Mouse immunoglobulin D: messenger RNA and genomic DNA sequences

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Immunoglobulin D (IgD) plays a crucial role in B cell development and function.
• Understanding IgD structure is key to deciphering its biological roles.
• Plasmacytoma tumors provide a model for studying aberrant immunoglobulin gene expression.

Purpose of the Study:

• To elucidate the molecular structure of mouse immunoglobulin D from a plasmacytoma tumor.
• To compare the tumor-derived IgD structure with the normal mouse gene sequence.
• To identify potential functional implications of structural variations in the IgD delta chain.

Main Methods:

• DNA sequencing of the mouse immunoglobulin D gene from a plasmacytoma tumor.
• Comparative analysis of the tumor gene sequence with the normal mouse gene.
• Homology considerations and sequence analysis to identify protein domains and regions.

Main Results:

• The tumor delta chain exhibits an unusual structure with two constant (C) domains (C delta 1 and C delta 3) separated by a hinge region lacking cysteine residues.
• A 26-amino acid segment (C delta DC) at the carboxyl end is coded by a downstream exon, potentially conferring membrane-binding function.
• A fifth potential exon (C delta AC) adjacent to C delta 3 could code for an additional 49 amino acids.

Conclusions:

• The identified structural anomalies in the tumor IgD delta chain suggest aberrant gene expression.
• The findings point to the existence of biologically significant, potentially novel, forms of IgD.
• The unusual structure, particularly the distally coded segment, may indicate alternative functional roles for IgD in B cells.