---
name: bulktrajblend-trajectory-interpolation
title: BulkTrajBlend trajectory interpolation
description: Extend scRNA-seq developmental trajectories with BulkTrajBlend by generating intermediate cells from bulk RNA-seq, training beta-VAE and GNN models, and interpolating missing states.
---

# BulkTrajBlend trajectory interpolation

## Overview
Invoke this skill when users need to bridge gaps in single-cell developmental trajectories using matched bulk RNA-seq. It follows [`t_bulktrajblend.ipynb`](../../omicverse_guide/docs/Tutorials-bulk2single/t_bulktrajblend.ipynb), showcasing how BulkTrajBlend deconvolves PDAC bulk samples, identifies overlapping communities with a GNN, and interpolates "interrupted" cell states.

## Instructions
1. **Prepare libraries and inputs**
   - Import `omicverse as ov`, `scanpy as sc`, `scvelo as scv`, and helper functions like `from omicverse.utils import mde`; run `ov.plot_set()`.
   - Load the reference scRNA-seq AnnData (`scv.datasets.dentategyrus()`) and raw bulk counts with `ov.utils.read(...)` followed by `ov.bulk.Matrix_ID_mapping(...)` for gene ID harmonisation.
2. **Configure BulkTrajBlend**
   - Instantiate `ov.bulk2single.BulkTrajBlend(bulk_seq=bulk_df, single_seq=adata, bulk_group=['dg_d_1','dg_d_2','dg_d_3'], celltype_key='clusters')`.
   - Explain that `bulk_group` names correspond to raw bulk columns and the method expects unscaled counts.
3. **Set beta-VAE expectations**
   - Call `bulktb.vae_configure(cell_target_num=100)` (or pass a dictionary) to define expected cell counts per cluster. Mention that omitting the argument triggers TAPE-based estimation.
4. **Train or load the beta-VAE**
   - Use `bulktb.vae_train(batch_size=512, learning_rate=1e-4, hidden_size=256, epoch_num=3500, vae_save_dir='...', vae_save_name='dg_btb_vae', generate_save_dir='...', generate_save_name='dg_btb')`.
   - Highlight resuming with `bulktb.vae_load('.../dg_btb_vae.pth')` and the need to regenerate cells with consistent random seeds for reproducibility.
5. **Generate synthetic cells**
   - Produce filtered AnnData via `bulktb.vae_generate(leiden_size=25)` and inspect compositions with `ov.bulk2single.bulk2single_plot_cellprop(...)`.
   - Save outputs to disk for reuse (`adata.write_h5ad`).
6. **Configure and train the GNN**
   - Call `bulktb.gnn_configure(max_epochs=2000, use_rep='X', neighbor_rep='X_pca', gpu=0, ...)` to set hyperparameters.
   - Train using `bulktb.gnn_train()`; reload checkpoints with `bulktb.gnn_load('save_model/gnn.pth')`.
   - Generate overlapping community assignments through `bulktb.gnn_generate()`.
7. **Visualise community structure**
   - Create MDE embeddings: `bulktb.nocd_obj.adata.obsm['X_mde'] = mde(bulktb.nocd_obj.adata.obsm['X_pca'])`.
   - Plot clusters vs. discovered communities using `sc.pl.embedding(..., color=['clusters','nocd_n'], palette=ov.utils.pyomic_palette())` and filtered subsets excluding synthetic labels with hyphens.
8. **Interpolate missing states**
   - Run `bulktb.interpolation('OPC')` (replace with target lineage) to synthesise continuity, then preprocess the interpolated AnnData (HVG selection, scaling, PCA).
   - Compute embeddings with `mde`, visualise with `ov.utils.embedding`, and compare to the original atlas.
9. **Analyse trajectories**
   - Initialise `ov.single.pyVIA` on both original and interpolated data to derive pseudotime, followed by `get_pseudotime`, `sc.pp.neighbors`, `ov.utils.cal_paga`, and `ov.utils.plot_paga` for topology validation.
10. **Defensive validation**
    ```python
    # Before BulkTrajBlend: verify bulk_group columns exist
    for g in bulk_group:
        assert g in bulk_df.columns, f"Bulk group '{g}' not in bulk data columns"
    # Verify celltype_key exists in reference
    assert celltype_key in adata.obs.columns, f"Cell type column '{celltype_key}' not in reference AnnData"
    # Verify gene name overlap
    shared = set(bulk_df.index) & set(adata.var_names)
    assert len(shared) > 100, f"Only {len(shared)} shared genes — harmonize gene IDs first"
    ```
11. **Troubleshooting tips**
    - If the VAE collapses (high reconstruction loss), lower `learning_rate` or reduce `hidden_size`.
    - Ensure the same generated dataset is used before calling `gnn_train`; regenerating cells changes the graph and can break checkpoint loading.
    - Sparse clusters may need adjusted `cell_target_num` thresholds or a smaller `leiden_size` filter to retain rare populations.

## Examples
- "Train BulkTrajBlend on PDAC cohorts, then interpolate missing OPC states in the trajectory."
- "Load saved beta-VAE and GNN weights to regenerate overlapping communities and plot cluster vs. nocd labels."
- "Run VIA on interpolated cells and compare PAGA graphs with the original scRNA-seq trajectory."

## References
- Tutorial notebook: [`t_bulktrajblend.ipynb`](../../omicverse_guide/docs/Tutorials-bulk2single/t_bulktrajblend.ipynb)
- Example datasets and checkpoints: [`omicverse_guide/docs/Tutorials-bulk2single/data/`](../../omicverse_guide/docs/Tutorials-bulk2single/data/)
- Quick copy/paste commands: [`reference.md`](reference.md)