Reassessment of the role of Mut S homolog 5 in Ig class switch recombination shows lack of involvement in cis- and trans-switching.
When B cells are activated after immunization or infection, they exchange the gene encoding the Ig H chain C region by class switch recombination (CSR). CSR generally occurs by an intrachromosomal deletional recombination within switch (S) region sequences. However, approximately 10% of CSR events occur between chromosome homologs (trans- or interallele CSR), suggesting that the homologous chromosomes are aligned during CSR. Because the Mut S homolog 4 (Msh4) and Msh5 bind to Holliday junctions and are required for homologous recombination during meiosis in germ cells, we hypothesized these proteins might be involved in trans-chromosomal CSR (trans-CSR). Indeed, Msh4-Msh5 has recently been suggested to have a role in CSR. However, we find a large variety of alternative splice variants of Msh5 mRNA in splenic B cells rather than the full-length form found in testis. Most of these mRNAs are unlikely to be stable, suggesting that Msh5 might not be functional. Furthermore, we find that msh5 nullizygous B cells undergo CSR normally, have unaltered levels of trans-CSR, normal levels of DNA breaks in the Smu region, and normal S-S junctions. We also show that the S-S junctions from cis- and trans-CSR events have similar lengths of junctional microhomology, suggesting trans-CSR occurs by nonhomologous end joining as does intrachromosome (cis)-CSR. From these data, we conclude that Msh5 does not participate in CSR.
Guikema
Jeroen E J
JE
Department of Molecular Genetics and Microbiology, Program in Immunology and Virology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
Schrader
Carol E
CE
Leus
Niek G J
NG
Ucher
Anna
A
Linehan
Erin K
EK
Werling
Uwe
U
Edelmann
Winfried
W
Stavnezer
Janet
J
D017398:Alternative Splicing / Q000235:genetics / Q000276:immunology; D019943:Amino Acid Substitution / Q000235:genetics / Q000276:immunology; D000818:Animals; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D012313:RNA / Q000096:biosynthesis; D011995:Recombination, Genetic / Q000276:immunology*; D012689:Sequence Homology, Nucleic Acid; D013154:Spleen / Q000166:cytology / Q000276:immunology / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C512847:Msh5 protein, mouse; D012313:RNA