Conserved regulation of the lymphocyte-specific expression of lck in the Fugu and mammals

The Ick gene encodes a lymphocyte-specific protein-tyrosine kinase that is implicated in T cell maturation and signaling. In mammals, the transcription of the Ick gene is regulated by two independent promoters, the proximal promoter, which is active in thymocytes, and the distal promoter, which dominates in mature T cells. In the human and mouse Ick gene loci, the two promoter elements are separated by at least 40 kb and 10 kb, respectively. In this study, we have cloned and sequenced 60 kb from the pufferfish (Fugu rubripes) Ick locus. The promoter region of the Fugu Ick spans only 4.2 kb and contains a proximal and a distal promoter in the 2.3-kb region adjacent to the coding sequence. By generating transgenic mice, we have demonstrated that the compact promoter of the Fugu Ick contains regulatory elements that direct expression to lymphoid organs of mice. We were able to localize the regulatory elements to a short region of 830 bp without losing specificity to cultured human T cell line. These results show that the basic mechanisms that mediate lymphocyte-specific expression are conserved between teleosts and mammals. The short promoter of the Fugu Ick isolated by us offers a powerful tool for labeling T cells, targeting expression, and manipulating T cell activity in fishes as well as in mammals.