Regulatory Elements Inserted into AAVs Confer Preferential Activity in Cortical Interneurons.

Cortical interneuron (CIN) dysfunction is thought to play a major role in neuropsychiatric conditions like epilepsy, schizophrenia and autism. It is therefore essential to understand how the development, physiology and functions of CINs influence cortical circuit activity and behavior in model organisms such as mice and primates. While transgenic driver lines are powerful tools for studying CINs in mice, this technology is limited in other species. An alternative approach is to use viral vectors such as AAV, which can be used in multiple species including primates and also have potential for therapeutic use in humans. Thus, we sought to discover gene regulatory enhancer elements (REs) that can be used in viral vectors to drive expression in specific cell types. The present study describes the systematic genome-wide identification of putative REs (pREs) that are preferentially active in immature CINs by histone modification ChIP-seq. We evaluated two novel pREs in AAV vectors, alongside the well-established Dlx I12b enhancer, and found that they drove CIN-specific reporter expression in adult mice. We also showed that the identified Arl4d pRE could drive sufficient expression of channelrhodopsin for optogenetic rescue of behavioral deficits in the Dlx5/6+/- mouse model of fast-spiking CIN dysfunction.Significance Statement Uncovering the contribution of cortical interneuron (CIN) dysfunction to neuropsychiatric conditions is pivotal to generating therapies for these debilitating disorders. To this end, it is important to study the development, physiology and function of CINs in model organisms. While transgenic driver lines are powerful tools to study CINs in mice, this technology is limited in other species. As an alternative, gene regulatory enhancer elements (REs) can be used in viral vectors to drive expression in multiple species including primates. The present study describes the genome-wide identification of REs preferentially active in CINs and the use of these RE AAVs for CIN-specific targeting in adult mice. The methodology and novel REs described here provide new tools for studying and targeting CINs.