ChromHMM Chromatin State Inference

Overview

This skill enables comprehensive chromatin state analysis using chromHMM for histone modification ChIP-seq data. ChromHMM uses a multivariate Hidden Markov Model to segment the genome into discrete chromatin states based on combinatorial patterns of histone modifications.

Main steps include:

• Refer to Inputs & Outputs to verify necessary files.
• Always prompt user if required files are missing.
• Always prompt user for genome assembly used.
• Always prompt user for the bin size for generating binarized files.
• Always prompt user for the bin size for the number of states the ChromHMM target.
• Run chromHMM workflow: Binarization → Learning.

When to use this skill

Use this skill when you need to infer chromatin states from histone modification ChIP-seq data using chromHMM.

Inputs & Outputs

Inputs

(1) Option 1: BED files of aligned reads

<mark1>.bed
<mark2>.bed
... # Other marks

(1) Option 2: BAM files of aligned reads

<mark1>.bam
<mark2>.bam
... # Other marks

Outputs

chromhmm_output/
  binarized/
    *.txt 
  model/
    *.txt
    ... # other files output by the ChromHMM

Decision Tree

Step 0: Initialize Project

Call:

• mcpproject-init-toolsproject_init

with:

• sample: all
• task: chromhmm

Step 1: Prepare the cellmarkfile (skip this step if signal files are provided)

• Prepare a .txt file (without header) containing following three columns:

- sample name - marker name - name of the BED/BAM file - control file of the sample (only provided if the input/control file is available)

• example of the cellmark.txt file

cell1    mark1    cell1_mark2.bam    cell1_control.bam
cell1   mark2    cell1_mark2.bam    cell1/control.bam

Step 2: Data Binarization

• For BAM inputs:

Call: - mcpchromhmm-toolsbinarizebam with: - pathchromsized: Provide by user or detect from the working directory - inputdir: Directory containing BAM files - cellmarkfile: Cell mark file defining histone modifications - outputdir: (e.g. binarized/) - binsize: Provided by user

• For BED inputs:

Call mcpchromhmm-toolsbinarize_bed instead.

• For Signal inputs:

Call: mcpchromhmm-toolsbinarizesignal with: - inputdir: Directory of signals - output_dir: (e.g. binarized/)

Step 3: Model Learning

Call

• mcpchromhmm-toolslearn_model

with:

• binarized_dir: Directory binarized file located in
• num_states: Provide by user (e.g. 15)
• outputmodeldir: (e.g. model15states/)
• genome: Provide by user (e.g. hg38)
• threads: Provide by user (e.g. 16)

Parameter Optimization

Number of States

• 8 states: Basic chromatin states
• 15 states: Standard comprehensive states
• 25 states: High-resolution states
• Optimization: Use Bayesian Information Criterion (BIC)

Bin Size

• 200bp: Standard resolution
• 100bp: High resolution (requires more memory)
• 500bp: Low resolution (faster computation)

State Interpretation

Common Chromatin States

1. Active Promoter: H3K4me3, H3K27ac
2. Weak Promoter: H3K4me3
3. Poised Promoter: H3K4me3, H3K27me3
4. Strong Enhancer: H3K27ac, H3K4me1
5. Weak Enhancer: H3K4me1
6. Insulator: CTCF
7. Transcribed: H3K36me3
8. Repressed: H3K27me3
9. Heterochromatin: Low signal across marks

Troubleshooting

• Memory errors: Reduce bin size or number of states
• Convergence problems: Increase iterations or adjust learning rate
• Uninterpretable states: Check input data quality and mark combinations
• Missing chromosomes: Verify chromosome naming consistency