Zdhhc15b Regulates Differentiation of Diencephalic Dopaminergic Neurons in Zebrafish

The aspartate-histidine-histidine-cysteine (DHHC) protein family shares a 50-amino acid cysteine-rich domain with a conserved DHHC signature motif. DHHC proteins play a critical role in several biological processes. Several DHHC family members have been implicated in neuronal differentiation and synaptic plasticity. And disruptions to their function can lead to disease in the nervous system. Here, we investigate the role of Zdhhc15b, a DHHC family member, in neurodevelopment in zebrafish. Whole-mount in situ hybridization (WISH) revealed that zdhhc15b, an ortholog to human ZDHHC15, is abundant in zebrafish (Danio rerio) forebrain, especially in the diencephalon. Downregulation of zdhhc15b resulted in a smaller diencephalon and a reduction in mature dopaminergic neurons (DA neurons). In the meanshile, mutant zdhhc15b zebrafish was associated with poor learning behavior as detected by T-maze testing. The expression of zdhhc15b was upregulated during DA neuronal differentiation whereas knock-down of zdhhc15b diminished DA neuronal differentiation. Tyrosine hydroxylase (TH) immunofluorescence of cultured DA neurons in vitro also showed that DA neurons were immature following zdhhc15b knock-down. Consistent with the decreased number of DA neurons following knock-down of zdhhc15b, the expression of fate determination-related transcription factors such as nurr1, foxA2, and lmx1a were also reduced in morphant zebrafish. Our results reveal that zdhhc15b controls DA neuronal fate decisions by regulating differentiation but not progenitor cell proliferation or DA neuronal survival.