Fig. 4. The hoxb1 duplicates have redundant functions in RS neuron specification. Retrograde labeling of 5-day larvae, merged confocal images, anterior towards the top, rhombomeres are numbered. (A) Wild-type control, note the bilateral r4-specific Mauthner neurons (M), the more lateral vestibular neurons (nV), and the smaller, laterally located r2-specific rol2 neurons. (B-D) Larvae injected with MOb1a at 1 mg/ml and MOb1b at 4 mg/ml. Note loss of Mauthners (*) and their replacement with smaller more medially located cells. In B, a unilateral Mauthner remains, although it is displaced posteriorly (M'). In C, ectopic lateral cells at the r5/6 level are indicated (red arrowhead).