Cloning, characterization, and functional analysis of the zebrafish Disrupted in Schizophrenia 1 ortholog

Schizophrenia is a psychiatric illness with an etiology in abnormal neural development. Insights into the basis of this devastating disorder have come from studies investigating the function of genes implicated in disease pathogenesis. One of the genes most highly associated with schizophrenia is Disrupted In Schizophrenia 1 (DISC1). DISC1 does not belong to any known protein families but has been intensively studied since its discovery. In vitro and in vivo evidence supports a role for DISC1 in neurite outgrowth and neuronal migration in the developing and adult brain. The research presented here sought to accomplish several goals. First, we wanted to determine the developmentally regulated pattern of expression of disc1 and previously identified interacting genes in a whole embryo, which had not been done previously. Second, we then desired to study the function of Disc1 in an ideal tissue in this developing organism to provide better insight into its numerous functions in embryo development. Finally, we wanted to introduce the zebrafish as a system in which to study the function of a schizophrenia susceptibility gene.;To begin our studies, we cloned the zebrafish ortholog of DISC1 (disc1). Overall, conservation of amino acid sequence was moderate between zebrafish and human Disc1 at 24%. Previously identified protein interaction domains were more highly conserved. disc1 was expressed in several tissues in the zebrafish embryo including the developing ear, notochord, pectoral fin, neural crest and the developing craniofacial skeleton. We compared this expression to the expression patterns of the zebrafish orthologs of two Disc1 interactors, ndel1 and lis1 , but saw little overlap in expression. Our functional analysis of Disc1 concentrated instead on the Ndel1 and Lis1 independent functions of Disc1 in development of cranial neural crest (CNC) cells. CNC cells share many similarities with the neural cells of the developing brain, adding to their relevance in the study of a schizophrenia susceptibility gene. Knockdown of Disc1 in the embryo resulted in enhanced expression of two transcription factors, foxd3 and sox10, in CNC cells in addition to delayed migration from the neural rod. Similarly, overexpression of Disc1 suppressed expression of these transcription factors. With loss of Disc1, development of some CNC cell derived structures was also abnormal; craniofacial development is defective and peripheral cranial glial populations were expanded. This abnormal CNC cell development was due to enhanced transcription factor expression as partial reductions of Sox10 levels suppressed the craniofacial defects. These data implicate Disc1 in the transcriptional regulation which is necessary for the proper migration and differentiation of CNC cells. This function may be conserved in the developing brain where neuronal migration is tightly coupled to the transcriptional control of cellular differentiation.