Using UCell with SingleCellExperiment
25 April 2023
Package
UCell 2.4.0
1 Introduction
SingleCellExperiment is Bioconductor’s data structure of choice for storing single-cell experiment data. The function ScoreSignatures_UCell() allows performing signature scoring with UCell directly on sce objects. UCell scores are returned in a altExp object: altExp(sce, 'UCell')
2 Get some testing data
For this demo, we will download a single-cell dataset of lung cancer (Zilionis et al. (2019) Immunity) through the scRNA-seq package. This dataset contains >170,000 single cells; for the sake of simplicity, in this demo will we focus on immune cells, according to the annotations by the authors, and downsample to 5000 cells.
library(scRNAseq)
lung <- ZilionisLungData()
immune <- lung$Used & lung$used_in_NSCLC_immune
lung <- lung[,immune]
lung <- lung[,1:5000]
exp.mat <- Matrix::Matrix(counts(lung),sparse = TRUE)3 Define gene signatures
Here we define some simple gene sets based on the “Human Cell Landscape” signatures Han et al. (2020) Nature. You may edit existing signatures, or add new one as elements in a list.
signatures <- list(
Tcell = c("CD3D","CD3E","CD3G","CD2","TRAC"),
Myeloid = c("CD14","LYZ","CSF1R","FCER1G","SPI1","LCK-"),
NK = c("KLRD1","NCAM1","NKG7","CD3D-","CD3E-"),
Plasma_cell = c("IGKC","IGHG3","IGHG1","IGHA1","CD19-")
)4 Run UCell on sce object
library(UCell)
library(SingleCellExperiment)
sce <- SingleCellExperiment(list(counts=exp.mat))
sce <- ScoreSignatures_UCell(sce, features=signatures,
assay = 'counts', name=NULL)
altExp(sce, 'UCell')## class: SummarizedExperiment
## dim: 4 5000
## metadata(0):
## assays(1): UCell
## rownames(4): Tcell Myeloid NK Plasma_cell
## rowData names(0):
## colnames(5000): bcHTNA bcHNVA ... bcGVZB bcHGKL
## colData names(0):Dimensionality reduction and visualization
library(scater)
library(patchwork)
#PCA
sce <- logNormCounts(sce)
sce <- runPCA(sce, scale=TRUE, ncomponents=10)
#UMAP
set.seed(1234)
sce <- runUMAP(sce, dimred="PCA")Visualize UCell scores on low-dimensional representation (UMAP)
pll <- lapply(names(signatures), function(x) {
plotUMAP(sce, colour_by = x, by_exprs_values = "UCell",
point_size=0.2) + theme(aspect.ratio = 1)
})
wrap_plots(pll)
5 Signature smoothing
Single-cell data are sparse. It can be useful to ‘impute’ scores by neighboring cells and partially correct this sparsity. The function SmoothKNN performs smoothing of single-cell scores by weighted average of the k-nearest neighbors in a given dimensionality reduction. It can be applied directly on SingleCellExperiment objects to smooth UCell scores:
sce <- SmoothKNN(sce, signature.names = names(signatures), reduction="PCA")## Warning in .check_altexp_columns(x, value, withDimnames = withDimnames, : 'colnames(value)' are not the same as 'colnames(x)' for 'altExp<-'.
## This will be an error in the next release of Bioconductor.a <- plotUMAP(sce, colour_by="Myeloid", by_exprs_values="UCell",
point_size=0.2) + ggtitle("UCell") + theme(aspect.ratio = 1)
b <- plotUMAP(sce, colour_by="Myeloid_kNN", by_exprs_values="UCell_kNN",
point_size=0.2) + ggtitle("Smoothed UCell") + theme(aspect.ratio = 1)
a | b
6 Resources
Please report any issues at the UCell GitHub repository.
More demos available on the Bioc landing page and at the UCell demo repository.
If you find UCell useful, you may also check out the scGate package, which relies on UCell scores to automatically purify populations of interest based on gene signatures.
See also SignatuR for easy storing and retrieval of gene signatures.
7 References
Appendix
- Andreatta, M., Carmona, S. J. (2021) UCell: Robust and scalable single-cell gene signature scoring Computational and Structural Biotechnology Journal
- Zilionis, R., Engblom, C., …, Klein, A. M. (2019) Single-Cell Transcriptomics of Human and Mouse Lung Cancers Reveals Conserved Myeloid Populations across Individuals and Species Immunity
- Amezquita, Robert A., et al. (2020) “Orchestrating single-cell analysis with Bioconductor.” Nature methods
A Session Info
sessionInfo()## R version 4.3.0 RC (2023-04-13 r84269)
## Platform: x86_64-pc-linux-gnu (64-bit)
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