title: A reappraisal of evidence for probabilistic models of allelic exclusion.
abstract: B cell development requires the coordinated rearrangement of Ig heavy (IgH) and light chain loci (IgL). Most mature B cells express a single B cell receptor of unique specificity, and a central question in immunology concerns the mechanisms that prevent the productive rearrangement of >1 IgH and IgL allele per cell. Probabilistic models of allelic exclusion maintain that simultaneous rearrangement of both alleles is rare, because the likelihood of undergoing rearrangement is low for a given Ig allele. Strong support for this idea came from studies in which a GFP marker was inserted into the Igk locus. In this system, the probability of high-level germ-line transcription and subsequent locus rearrangement appeared to be low in pre-B cells. Readdressing the validity of GFP expression as a reporter for the level of germ-line transcription, we found a striking discordance between GFP transcript and protein levels at the pre-B cell stage, which is explained at least in part by the developmentally regulated usage of 2 alternative Igk-J germ-line promoters. These results question the validity of the kappa-GFP system as evidence for probabilistic models of allelic exclusion.
authors.affiliation: Lymphocyte Development Group and ES Cell and Transgenics Facility, Medical Research Council Clinical Sciences Centre, Imperial College London, Du Cane Road, London W12 0NN, United Kingdom.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Taylor
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Cobb
authors.forename: Ludovica
authors.initials: L
authors.lastname: Bruno
authors.forename: Zoe
authors.initials: Z
authors.lastname: Webster
authors.forename: Amanda G
authors.initials: AG
authors.lastname: Fisher
authors.forename: Matthias
authors.initials: M
authors.lastname: Merkenschlager
mesh_terms: D000483:Alleles; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D001854:Bone Marrow Cells; D002478:Cells, Cultured; D015321:Gene Rearrangement; D049452:Green Fluorescent Proteins; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007147:Immunoglobulin Light Chains / Q000235:genetics; D007136:Immunoglobulins / Q000235:genetics; D051379:Mice; D015233:Models, Statistical; D011947:Receptors, Antigen, B-Cell / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: C014609:IgK; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007136:Immunoglobulins; D011947:Receptors, Antigen, B-Cell; D049452:Green Fluorescent Proteins