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Mitotic recombination in germ cells generated two major histocompatibility complex mutant genes shown to be identical
Abstract:
RNA sequencing represents a major procedural simplification for nucleotide sequence analysis of a transcribed gene. Using newly adapted mRNA and cDNA sequencing procedures, we have sequenced 855 nucleotides of Kbm9 mRNA, corresponding to the codons for the aminoterminal 285 amino acids. The inferred DNA sequence of the Kbm9 gene differs from the parental Kb sequence by single nucleotide alterations in each of codons 116 and 121, resulting in Tyr----Phe and Cys----Arg substitutions, respectively. The Kbm9 sequence is identical to that of another independently arising MHC mutant gene, Kbm6. As both the Kbm9 and Kbm6 genes were generated by recombination between the Kb and Q4 genes, our data indicate that the identical genetic interactions have occurred at least twice. The relatively large extent of identity between Q4 and Kb may be responsible for frequent recombination between the two genes. The parents of the original bm9 mutant mice had five identical mutant offspring, which can be explained by mitotic recombination in the germ cells, producing gonadal mosaicism in the C57BL/6 mother. Thus, mitotic recombination, and not meiotic recombination, appears to be responsible for the formation of at least some of the Kb mutants. Such a mechanism probably plays a major role in the generation of diversity in the major histocompatibility complex.
Insights
RNA sequencing simplifies gene analysis. Researchers found identical mutations in Kbm9 and Kbm6 genes, suggesting frequent recombination and a key role for mitotic recombination in major histocompatibility complex diversity.
Area of Science:
- Molecular Biology
- Immunogenetics
- Genomics
Background:
- The Major Histocompatibility Complex (MHC) plays a crucial role in immune responses.
- Understanding mutations within MHC genes is vital for comprehending immune diversity.
Purpose of the Study:
- To analyze the nucleotide sequence of the Kbm9 gene and compare it to the parental Kb sequence.
- To investigate the genetic mechanisms responsible for the generation of MHC mutants.
Main Methods:
- RNA sequencing of Kbm9 mRNA.
- cDNA sequencing procedures.
- Comparative sequence analysis of Kbm9, Kb, and Q4 genes.
Main Results:
- Sequenced 855 nucleotides of Kbm9 mRNA, encoding 285 amino acids.
- Identified single nucleotide alterations in codons 116 and 121 of Kbm9, leading to amino acid substitutions.
- Kbm9 sequence is identical to Kbm6, indicating recurrent genetic events.
- Recombination between Kb and Q4 genes is proposed as the mechanism for Kbm9 and Kbm6 generation.
- Mitotic recombination in germ cells is suggested as the cause for multiple identical mutants in offspring.
Conclusions:
- Identical MHC mutant genes (Kbm9 and Kbm6) arose from similar recombination events between Kb and Q4 genes.
- Frequent recombination is likely due to sequence identity between Q4 and Kb.
- Mitotic recombination, not meiotic, is implicated in the formation of certain Kb mutants.
- Mitotic recombination is a significant factor in generating diversity within the major histocompatibility complex.