Fig. 6. The hoxb1a and hoxb1b genes have non-identical biochemical functions. BM neurons are revealed with islet1. (A,B) islet-GFP transgenics, (C,D) islet1 in situ hybridization, embryos at 28 hours with anterior towards left. (A,C) Embryos injected with hoxb1b mRNA at 20 µg/ml show posteriorizing transformations at the r2 level (V neurons are transformed to VII'); (B,D) embryos co-injected with MOb1a (1 mg/ml) and hoxb1b mRNA do not show either rescue of the hoxb1a loss-of-function phenotype, or any gain-of-function phenotype. o, otic vesicle.