Aberrantly resolved RAG-mediated DNA breaks in Atm-deficient lymphocytes target chromosomal breakpoints in cis

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Canonical chromosomal translocations are hallmarks of lymphoid malignancies, often arising from double-strand breaks (DSBs) at antigen receptor loci and oncogenes.
• Recombinase activating gene (RAG) proteins generate DSBs during lymphocyte development, which are typically resolved correctly.
• Aberrant resolution of RAG DSBs in ataxia telangiectasia mutated (ATM)-deficient lymphocytes leads to translocations and predisposes to lymphoid malignancies.

Purpose of the Study:

• To investigate the breakpoint targets of aberrantly resolved RAG DSBs in ATM-deficient lymphocytes.
• To minimize selection biases in analyzing these lesions and understand their formation mechanisms.
• To identify non-selected chromosomal lesions formed by RAG DSBs in ATM-deficient cells.

Main Methods:

• Isolation of a large cohort of breakpoint targets from aberrantly resolved RAG DSBs in Atm-deficient lymphocytes.
• Utilizing an approach that minimizes selection biases to study non-selected lesions.
• Analysis of breakpoint target selection in RAG DSB resolution.

Main Results:

• Frequently, the breakpoint targets for aberrantly resolved RAG breaks are other DSBs.
• These non-selected lesions show a bias for using breakpoints in cis, leading to small chromosomal deletions.
• In contrast, breakpoints in trans, which form chromosomal translocations, were less common.

Conclusions:

• Aberrantly resolved RAG DSBs in ATM-deficient lymphocytes preferentially target other DSBs.
• The mechanism favors intrachromosomal deletions (in cis) over interchromosomal translocations (in trans) when selection is minimized.
• This finding provides a new perspective on the formation of chromosomal abnormalities in lymphoid malignancies.