κ chain monoallelic demethylation and the establishment of allelic exclusion

  1. Raul Mostoslavsky1,
  2. Nandita Singh3,
  3. Andrei Kirillov1,
  4. Roberta Pelanda4,
  5. Howard Cedar2,6,
  6. Andrew Chess3,5, and
  7. Yehudit Bergman1
  1. 1The Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, and 2Department of Cellular Biochemistry, The Hebrew University Hadassah Medical School, Jerusalem 91120, Israel; 3Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, Massachusetts 02142 USA; 4Max-Planck Institute for Immunobiology, Freiburg, Germany 79108; 5Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 USA

Abstract

Allelic exclusion in κ light-chain synthesis is thought to result from a feedback mechanism by which the expression of a functional κ light chain on the surface of the B cell leads to an intracellular signal that down-regulates the V(D)J recombinase, thus precluding rearrangement of the other allele. Whereas such a feedback mechanism clearly plays a role in the maintenance of allelic exclusion, here we provide evidence suggesting that the initial establishment of allelic exclusion involves differential availability of the two κ alleles for rearrangement. Analysis of κ+ B-cell populations and of individual κ+ B cells that have rearranged only one allele demonstrates that in these cells, critical sites on the rearranged allele are unmethylated, whereas the nonrearranged allele remains methylated. This pattern is apparently generated by demethylation that is initiated at the small pre-B cell stage, on a single allele, in a process that occurs prior to rearrangement and requires the presence in cis of both the intronic and 3′ κ enhancers. Taken together with data demonstrating that undermethylation is required for rearrangement, these results indicate that demethylation may actually underly the process of allelic exclusion by directing the initial choice of a single κ allele for rearrangement.

Keywords

Footnotes

  • 6 Corresponding author.

  • E-MAIL cedar{at}md2.huji.ac.il; FAX 972-2 641-5848.

    • Received January 29, 1998.
    • Accepted April 13, 1998.
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