Germline transcripts of the murine immunoglobulin γ2a gene: structure and induction by IFN-γ

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Abstract
The switch in expression by B cells from IgM to IgG, IgE, or IgA is accomplished by a DNA deletion. The deletion event is regulated, in that specific cytokines direct the B cell to switch to one, or sometimes two, of the six possible murine heavy chain genes. Prior to switch recombination, cytokine treatment also induces the transcription of the constant, switch, and upstream regions of the targeted heavy chain. Much evidence indicates that IFN-γ directs switch recombination to the murine γ2a gene. By developing probes specific for the γ2a gene, we demonstrate that IFN-γ increases germline transcription of this gene in both normal B cells and in the 18.81.A20 pre-B lymphoma. We have obtained cloned copies of three different germline γ2a; transcripts, each with a different donor splice site. We have also located the 5′ ends of these transcripts. The vast majority of the germline γ2a; transcripts have a long first exon (>700 bp), consistent with observations by Severinson and her colleagues.

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