Defective hair-cell function. (A) In a WT (Upper) and a mutant (Lower) larva at 6 dpf, arrowheads indicate neuromasts labeled by Tg(pou4f3:gap43-mGFP) (green). (B) Upon exposure to FM4–64 (red), the WT specimen (Upper) shows robust incorporation of the fluorophore into hair cells but the mutant (Lower) shows none. (C) In the inner ears of WT (Upper) and mutant (Lower) animals at 5 dpf, Tg(pou4f3:gap43-mGFP) (green) marks the anterior (AC), medial (MC), and posterior cristae (PC). (D) Pressure-injection of FM4–64 (red) into the otic cavities labels hair cells in the cristae of WT (Upper) but not mutant (Lower) fish. (E) Averaged extracellular recordings of microphonic potentials measured at 5–7 dpf from the inner ears of eight WT larvae show a clear response at twice the stimulus frequency, whereas the record from eight mutant larvae shows only a stimulus artifact. (Scale bars, 200 μm in A and B; 20 μm in C and D.)
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