fasta file for the reference genome
  -d F_REGION, --f_region F_REGION
                        tab-separated .csv file, DMRs should be given with
                        mean methylation level of each cell type, chr, start
                        and end. n_regions will be selected from hg19 CpG
                        islands if the file is not given
  -o OUTPUT_DIR, --output_dir OUTPUT_DIR
                        a directory where all generated results will be saved
                        (default: ./)
  --save_img            Save simulated methylation patterns as a .png file
                        (default: False)
  -ng N_REGIONS, --n_regions N_REGIONS
                        Number of regions to select from CGIs when the region
                        file is not given (default: 100)
  -a A, --a A           alpha parameter of the beta-binomial distribution to
                        simulate read-level methylomes (default: 1e-6)
  -b B, --b B           beta parameter of the beta-binomial distribution to
                        simulate read-level methylomes (default: 5)
  -nr N_READS, --n_reads N_READS
                        Read coverage to simulate in each DMR (default: 120)
  -k K_MER, --k_mer K_MER
                        K to process the simulated read sequences into K-mer
                        sequence (default: 1)
  -l LEN_READ, --len_read LEN_READ
                        Read length to simulate (default: 150)
  --seed SEED           seed number (default: 950410)
  --bulk                Whether you want to generate pseudo-bulks or the
                        entire dataset (default: False)
  -nb N_BULKS, --n_bulks N_BULKS
                        Number of bulks, Applicable only when --bulk is True
                        (default: 1)
  -s STD, --std STD     Standard deviation to sample local proportions. The
                        larger value is given, the more varying local
                        proportions are sampled from a Gaussian distribution
                        centred at the global proportion (default: 0.0)

Output example

If --save_img option is on, you can get the summary of results as figures in the designated output_dir.

Sampled region-wise methylation level

Simulated read-level methylomes