Neurogenesis, the switch from proliferation to differentiation, is a poorly understood event in the developing nervous system. Now, on p. 3027, Yamaguchi et al. reveal that in zebrafish, histone deacetylase 1 (Hdac1) regulates retinal neurogenesis by suppressing the Wnt and Notch signalling pathways, which promote retinal proliferation and inhibit retinal neurogenesis, respectively. The researchers describe add (ascending and descending), a zebrafish mutant in which retinal progenitors continue to proliferate. Hdac1,they show, is encoded by the add gene, and manipulating Hdac1 levels in normal zebrafish embryos alters the ratio of proliferating to differentiating cells in the retina. The researchers also report that the Wnt and Notch signalling pathways are activated in add mutant retinas,and that their blockade suppresses cell proliferation and encourages differentiation. Thus, they conclude, Hdac1 acts as a dual switch to control zebrafish retinal neurogenesis.