SpatialNF

Spatial transcriptomics NextFlow pipelines

SpatialNF is a collection of Nextflow DSL2 pipelines for analyzing spatial transcriptomics data.

We offer pipelines for:

• basic processing of spatial transcriptomics data
• identification of spatially variable genes
• segmentation-free analysis
• label-transfer from single cell RNAseq to spatial transcriptomics data

SpatialNF is implemented in the VSN-framework: https://github.com/vib-singlecell-nf/vsn-pipelines.

Supported data

SpatialNF can be used for FISH-based data like MERFISH or Molecular cartography and sequencing-based data like 10X Visium. As we do not offer automated segmentation pipelines within SpatialNF, FISH-based data has to be segmented in advance and converted into a supported data format.

For all data types, input data should contain raw counts. SpatialNF supports the following data formats:

Spatial CSV file formats

A coordinate CSV file coords.csv contains three columns: an ID for the parent_cell, X and Y coordinates:

parent_cell,X,Y
1,1952.8673508171798,3899.5127328012163
2,1946.5086419753086,4047.905679012346
3,1952.432242022379,3966.5445503522587
4,1963.7581227436824,4089.649097472924
5,1988.4492753623188,4047.0072463768115
...

A count matrix CSV file matrix.csv contains a column with parent_cell IDs matching IDs in the coords.csv and columns for each transcript:

parent_cell,Act79B,Act88F,AkhR,AstC-R2,Awh,CCAP-R,CG32121,Cralbp,FASN2
1,0,0,1,0,0,0,0,0,0
2,0,0,0,0,0,0,0,0,31
3,0,0,1,0,0,0,0,0,34
4,0,0,0,0,0,0,0,0,7
5,0,0,0,0,0,0,0,0,1
7,0,0,0,0,0,0,0,0,4
8,0,0,0,0,0,0,0,0,1
9,0,0,2,0,0,0,0,0,0
11,0,0,0,0,0,0,0,1,0
...

Coordinates CSV file formats

Coordinates CSV files contain the coordinates of each detected transcript per row. The should include a header, x and y columns.

gene,x,y
Rora,755,935
Rora,829,574
Rora,1071,1941
...
Slc17a7,2110,1458
Slc17a7,2110,1873
Slc17a7,2111,302

Counts per gene will be collated in a grid. The bin size can be speficied with binsize.

Pipelines for basic processing

These pipelines assemble spatial transcriptomics data into AnnData and SCope (https://scope.aertslab.org) compatible loom files. They perform QC, filtering and clustering of the data

When running multi_sample pipelines, add file_concatenator to utils in the config file to combine the input files:

   utils {
      ...
      file_concatenator {
         join = 'outer'
         off = 'h5ad'
      }
      ...
   }

Pipelines for identifying spatially variable genes

For detecting spatially variable genes, we implemented a pipeline using SpatialDE inlcuding their AEH approach for identifying spatial patterns.

Pipelines for label-transfer from scRNAseq

For label-transfer from scRNA-seq to spatial transcriptomics data, we offer pipelines for spot-based or segmented data using Tangram and SpaGE. In addition, for segmentation-free label-transfer, SpatialNF contains a spage2vec pipeline. Optionally, Squidpy can be used for computing enrichments of co-localized labels. And Tangram can also be used to project gene expression from single cell data which will overwrite the count matrix.

The reference scRNAseq data should be a processed and filtered AnnData object .h5ad and contain raw counts, as well as the annotation as obs entry.

Running SpatialNF pipelines

Initial configs can be generated with a nextflow config command. See the SpatialNF/examples folder for pipeline configuration files. For example, to generate a config for mouse 10X spaceranger data and the single_sample_spatialde workflow:

nextflow config SpatialNF/main.nf \
    -profile mm10,tenx,singularity,single_sample,spatialde > single_sample_spatialde_aeh.config

After changing file names and parameters in the config, the pipeline can be run with the following command:

nextflow -C single_sample_spatialde_aeh.config run SpatialNF/main.nf \
   -entry single_sample_spatialde \
   -with-report report.html \
   -with-trace \
   -resume

Output data

SpatialNF generates AnnData .h5ad and SCope (https://scope.aertslab.org) compatible loom .loom files. Output data are written to out/data/ including intermediate data files out/data/intermediate/. Reports are stored as Jupyter notebooks and HTML files in out/notebooks/.

Resource management

SpatialNF pipelines can be run locally or each step can be seperately submitted to as a job to a HPC. Resource limits and parameters can be specified in the process section of a config file.

Prerequisites

SpatialNF requires singularity to run Docker containers and Nextflow. Currently, only Nextflow version 21.04 is supported. A compatible Netxtflow binary can be downloaded here: https://github.com/nextflow-io/nextflow/releases/download/v21.04.0/nextflow-21.04.0-all

Notes on Docker images

We are currenty providing Docker images at Docker hub on a free license. In case these Docker images become unavailable in the future, they can be rebuild from the Dockerfile in the workflow specific subfolders in the src directory.

References

All pipelines are using SCANPY:

Wolf, Angerer, & Theis (2018). SCANPY: large-scale single-cell gene expression data analysis. Genome Biol., 19:1-5. https://github.com/scverse/scanpy

SpatialDE:

Svensson Teichmann & Stegle (2018). SpatialDE: identification of spatially variable genes. Nat. Methods, 15:343-346) https://github.com/Teichlab/SpatialDE

Tangram:

Biancalani, Scalia, Buffoni, Avasthi, Lu, Sanger, ... & Regev (2021). Deep learning and alignment of spatially resolved single-cell transcriptomes with Tangram. Nat. Methods, 18:1352-1362. https://github.com/broadinstitute/Tangram

SpaGE:

Abdelaal, Mourragui, Mahfouz, & Reinders (2020). SpaGE: spatial gene enhancement using scRNA-seq. Nucleic Acids Res., 48:e107-e107. https://github.com/tabdelaal/SpaGE

spage2vec:

Partel & Waehlby (2021). Spage2vec: Unsupervised representation of localized spatial gene expression signatures. FEBS J., 288:1859-1870. https://github.com/wahlby-lab/spage2vec

Squidpy:

Palla, Spitzer, Klein, Fischer, Schaar, Kuemmerle, ... & Theis (2022). Squidpy: a scalable framework for spatial omics analysis. Nat. Methods, 19:171-178. https://github.com/scverse/squidpy