Arboreto

Overview

Arboreto is a computational library for inferring gene regulatory networks (GRNs) from gene expression data using parallelized algorithms that scale from single machines to multi-node clusters.

Core capability: Identify which transcription factors (TFs) regulate which target genes based on expression patterns across observations (cells, samples, conditions).

Quick Start

Install arboreto:

uv pip install arboreto

Basic GRN inference:

import pandas as pd
from arboreto.algo import grnboost2

if __name__ == '__main__':
    # Load expression data (genes as columns)
    expression_matrix = pd.read_csv('expression_data.tsv', sep='\t')

    # Infer regulatory network
    network = grnboost2(expression_data=expression_matrix)

    # Save results (TF, target, importance)
    network.to_csv('network.tsv', sep='\t', index=False, header=False)

Critical: Always use if __name__ == '__main__': guard because Dask spawns new processes.

Core Capabilities

1. Basic GRN Inference

For standard GRN inference workflows including:

• Input data preparation (Pandas DataFrame or NumPy array)
• Running inference with GRNBoost2 or GENIE3
• Filtering by transcription factors
• Output format and interpretation

See: references/basic_inference.md

Use the ready-to-run script: scripts/basic_grn_inference.py for standard inference tasks:

python scripts/basic_grn_inference.py expression_data.tsv output_network.tsv --tf-file tfs.txt --seed 777

2. Algorithm Selection

Arboreto provides two algorithms:

GRNBoost2 (Recommended):

• Fast gradient boosting-based inference
• Optimized for large datasets (10k+ observations)
• Default choice for most analyses

GENIE3:

• Random Forest-based inference
• Original multiple regression approach
• Use for comparison or validation

Quick comparison:

from arboreto.algo import grnboost2, genie3

# Fast, recommended
network_grnboost = grnboost2(expression_data=matrix)

# Classic algorithm
network_genie3 = genie3(expression_data=matrix)

For detailed algorithm comparison, parameters, and selection guidance: references/algorithms.md

3. Distributed Computing

Scale inference from local multi-core to cluster environments:

Local (default) - Uses all available cores automatically:

network = grnboost2(expression_data=matrix)

Custom local client - Control resources:

from distributed import LocalCluster, Client

local_cluster = LocalCluster(n_workers=10, memory_limit='8GB')
client = Client(local_cluster)

network = grnboost2(expression_data=matrix, client_or_address=client)

client.close()
local_cluster.close()

Cluster computing - Connect to remote Dask scheduler:

from distributed import Client

client = Client('tcp://scheduler:8786')
network = grnboost2(expression_data=matrix, client_or_address=client)

For cluster setup, performance optimization, and large-scale workflows: references/distributed_computing.md

Installation

uv pip install arboreto

Dependencies: scipy, scikit-learn, numpy, pandas, dask, distributed

Common Use Cases

Single-Cell RNA-seq Analysis

import pandas as pd
from arboreto.algo import grnboost2

if __name__ == '__main__':
    # Load single-cell expression matrix (cells x genes)
    sc_data = pd.read_csv('scrna_counts.tsv', sep='\t')

    # Infer cell-type-specific regulatory network
    network = grnboost2(expression_data=sc_data, seed=42)

    # importance is unbounded (not a 0-1 probability); keep the top links
    # per target rather than applying an absolute threshold.
    top_links = network.sort_values('importance', ascending=False).groupby('target').head(10)
    top_links.to_csv('grn_top_links.tsv', sep='\t', index=False)

Bulk RNA-seq with TF Filtering

from arboreto.utils import load_tf_names
from arboreto.algo import grnboost2

if __name__ == '__main__':
    # Load data
    expression_data = pd.read_csv('rnaseq_tpm.tsv', sep='\t')
    tf_names = load_tf_names('human_tfs.txt')

    # Infer with TF restriction
    network = grnboost2(
        expression_data=expression_data,
        tf_names=tf_names,
        seed=123
    )

    network.to_csv('tf_target_network.tsv', sep='\t', index=False)

Comparative Analysis (Multiple Conditions)

from arboreto.algo import grnboost2

if __name__ == '__main__':
    # Infer networks for different conditions
    conditions = ['control', 'treatment_24h', 'treatment_48h']

    for condition in conditions:
        data = pd.read_csv(f'{condition}_expression.tsv', sep='\t')
        network = grnboost2(expression_data=data, seed=42)
        network.to_csv(f'{condition}_network.tsv', sep='\t', index=False)

Output Interpretation

Arboreto returns a DataFrame with regulatory links:

Column	Description
TF	Transcription factor (regulator)
target	Target gene
importance	Regulatory importance score (higher = stronger)

Filtering strategy: importance is an unbounded relative score (derived from tree feature importances), not a probability or correlation — do not apply absolute cutoffs like > 0.5. Prefer:

• Top N links per target gene
• A quantile cutoff computed from the run's own distribution
• In a SCENIC workflow, keep all links and let downstream cisTarget motif pruning do the filtering

Integration with pySCENIC

Arboreto is a core component of the SCENIC pipeline for single-cell regulatory network analysis:

# Step 1: Use arboreto for GRN inference
from arboreto.algo import grnboost2
network = grnboost2(expression_data=sc_data, tf_names=tf_list)

# Step 2: Use pySCENIC for regulon identification and activity scoring
# (See pySCENIC documentation for downstream analysis)

Reproducibility

Always set a seed for reproducible results:

network = grnboost2(expression_data=matrix, seed=777)

GRNBoost2 is stochastic, so a single seed pins one run but does not establish robustness. For a consensus network, run several seeds and keep links that recur, averaging their importance:

import pandas as pd
from distributed import LocalCluster, Client
from arboreto.algo import grnboost2

if __name__ == '__main__':
    client = Client(LocalCluster())

    seeds = [42, 123, 777]
    networks = [
        grnboost2(expression_data=matrix, client_or_address=client, seed=s)
        for s in seeds
    ]
    client.close()

    # Consensus: keep edges present in every run, average their importance
    combined = pd.concat(networks)
    consensus = (combined.groupby(['TF', 'target'])
                 .agg(importance=('importance', 'mean'), n_runs=('importance', 'size'))
                 .reset_index())
    consensus = consensus[consensus['n_runs'] == len(seeds)]

Troubleshooting

Memory errors: Reduce dataset size by filtering low-variance genes or use distributed computing

Slow performance: Use GRNBoost2 instead of GENIE3, enable distributed client, filter TF list

Dask errors: Ensure if __name__ == '__main__': guard is present in scripts

Empty results: Check data format (genes as columns), verify TF names match gene names