Last updated: 2024-12-24

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Rmd f0f7a57 Dave Tang 2024-12-24 Finding Markers with Seurat

Use the Peripheral Blood Mononuclear Cells (PBMCs) 2,700 cells dataset to test finding markers with Seurat.

Install the following packages, if necessary.

install.packages("remotes")
remotes::install_github("immunogenomics/presto")
install.packages("Seurat")
install.packages("bench")

Load Seurat and bench for some benchmarking.

suppressPackageStartupMessages(library("Seurat"))
suppressPackageStartupMessages(library("bench"))
suppressPackageStartupMessages(library("presto"))

Data

To follow the tutorial, you’ll need the 10X data, which can be download from AWS.

mkdir -p data/pbmc3k && cd data/pbmc3k
wget -c https://s3-us-west-2.amazonaws.com/10x.files/samples/cell/pbmc3k/pbmc3k_filtered_gene_bc_matrices.tar.gz
tar -xzf pbmc3k_filtered_gene_bc_matrices.tar.gz

Seurat object

Load 10x data into a matrix using Read10X().

pbmc.data <- Read10X(
  data.dir = "data/pbmc3k/filtered_gene_bc_matrices/hg19/"
)

Create the Seurat object using CreateSeuratObject; see ?SeuratObject for more information on the class.

seurat_obj <- CreateSeuratObject(
  counts = pbmc.data,
  min.cells = 3,
  min.features = 200,
  project = "pbmc3k"
)
Warning: Feature names cannot have underscores ('_'), replacing with dashes
('-')
class(seurat_obj)
[1] "Seurat"
attr(,"package")
[1] "SeuratObject"

Seurat workflow

Run the workflow as separate steps; they can be piped together but sometimes errors occur, so it is useful to split up the steps.

debug_flag <- FALSE
seurat_obj <- NormalizeData(seurat_obj, normalization.method = "LogNormalize", scale.factor = 1e4, verbose = debug_flag)
seurat_obj <- FindVariableFeatures(seurat_obj, selection.method = 'vst', nfeatures = 2000, verbose = debug_flag)
seurat_obj <- ScaleData(seurat_obj, verbose = debug_flag)
seurat_obj <- RunPCA(seurat_obj, verbose = debug_flag)
seurat_obj <- RunUMAP(seurat_obj, dims = 1:30, verbose = debug_flag)
Warning: The default method for RunUMAP has changed from calling Python UMAP via reticulate to the R-native UWOT using the cosine metric
To use Python UMAP via reticulate, set umap.method to 'umap-learn' and metric to 'correlation'
This message will be shown once per session
seurat_obj <- FindNeighbors(seurat_obj, dims = 1:30, verbose = debug_flag)
seurat_obj <- FindClusters(seurat_obj, resolution = 0.5, verbose = debug_flag)

seurat_obj
An object of class Seurat 
13714 features across 2700 samples within 1 assay 
Active assay: RNA (13714 features, 2000 variable features)
 3 layers present: counts, data, scale.data
 2 dimensional reductions calculated: pca, umap

Find all markers

FindAllMarkers() will find markers (differentially expressed genes) for each of the identity classes in a dataset.

levels(Idents(seurat_obj))
[1] "0" "1" "2" "3" "4" "5" "6" "7"

Find all markers.

all_markers <- FindAllMarkers(seurat_obj, verbose = debug_flag)
dim(all_markers)
[1] 17899     7

Find markers

FindMarkers() finds markers (differentially expressed genes) for identity classes.

cluster_0_markers <- FindMarkers(seurat_obj, ident.1 = "0")
dim(cluster_0_markers)
[1] 8434    5

Cluster 0 markers from FindAllMarkers().

all_markers |>
  dplyr::filter(cluster == 0) |>
  dim()
[1] 3139    7

The start of the results are the same.

head(cluster_0_markers)
                 p_val avg_log2FC pct.1 pct.2     p_val_adj
LDHB     1.547138e-240  1.9351689 0.922 0.473 2.121746e-236
RPS12    3.595829e-228  0.8665851 1.000 0.987 4.931320e-224
CD74     2.127919e-225 -3.1636831 0.735 0.925 2.918227e-221
HLA-DRB1 3.113535e-225 -4.3722870 0.129 0.715 4.269901e-221
CYBA     2.054958e-213 -1.8108145 0.730 0.933 2.818169e-209
HLA-DRA  7.109002e-213 -4.6393725 0.291 0.765 9.749286e-209
all_markers |>
  dplyr::filter(cluster == 0) |>
  dplyr::select(-cluster, -gene) |>
  head()
                 p_val avg_log2FC pct.1 pct.2     p_val_adj
LDHB     1.547138e-240  1.9351689 0.922 0.473 2.121746e-236
RPS12    3.595829e-228  0.8665851 1.000 0.987 4.931320e-224
CD74     2.127919e-225 -3.1636831 0.735 0.925 2.918227e-221
HLA-DRB1 3.113535e-225 -4.3722870 0.129 0.715 4.269901e-221
CYBA     2.054958e-213 -1.8108145 0.730 0.933 2.818169e-209
HLA-DRA  7.109002e-213 -4.6393725 0.291 0.765 9.749286e-209

The tail of the results are the same too, except that in FindAllMarkers() results have been trimmed.

cluster_0_markers[3134:3139, ]
             p_val avg_log2FC pct.1 pct.2 p_val_adj
SCML1  0.009913768  1.2125839 0.028 0.014         1
CGGBP1 0.009914211  0.3048076 0.152 0.117         1
CCT3   0.009950407  0.2610577 0.231 0.190         1
ZNF32  0.009955859  0.1339321 0.108 0.079         1
RNF214 0.009977100  0.8208791 0.043 0.025         1
P2RX7  0.009979523 -1.7709166 0.003 0.013         1
all_markers |>
  dplyr::filter(cluster == 0) |>
  dplyr::select(-cluster, -gene) |>
  tail()
             p_val avg_log2FC pct.1 pct.2 p_val_adj
SCML1  0.009913768  1.2125839 0.028 0.014         1
CGGBP1 0.009914211  0.3048076 0.152 0.117         1
CCT3   0.009950407  0.2610577 0.231 0.190         1
ZNF32  0.009955859  0.1339321 0.108 0.079         1
RNF214 0.009977100  0.8208791 0.043 0.025         1
P2RX7  0.009979523 -1.7709166 0.003 0.013         1

Trimming seems to be from p_val < 0.01

cluster_0_markers[3139:3142, ]
            p_val avg_log2FC pct.1 pct.2 p_val_adj
P2RX7 0.009979523 -1.7709166 0.003 0.013         1
CBFB  0.010029322  0.6492086 0.068 0.046         1
ATF6B 0.010045052 -0.4047457 0.130 0.165         1
PCNT  0.010051913 -1.8088730 0.003 0.013         1

sessionInfo()
R version 4.4.1 (2024-06-14)
Platform: x86_64-pc-linux-gnu
Running under: Ubuntu 22.04.5 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.20.so;  LAPACK version 3.10.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Etc/UTC
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] presto_1.0.0       data.table_1.16.2  Rcpp_1.0.13        bench_1.1.3       
[5] Seurat_5.1.0       SeuratObject_5.0.2 sp_2.1-4           workflowr_1.7.1   

loaded via a namespace (and not attached):
  [1] RColorBrewer_1.1-3     rstudioapi_0.17.1      jsonlite_1.8.9        
  [4] magrittr_2.0.3         spatstat.utils_3.1-0   farver_2.1.2          
  [7] rmarkdown_2.28         fs_1.6.4               vctrs_0.6.5           
 [10] ROCR_1.0-11            spatstat.explore_3.3-3 htmltools_0.5.8.1     
 [13] sass_0.4.9             sctransform_0.4.1      parallelly_1.38.0     
 [16] KernSmooth_2.23-24     bslib_0.8.0            htmlwidgets_1.6.4     
 [19] ica_1.0-3              plyr_1.8.9             plotly_4.10.4         
 [22] zoo_1.8-12             cachem_1.1.0           whisker_0.4.1         
 [25] igraph_2.1.2           mime_0.12              lifecycle_1.0.4       
 [28] pkgconfig_2.0.3        Matrix_1.7-0           R6_2.5.1              
 [31] fastmap_1.2.0          fitdistrplus_1.2-1     future_1.34.0         
 [34] shiny_1.9.1            digest_0.6.37          colorspace_2.1-1      
 [37] patchwork_1.3.0        ps_1.8.1               rprojroot_2.0.4       
 [40] tensor_1.5             RSpectra_0.16-2        irlba_2.3.5.1         
 [43] progressr_0.15.0       fansi_1.0.6            spatstat.sparse_3.1-0 
 [46] httr_1.4.7             polyclip_1.10-7        abind_1.4-8           
 [49] compiler_4.4.1         withr_3.0.2            fastDummies_1.7.4     
 [52] R.utils_2.12.3         MASS_7.3-60.2          tools_4.4.1           
 [55] lmtest_0.9-40          httpuv_1.6.15          future.apply_1.11.3   
 [58] goftest_1.2-3          R.oo_1.27.0            glue_1.8.0            
 [61] callr_3.7.6            nlme_3.1-164           promises_1.3.0        
 [64] grid_4.4.1             Rtsne_0.17             getPass_0.2-4         
 [67] cluster_2.1.6          reshape2_1.4.4         generics_0.1.3        
 [70] gtable_0.3.6           spatstat.data_3.1-2    R.methodsS3_1.8.2     
 [73] tidyr_1.3.1            utf8_1.2.4             spatstat.geom_3.3-3   
 [76] RcppAnnoy_0.0.22       ggrepel_0.9.6          RANN_2.6.2            
 [79] pillar_1.9.0           stringr_1.5.1          spam_2.11-0           
 [82] RcppHNSW_0.6.0         later_1.3.2            splines_4.4.1         
 [85] dplyr_1.1.4            lattice_0.22-6         survival_3.6-4        
 [88] deldir_2.0-4           tidyselect_1.2.1       miniUI_0.1.1.1        
 [91] pbapply_1.7-2          knitr_1.48             git2r_0.35.0          
 [94] gridExtra_2.3          scattermore_1.2        xfun_0.48             
 [97] matrixStats_1.4.1      stringi_1.8.4          lazyeval_0.2.2        
[100] yaml_2.3.10            evaluate_1.0.1         codetools_0.2-20      
[103] tibble_3.2.1           cli_3.6.3              uwot_0.2.2            
[106] xtable_1.8-4           reticulate_1.39.0      munsell_0.5.1         
[109] processx_3.8.4         jquerylib_0.1.4        globals_0.16.3        
[112] spatstat.random_3.3-2  png_0.1-8              spatstat.univar_3.0-1 
[115] parallel_4.4.1         ggplot2_3.5.1          dotCall64_1.2         
[118] listenv_0.9.1          viridisLite_0.4.2      scales_1.3.0          
[121] ggridges_0.5.6         leiden_0.4.3.1         purrr_1.0.2           
[124] rlang_1.1.4            cowplot_1.1.3