Fezf2 Regulates Multilineage Neuronal Differentiation through Activating Basic Helix-Loop-Helix and Homeodomain Genes in the Zebrafish Ventral Forebrain

Transcription factors of the achaete-scute and atonal bHLH proneural gene family play important roles in neuronal differentiation. They are also involved in neuronal subtype specification through collaboration with homeodomain (HD) transcription factors. However, concerted regulation of these genes and in turn progenitor fate toward distinct lineages within the developing vertebrate brain is not well understood. Fezf2 is an evolutionarily conserved zinc finger protein important for monoaminergic neuronal development in zebrafish. Here, we show that Fezf2 is also critical for GABAergic neuronal fate and investigate how a single transcription factor regulates the identity of multiple neuronal lineages in the developing ventral forebrain. First, our genetic analyses reveal the requirement of the achaete-scute-like genes ascl1a and 1b in serotonergic and GABAergic neuron development, but they are dispensable for the specification of dopaminergic neurons, which is dependent on the atonal-like gene neurog1. Second, the expression of fezf2, ascl1a/1b, and neurog1 demarcates distinct progenitor subpopulations, where fezf2 is required for activating but not maintaining the expression of bHLH genes. Third, Fezf2 is required to activate HD genes otpb and dlx2, which are involved in dopaminergic and GABAergic neuronal development, respectively. Finally, we uncover that Fezf2 is sufficient to increase dopaminergic neuronal numbers but not serotonergic or GABAergic lineages. Together, these findings reveal new mechanisms by which multilineage differentiation is coordinately regulated by a single transcription factor in the vertebrate ventral forebrain.