Using In Silico Pseudobulk Differential Expression and Trajectory Analysis of Single Cell RNA Sequencing to Reveal Stem Cell State Transitions in Colonic Inflammation.

Colonic inflammation induces profound alterations in the intestinal mucosa that are evident at both macroscopic and microscopic levels, including disruption of epithelial barrier integrity, crypt fission, and immune cell infiltration. Recent advances in single-cell and spatial RNA sequencing have greatly expanded our understanding of the cellular diversity of the colonic mucosa, enabling pathological features to be directly linked to underlying cellular and molecular mechanisms. This chapter demonstrates the application of single-cell RNA sequencing (scRNA-seq) analysis techniques to interrogate stem cell dynamics in the context of inflammatory bowel disease. Using publicly available datasets, the chapter provides a step-by-step workflow implemented in Python, covering data access, loading, integration of multiple datasets, and initial preprocessing. Cells are mapped to large single-cell atlas references to infer cell identities, followed by a pseudobulk analysis strategy to assess inflammation-associated changes in cell phenotypes. Finally, trajectory inference approaches are applied to explore potential mechanisms governing the specification and modulation of key cell types during inflammation. Accompanied by an online resource containing fully annotated scripts, this chapter offers guided instruction in contemporary scRNA-seq analysis workflows. It is intended as an accessible introduction for researchers seeking to develop practical skills in single-cell data analysis that can be readily applied to their own biological questions.