Cell and tissue-specific glycosylation pathways and transcriptional regulation informed by single-cell transcriptomics

Abstract While single cell studies have made significant impact in various subfields of biology, they lag behind in the Glycosciences. To address this gap, we analyzed glycogene expressions in the Tabula Sapiens (TS) dataset containing ∼500,000 human cells from various tissues and cell types using a recently developed glycosylation-specific gene ontology (GlycoEnzOnto). At the median sequencing (count) depth of the dataset, ∼40-50 out of 400 glycogenes were detected in individual cells. Upon increasing the sequencing depth, the number of detectable glycogenes saturates at ∼200 glycogenes, suggesting that the average human cell expresses ∼50% of the glycogene repertoire. Hierarchies in glycogene and glycopathway expressions at single-cell level emerged from our analysis: nucleotide-sugar synthesis and transport exhibited the highest gene expressions, followed by genes for core enzymes, glycan modification and extensions, and finally terminal modifications. Notably, the same cell types showed variable glycopathway expressions based on their organ or tissue origin, suggesting nuanced, cell- and tissue-specific glycosylation patterns. Probing deeper into the transcription factors of glycogenes, we identified distinct transcriptional regulatory modules controlling terminal modifications versus other glycopathways. Finally, we developed webtools for exploring glycogene and glycopathway expressions, and transcription factors regulating glycosylation in different human cell/tissue types. Overall, the study presents an overview of glycosylation related genes and pathways across multiple human organ systems.