CtIP promotes microhomology-mediated alternative end joining during class-switch recombination

Area of Science:

• Molecular Biology
• Immunology
• DNA Repair

Background:

• Class-switch recombination (CSR) is crucial for adaptive immunity, involving DNA double-strand breaks (DSBs) in the immunoglobulin heavy chain (Igh) locus.
• Two main DNA repair pathways, canonical nonhomologous end joining (C-NHEJ) and alternative nonhomologous end joining (A-NHEJ), are implicated in resolving these DSBs during CSR.

Purpose of the Study:

• To investigate the role of the DNA end-processing factor CtIP in A-NHEJ during CSR.
• To determine if CtIP is involved in microhomology-directed ligation.
• To explore the interplay between CtIP, C-NHEJ, and A-NHEJ in the context of CSR.

Main Methods:

• Depletion of CtIP and Ku70 using molecular biology techniques.
• Analysis of DNA ligation junctions during CSR.
• Biochemical assays to detect CtIP binding to switch-region DNA.

Main Results:

• CtIP is required for microhomology-directed A-NHEJ during CSR.
• Microhomology-mediated end joining, even when C-NHEJ is impaired, depends on CtIP.
• CtIP binding to switch-region DNA is dependent on activation-induced cytidine deaminase.

Conclusions:

• CtIP is a key component of microhomology-dependent A-NHEJ.
• A previously unrecognized role for microhomology-mediated end joining exists in a C-NHEJ-proficient environment during CSR.
• These findings advance our understanding of DNA repair mechanisms in immunoglobulin gene diversification.