The sequential synaptic integration of adult-born neurons has been widely examined in rodents, but the mechanisms regulating the integration remain largely unknown. The primary cilium, a microtubule–based signaling center, plays essential roles in vertebrate development, including the development of the central nervous system. Here we examined the assembly and function of the primary cilium in the synaptic integration of adult-born hippocampal neurons. Strikingly, primary cilia are absent in young adult-born neurons but assemble precisely at the stage when newborn neurons approach their final destination, further extend dendrites and form synapses with entorhinal cortical projections. Conditional cilia deletion from adult-born neurons induced severe defects in dendritic refinement and synapse formation. Primary cilia deletion leads to enhanced Wnt/β-catenin signaling which may account for these developmental defects. Taken together, our study identifies the assembly of primary cilia as a critical regulatory event in the dendritic refinement and synaptic integration of adult-born neurons.

Disrupted-in-schizophrenia 1 (DISC1) is a gene disrupted by a (1;11) (q42.1;q14.3) translocation that segregates with major psychiatric disorders in a Scottish family. To investigate how DISC1 confers susceptibility to psychiatric disorders, we previously identified fasciculation and elongation protein zeta-1 and Kendrin as DISC1-interacting molecules in a yeast twohybrid screen of a human brain complementary DNA library. Here, we have further identified a novel DISC1-interacting protein, termed DISC1-Binding Zinc-finger protein (DBZ), which has a predicted C 2 H 2 -type zinc-finger motif and coiled-coil domains. DBZ was co-immunoprecipitated with DISC1 in lysates of PC12 cells and rat brain tissue. The domain of DISC1 interacting with DBZ was close to the translocation breakpoint in the DISC1 gene. DBZ messenger RNA (mRNA) was expressed in human brains, but not in peripheral tissues. In situ hybridization revealed high expression of DBZ mRNA in the hippocampus, olfactory tubercle, cerebral cortex and striatum in rats. Because this pattern of localization was similar to that of the pituitary adenylate cyclase (PAC 1 ) receptor for pituitary adenylate cyclase-activating polypeptide (PACAP), which has recently been implicated in neuropsychological functions, we examined whether DISC1/DBZ interaction was involved in the PACAP signaling pathway. PACAP upregulated DISC1 expression and markedly reduced the association between DISC1 and DBZ in PC12 cells. A DISC1-binding domain of DBZ reduced the neurite length in PC12 cells after PACAP stimulation and in primary cultured hippocampal neurons. The present results provide some new molecular insights into the mechanisms of neuronal development and neuropsychiatric disorders.

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