The cDNA and genomic sequences of IgD and IgZ were characterized in grass carp Ctenopharyngodon idella in the present study, and with the identification of a BAC clone covering zeta, mu, and delta genes, the IgH locus containing these Ig genes and other V, D, J genes was also illustrated in this fish. Secretory and membrane-bound IgZ were identified, with two transmembrane exons spliced within the CH4 exon, as reported in IgM of mammals and IgZ in other teleost fish. The first and second constant domains of IgZ shows more than 90% nucleotide identity with respective domains of grass carp IgM. The IgD has a structure of delta 1-(delta 2-delta 3-delta 4)(2)-delta 5-delta 6-delta 7-TM-UTR, with the repeat of delta 2-delta 3-delta 4; but intron was not found between the two repeat, i.e. between the first delta 2-delta 3-delta 4 (delta 2.1-delta 3.1-delta 4.1) and the second delta 2-delta 3-delta 4 (delta 2.2-delta 3.2-delta 4.2), and the intron between delta 3.1 and delta 4.1 was much shorter than the intron between delta 3.2 and delta 4.2. The genomic organization of the IgH locus has a pattern of Vn-Dn-Jn-C zeta-Dn-Jn-C mu-C delta, as reported in other teleost fish. Thirteen V-H, fourteen D, and twelve J(H) genes were observed in this locus, with the similarity of three D segments and four J(H) segments being the same in the upstream of C zeta, and C mu. The transcriptional enhancer located at the mu-delta intergenic region was also analyzed and it seems possible that this enhancer is functional as verified in zebrafish and channel catfish. (C) 2010 Elsevier Ltd. All rights reserved
