Library Size in spatial-ATAC-seq: Technical Confounder or Biology?

Spatially resolved assay for transposase-accessible chromatin with sequencing (spATAC-seq) is an emerging technology for studying spatial variation in gene regulatory landscapes within tissues. Current analysis pipelines commonly apply library size normalization, assuming that variation in library size across cells represents a technical confounder rather than biological signal. While recent studies have shown that library size can confound biological interpretation in spatial transcriptomics, its impact in spATAC-seq remains poorly understood. Here, we show that library size in spATAC-seq data is biologically informative and that standard normalization methods can obscure important biological signals and hinder downstream analyses. These findings underscore the need for caution and for the development of improved approaches to address library size in spATAC-seq analysis.