Structure of extrachromosomal circular DNAs generated by immunoglobulin light chain gene rearrangements

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Recombination at immunoglobulin light chain loci (kappa and lambda) can produce extrachromosomal circular DNA (eccDNA).
• Understanding the formation and characteristics of eccDNA is crucial for comprehending gene rearrangement processes in B cells.

Purpose of the Study:

• To isolate and characterize eccDNA generated from immunoglobulin kappa and lambda light chain loci in adult mouse spleen cells.
• To investigate the genomic organization and recombination features of these circular DNA molecules.

Main Methods:

• Isolation of eccDNA from adult mouse spleen cells.
• Construction and characterization of a circular DNA clone library.
• Sequence analysis of J kappa- and J lambda 1-positive clones to identify coding and signal joints.

Main Results:

• Four J kappa-positive and one J lambda 1-positive eccDNA clones were isolated and characterized.
• J kappa clones contained both coding and signal joints of V kappa-J kappa joining; the J lambda 1 clone contained a V lambda 1-J lambda 1 signal joint.
• Genomic analysis suggested excision preceded by inversion, with P dinucleotide insertion in two coding joints. Three coding joints were out-of-frame.

Conclusions:

• Kappa-positive eccDNAs are likely formed by secondary recombination events that excise non-productive primary rearrangements from the chromosome.
• These findings provide insights into the mechanisms of immunoglobulin gene rearrangement and the fate of DNA fragments generated during this process.