Human J chain gene. Structure and expression in B lymphoid cells.

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• The regulation of gene expression in B cell development is crucial for immune function.
• The J chain protein plays a role in immunoglobulin polymerization.

Purpose of the Study:

• To obtain and characterize the genomic DNA clone encoding the human J chain protein.
• To analyze J chain gene expression in human B cell development.
• To investigate the relationship between J chain expression and immunoglobulin secretion.

Main Methods:

• Genomic DNA cloning and nucleotide sequencing of the human J chain gene.
• RNA detection using gene probes in human pre-B and B cell lines.
• S1 nuclease protection assays to determine the 3' end of the J chain gene.

Main Results:

• A 137 amino acid sequence for the mature human J chain protein was determined.
• J chain RNA was detected in pre-B and B lymphocytes, but expression is not exclusively linked to IgM or IgA secretion.
• The 3' end of the J chain gene was identified, revealing homology to mouse J chain cDNA.

Conclusions:

• Human J chain gene expression occurs in B lymphocytes and is not strictly tied to IgM or IgA secretion.
• The findings do not support the hypothesis that J chain synthesis precedes mu chain synthesis in B cell differentiation.
• The characterized human J chain gene provides a basis for further studies on its regulation and function.