llb mutation affects the outgrowth of axons of all classes of motor neurons. A–D: Expression of isl1 and isl2a in the wild-type (A, C) and llb embryos (B, D) at 28 hpf. Lateral views with anterior at left. Brackets, spinal cord region; filled arrowheads, RB neurons; open arrowheads, primary motor neurons. E–J: Motor neuron and interneuron phenotypes of the wild-type and llb embryos. Primary motor neurons and GAD-positive interneurons at 28 hpf (E, H). Secondary motor neurons and GAD-positive interneurons at 48 hpf (F, I). Pectoral fin motor neurons and GAD-positive interneurons at 72 hpf (left) and 48 hpf (right) (G, J). Left panels are lateral views with anterior at left; right panels are transverse views. Filled arrowheads, each motor neuron; open arrowheads, ectopically induced GAD-positive neurons; broken lines, somite boundaries (E, F, H, I) and margin of the pectoral fin (G, J). K–P: Quantitative data for the motor neuron and interneuron phenotypes of the wild-type, llb, and isl1 morphant embryos. Data are mean ± SEM; n = number of sections; *P < 0.05, different from the wild-type embryos using 2-tailed paired Student′s t-test.
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