Cloning and expression analysis of Atlantic halibut (Hippoglossus hippoglossus) CD3 genes

The CD3 complex is in higher vertebrates shown to be important for the activation of T-cells. The T-cell system in fish is believed to be similar to that in higher vertebrates, and the CD3 chains could therefore be an important marker for identification of T-cells in fish. Here, we report the cDNA and corresponding gene sequence of Atlantic halibut (Hippoglossus hippoglossus) CD3 gamma delta, CD3 epsilon, and CD3 zeta, chains, and the tissue-specific expression pattern of CD3 and T- cell receptor (TCR) genes. Important structural characteristics defining the CD3 genes seemed to be conserved in the halibut CD3 chains, such as a signal peptide, an extracellular region, a transmembrane helix having a negatively charged residue, and an ITAM bearing cytoplasmic tail. The extracellular domain of halibut CD3 gamma delta and CD3 epsilon included two cysteines presumably involved in Ig-fold stabilisation and the CxxCxE motif important for dimerization. A spliced variant of CD3 epsilon was identified, lacking the Ig-fold, but with the CxxCxE motif intact. The real time RT-PCR analysis revealed a highly similar expression pattern of the CD3 genes and the TCR alpha and TCRP genes, indicating that the functional relationship between the TCR and the CD3 genes are preserved in teleosts. (C) 2009 Elsevier Ltd. All rights reserved.