Molecular characterization of the Japanese flounder, Paralichthys olivaceus, CD3ɛ and evolution of the CD3 cluster

A second CD3 gene, i.e. CD3ɛ, has been cloned and sequenced in Japanese flounder. The full length cDNA is 1006 bp and encodes 164 amino acids. When compared with other known CD3ɛ peptide sequences, the most conserved region of the Japanese flounder CD3ɛ chain peptide is the cytoplasmic domain and the least conserved is the extracellular domain. A phylogenetic analysis based on the deduced amino acid sequence grouped the two Japanese flounder CD3 sequences with CD3ɛ and CD3γ(δ, respectively. The Japanese flounder CD3ɛ gene has Lyf-1, GATAs, Oct-1, CEBPs, AP-1, and NF-AT but lacks TATA and CCAAT elements in the 5′ flanking region. The Japanese flounder CD3 cluster (consisting of CD3ɛ and CD3γ(δ) spans only 10.4 kb. The two genes are oppositely transcribed only 3.8 kb apart. Both Japanese flounder CD3 genes have five exons. The two Japanese flounder CD3 genes were predominantly expressed in PBLs, kidney, spleen, and gills. A polyclonal rabbit antiserum that reacts with the CD3 marker on human T cells also reacted with Japanese flounder CD3ɛ. The epitope highly conserved between mammalian and non-mammalian CD3ɛs, this antibody bound to a single 15 kDa peptide.