Schizophrenia is a debilitating psychiatric disorder that affects ~1% of the world's population. Genetic and clinical association studies have identified disrupted-in-schizophrenia 1 (DISC1) as a strong candidate risk gene for schizophrenia and other major mental illnesses. DISC1 was initially associated with mental illness upon the discovery that its coding sequence is interrupted by a balanced chr(1;11) translocation in a Scottish family, in which the translocation cosegregates with schizophrenia, bipolar disorder and major depression1-3. DISC1 modulates many neuronal processes, including proliferation, Wnt signaling, synaptic maturation, neurite outgrowth, and neuronal migration4. Adding to the complexity of DISC1 biology, over 50 transcribed DISC1 splice variants have been identified in the developing and adult human brain5. The relevance of a DISC1 loss-of-function versus gain-of-function model to the human disease state is still unknown. As the expression patterns of DISC1 variants differ between humans and rodents, exploration of disease-relevant DISC1 expression and function is best accomplished in human cells.
I aim to characterize the the expression profile of DISC1 during neuronal differentiation of human induced pluripotent stem (iPS) cells. I will further explore the functional consequences of interruption at the DISC1 locus in cells from t(1;11) patients and cells with total or disease-relevant DISC1-interruption resulting from transcription activator-like effector nucleases (TALENs) or the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system. DISC1 expression over neuronal differentiation will be assayed using a custom Nanostring probe set. Disease- relevant and total DISC1-disrupted cells will be differentiated to neural progenitor cells (NPCs) and cortical neurons and examined for altered cell fate, Wnt signaling, proliferation, morphology, and migration. My hypothesis is that interruption of DISC1 at the site of the Scottish translocation will result in nonsense- mediated decay of longer transcripts, leaving shorter transcripts intact, which in turn will disrupt a subset of DISC1-dependent processes. Based on published work and my preliminary data, I anticipate that disease-relevant DISC1 interruption will impair Wnt signaling and neuronal migration, but will not grossly alter gene expression or neurite length. In contrast, I expect that total DISC1 loss wil reduce neurite outgrowth in addition to altering Wnt signaling and neuronal migration. This study will reveal functions of DISC1 in human neural cells and highlight the functions of DISC1 disrupted by a disease-relevant mutation. These data will indicate those functions of DISC1 likely to be perturbed in patients with the chr(1;11) translocation and which, when disrupted, contribute to the development of mental illness.
It is essential to understand the mechanisms underlying disease development in order to develop enhanced therapies for the treatment of major mental illnesses. We will use patient-derived and genetically engineered induced pluripotent stem cells to study the causes of major mental illness at the molecular and cellular level. In particular, we will investigate potential changes in gene expression and neuronal characteristics that result from mutations that increase susceptibility to mental illness.