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The human immunoglobulin C mu-C delta locus: complete nucleotide sequence and structural analysis
C J Word1, M B White, W A Kuziel
1Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235.
International Immunology
|January 1, 1989
Summary
Researchers sequenced the human immunoglobulin IgM (mu) and IgD (delta) heavy chain genes. They found significant differences in the intergenic region and C delta gene compared to mice, with notable human polymorphisms identified.
Area of Science:
- Immunology
- Genetics
- Molecular Biology
Background:
- The constant region genes of immunoglobulin heavy chains, specifically IgM (mu) and IgD (delta), are crucial for B cell function.
- Understanding the structural organization and evolutionary conservation of these genes provides insights into immune system development and disease.
Purpose of the Study:
- To determine the complete nucleotide sequence of the human immunoglobulin IgM (mu) and IgD (delta) heavy chain constant region genes.
- To compare the human C mu-C delta region with its murine counterpart and identify unique features or evolutionary divergences.
Main Methods:
- DNA sequencing of the approximately 20 kbp region spanning the human C mu and C delta genes.
- Analysis of DNA from B cells of patients with chronic lymphocytic leukemia producing both IgM and IgD.
Main Results:
- The nucleotide sequence of the human C mu-C delta region was fully determined.
- No rearrangement was observed in the C mu-C delta region of the leukemic B cells.
- The human C mu locus shows high conservation with mouse, except for a divergent nucleotide sequence between specific exons.
- The intergenic sequence between human C mu and C delta is larger than in mice and contains unique elements, including direct repeats and tandem copies.
- The human C delta gene has two additional exons compared to mouse C delta, but shares distal coding segments for secreted and membrane forms.
- Several polymorphisms were identified in the human intergenic region and C delta gene, but not in C mu.
Conclusions:
- The human IgM and IgD heavy chain constant region genes exhibit significant structural differences compared to mice, particularly in the intergenic region and C delta gene.
- These findings highlight evolutionary divergence in immunoglobulin gene organization between species.
- The identified human polymorphisms in the C mu-C delta region may have implications for immune responses and disease susceptibility.