First expressed at 15 hours post-fertilization (hpf), segmentally in the ventral region of the spinal cord (primary motoneurons) and then later in the dorsal regions (Rohan-Beard neurons). At 18 hpf, also expressed in tail bud and pronephric duct. At 24 hpf, expressed strongly in trigeminal ganglia. At 30 hpf, expressed transiently in pectoral fin bud.