RNA splicing mutation in an aberrantly rearranged immunoglobulin lambda I gene

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• The mouse myeloma cell line MOPC 315 produces immunoglobulin A (IgA) with lambda II light chains.
• A derivative, MOPC 315-26, was identified that secretes intact lambda II chains but lacks heavy chains.

Purpose of the Study:

• To investigate the genetic basis for the aberrant immunoglobulin production in the MOPC 315-26 cell line.
• To characterize the structure of the rearranged lambda I gene in this derivative.

Main Methods:

• Cloning of the rearranged lambda I gene into bacteriophage lambda DNA.
• Structural analysis of the cloned gene, focusing on the V-J joining region and surrounding sequences.

Main Results:

• The MOPC 315-26 cell line contains both a rearranged lambda II gene and a rearranged lambda I gene.
• The rearranged lambda I gene resulted from an aberrant recombination event, featuring a single base insertion at the V-J junction.
• Multiple point mutations were observed near the V-J junction, including two in the donor splice sequence for intron removal.

Conclusions:

• The aberrant recombination and subsequent mutations in the lambda I gene suggest a defect in immunoglobulin gene rearrangement.
• The identified mutations, particularly in the splice sequence, indicate that RNA transcribed from this gene would likely not undergo proper splicing.
• This molecular defect provides insight into the mechanisms of aberrant immunoglobulin gene expression in myeloma cells.