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Process Narrative

A chronological account of decisions, pivots, and surprises — the honest story of what happened.

This narrative documents the evolution of analysis approaches from December 2024 through September 2025, organized by phase. Each phase highlights the key decision or pivot that defined that period.

Phase 1 (Dec 2024 – Jan 2025): Integrated Analysis Attempt

Why Integration Seemed Obvious

The natural starting point was to pool all available datasets together and run a combined analysis — this approach maximizes sample size and, in theory, enables detection of weak signals.

Week of Dec 4, 2024

Attempted: Running nf-core pipeline on 4 combined datasets

Outcome: ❌ Failed - compute resource limits and too many unaccounted nuances

Key Insight

"Too many nuances that can't be accounted for when everything is pooled"

Related:

January 2025: Differential Abundance Beginnings

Jan 3 activities:

  • Issue #3: Created merged metadata
  • Issue #4: Differential abundance initial approach
  • Toy example: ✅ Success
  • GTF file issues encountered
  • Applied mutual information to Perkinsus datasets

Outcome: Merged counts table obtained, but separation by trait was weak

Jan 16:

Attempted: Subset data to improve separation

Outcome: ❌ Didn't help significantly

Considerations identified:

  • Fixed vs. random effects
  • Sample size limitations
  • Control group treatment
  • Batch corrections needed

Issues opened:

Big Lesson #1: When Integration Fails

Integrated data analysis does not work when data is noisy (too much within and/or across study variation) and signal is not strong enough.

Pivot discussed: Meta-analysis approach (inspired by BMC paper with Erin Witkop, Dina co-author)

Phase 2 (Feb 2025): Confronting Batch Effects

Key finding: Study-specific effects are much stronger than trait effects

Attempted:

  • Issue #18: Batch correction
  • COMBAT
  • RemoveBatchEffect

Outcome: ❌ Little effect on improving trait-based separation

Big Lesson #2: Traits Were Oversimplified

Generalized trait definitions across studies were insufficient. Study-specific effects dominated.

Alternative approach: Limit variation within study by subsetting for common time points, compare DEGs against control groups

Phase 3 (Apr – Jun 2025): Shift to Per-Dataset Independent Analysis; TAG-seq Discovery

Strategy Shift: Independent Dataset Analysis

New approach: Running DifferentialAbundance on each dataset independently

TAG-seq Parameter Problems (April 2025)

  • Issue #26: What flags to use? Discovered GC bias
  • Critical finding: Johnson dataset used TAG-seq; initial RNA-seq analysis parameters were inappropriate
  • Issue #28: Rerun Johnson data with different parameters

Related:

Deferred Work (April 2025)

  • Issue #29 & #31: Ran differential abundance on all datasets together but didn't interpret results yet

Could return to this

Results exist but interpretation was postponed to focus on per-dataset approach

Per-Dataset Deep Dives (June 2025)

Issue #32: Attempted differentialabundance on datasets separately

  • Steve: Focused on study 5
  • Shelly: Focused on study 1
  • Goal: Understand parameters and how to best run differential abundance

Phase 4 (Jul 2025): Normalization and Study-Combination Experiments

Study Combination Experiment

Issue #34: Combine study 4 (injected group) + study 5

Research question: Will study 4 injected group cluster with resistance or susceptible group from study 5?

Learning: Gained deeper understanding of the differentialabundance pipeline

  • PCAs are generated before any differential abundance analysis happens
  • Normalization timing matters for interpretation

Batch correction attempt:

  • Compared PCAs with and without batch correction on top 500 most variable genes
  • Result: Starting to see evidence of innate trait

Could return to this

Analysis exists showing 567 genes with significant differential abundance (DESeq). Could revisit to see if these genes show greater clustering than the top 500 most variable.

Related:

Outstanding Questions

Issue #39: Compare DE results from papers and create list of DEGs/markers

Remaining to be done

Systematic comparison with published literature still pending

Phase 5 (Aug 2025): Stepwise Differential Abundance; Discovery of Innate-Signal Problem

GSEA Integration

Activity: Run differentialabundance with GSEA

  • Created GMT file with gene descriptions
  • Issue #45: Understand GSEA (not completed)

Related:

Stepwise Differential Abundance

Issue #41: Two-step approach

Steps:

  1. Step 1: Controls vs. treated (identify stress-responsive genes)
  2. Step 2: Resistant vs. sensitive (from step 1 genes)

Implementation: analyses/stepwise_differentialabundance/

Shelly's results on dataset 1:

  • Only 1 significant gene found
  • Problem: DESeq isn't ideal for highly pared-down gene sets (VST couldn't work well with only ~50 genes)

Big Lesson #3: Biomarkers in Controls

Are we removing biomarkers that are innate? If resilience biomarkers are constitutively expressed (present in controls), the stepwise filtering approach removes them!

Phase 6 (Aug – Sep 2025): Two-Step Classifier Development; 6-Gene Panel Validation

Classifier Development Begins

Issue #42: Validate SR320 classification results

Question: Are the ~50 markers convincing about the difference between sensitive vs. resistant?

Issue #43: SR320's AI model

Issue #44: Combined datasets 1 & 5

Comparison: Integrated data analysis vs. post-data integration approaches

Result: ✅ 6-gene classifier completed!

Pipeline:

  • Step 1: Rank genes based on:
  • Reproducibility across datasets
  • Consistency of directionality in expression differences
  • Heterogeneity assessment
  • Step 2: Logistic regression to find minimum gene set for good classification

Six-Gene Classifier Panel Identified

Strong separation between tolerant and sensitive phenotypes achieved

Big Lesson #4: Training Set in Test Set

Only include training set in test set if exploring within study. If trying to predict phenotypes in other studies, you should definitely not include the training data in the test set (avoid overfitting/leakage).

Related:

September 2025: Validation & Characterization

Cross-Study Comparison

Issue #36: Run differentialabundance independently for each dataset and compare DEGs

Theme: Post-data integration → do we see more overlap?

Could return to this

Good question about post-data integration vs. integrated data analysis, but uncertain about subsetting approach mentioned in the issue

Status: Not completed

6-Gene Panel Characterization

Issue #49: Plot 6 genes to gain confidence

Goal: Visualize how well these 6 genes distinguish phenotypes

Related:

Issue #53: Innate vs. reactive gene expression

Critical insight: Biomarkers may be constitutively different in resistant vs. sensitive oysters (innate), not just reactive to stress

Related:

Key Takeaways

See Big Lessons Learned for a distilled list of insights from this project.

Successful Methodologies

✅ Per-dataset differential abundance analysis
✅ Post-data integration (compare results across datasets)
✅ Two-step classifier pipeline (reproducibility + logistic regression)
✅ Leave-One-Study-Out (LOSO) validation
✅ Innate vs. reactive DEG characterization

Open Questions

  • Systematic comparison with published DEG lists
  • Optimal visualization of 6-gene panel across studies
  • Additional dataset integration for broader validation

Next: Read the distilled Big Lessons Learned, or jump to Methods & Pipelines