ABSTRACT
ZT3, isolated from a murine muscle cell cDNA library by a low-stringency hybridization, encodes a zinc finger domain containing factor with a transcript of 5.0 kb. A 3' 2.5 kb partial nucleotide sequence contains an ORF of 1.5 kb where 17 canonical C2H2 zinc finger domains organized in tandem were identified. It maps on mouse chromosome 11, close to two mutations which affect skeletal formation. ZT3 expression depends upon differentiation of myogenic cells in culture, since it is upregulated with myogenin and inhibited in scr-transfected C2C12 cells. ZT3 is not expressed in NIH3T3 or C3H10T1/2 fibroblasts, but is induced when fibroblasts are myogenically converted by transfection with the muscle regulatory genes (MRFs). Its expression is also upregulated in the rhabdomyosarcoma cell line RD induced to myogenic differentiation by TPA treatment. In postimplantation embryos, ZT3 is diffusely expressed but higher expression is detectable in the neural tube and encephalic vesicles, in the somites and, at a high level, in the limb buds as they form. During further development ZT3 is expressed in many tissues of neuroectodermal and mesodermal origin, but its expression decreases during fetal development and in the adult it is restricted to skeletal and cardiac muscle and to spleen. This pattern of expression suggests a possible role played by ZT3 in differentiating skeletal muscle. Its expression in other tissues is compatible with the suggestion that members of this class of DNA-binding factors play different roles during post-implantation development and in the adult life.