Somatic recombination

Somatic recombination, as opposed to the genetic recombination that occurs in meiosis, is an alteration of the DNA of a somatic cell that is inherited by its daughter cells. The term is usually reserved for large-scale alterations of DNA such as chromosomal translocations and deletions and not applied to point mutations. Somatic recombination occurs physiologically in the assembly of the B cell receptor and T-cell receptor genes (V(D)J recombination),[1] as well as in the class switching of immunoglobulins.[2] Somatic recombination is also important in the process of carcinogenesis.[3]

In neurons of the human brain, somatic recombination occurs in the gene that encodes the amyloid precursor protein APP.[4] Neurons from individuals with sporadic Alzheimer's disease show greater APP gene diversity due to somatic recombination than neurons from healthy individuals.[4]

Plants

See also: Bud sport

Intrachromosomal homologous recombination in Arabidopsis thaliana plants was found to occur in all organs examined from the seed stage to the flowering stage of somatic plant development.[5] Recombination frequencies were typically in the range of 10^−6 to 10^−7 events per genome.[5] A. thaliana mutants selected for hypersensitivity to X-irradiation also proved to be simultaneously hypersensitive to the DNA damaging agents mitomycin C and/or methyl methanesulfonate.[6] The mutants were also deficient in somatic homologous recombination.[6] These findings suggest that repair of some types of DNA damage requires a recombinational process that was defective in the mutants studied. In nature, plants are continuously exposed to UV-B (280–320 nm) radiation, a component of sunlight that damages the DNA of somatic cells.[7] Cyclobutane pyrimidine dimers (CPD) are a type of damage induced by UV-B. In A. thaliana, homologous recombination appears to be directly involved in repairing CPD damage.[7]

References

1. Gellert M (1992). "Molecular analysis of V(D)J recombination". Annu Rev Genet. 26: 425–46. doi:10.1146/annurev.ge.26.120192.002233. PMID 1482120.
2. Hein K, Lorenz MG, Siebenkotten G, et al. (1998). "Processing of switch transcripts is required for targeting of antibody class switch recombination". J Exp Med. 188 (12): 2369–74. doi:10.1084/jem.188.12.2369. PMC 2212419. PMID 9858523.
3. Ramel C, Cederberg H, Magnusson J, et al. (1996). "Somatic recombination, gene amplification and cancer". Mutat Res. 353 (1–2): 85–107. Bibcode:1996MRFMM.353...85R. doi:10.1016/0027-5107(95)00243-x. PMID 8692194.
4. Lee MH, Siddoway B, Kaeser GE, Segota I, Rivera R, Romanow WJ, Liu CS, Park C, Kennedy G, Long T, Chun J (November 2018). "Somatic APP gene recombination in Alzheimer's disease and normal neurons". Nature. 563 (7733): 639–645. Bibcode:2018Natur.563..639L. doi:10.1038/s41586-018-0718-6. PMC 6391999. PMID 30464338.
5. Swoboda P, Gal S, Hohn B, Puchta H (January 1994). "Intrachromosomal homologous recombination in whole plants". EMBO J. 13 (2): 484–9. doi:10.1002/j.1460-2075.1994.tb06283.x. PMC 394832. PMID 8313893.
6. Masson JE, Paszkowski J (October 1997). "Arabidopsis thaliana mutants altered in homologous recombination". Proc Natl Acad Sci U S A. 94 (21): 11731–5. Bibcode:1997PNAS...9411731M. doi:10.1073/pnas.94.21.11731. PMC 23619. PMID 9326679.
7. Ries G, Buchholz G, Frohnmeyer H, Hohn B (November 2000). "UV-damage-mediated induction of homologous recombination in Arabidopsis is dependent on photosynthetically active radiation". Proc Natl Acad Sci U S A. 97 (24): 13425–9. Bibcode:2000PNAS...9713425R. doi:10.1073/pnas.230251897. PMC 27240. PMID 11069284.