Mitogen and growth factor-induced activation of a STAT-like molecule in channel catfish lymphoid cells

This article describes the identification of a putative STAT molecule in the channel catfish ( Ictalurus punctatus), the first report of such a molecule in a ‘lower’ vertebrate. A monoclonal antibody against human STAT6 recognizes an ∼100 kDa molecule that becomes activated and translocates to the nucleus upon both growth factor and mitogen stimulation of catfish leukocytes. This presumed catfish STAT binds the mammalian interferon- γ activation site; IRF, interferon response factor; EMSA, electromobility shift assay. activation site, a known motif of mammalian STAT binding, as shown by electromobility shift assays. Purification of the proteins present in these DNA complexes confirms that the catfish reactive molecule binds to the interferon- γ activation site sequence. These results suggest that STAT molecules have been highly conserved in vertebrate evolution.