A major challenge to the investigation of cellular mechanisms underlying autism spectrum disorders (ASDs) is to identify convergent neural ‘signatures’ linking common cognitive and behavioral changes with the great diversity of ASD-associated genes. In addition, the use of constitutive and conditional transgenic models limits the ability to distinguish phenotypes arising from developmental gene disruption from those resulting from dysregulation of the mature brain. Finally, we currently lack high-throughput assays for the analysis of in vivo brain circuit functions, such as sensory processing and cognition, in the context of ASD-linked gene mutations.
To address these issues, Jess Cardin and Michael Higley plan to assess the effects of targeted mutations in several ASD risk genes on spontaneous and sensory-evoked cortical dynamics in awake behaving mice. To do so, they will combine novel adeno-associated viral (AAV) constructs carrying SaCas9 and gene-specific guide RNAs (sgRNAs) with cutting-edge two-photon and mesoscale calcium imaging. They will initially target five genes that are strongly associated with ASD (as determined by the SFARI Gene scoring system): Grin2B, a subunit of the NMDA-type glutamate receptor (NMDAR); Syngap1, a postsynaptic density protein that binds NMDARs; Shank3, a synaptic scaffolding protein; Mecp2, a transcriptional regulator; and Chd8, a chromatin remodeler and transcriptional repressor.
In a series of experiments carried out in awake mice, Cardin and Higley will identify the impact of gene disruption on state-dependent regulation of spontaneous local and long-range cortical circuit dynamics. Additionally, they will determine the impact of ASD-linked mutations on sensory-evoked activity. Simultaneous multiscale imaging will allow the examination of the relationships among single cells and between these neurons and ongoing patterned network activity across the entire neocortex.
In summary, these studies will combine cutting-edge tools for genetic manipulation and in vivo neural imaging to generate a large-scale, highly sensitive functional screen for comparing neurodevelopmental disruptions of cortical networks. The results of these studies are expected to bridge the gaps between genes, cells and systems, helping to reveal common functional signatures of cortical dysregulation across diverse models of ASD.