The zebrafish IgH locus contains multiple transcriptional regulatory regions

Many fish have, in addition to IgM and IgD, a third isotype called IgZ or IgT. The zeta-chain locus is embedded among the Ig heavy chain V-, D- and J-elements in a manner reminiscent of the TcR delta/alpha locus. Isotype selection thus occurs during VDJ recombination, a process that is facilitated by intralocus transcription. Using in silico analyses and enhancer reporter vectors we identified 3 new regions within the zebrafish IgH locus through which transcription can be activated in catfish B-cell lines. Two of these, termed E zeta i (J zeta to C zeta 1 intronic) and E zeta 3' regions flank the zeta-chain constant domain exons. A third region, E delta 3', resides downstream of the delta-chain exons. All regions contain predicted binding sites for transcription factors that contribute to B-cell specific transcription in fish and mammals. Each region also has proximal matrix attachment regions, which may further contribute to transcriptional activation and chromatin remodeling. We discuss possible roles for these regions during VDJ recombination. (C) 2010 Elsevier Ltd. All rights reserved.