Stag2-mediated chromatin dynamics regulates antibody class switch recombination

Area of Science:

• Immunology
• Molecular Biology
• Epigenetics

Background:

• Class switch recombination (CSR) generates diverse antibody isotypes by altering immunoglobulin heavy chain constant regions.
• Chromatin loop extrusion is a proposed mechanism regulating CSR, involving cohesin components Stag1 and Stag2.
• The specific roles of Stag1 and Stag2 in CSR remain largely uncharacterized.

Purpose of the Study:

• To investigate the distinct roles of Stag1 and Stag2 in regulating CSR in B lymphocytes.
• To elucidate the molecular mechanisms by which Stag2 influences CSR.
• To assess the clinical relevance of Stag2 expression in relation to CSR levels.

Main Methods:

• CRISPR-Cas9 mediated gene knockout of Stag1 and Stag2 in B cells.
• Quantitative PCR and Western blotting to assess gene and protein expression.
• Chromatin conformation capture (3C) assays to measure chromatin interactions.
• Flow cytometry for B cell phenotyping and immunoglobulin isotype analysis.

Main Results:

• Stag2 deficiency significantly impaired CSR, whereas Stag1 deficiency had minimal impact.
• Loss of Stag2 reduced chromatin interactions between acceptor C_H genes and the CSR center, decreasing transcription and synapsis.
• Stag2 deficiency decreased Stag1 binding at the Igh locus, while Stag2 could compensate for Stag1 loss.
• Stag2 expression was higher than Stag1 in germinal center B cells and correlated with CSR levels in patients.

Conclusions:

• Stag2 is a specific and critical cohesin component for regulating CSR, distinct from Stag1.
• Stag2 facilitates CSR by promoting appropriate chromatin interactions and transcription at the Igh locus.
• Stag2 expression levels are a potential biomarker for CSR activity in immune responses and cancer.