Transgenic zebrafish highlight specific cell lineages and/or growth factor signaling activity. Confocal projections of the zebrafish ceratohyal demonstrate cells of developing cartilage (A; sox9a:EGFP) or bone (B; sp7:EGFP) in living animals. Other transgenic zebrafish lines reveal which cells are responding to growth factor signaling, such as bone morphogenetic protein signaling (C; BRE:EGFP), producing results similar to more traditional immunocytologic techniques (D; anti-phospho-Smad1/5/8), except that the former approach can be done in living animals.