The genetic complexity underlying the vast majority of mental disorders has made the study of these diseases exceptionally challenging. Many risk-associated genes have been identified but the biological role of these genes is largely unknown. Disrupted in Schizophrenia 1 (DISC1) is a gene in which mutations have been associated with increased risk for schizophrenia and affective disorders. The functional role of this gene has been investigated in mice and was shown to have a prominent influence on many aspects of neuronal development including cell morphology and migration. However, the role of this gene in human neuronal development has not been explored, primarily due to the limited access to human neurons. This constitutes a significant gap in our knowledge because of the relatively low homology between mouse Disc1 and human DISC1 genes (~60% sequence homology). Using an innovative human stem cell-based approach, this proposal is focused on induced pluripotent stem cells (iPSCs) generated from patients harboring a rare 4bp deletion in DISC1 who belong to an American family with a history of mental illness. Because iPSCs retain the genetic information of the donor individual, human neurons derived from these patient-specific iPSCs and those of healthy family members without the deletion will be evaluated to determine the functional role of DISC1. The hypothesis that this mutation in DISC1 will alter development of human neurons will be investigated through three specific aims. (1) Generate isogenic iPSC lines that differ exclusively at this DISC1 4bp locus using a gene targeting and editing technique called transcription activator-like effector nucleases (TALENs). This technique will allow for the generation of rescue lines in which the 4bp deletion has been corrected in patient-derived iPSCs, and deletion lines in which the 4bp deletion will be introduced to intact control-iPSCs. These complementary isogenic iPSCs will provide the basis for a functional evaluation of mutations in DISC1 with a controlled genetic background. (2) Characterize neuronal development in human neurons derived from deletion and intact DISC1 iPSCs. After differentiating iPSCs into neurons, the molecular, cellular, physiological and functional properties of the deletion lines and intact lines will be analyzed both in vitro and in vivo. (3) T determine the role of DISC1 in the AKT-mTOR pathway. In mice, Disc1 has been shown to interact with this pathway to regulate neuronal development. Determining the interaction between DISC1 and AKT-mTOR will provide critical information regarding the functional overlap between mouse Disc1 and human DISC1. Furthermore, components of the mTOR pathway have also been implicated in risk for mental disorders and investigation of key proteins in this pathway may lead to additional insight into the role of this pathway as a potential locus of convergence in genetic regulation of human neuronal development.
Several major mental disorders, including schizophrenia, are highly heritable but genetically complex. Many risk genes have been identified but the biological role of most of these genes in the human nervous system is unknown. Generating isogenic induced pluripotent stem cells and human neurons from patients with a mutation in Disrupted in Schizophrenia 1 (DISC1), an identified risk-associated gene, will enable targeted investigation of the role of this gene in regulating neuronal functions that may be disrupted in the pathophysiology of mental disorders.
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