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Enhanced evolvability in immunoglobulin V genes under somatic hypermutation
L G Cowell1, H J Kim, T Humaljoki
1Biomathematics Graduate Program, Department of Statistics, North Carolina State University, Raleigh, NC 27695-8203, USA.
Journal of Molecular Evolution
|June 16, 1999
Summary
Mutations in immunoglobulin genes are not random. This study shows mutations preferentially target complementarity-determining regions (CDRs) over framework regions (FRs), supporting a genetic control mechanism.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Darwinian theory posits mutations occur non-anticipatorily.
- Immunoglobulins (antibodies) acquire mutations during infection for improved antigen binding.
- Hypotheses suggest differential mutation rates in immunoglobulin regions (CDRs vs. FRs) due to genetic control.
Purpose of the Study:
- To investigate whether mutation rates differ between complementarity-determining regions (CDRs) and framework regions (FRs) in human immunoglobulin genes.
- To provide direct evidence for preferential mutation targeting in CDRs.
Main Methods:
- Analysis of 115 nonproductively rearranged human immunoglobulin sequences.
- Examination of mutation patterns in unexpressed genes to reflect inherent mutation biases.
- Statistical analysis (chi-squared test) to compare mutation frequencies in CDRs versus FRs.
Main Results:
- Unexpressed immunoglobulin genes showed a significantly higher number of mutations in the complementarity-determining regions (CDRs) compared to the framework regions (FRs).
- These findings reflect inherent, unselected mutation biases within the immunoglobulin gene sequences.
Conclusions:
- The results provide direct evidence supporting the hypothesis that mutations are preferentially targeted into the CDRs of immunoglobulin genes.
- This preferential targeting suggests an underlying genetic control mechanism that modulates mutation frequency based on sequence location.