GNNome

A framework for training graph neural networks to untangle assembly graphs obtained from OLC-based de novo genome assemblers.

Figure generated with DALL-E 3.

Installation

Requirements

• Linux (tested on Ubuntu 20.04)
• conda 4.6+
• CUDA 11.1+
• gcc 7.5+
• zlib 1.2.8+
• cmake 3.11+

Setting up the environment

1. Clone the repository

git clone https://github.com/lbcb-sci/GNNome.git
cd GNNome

2. Create a conda virtual environment

conda create -n gnnome python=3.8 pip
conda activate gnnome

2a. Install cmake and zlib

In case you don't already have them installed on your system you can install cmake and zlib inside your conda environment:

conda install cmake
conda install zlib

2b. If you are using CUDA 12.0 or higher, install cudatoolkit v11.0

conda install cudatoolkit=11.0

3. Install the requirements with pip (~3 min)

For GPU and CUDA 11.0+ run:

pip install -r requirements.txt

If you have no GPUs and no CUDA, we recommend running inference only. You can install the requirements with:

pip install -r requirements_cpu.txt

4. Install tools used for constructing assembly graphs

python install_tools.py

This will install hifiasm and Raven which are used to generate HiFi and ONT assembly graphs, respectively. It also installs PBSIM which is used for simulating raw reads. All the tools are installed inside the GNNome/vendor directory.

Example

The data needed to run the example consists of simulated E. coli reads (FASTA format) and an assembly graph of those reads generated with hifiasm (GFA format). Both can be found in the example directory. To run the example, there are three steps:

1. Construct the assembly graph with hifiasm (<1 min)

mkdir -p example/hifiasm/output
./vendor/hifiasm-0.18.8/hifiasm --prt-raw -o example/hifiasm/output/ecoli_asm -t32 -l0 example/ecoli.fasta.gz

2. Construct the neccesary data structures (DGL graphs and auxiliary dictionaries). (<1 min)

python create_inference_graphs.py --reads example/ecoli.fasta.gz --gfa example/hifiasm/output/ecoli_asm.bp.raw.r_utg.gfa --asm hifiasm --out example

The last command will create the following data inside the example/hifiasm directory.

• a DGL graph inside example/hifiasm/processed directory
• auxiliary data inside example/hifiasm/info directory

3. Run the inference module. (<1 min)

python inference.py --data example --asm hifiasm --out example/hifiasm

The edge-probabilities will be computed with the deafult model (reported in the paper). The directories assembly, decode, and checkpoint will be created inside example/hifiasm. You can find the assembly sequence in example/hifiasm/assembly/0_assembly.fasta.

Usage

To run the model on a new genome, first you need to run another assembler which can output a non-reduced graph in a GFA format. Note: this tool has been optimized for haploid assembly, and this tutorial mainly focuses on this.

Construct the assembly graphs from HiFi sequences

For HiFi data, we recommend using hifiasm.

Run hifiasm with the following command:

./vendor/hifiasm-0.18.8/hifiasm --prt-raw -o <out> -t <threads> -l0 <reads>

where <reads> is the path to the sequences in FASTA/FASTQ format, and <out> is the prefix for the output files. The GFA graph can then be found in the current directory under the name <out>.bp.raw.r_utg.gfa.

Construct the assembly graphs from ONT sequences

For ONT data, we recommend using Raven.

Run Raven with the following command:

./vendor/raven-1.8.1/builld/bin/raven -t <threads> -p0 <reads> > assembly.fasta

where <reads> is the path to the sequences in FASTA/FASTQ format. The graph can then be found in the current directory under the name graph_1.gfa.

Process the assembly graphs

From the reads in FASTA/Q format and the graph in the GFA format, we can produce the graph in the DGL format and auxiliary data:

python create_inference_graphs.py --reads <reads> --gfa <gfa> --asm <asm> --out <out>

  <reads>
    input file in FASTA/FASTQ format (can be compressed with gzip)
  <gfa> 
    input file in GFA format
  <asm>
    assembler used for the assembly graph construction [hifiasm|raven]
  <out>
    path to where the processed data will be saved

The resulting data can be found in the <out>/<asm>/processed/ and <out>/<asm>/info/ directories.

Generating the assembly

python inference.py --data <data> --asm <asm> --out <out>

  <data>
    path to where the processed data is saved (same as <out> in the previous command)
  <asm>
    assembler used for the assembly graph construction [hifiasm|raven]
  <out>
    path to where the assembly will be saved
  
  optional:
    --model <model>
      path to the model used for decoding (deafult: weights/weights.pt)

Training the network

Generate the training/validation data

You can generate synthetic training data by first simulating reads with PBSIM and then constructing assembly graphs with hifiasm or Raven. This consists of several steps.

Step 1. Specify which chromosomes you want to have in training and validation set, by editing values in the dictionaries in train_valid_chrs.py.

Step 2. Since the training is performed on individual chromosomes, you also need to have the sequences (references) of these chromosomes saved in a format chr1.fasta, chr2.fasta, etc. Full path to the directory where these chromosome references are stored is provided as an argument to the generate_data.py script (see below).

Step 3. PBSIM requires a sample profile files (e.g. sample_pofile_ID.fastq and sample_pofile_ID.stats) stored inside the vendor/pbsim3 directory. You can download these files by running

bash download_profile.sh

The downloaded files correspond to the sample_profile_ID stated in the config.py dictionary. Alternatively, if you already have these files, copy them into vendor/pbsim3 and edit the value of the dictionary in config.py under the key sample_pofile_ID. You can also create a new profile by editting values in the dictionary in config.py under the keys sample_pofile_ID and sample_file. Make sure to provide a unique ID for sample_profile_ID, and a path to an existing FASTQ file for sample_file. For more information, check PBSIM3.

Step 4. Finally, run the generate_data.py script:

python generate_data.py --datadir <datadir> --chrdir <chrdir> --asm <asm> --threads <threads>

  <datadir>
    path to directory where the generated data will be saved
  <chrdir>
    path to directory where the chromosome references are stored
  <asm>
    assembler used for the assembly graph construction [hifiasm|raven]
  <threads>
    number of threads used for running the assembler

Split the generated data into training and validation datasets.

Once the data has been generated and stored in the main database (the <datadir> that you provided in the previous step), you have to split it into training and validation datasets. This will copy data from the main database <datadir> into <savedir> (see below). Run the following command:

python split_data.py --datadir <datadir> --savedir <savedir> --name <name> --asm <asm>
  <datadir>
    path to directory where the generated data is saved
  <savedir>
    path to directory where the trainig/validation datasets will be copied
  <name>
    name assigned to the training and validation datasets
  <asm>
    assembler used for the assembly graph construction [hifiasm|raven]

Once all the data is copied, the script will print out the full paths of the training and validation directories. You can provide those paths as arguments to train.py script (see the next step).

Train the model

python train.py --train <train> --valid <valid> --asm <asm>
  
  <train>
    Ppth to directory where the training data (provided by split_data.py)
  <valid>
    path to directory where the validation data (provided by split_data.py)
  <asm>
    assembler used to generate the training data [hifiasm|raven]

  optional:
    --name <name>
      name of the model that will be trained (default: date/time of execution)
    --overfit
      overfit on the training data
    --resume
      resume from a checkpoint, the <name> option has to be specified
    --dropout <dropout>
      dropout for training the model (default: 0)
    --seed <seed>
      seed for training the model (default: 1)

By default, the trained models and checkpointbs will be saved in the models and checkpoints directories, respectively. This can be changed in config.py. The name under which the model and checkpoint are saved is, by default, the timestamp of the run, if argument --name is not specified.

Reproducibility

All the results in the paper can be reproduced by downloading the relevant data (link in the manuscript) and following the steps in the Usage section. Use the default weights for the model, available under weights/weights.pt.