The central objective of this research is to elucidate the function of genes that are strongly associated with autism spectrum disorders (ASD) in fundamental processes of vertebrate brain development. While whole-exome sequencing has led to a growing list of ?high confidence? ASD (hcASD) risk genes, which are beginning to converge on common pathways, our understanding of the mechanisms by which hcASD gene disruption alters the development of specific cell types and neural circuits, resulting in behavioral dysfunction, remains limited. The long-term goal of this research is to illuminate the basic biological mechanisms underlying ASD, which will provide a much-needed avenue for the discovery of targeted pharmacological treatments. Here, we will capitalize on the unique advantages of zebrafish as an in vivo, biologically relevant system for the rapid functional analysis of multiple hcASD genes in parallel, including: (i) the ability to directly visualize basic neurodevelopmental processes and neural activity in a whole vertebrate brain through transparent embryos; (ii) large progenies, which are ideal for conducting high-throughput in vivo screens to identify small molecule suppressors of behavioral phenotypes; and (iii) ease of genetic manipulation, such that we have already generated zebrafish mutants in 10 top hcASD genes, which we will analyze in the present study. Our central hypothesis is that zebrafish mutants of hcASD genes will display quantifiable morphological, simple behavioral, and circuit-level phenotypes that will converge on common pathways, providing new insights into the roles of these genes in the developing vertebrate brain. This hypothesis is based on evidence from our study of zebrafish mutants of the ASD risk gene, CNTNAP2, which revealed dysregulation of GABAergic and glutamatergic signaling and identified a novel pharmacological suppressor of an ASD gene-associated mutant behavioral phenotype. To test this hypothesis, we will pursue the following aims: 1) Identify quantifiable brain phenotypes across 10 hcASD mutants using light-sheet imaging and automated deep phenotyping of CNS- specific markers; 2) Conduct high-throughput pharmaco-behavioral profiling of hcASD mutants using a novel, automated visual-startle assay and perform small molecule screens to identify suppressors of mutant startle phenotypes; and 3) Characterize neural circuit deficits underlying altered sensory processing behaviors in hcASD mutants and identify the circuit-level mechanisms of pharmacological suppressors using whole-brain in vivo two-photon imaging. This approach is highly innovative and is the first to analyze the function of multiple hcASD genes in parallel at the structural, behavioral, and circuit levels, allowing us to progress rapidly from risk gene discovery to the elucidation of convergent pathways with relevance to ASD. Therefore, we expect that this research will lead to critical advances in our understanding of the basic biology of ASD and provide a path forward in the discovery of mechanism-based pharmacological treatments.
The goal of the proposed studies is to provide new insights into the function of multiple risk genes for autism spectrum disorders (ASD) using an innovative, large-scale approach, which will advance our understanding of the basic biological mechanisms underlying ASD. This research is highly relevant, given the increasing prevalence of ASD in the U.S., and the need for novel approaches to elucidate the biology of ASD and develop improved treatments. We anticipate that this research will greatly enhance our knowledge of how the disruption of ASD risk genes alters fundamental processes in brain development, providing a path forward in the discovery of novel, mechanism-based treatments.
|Sakai, Catalina; Ijaz, Sundas; Hoffman, Ellen J (2018) Zebrafish Models of Neurodevelopmental Disorders: Past, Present, and Future. Front Mol Neurosci 11:294|