Mitotic recombination between homologous chromosomes generates H-2 somatic cell variants in vitro | JoVE Visualize

Mitotic recombination between homologous chromosomes generates H-2 somatic cell variants in vitro

Proceedings of the National Academy of Sciences of the United States of America|March 1, 1987

View abstract on PubMed

Summary

Researchers identified a cell variant lacking specific H-2Dd and H-2Ld molecules. This finding suggests mitotic recombination in somatic cells may be common, potentially leading to homozygous deleterious alleles.

Area of Science:

Immunogenetics
Molecular Biology
Somatic Cell Genetics

Background:

The H-2 complex, crucial for immune responses, is located on mouse chromosome 17.
Understanding gene regulation and mutation in somatic cells is vital for immunology and cancer research.
F1 hybrid cell lines provide a model for studying allelic interactions and genetic events.

Purpose of the Study:

To investigate the genetic mechanisms behind the spontaneous loss of H-2Dd and H-2Ld gene expression in a somatic cell variant.
To explore the potential role of mitotic recombination in generating genetic diversity in somatic cells.
To characterize the genetic makeup of a variant cell line with altered H-2 antigen expression.

Main Methods:

Immunoselection was used to isolate a variant cell clone from an (H-2b X H-2d)F1 cell line.
Southern blot analysis was performed to assess gene presence and copy number at H-2 loci.
Karyotype analysis was conducted to examine chromosomal integrity, specifically for deletions on chromosome 17.

Main Results:

A variant clone lacking H-2Dd and H-2Ld molecules, but retaining H-2Kb, H-2Db, and H-2Kd, was successfully isolated.
The variant showed heterozygosity at H-2K, I, and S loci but had lost H-2Dd and H-2Ld genes.
Quantitative Southern blot revealed homozygosity for the H-2Db gene in the variant, suggesting recombination between chromosome 17 homologues.

Conclusions:

Mitotic recombination between homologous chromosomes, though historically difficult to demonstrate, appears to be a significant mechanism for generating genetic variation in somatic cells.
This recombination event can lead to the loss of specific genes and homozygosity for others, as observed with the H-2Dd, H-2Ld, and H-2Db genes.
The findings imply that such recombination in vivo could contribute to the emergence of homozygous cells, potentially including those with deleterious alleles, even in heterozygous individuals.