NRSA for Ricardo Raudales: Genetic Dissection of Cortical Parvalbumin Interneuron Subtypes

Abstract The inhibitory control and dynamic tuning of cortical circuits is mediated by a diversity of GABAergic cell types, but the biological basis of interneuron identity and diversity is not well understood. Here, we combine developmental genetic, anatomic and transcriptomic approaches to define and discover bona fide cell types within a broad class of cortical interneurons. Parvalbumin containing, fast-spiking basket cells (PVCs) are the largest population of interneurons in the neocortex and integrate in infragranular, granular (layer IV), and supragranular circuits, each with unique input/output connectivity. Recent findings from our laboratory and others suggest heterogeneity in PVC morphology, synaptic properties, and connectivity, but it is uncertain how many of these represent distinct subtypes. Using a developmental genetic strategy, we take advantage of the inside-out laminar specification of PVCs to identify and characterize subtypes based on lineage and birth time restricted cohorts. PVCs are derived from the medial ganglionic eminence (MGE), and the transition from progenitor to differentiated neuron is marked by the upregulation of proneural transcription factors. By intersecting inducible Ascl1-CreER and Dlx1-CreER mice with PV-Flp mice and an intersectional reporter and inducing in mid-to-late embryogenesis, we have begun parsing adult laminar PVC subtypes for multifactorial single-cell analysis. We quantify the laminar position and morphology of lineage restricted and birth-dated PVC cohorts. We will also carry out single cell RNAseq to analyze their transcription profiles. The integration of morphological and anatomical characterization with single cell RNAseq will increase our understanding of cell identity in PVCs and can potentially uncover new underlying cellular properties. Because PVCs are implicated in schizophrenia, autism, and other mental disorders, their complete profiling at the single cell level could aid in understanding pathophysiology and suggest better treatment strategies.