$npx -y skills add GPTomics/bioSkills --skill single-cell-splicingAnalyzes alternative splicing at single-cell resolution. The first decision is library chemistry — 10X 3' is fundamentally limited (RT primes from poly-A, R2 falls in 3' UTR, <0.1 junction read per cell per AS event). Plate-based full-length methods (Smart-seq3, FLASH-seq, VASA-s
| 1 | ## Version Compatibility |
| 2 | |
| 3 | Reference examples tested with: MARVEL 2.0+, BRIE2 0.2.4+, scQuint 0.1+, SpliZ 0.0.1+, Sierra 1.0+, Psix 0.1+, anndata 0.10+, scanpy 1.10+, pandas 2.2+, scipy 1.13+ |
| 4 | |
| 5 | Before using code patterns, verify installed versions match. If versions differ: |
| 6 | - Python: `pip show <package>` then `help(module.function)` to check signatures |
| 7 | - R: `packageVersion('<pkg>')` then `?function_name` to verify parameters |
| 8 | - CLI: `<tool> --version` then `<tool> --help` to confirm flags |
| 9 | |
| 10 | If code throws ImportError, AttributeError, or TypeError, introspect the installed |
| 11 | package and adapt the example to match the actual API rather than retrying. |
| 12 | |
| 13 | # Single-Cell Splicing Analysis |
| 14 | |
| 15 | The fundamental decision is **chemistry**, not tool. Most droplet 3' scRNA-seq cannot support transcriptome-wide splicing inference because reverse transcription primes from the poly(A) tail and most reads land in the 3' UTR — far from CDS-region splicing events. Plate-based full-length methods and single-cell long-read sequencing are the chemistries that give per-cell isoform structure across the gene body. |
| 16 | |
| 17 | ## The 10X 3' Problem (Quantified) |
| 18 | |
| 19 | Three compounding mechanisms make 10X Chromium 3' (v3.1, GEM-X, v4) hostile to splicing: |
| 20 | |
| 21 | 1. **3' enrichment**: median fragment <1 kb from poly(A); >70% of unique reads fall within 3' UTR. |
| 22 | 2. **Short R2 (~91 nt)**: each read straddles at most one junction; usually none, because R2 lands in 3' UTR. |
| 23 | 3. **PCR concatemers and TSO artifacts**: pollute junction detection; UMI collapse is gene-level, not isoform-level. |
| 24 | |
| 25 | **Quantitative estimate:** Only a small fraction of cassette exons sit close enough to the polyA site to be sampled by 3' chemistry (empirical estimates from APA/3'-end atlases — see Tian & Manley 2017 *Nat Rev Mol Cell Biol* for the 3' UTR isoform landscape). Effective junction read yield from 10X 3' is **<0.1 per cell per AS event** — vs the 5-10 needed for stable per-cell PSI. Most splicing analyses on 10X 3' data report artifacts. |
| 26 | |
| 27 | **The 5' kit (10X 5' GEX) does not solve this** — it shifts capture from 3' UTR to 5' UTR / TSS-proximal regions. Marginal improvement; not a transcriptome-wide solution. Note that V(D)J recovery requires the **10X Chromium Single Cell Immune Profiling kit** (with TCR/BCR-specific enrichment), not 5' GEX alone — postdocs designing immune-repertoire experiments must use the dedicated V(D)J kit. |
| 28 | |
| 29 | ## Decision: Does the Chemistry Support Splicing Analysis? |
| 30 | |
| 31 | | Chemistry | Splicing analysis viable? | Best alternative if no | |
| 32 | |-----------|----------------------------|--------------------------| |
| 33 | | 10X 3' (Chromium v3, GEM-X, v4, Flex) | No (transcriptome-wide); maybe near-3'-end events | Sierra for APA | |
| 34 | | 10X 5' GEX | Limited; near-5'-end events only | Sierra for alternative TSS; switch to MAS-Iso-seq | |
| 35 | | Smart-seq2 | Yes (full transcript) | MARVEL or BRIE2 | |
| 36 | | Smart-seq3 / Smart-seq3xpress | Yes + UMI molecule counting | MARVEL or BRIE2 | |
| 37 | | FLASH-seq | Yes (faster, cheaper Smart-seq3) | MARVEL or BRIE2 | |
| 38 | | VASA-seq | Yes + total RNA (incl. nascent, IR) | MARVEL with IR analysis | |
| 39 | | STORM-seq | Yes + total RNA + ribodepletion | MARVEL with IR analysis | |
| 40 | | MAS-Iso-seq + 10X 5' (PacBio Kinnex) | Yes — full isoforms per cell | FLAMES, scNanoGPS, IsoQuant, see long-read-splicing | |
| 41 | | scISOr-Seq2 (PacBio + 10X) | Yes — full isoforms with cell-typing | FLAMES, IsoQuant | |
| 42 | | ONT direct cDNA scRNA | Yes | FLAMES | |
| 43 | | ONT direct RNA scRNA | Yes + native modifications | FLAMES | |
| 44 | |
| 45 | ## Tool Selection Matrix |
| 46 | |
| 47 | | Tool | Best for | Input | Strengths | Fails when | |
| 48 | |------|----------|-------|-----------|------------| |
| 49 | | MARVEL | Smart-seq plate-based and (v2+) 10X droplet unified workflow | Plate or droplet BAMs + Seurat | SE/A5SS/A3SS/MXE/RI/AFE/ALE; modality classification; native Seurat integration; v2 droplet support | R-only | |
| 50 | | BRIE2 | Plate-based with regulatory feature prior | Plate BAM + GFF3 events | Bayesian variational PSI + ELBO_gain test; principled uncertainty; CLI-driven (`brie-count`, `brie-quant`) | TensorFlow depen |