title: An extrachromosomal switch recombination substrate reveals kinetics and substrate requirements of switch recombination in primary murine B cells.
abstract: Ig class switch recombination occurs in B lymphocytes upon activation, and is targeted to distinct switch (S) regions by cytokine-mediated induction of switch transcripts spanning the entire S region and the adjacent constant region gene segments. Using a novel type of switch recombination substrate, constructed according to the intron-exon structure of the IgH locus, but with heterologous elements, we here have tested the structural requirements for targeting and the kinetics of switch recombination in activated primary murine B cells. When transfected at various times after activation, up to 10% of the transfected B cells perform recombination of the substrate within 12 h. Switch recombination in primary B cells is restricted to the first 72 h after onset of activation, then rapidly decreases to background levels, as obtained in plasmacytoma cells or with substrates carrying no S region sequences. In terms of structural requirements, switch recombination is targeted to any transcription unit that contains an intronic S region and depends on processing of the primary transcript by splicing.
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D006183:H-2 Antigens / Q000032:analysis; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation; D051379:Mice; D008807:Mice, Inbred BALB C; D012326:RNA Splicing; D011995:Recombination, Genetic; D014162:Transfection