With the advancement of human genome sequencing, it is clear that complex brain disorders are shaped by both rare and common disease variants. This progress has been most exciting in the field of neuropsychiatric disorders like schizophrenia, autism spectrum disorders, and Tourette Syndrome, as we are discovering important risk factors/alleles which can elevate disease risk by several fold. We are interested in leveraging these genetic clues in combination with human induced pluripotent stem cells (iPSCs), such that we can experimentally capture human genetic variation and test their functionality in neurodevelopment and synaptic biology. We utilize CRISPR/Cas9 genome editing in iPSCs to engineer disease mutations in control genetic backgrounds and generate donor-derived iPSCs from patients with specific neuropsychiatric disorders paired with controls. These iPSCs can be differentiated into specific neural cell types in 2D and 3D for us to probe their developmental trajectories, cell biology, gene expression, and functional connectivity.
During postdoc work with Dr. Sudhof at Stanford University, our studies on schizophrenia associated NRXN1 (2p16.3 del) copy number variants (CNVs) generated a set of iPSC lines that are conditionally mutant for NRXN1 in two different control genetic backgrounds as well as cell lines where NRXN1 is deleted naturally in individuals with schizophrenia (Pak et al., 2015 Cell Stem Cell, Pak et al., 2021 PNAS). Induced cortical excitatory neurons carrying NRXN1 deletions showed defects in synaptic transmission without changes in neuronal morphology and synapse density. Transcriptomic analysis of neurons differentiated from patient iPSCs revealed that NMDAR signaling could be altered.
A more recent follow up study utilized 3D differentiation protocols where NRXN1 deletion was investigated in a control genetic background and in schizophrenia genetic background during brain organoid development (Sebastian & Jin et al., 2023 Nat. Comm.). Using single cell transcriptomics, we found that NRXN1 deletions in schizophrenia genetic background induces divergent neurodevelopmental phenotypes mediated by transcriptional and cell composition changes in early neural progenitors compared to isogenic NRXN1 deletions, while both isogenic and patient NRXN1 deletions share a core set of gene modules that disrupt RNA splicing, ubiquitin-mediated pathway and NMDAR signaling. This study is the first to demonstrate the differential impact of NRXN1 CNVs in disease and isogenic backgrounds in the developing human brain organoid system. We would like to further pursue this interesting interaction between common and rare variants in neuropsychiatric disorders by using multiple disease genetic backgrounds.
Several other projects are ongoing in the lab through collaborations (Lim lab at UMass Med, Scharf lab at MGH, and SFARI), including investigating the functional effects of schizophrenia/autism related CNVs in neurodevelopmental and synaptic function, as well as understanding the underlying biological mechanisms of Tourette Syndrome through the use of iPSCs.
Funding sources supporting these projects include:
NIMH R01, Tourette Association of America YI grant
Highlighted papers:
Pak et al., 2015, Pak et al., 2021, Fuccillo and Pak, 2021, Sebastian & Jin et al., 2023