Transgenic medaka with brilliant fluorescence in skeletal muscle under normal light

Green fluorescent protein (GFP) and red fluorescent protein (RFP) genes regulated by the medaka skeletal muscle actin promoter were microinjected into fertilized d-rR medaka eggs to establish transgenic medaka lines. Intense fluorescence was detected in skeletal muscle. During development, GFP and RFP became detectable in anterior somites at the 12- and 30-somete stages, respectively. After hatching, intense fluorescence in skeletal muscle enabled individual fish to be identified under normal lighting without fluorescent microscopy. Fluorescence was also observed in the gills and esophagus of the adult fish. These data indicated that medaka lines are convenient not only for the study of skeletal muscle but also for the identification of cells or individuals in various studies.