Research into the developmental underpinnings of autism spectrum disorder (ASD) is hampered by a lack of techniques for describing neural development at the cellular and circuit levels. Ethan Scott and his colleagues plan to use zebrafish as a platform for anatomical and functional analyses of ASD etiology at the level of individual neurons and the circuits that they form. Zebrafish larvae are transparent, allowing neural development in the intact animal to be examined with a range of microscopic and optogenetic techniques.
Scott generated targeted mutations in six ASD candidate risk genes as part of his previous SFARI Explorer grant. For the current project, Scott’s team will fluorescently label individual neurons in the brain and perform time-lapse imaging of their development in order to gauge whether these mutations affect the morphology or dynamics of developing neurons. This approach will permit the team to describe both static structures and the rates at which neurons add or retract neurites as they develop. Because cerebellar Purkinje neurons have been implicated in ASD, and due to their morphological complexity, the initial focus will be on morphologically assessing these neurons. Using a genetically encoded calcium indicator and selective plane illumination microscopy, Scott and his colleagues will also assess the calcium dynamics of thousands of neurons simultaneously at single-cell resolution. These data will allow the team to look for changes in spontaneous activity and the formation of functional ensembles that might occur in the mutant zebrafish. The team will also perform behavioral analyses of the mutant zebrafish larvae; these assays will focus on assessing locomotor behavior, motor coordination and motor learning behaviors relevant to ASD phenotypes.
The combined use of these approaches will reveal the anatomical, dynamic and functional properties of cells and circuits in the brain, and will show how such circuitry is altered by mutations in ASD candidate risk genes. The overall goal of the project is to link behavioral deficits to perturbations in the cells or circuits of the developing brain that preceded them. This will generate insights into the developmental mechanisms by which ASD arises.