Cortical interneurons are a diverse inhibitory neuron population in the cortex whose dysfunction is strongly linked with neuropsychiatric illness. How diversity comes about in interneurons is a poorly understood process. Elucidating molecular and transcriptional mechanisms governing interneuron diversity would greatly facilitate our understanding of how interneurons contribute to disease. It would also facilitate efforts to model neuropsychiatric disease with human stem cell-derived neurons and help to uncover novel therapeutic avenues. Current tools to study the molecular mechanisms driving interneuron diversity are limited in two important aspects: 1) sample material is limited because the embryonic progenitor domains for interneurons are small and not well-suited to applications such as biochemistry, screening and ChIP sequencing; 2) manipulating conditions by mouse genetics is relatively low- throughput. Objective: We therefore propose to develop a stem cell differentiation-based model of interneuron development. Approach: It is based on an existing system that we developed earlier but will now 1) encompass the entire interneuron lineage and has the capacity to differentially label MGE and CGE lineages. As an initial assay to test the validity of our new model, we will 2) examine the effects of transcriptionally-specifying both MGE and CGE lineages with a newly-identified Wnt-Ryk signaling pathway. We recently found that Wnt- Ryk regulates MGE interneuron identity, and this study will examine its potential role in regulating CGE identity. Interneurons generated from this new model will be assay by in vitro differentiation as well as by 3) in utero transplantation, which will stringently assay their capacity to engraft, migrated and integrate with host circuitry. The proposed experiments will allow us to definitively characterize our new in vitro model, opening the way to more expansive studies in which a stem cell-based model serves as a powerful platform to identify molecular and genetic pathways that govern cortical interneuron lineage specification.