Bio Workflows Grn Pipeline

Gene Regulatory Network Pipeline

Complete workflow from processed single-cell data to regulon discovery and perturbation simulation.

Pipeline Overview

Processed AnnData (QC'd, normalized, clustered)
    |
    +----- RNA only? -------> Path A: pySCENIC (3-step)
    |                              |
    |                              v
    |                         [1. GRNBoost2] ----> TF-target adjacencies
    |                              |
    |                              v
    |                         [2. RcisTarget] ---> Regulon pruning (motif enrichment)
    |                              |
    |                              v
    |                         [3. AUCell] -------> Regulon activity scoring
    |
    +----- Multiome? -------> Path B: SCENIC+
    |                              |
    |                              v
    |                         [1. cisTopic] -----> Topic modeling on ATAC
    |                              |
    |                              v
    |                         [2. pycistarget] --> Enhancer-TF mapping
    |                              |
    |                              v
    |                         [3. SCENIC+] ------> eGRN construction
    |
    +---> [CellOracle Perturbation Simulation] (either path)
              |
              v
         Perturbation scores + predicted cell state shifts

Path A: pySCENIC (RNA-Only)

Step 1: GRN Inference with GRNBoost2

import scanpy as sc
import pandas as pd
from arboreto.algo import grnboost2
from ctxcore.genesig import GeneSignature

adata = sc.read_h5ad('processed.h5ad')

# Extract expression matrix (raw counts recommended for GRNBoost2)
expr_matrix = pd.DataFrame(
    adata.raw.X.toarray() if hasattr(adata.raw.X, 'toarray') else adata.raw.X,
    index=adata.obs_names, columns=adata.raw.var_names
)

# TF list from cisTarget resources
# Human: https://resources.aertslab.org/cistarget/tf_lists/
tf_names = pd.read_csv('allTFs_hg38.txt', header=None)[0].tolist()
tf_names = [tf for tf in tf_names if tf in expr_matrix.columns]

adjacencies = grnboost2(expr_matrix, tf_names=tf_names, seed=42, verbose=True)
adjacencies.to_csv('adjacencies.tsv', sep='\t', index=False, header=False)

Step 2: Regulon Pruning with RcisTarget

from pyscenic.prune import prune2df, df2regulons
from ctxcore.rnkdb import FeatherRankingDatabase

# cisTarget databases (~10 GB each, download once)
# Human: hg38_10kbp_up_10kbp_down_full_tx_v10_clust.genes_vs_motifs.rankings.feather
# Mouse: mm10_10kbp_up_10kbp_down_full_tx_v10_clust.genes_vs_motifs.rankings.feather
dbs = [FeatherRankingDatabase(db) for db in [
    'hg38_500bp_up_100bp_down.genes_vs_motifs.rankings.feather',
    'hg38_10kbp_up_10kbp_down.genes_vs_motifs.rankings.feather'
]]

motif_annotations = 'motifs-v10nr_clust-nr.hgnc-m0.001-o0.0.tbl'

# Create modules from adjacencies (top 50 targets per TF)
modules = [GeneSignature(name=tf, gene2weight=dict(zip(grp['target'], grp['importance'])))
           for tf, grp in adjacencies.groupby('TF')
           if len(grp) >= 10]

# Prune modules using motif enrichment
# NES threshold 3.0: Standard; lower to 2.5 for more permissive
df_motifs = prune2df(dbs, modules, motif_annotations, num_workers=8)
regulons = df2regulons(df_motifs)

print(f'Discovered {len(regulons)} regulons')

Step 3: AUCell Activity Scoring

from pyscenic.aucell import aucell

auc_matrix = aucell(expr_matrix, regulons, num_workers=8)

adata.obsm['X_aucell'] = auc_matrix.loc[adata.obs_names].values
adata.uns['regulon_names'] = [r.name for r in regulons]

QC Checkpoint: GRN Inference

def validate_grn(regulons, auc_matrix, adata, cell_type_key='cell_type'):
    '''
    QC gates after GRN inference.
    - 50-500 regulons is typical range
    - Known lineage TFs should appear (e.g., PAX6 in neurons, GATA1 in erythroid)
    - AUCell scores should separate known cell types
    '''
    n_regulons = len(regulons)
    regulon_names = [r.name for r in regulons]

    # Gate 1: Regulon count
    if n_regulons < 50:
        print(f'WARNING: Only {n_regulons} regulons. Check TF list or lower NES threshold.')
    elif n_regulons > 500:
        print(f'WARNING: {n_regulons} regulons found. Consider stricter pruning.')
    else:
        print(f'OK: {n_regulons} regulons in expected range (50-500)')

    # Gate 2: Known TFs present
    known_tfs = ['PAX6', 'SOX2', 'GATA1', 'SPI1', 'FOXP3', 'TBX21', 'EBF1']
    found = [tf for tf in known_tfs if tf in regulon_names]
    print(f'Known lineage TFs found: {found}')

    # Gate 3: AUCell separates cell types
    import scipy.stats as stats
    cell_types = adata.obs[cell_type_key].unique()
    if len(cell_types) >= 2:
        ct1_idx = adata.obs[cell_type_key] == cell_types[0]
        ct2_idx = adata.obs[cell_type_key] == cell_types[1]
        n_differential = 0
        for i, rname in enumerate(regulon_names[:min(50, len(regulon_names))]):
            stat, pval = stats.mannwhitneyu(
                auc_matrix.values[ct1_idx, i], auc_matrix.values[ct2_idx, i]
            )
            if pval < 0.01:
                n_differential += 1
        print(f'Differentially active regulons between top 2 types: {n_differential}/50')

    return n_regulons

Path B: SCENIC+ (Multiome)

Step 1: ATAC Topic Modeling with cisTopic

import pycisTopic
from pycisTopic.cistopic_class import create_cistopic_object
from pycisTopic.lda_models import run_cgs_models

# Create cisTopic object from fragments
cistopic_obj = create_cistopic_object(
    fragment_matrix=adata_atac.X,
    cell_names=adata_atac.obs_names.tolist(),
    region_names=adata_atac.var_names.tolist()
)

# Run LDA topic modeling
# n_topics: test range around expected cell types (e.g., 2x number of clusters)
models = run_cgs_models(
    cistopic_obj,
    n_topics=[10, 20, 30, 40, 50],
    n_cpu=8, n_iter=300, random_state=42
)

# Select best model by log-likelihood
from pycisTopic.lda_models import evaluate_models
model = evaluate_models(models, select_model=True)
cistopic_obj.add_LDA_model(model)

Step 2: Enhancer-TF Mapping

from pycistarget.utils import region_names_to_coordinates
from pycistarget.motif_enrichment_cistarget import run_cistarget

region_sets = {}
from pycisTopic.topic_binarization import binarize_topics
region_bin = binarize_topics(cistopic_obj, method='otsu')

for topic in region_bin:
    region_sets[topic] = region_bin[topic]

# Run motif enrichment on accessible regions
cistarget_results = run_cistarget(
    region_sets=region_sets,
    species='homo_sapiens',
    auc_threshold=0.005,
    nes_threshold=3.0,
    rank_threshold=0.05,
    n_cpu=8
)

Step 3: eGRN Construction

from scenicplus.scenicplus_class import create_SCENICPLUS_object
from scenicplus.grn_builder.gsea_approach import build_grn

scplus_obj = create_SCENICPLUS_object(
    adata_rna=adata_rna,
    cistopic_obj=cistopic_obj,
    menr=cistarget_results
)

build_grn(
    scplus_obj,
    min_target_genes=10,
    adj_pval_thr=0.1,
    min_regions_per_gene=0
)

print(f'eGRNs: {len(scplus_obj.uns["eRegulon_AUC"].columns)} enhancer-driven regulons')

CellOracle Perturbation Simulation

import celloracle as co

oracle = co.Oracle()
oracle.import_anndata_as_raw_count(
    adata=adata,
    cluster_column_name='cell_type',
    embedding_name='X_umap'
)

# Import GRN (from pySCENIC adjacencies or SCENIC+ eGRNs)
links = co.utility.load_links(adjacencies)
oracle.addTFinfo_dictionary(links)

oracle.perform_PCA()
oracle.knn_imputation(k=30)

# Simulate TF knockout
oracle.simulate_shift(perturb_condition={'MYC': 0.0}, n_propagation=3)
oracle.estimate_transition_prob(n_neighbors=200, knn_random=True, sampled_fraction=1)

# Perturbation score: magnitude of predicted shift
oracle.calculate_embedding_shift(sigma_corr=0.05)

# QC: shifts should match known biology (e.g., MYC KO reduces proliferation)
gradient = oracle.gradient_fitting(n_jobs=8)

QC Checkpoint: Perturbation

def validate_perturbation(oracle, perturbed_tf, expected_affected_cluster=None):
    '''
    QC gate: perturbation shifts should match known biology.
    - Transition probabilities should show directional shift
    - If expected_affected_cluster known, check it shows largest change
    '''
    ps = oracle.perturbation_scores
    mean_shift = ps.groupby(oracle.adata.obs['cell_type']).mean()

    print(f'Mean perturbation scores by cell type after {perturbed_tf} KO:')
    print(mean_shift.sort_values(ascending=False))

    if expected_affected_cluster:
        if expected_affected_cluster in mean_shift.index[:3]:
            print(f'OK: {expected_affected_cluster} among top affected clusters')
        else:
            print(f'WARNING: {expected_affected_cluster} not among top affected')

    return mean_shift

Complete Pipeline Script

import scanpy as sc
import pandas as pd
from arboreto.algo import grnboost2
from pyscenic.prune import prune2df, df2regulons
from pyscenic.aucell import aucell
from ctxcore.rnkdb import FeatherRankingDatabase
from ctxcore.genesig import GeneSignature

def run_scenic_pipeline(adata_path, tf_list_path, db_paths, motif_annotations_path, output_prefix):
    '''Run complete pySCENIC pipeline.'''
    adata = sc.read_h5ad(adata_path)

    expr_matrix = pd.DataFrame(
        adata.raw.X.toarray() if hasattr(adata.raw.X, 'toarray') else adata.raw.X,
        index=adata.obs_names, columns=adata.raw.var_names
    )

    tf_names = pd.read_csv(tf_list_path, header=None)[0].tolist()
    tf_names = [tf for tf in tf_names if tf in expr_matrix.columns]

    print(f'Step 1: GRN inference with {len(tf_names)} TFs')
    adjacencies = grnboost2(expr_matrix, tf_names=tf_names, seed=42, verbose=True)

    print('Step 2: Regulon pruning')
    dbs = [FeatherRankingDatabase(db) for db in db_paths]
    modules = [GeneSignature(name=tf, gene2weight=dict(zip(grp['target'], grp['importance'])))
               for tf, grp in adjacencies.groupby('TF') if len(grp) >= 10]
    df_motifs = prune2df(dbs, modules, motif_annotations_path, num_workers=8)
    regulons = df2regulons(df_motifs)
    print(f'Discovered {len(regulons)} regulons')

    print('Step 3: AUCell scoring')
    auc_matrix = aucell(expr_matrix, regulons, num_workers=8)
    adata.obsm['X_aucell'] = auc_matrix.loc[adata.obs_names].values
    adata.uns['regulon_names'] = [r.name for r in regulons]

    adata.write(f'{output_prefix}_scenic.h5ad')
    auc_matrix.to_csv(f'{output_prefix}_aucell.csv')

    print(f'Pipeline complete: {len(regulons)} regulons, AUCell matrix saved')
    return adata, regulons, auc_matrix

Parameter Recommendations

Troubleshooting

Related Skills

• gene-regulatory-networks/scenic-regulons - pySCENIC implementation details
• gene-regulatory-networks/multiomics-grn - SCENIC+ enhancer-driven GRNs
• gene-regulatory-networks/perturbation-simulation - CellOracle details
• single-cell/clustering - Upstream cell type annotation
• single-cell/preprocessing - QC and normalization before GRN inference