Transcriptional regulations underlying cell type specific terminal differentiation of cortical interneurons - Project Summary/Abstract Cortical inhibition provided by GABAergic interneurons (INs) plays a key role in both normal brain function and pathogenesis of several brain disorders such as schizophrenia, autism, epilepsy as well as injury-induced brain dysfunction such as chronic pain. Cortical INs (cINs) comprise a variety of subtypes that differ in morphology, electrophysiological properties, connectivity, gene expression, and circuit/behavior functions. Diverse modes of inhibitory regulations mediated by different cIN subtypes are necessary for the integrity of the cortical inhibitory function. Therefore, elucidating the genetic mechanisms underlying cIN diversification is imperative for not only understanding the origin of cIN functional diversity but also developing cell type specific treatments using drugs and stem cells. However, the transcriptional basis for cIN subtype specification remains poorly understood. The objective of our proposal is to characterize the expression of candidate cell type preferential TFs and determine their essential role in the synaptic organization of the cIN subtype during postmitotic terminal differentiation by in vivo functional screening. To achieve this goal, we will perform a series of experiments using the chandelier cell (ChC), which exclusively innervates axon initial segments of pyramidal neurons (PNs) and thus powerfully controls spike generation in PNs. The stereotypy of the axonal/synaptic organization makes ChCs ideal for studying development of cIN subtypes. Our published and preliminary studies identified TFs and CAMs that are predominantly expressed in postmitotic ChC precursors and showed that some of these CAMs critically control ChC synaptic development and specificity. Based on these results, we propose to test the hypothesis that ChC preferential TFs postmitotically control the synaptic organization characteristic of ChCs. We will pursue the following specific aims to achieve the above objective. To ensure feasibility for the proposed experiments, we developed in vivo genetic strategies that allow us to reliably manipulate murine young postmitotic ChCs as well as a single cell genotyping approach that links genotypes to phenotypes in ChCs subjected to genome editing. In Aim 1, we will characterize the expression of the ChC preferential genes identified by bulk RNA-seq, at single cell levels during postnatal development. In Aim 2, we will identify TFs that postmitotically control the ChC synaptic organization. Our study will unravel the transcriptional basis for the cell type specific cIN synaptic organization and provide an entry point into understanding the transcriptional principle of postmitotic cIN terminal differentiation. The genetic insight into cell type specific cIN terminal differentiation obtained from this study will ultimately serve as a foundation for differentiating human pluripotent stem cells into specific cIN subtypes, which will benefit a cell transplantation-based therapy and drug discovery.
