Brain-specific-homeobox is required for the specification of neuronal types in the Drosophila optic lobe

► Roles of brain-specific-homeobox (bsh) in Drosophila optic lobe development are shown. ► bsh is required and largely sufficient for Mi1 type neuron formation in the medulla. ► bsh is required and largely sufficient for L4 type neuron formation in the lamina. ► bsh is at least required for L5 type neuron formation in the lamina.