Marked Diversity of Unique Cortical Enhancers Enables Neuron-Specific Tools by Enhancer-Driven Gene Expression

Abstract

Understanding neural circuit function requires individually addressing their component parts: specific neuronal cell types. However, not only do the precise genetic mechanisms specifying neuronal cell types remain obscure, access to these neuronal cell types by transgenic techniques also remains elusive. Whereas most genes are expressed in the brain, the vast majority are expressed in many different kinds of neurons, suggesting that promoters alone are not sufficiently specific to distinguish cell types. However, there are orders of magnitude more distal genetic cis-regulatory elements controlling transcription (i.e., enhancers), so we screened for enhancer activity in microdissected samples of mouse cortical subregions. This identified thousands of novel putative enhancers, many unique to particular cortical subregions. Pronuclear injection of expression constructs containing such region-specific enhancers resulted in transgenic lines driving expression in distinct sets of cells specifically in the targeted cortical subregions, even though the parent gene's promoter was relatively non-specific. These data showcase the promise of utilizing the genetic mechanisms underlying the specification of diverse neuronal cell types for the development of genetic tools potentially capable of targeting any neuronal circuit of interest, an approach we call enhancer-driven gene expression (EDGE).

Erratum

“…Interestingly, these genetically defined subdivisions of EC were also recognized in birds and reptiles (Medina, Abellan, & Desfilis, 2017). In line with this is a report that LEC and MEC in adult mice show strikingly different enhancer-expression profiles (Blankvoort, Witter, Noonan, Cotney & Kentros, 2018).…”

Genetic dissection of glutamatergic neuron subpopulations and developmental trajectories in the cerebral cortex

“…Our study suggests that strategic design of intersectional scheme, leveraging established and characterized driver lines, will substantially expand and improve the specificity and comprehensiveness of PyN targeting. Recent advances in enhancer-based usage of AAV vectors show significant promise in achieving subpopulation restriction 72 . The intersection of enhancer AAVs with strategically designed driver lines may substantially increase the specificity, ease, and throughput of neuronal cell type access.…”

Cell Type-Specific Oxidative Stress Genomic Signatures in the Globus Pallidus of Dopamine-Depleted Mice

“…This Sun1GFP variant can be easily incorporated into other constructs to achieve unprecedented access to small cell populations in a strain-independent manner. For example, the Sun1GFP gene could be expressed under the control of a cell type, region, or condition-specific regulatory element ( Blankvoort et al, 2018 ). Unlike the generation of new transgenic lines, new cSNAIL adaptations can be simply created through vector cloning and have the potential to be transferrable across species.…”