$npx -y skills add GPTomics/bioSkills --skill enhancer-gene-linkingPredict enhancer-gene regulatory connections from ATAC-seq using ABC, ENCODE-rE2G, HiChIP, or Cicero. Use when linking distal enhancers to target genes, choosing between contact-aware (ABC, ENCODE-rE2G), accessibility-only (Cicero), and orthogonal (HiChIP H3K27ac, EpiMap) approac
| 1 | ## Version Compatibility |
| 2 | |
| 3 | Reference examples tested with: ABC-Enhancer-Gene-Prediction 0.2.2+ (Engreitz lab), ENCODE-rE2G v1.0+ (EngreitzLab), Cicero 1.20+, GenomicInteractions 1.36+, FitHiChIP 9.1+, HiC-Pro 3.1+, FAN-C 0.9+, MACS3 3.0+, samtools 1.19+, bedtools 2.31+. |
| 4 | |
| 5 | Verify before use: |
| 6 | - CLI: `<tool> --version` then `<tool> --help` to confirm flags |
| 7 | - R: `packageVersion('<pkg>')` then `?function_name` to verify parameters |
| 8 | - Python: `pip show <package>` then `help(module.function)` to check signatures |
| 9 | |
| 10 | If code throws unexpected errors, introspect the installed package and adapt rather than retrying. |
| 11 | |
| 12 | # Enhancer-Gene Linking |
| 13 | |
| 14 | **"Which gene does this distal accessible region regulate?"** -> Predict the enhancer's target gene using a model that combines accessibility activity, 3D contact frequency, and (optionally) sequence-based chromatin predictions. Output is a per-(enhancer, gene) score that can be thresholded for high-confidence calls. |
| 15 | |
| 16 | - CLI: ABC pipeline (`run.neighborhoods.py`, `predict.py` from Engreitz lab) |
| 17 | - CLI: ENCODE-rE2G (Snakemake-based; ENCODE 4 enhancer-gene standard) |
| 18 | - R: Cicero (ATAC-only; covered in atac-seq/co-accessibility) |
| 19 | - CLI: FitHiChIP / hichipper for HiChIP H3K27ac loops |
| 20 | - Database: EpiMap (Boix 2021), GeneHancer, FANTOM5 (pre-computed reference) |
| 21 | |
| 22 | ABC and ENCODE-rE2G are the canonical predictors when Hi-C/Micro-C data is available. Cicero is the ATAC-only fallback. CRISPRi-FlowFISH (Fulco 2019) is the gold-standard experimental validation. |
| 23 | |
| 24 | ## Algorithmic Taxonomy |
| 25 | |
| 26 | | Method | Inputs | Mathematics | Strength | Fails when | |
| 27 | |--------|--------|-------------|----------|------------| |
| 28 | | ABC (Fulco 2019, Nasser 2021) | ATAC + H3K27ac + Hi-C/Micro-C | ABC = (Activity_E x Contact_E,G) / sum_e(Activity_e x Contact_e,G); threshold typically >= 0.02 | Mechanistically grounded; published gold-standard for human cell lines | Requires matched Hi-C / Micro-C; cell-type-specific; default contact uses average across 10 ENCODE cell types if Hi-C not available | |
| 29 | | ENCODE-rE2G (Gschwind 2023) | ATAC + H3K27ac + (Hi-C optional) | Logistic regression trained on CRISPRi-FlowFISH ground truth; uses ABC features + sequence features + distance | ENCODE 4 standard; pre-trained models for many cell types | Pre-trained models only available for ENCODE cell types; retraining requires CRISPRi data | |
| 30 | | Cicero (Pliner 2018) | scATAC peak-cell matrix | Graphical lasso on metacell co-accessibility | ATAC-only; works without Hi-C | Less concordant with Hi-C than ABC; cis-distance-limited; alpha-sensitive | |
| 31 | | HiChIP H3K27ac + FitHiChIP | H3K27ac HiChIP | Statistically significant loops at FDR < 0.05 | Direct experimental loop measurement; cell-type-specific; orthogonal to ATAC | Requires HiChIP wet-lab; only captures loops within HiChIP resolution (~10 kb) | |
| 32 | | Hi-C + HiCCUPS | Bulk Hi-C | Fold-enrichment loop calling | Most-validated 3D contact method | Resolution typically 5-25 kb; misses sub-loop fine structure | |
| 33 | | Capture Hi-C / PCHi-C (CHiCAGO) | Promoter Capture Hi-C | Asymptotic CHiCAGO score | High-resolution promoter-anchored | Wet-lab cost; promoter capture only | |
| 34 | | EpiMap (Boix 2021) reference | None (pre-computed lookup) | Bulk-derived enhancer-gene predictions in 833 epigenomes | Fast, comprehensive | Cell-type-agnostic for tissues outside the reference set | |
| 35 | | GeneHancer / FANTOM5 (legacy) | None (pre-computed lookup) | Pre-computed; varied methods per database | Comprehensive lookup; widely cited | Older; less reliable than ABC for cell-type-specific | |
| 36 | |
| 37 | Methodology evolves; verify against current Engreitz lab releases (ABC), ENCODE 4 publications (ENCODE-rE2G), and Mumbach 2017 (HiChIP) before locking pipelines. |
| 38 | |
| 39 | ## ABC Mathematics |
| 40 | |
| 41 | For each candidate (enhancer E, gene G) pair within the cis window (default 5 Mb): |
| 42 | |
| 43 | ``` |
| 44 | ABC(E -> G) = Activity_E * Contact_E,G / sum_{all e in window}(Activity_e * Contact_e,G) |
| 45 | ``` |
| 46 | |
| 47 | - **Activity_E** = ATAC reads at E * H3K27ac reads at E (geometric mean of normalized signals; reflects "enhancer strength") |
| 48 | - **Contact_E,G** = Hi-C/Micro-C contact frequency from E to G's TSS (after distance-correction) |
| 49 | - **Window** = +/- 5 Mb cis (default; ENCODE-rE2G uses 1 Mb) |
| 50 | |
| 51 | Threshold typical: ABC >= 0.02 for high-confidence; >= 0.01 for exploratory. |
| 52 | |
| 53 | When Hi-C is unavailable, ABC uses an "average contact" averaged across 10 ENCODE Hi-C cell types as proxy (Nasser 2021); it performs comparably to cell-type-matched Hi-C. The alternat |