Characterization of Tg(atoh1a:Gal4TA4)^hzm2 transgenic zebrafish. Lateral view of an offspring of Tg(atoh1a:Gal4TA4)^hzm2 x Tg(4xUAS:GFP)^hzm3 transgenic fish at 24 hpf. (A) Endogenous atonal1a expression in the rhombic lip as revealed by in situ hybridization (black). (B) Immunostaining for GFP after in situ hybridization for atonal1a on Tg(atoh1a:Gal4TA4)^hzm2/Tg(4xUAS:GFP)^hzm3 double-transgenic fish shows expression of GFP (green) in the rhombic lip in atonal1a-expressing cells (black). (C) In addition, some GFP-expressing cells can be found in the retina, the midbrain tegmentum, and the tectum of Tg(atoh1a:Gal4TA4)^hzm2/Tg(4xUAS:GFP)^hzm3 double-transgenic fish. (D) Enlargement of boxed area in A showing in situ hybridization for atonal1a in the hindbrain. (E) Immunostaining for GFP. (F) Overlay of D and E. These data show that KalTA4 expression in Tg(atoh1a:Gal4TA4)^hzm2 embryos faithfully recapitulates rhombic lip expression of endogenous atonal1a. MHB, midbrain–hindbrain boundary; URL, upper rhombic lip.