Biologically indeterminate yet ordered promiscuous gene expression in single medullary thymic epithelial cells

Area of Science:

• Immunology
• Cell Biology
• Genomics

Background:

• Medullary thymic epithelial cells (mTEC) are crucial for central T-cell tolerance.
• mTEC express a wide array of tissue-restricted antigens (TRAs) through promiscuous gene expression (PGE).
• Understanding mTEC heterogeneity and PGE regulation is vital for immune system development.

Purpose of the Study:

• To investigate the diversity and transcriptional regulation of mTEC.
• To determine if promiscuous gene expression (PGE) in mTEC is stochastic or coordinated.
• To characterize novel mTEC subsets and their functional implications.

Main Methods:

• Single-cell RNA sequencing of 6,894 mTEC.
• Bioinformatic analysis to identify distinct mTEC subpopulations.
• Analysis of gene co-expression modules and spatial distribution of specific TRA-expressing cells.

Main Results:

• Identified 15 distinct mTEC subpopulations with unique maturational trajectories.
• Discovered novel mTEC subsets, including chemokine-expressing and ciliated TEC.
• Defined 50 gene co-expression modules, indicating coordinated PGE independent of chromosomal location or pathway.
• Observed random spatial distribution of TSPAN8+ and GP2+ mTEC within thymic medullary islands.

Conclusions:

• Promiscuous gene expression (PGE) in mTEC is an ordered, coordinated process, not stochastic.
• The combination of ordered co-expression and random spatial distribution of TRAs optimizes T-cell education.
• Further research is needed to elucidate the mechanisms governing ordered PGE in mTEC.