Omicverse Single Cell Rna Velocity

OmicVerse Single-Cell RNA Velocity

Goal

Run reusable RNA velocity analysis on a velocity-ready AnnData: map spliced/unspliced layers if needed, fit moments and dynamics, estimate velocity, build the velocity graph, compute UMAP/Leiden, and render the stream plot. Use this same skill for method-comparison notebooks that branch across scvelo, dynamo, latentvelo, and graphvelo. If you still need FASTQ -> h5ad generation, hand off to the kb alignment skill first.

Quick Workflow

1. Start from a velocity-ready AnnData.
2. Map source-specific layers such as mature/nascent to spliced/unspliced when needed.
3. Pick the branch trio up front: recipe, backend, and method.
4. Instantiate ov.single.Velo(adata) and run filter_genes, preprocess, moments, dynamics, and cal_velocity.
5. Build the velocity graph, neighbors, UMAP, Leiden, and velocity embedding.
6. If the notebook includes a GraphVelo refinement stage, run it after an initial velocity layer exists.
7. Plot the embedding and stream plot.
8. Validate the stored keys before treating the result as finished.

Interface Summary

• ov.single.Velo(adata) creates the velocity workflow wrapper.
• Velo.filter_genes(min_shared_counts=20) keeps velocity-usable genes.
• Velo.preprocess(recipe='monocle', n_neighbors=30, n_pcs=30, **kwargs) uses Dynamo preprocessing and then builds a PCA-based neighbor graph.
• Velo.moments(backend='dynamo'|'scvelo', ...) and Velo.dynamics(backend='dynamo'|'scvelo', ...) branch on the requested backend.
• Velo.cal_velocity(method='dynamo'|'scvelo'|'latentvelo'|'graphvelo', ...) selects the velocity estimator and controls the output key family.
• Velo.graphvelo(xkey='Ms', vkey='velocity_S', n_jobs=1, basis_keys=['X_umap', 'X_pca'], gene_subset=...) refines an existing velocity layer and projects it to UMAP/PCA.
• Velo.velocity_graph(vkey='velocity_S', ...) and Velo.velocity_embedding(basis='umap', vkey='velocity_S', ...) project and store velocity outputs.
• ov.pp.neighbors(..., method='umap'|'gauss'|'rapids', transformer=...) builds the graph.
• ov.pp.umap(adata, method='umap'|'rapids'|'torchdr'|'mde'|'pumap', **kwargs) switches embedding backends.
• ov.pp.leiden(...) uses ov.settings.mode to choose CPU, mixed, or RAPIDS execution.
• ov.pl.embedding(...) and ov.pl.add_streamplot(...) render the final plot.

Boundary

• Keep this skill on the analysis side of the notebook.
• Do not absorb FASTQ download, reference building, or kb counting here.
• If you need raw quantification, hand off to the kb alignment skill first.
• If the notebook only changes velocity method, backend, recipe, or mode, keep it in this skill instead of creating a duplicate skill.
• If the notebook introduces a truly different analysis family or input contract, split it.

GraphVelo Refinement

• Use this branch after an initial velocity layer already exists in adata.
• Pick the matching input layer as vkey and use the corresponding ..._genes mask when the notebook provides one.
• Call Velo.graphvelo(..., basis_keys=['X_umap', 'X_pca']) to project GraphVelo refinement back onto the existing manifold.
• Then call Velo.velocity_graph(vkey='velocity_gv', xkey='Ms', n_jobs=8) and Velo.velocity_embedding(basis='umap', vkey='velocity_gv').
• Expect GraphVelo to add velocity_gv, velocity_gv_genes, gv_X_umap, and gv_X_pca; the downstream graph and embedding calls add velocity_gv_graph and velocity_gv_umap.

Branch Selection

• Use recipe='monocle' for the notebook path; the live Dynamo Preprocessor also exposes seurat, sctransform, pearson_residuals, and monocle_pearson_residuals.
• Use backend='scvelo' for moments and dynamics when the input already has spliced/unspliced counts.
• Use backend='dynamo' when you want the Dynamo kinetics branch.
• Use method='scvelo' for cal_velocity on the portable notebook path.
• Use method='dynamo' when you want the Dynamo velocity branch.
• Use method='latentvelo' only when you have the required model inputs and a representative GPU or import-only smoke path.
• Use method='graphvelo' when you want the graph-based velocity branch; keep n_jobs small in smoke tests.
• Use method='umap' in ov.pp.neighbors unless you intentionally want the gauss or rapids graph branch.
• Set ov.settings.mode explicitly before ov.pp.umap and ov.pp.leiden if you need reproducible CPU, mixed, or GPU behavior.
• Use ov.settings.cpu_init() for the portable path; use cpu_gpu_mixed_init() or gpu_init() only when the hardware and dependencies actually support those modes.
• For notebook comparisons, keep the same input object and vary only the branch parameters you are studying.

Input Contract

• Begin with an AnnData that already contains raw velocity counts or velocity-ready layers.
• If the source layers are named mature and nascent, rename or copy them to spliced and unspliced.
• preprocess should create X_pca; neighbors should then consume X_pca.
• velocity_embedding and the stream plot need X_umap.
• Keep the dataset large enough for stream plotting; tiny synthetic sets can fail because the grid helper derives its own neighbor count from cell number.

Minimal Execution Patterns

import omicverse as ov
import scanpy as sc

adata = sc.read_h5ad("velocity-ready.h5ad")
if "spliced" not in adata.layers and "mature" in adata.layers:
    adata.layers["spliced"] = adata.layers["mature"]
if "unspliced" not in adata.layers and "nascent" in adata.layers:
    adata.layers["unspliced"] = adata.layers["nascent"]

ov.settings.cpu_init()
velo = ov.single.Velo(adata)
velo.filter_genes(min_shared_counts=20)
velo.preprocess(recipe="monocle", n_neighbors=30, n_pcs=30)
velo.moments(backend="scvelo", n_neighbors=30, n_pcs=30)
velo.dynamics(backend="scvelo", n_jobs=1)
velo.cal_velocity(method="scvelo")
velo.velocity_graph(vkey="velocity_S", xkey="Ms", n_jobs=1)
ov.pp.neighbors(adata, n_neighbors=15, use_rep="X_pca")
ov.pp.umap(adata)
ov.pp.leiden(adata, resolution=0.2)
velo.velocity_embedding(basis="umap", vkey="velocity_S")

# Method-comparison branch sketch
velo.moments(backend="dynamo")
velo.dynamics(backend="dynamo")
velo.cal_velocity(method="dynamo")

velo.cal_velocity(method="graphvelo", n_jobs=1)

velo.cal_velocity(
    method="latentvelo",
    batch_key="batch",
    celltype_key="celltype",
    velocity_key="velo_latentvelo",
)

Validation

• Confirm X_pca, X_umap, and leiden are present after preprocessing and clustering.
• Confirm Ms, Mu, the chosen velocity_key, and the derived graph/embedding keys are present after the velocity steps.
• When you keep the default velocity_key='velocity_S', confirm velocity_S_graph and velocity_S_umap.
• Confirm ov.pl.add_streamplot(...) returns an axes object and does not raise.
• If you switch ov.settings.mode, confirm the backend-specific messages match the selected mode.
• Validate latentvelo and any GPU-heavy path with a representative smoke or import-only interface check if a full run is not practical.
• For GraphVelo smoke on synthetic data, use a broad gene subset so the internal PCA has enough features.

Resource Map

• Read references/branch-selection.md when choosing the recipe, backend, method, or mode branch.
• Read references/source-notebook-map.md when you need to see how the notebook splits into comparison branches and where the skill boundary sits.
• Read references/source-grounding.md for inspected signatures and source behavior.
• Read references/compatibility.md for smoke-path caveats and runtime notes.