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Joined 2026-09-21 Message
Incoming links: Slide-seq
Past exam of the systems biology course of the University of Cambridge 2024 Paper 2 2 ii Solution 2026-10-20
The central principle is to attach a recoverable spatial address to an RNA-derived molecule before the tissue's positional organization is destroyed. After sequencing, each read identifies both a transcript and a capture location.
In the original array-based spatial transcriptomics method, a thin tissue section is placed on a slide carrying spatially indexed capture primers. The tissue is imaged for histology, then permeabilized. Polyadenylated messenger RNA binds the oligo(dT) region of the primers and is copied by reverse transcription. The resulting cDNA carries the positional barcode. Sequencing identifies the expressed gene, and a barcode lookup places its counts back on the tissue image. The first published array used approximately capture features, so a feature could contain contributions from several cells; it was not a single-cell measurement by construction.[ref]
Visualization and analysis of gene expression in tissue sections by spatial transcriptomics by Patrik L. Ståhl and others. pp. 78–80, spatially localized cDNA synthesis, positional barcodes and array features
Slide-seq applies the same addressing idea using a dense monolayer of roughly barcoded beads. The bead barcode–position map is decoded in advance. A tissue section is transferred onto the beads, released RNA is captured, and the sequenced molecular addresses recover the bead-level expression map. This gives much finer spatial sampling than the original coarse array, although RNA capture efficiency and assignment to individual cells remain limiting.[ref]
Slide-seq: A scalable technology for measuring genome-wide expression at high spatial resolution by Samuel G. Rodriques and others. pp. 1463–1465, bead puck construction, positional decoding and RNA capture
Some assays also incorporate a unique molecular identifier so that amplified reads from one captured molecule can be collapsed, reducing polymerase chain reaction duplication bias. Spatial barcodes identify capture locations; unique molecular identifiers identify molecules within those locations. Neither alone supplies cell boundaries.
For either method, align the coordinate map with histology, account for capture efficiency and background, and use independent tissue specimens as biological replicates. A smaller capture feature improves sampling granularity but does not guarantee equal effective spatial resolution or a pure single-cell transcriptome: tissue thickness, diffusion and mixed cell boundaries still matter.