title: Tracking germinal center B cells expressing germ-line immunoglobulin gamma1 transcripts by conditional gene targeting.
abstract: Germinal centers (GCs) represent the main sites for the generation of high-affinity, class-switched antibodies during T cell-dependent antibody responses. To study gene function specifically in GC B cells, we generated Cgamma1-cre mice in which the expression of Cre recombinase is induced by transcription of the Ig gamma1 constant region gene segment (Cgamma1). In these mice, Cre-mediated recombination at the fas, Igbeta, IgH, and Rosa26 loci occurred in GC B cells as early as 4 days after immunization with T cell-dependent antigens and involved >85% of GC B cells at the peak of the GC reaction. Less than 2% of IgM(+) B cells showed Cre-mediated recombination. These cells carried few Ig somatic mutations, expressed germ-line Cgamma1- and activation-induced cytidine deaminase-specific transcripts and likely include GC B cell founders and/or plasma cell precursors. Cre-mediated recombination involved most IgG1, but also a fraction of IgG3-, IgG2a-, IgG2b-, and IgA-expressing GC and post-GC B cells. This result indicates that a GC B cell can transcribe more than one downstream C(H) gene before undergoing class switch recombination. The efficient induction of Cre expression in GC B cells makes the Cgamma1-cre allele a powerful tool for the genetic analysis of these cells, as well as, in combination with a suitable marker for Cre-mediated recombination, the tracking of class-switched memory B and plasma cells in vivo. To expedite the genetic analysis of GC B cells, we have established Cgamma1-cre F(1) embryonic stem cells, allowing further rounds of gene targeting and the cloning of compound mutants by tetraploid embryo complementation.
authors.affiliation: CBR Institute for Biomedical Research, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA. stefano.casola@ifom-ieo-campus.it
authors.forename: Stefano
authors.initials: S
authors.lastname: Casola
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cattoretti
authors.forename: Nathalie
authors.initials: N
authors.lastname: Uyttersprot
authors.forename: Sergei B
authors.initials: SB
authors.lastname: Koralov
authors.forename: Jane
authors.initials: J
authors.lastname: Seagal
authors.forename: Jane
authors.initials: J
authors.lastname: Segal
authors.forename: Zhenyue
authors.initials: Z
authors.lastname: Hao
authors.forename: Ari
authors.initials: A
authors.lastname: Waisman
authors.forename: Angela
authors.initials: A
authors.lastname: Egert
authors.forename: Dvora
authors.initials: D
authors.lastname: Ghitza
authors.forename: Klaus
authors.initials: K
authors.lastname: Rajewsky
mesh_terms: D000483:Alleles; D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D001755:Blastocyst / Q000378:metabolism; D002478:Cells, Cultured; D004274:DNA, Recombinant / Q000235:genetics; D015322:Gene Rearrangement, B-Lymphocyte; D005854:Germ Cells / Q000276:immunology / Q000378:metabolism*; D018858:Germinal Center / Q000276:immunology / Q000378:metabolism*; D007142:Immunoglobulin gamma-Chains / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D015847:Interleukin-4 / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D011003:Ploidies; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D004274:DNA, Recombinant; D007142:Immunoglobulin gamma-Chains; D015847:Interleukin-4