Spatial transcriptome sequencing of FFPE tissues at the cellular level

Formalin-fixed paraffin-embedded (FFPE) tissues are the most abundant archivable specimens in clinical tissue banks, but unfortunately incompatible with single-cell level whole transcriptome sequencing due to RNA degradation in storage and RNA damage in extraction. We developed an in-tissue barcoding approach namely DBiT-seq for spatially revolved whole transcriptome sequencing at cellular level, which required no tissue dissociation or RNA exaction, thus potentially more suited for FFPE samples. Herein, we demonstrated spatial transcriptome sequencing of embryonic and adult mouse FFPE tissue sections at cellular level (25m pixel size) with high coverage (>1,000 genes per pixel). Spatial transcriptome of an E10.5 mouse embryo identified all major anatomical features in the brain and abdominal region. Integration with singlecell RNA-seq data for cell type identification indicated that most tissue pixels were dominated by single-cell transcriptional phenotype. Spatial mapping of adult mouse aorta, atrium, and ventricle tissues identified the spatial distribution of a variety of cell types. Spatial transcriptome sequencing of FFPE samples at cellular level may provide enormous opportunities in a wide range of biomedical research. It may allow us to exploit the huge resource of clinical tissue specimens to study human disease mechanisms and discover tissue biomarkers or therapeutic targets.