Immunoglobulin genes and their transcriptional control in teleosts

Immunoglobulin (Ig), which exists only in jawed vertebrates, is one of the most important molecules in adaptive immunity. In the last two decades, many teleost Ig genes have been identified by in silico data mining from the enormous gene and EST databases of many fish species. In this review, the organization of Ig gene segments, the expressed Ig isotypes and their transcriptional controls are discussed. The Ig heavy chain (IgH) locus in teleosts encodes the variable (V), the diversity (D), the joining (J) segments and three different isotypic constant (C) regions including C mu, C delta, and C zeta/T genes, and is organized as a translocon type like the IgH loci of higher vertebrates. In contrast, the Ig light (L) chain locus is arranged in a multicluster or repeating set of VI., JL, and CL segments. The IgL chains have four isotypes; two kappa L1/G and I3/F), sigma (L2) and lambda. The transcription of IgH genes in teleosts is regulated by a VH promoter and the E mu 3' enhancer, which both function in a B cell-specific manner. The location of the IgH locus, structure and transcriptional function of the E mu 3' enhancer are important to our understanding of the evolutional changes that have occurred in the IgH gene locus. (C) 2010 Elsevier Ltd. All rights reserved.