Linking genotype to phenotype in autism: mechanisms of cell-type specific presynaptic dysfunction in Chd8 haploinsufficiency

点击翻译按钮获取中文摘要

Autism is a neurodevelopmental disorder for which there is a severe lack of effective treatments for those who need them. A major problem in the development of new treatments is our poor understanding of its underlying biology. While there is clearly a strong genetic component, we now know that there are hundreds of different gene mutations that increase the risk of developing autism. Many of these risk genes are involved in synapse function or formation, suggesting that synapses (the site of communication between neurons in the brain) may be a key part of autism biology. However, an even larger group of autism risk genes simply regulate the expression of other genes. What happens downstream of these genes? Might they also affect synaptic function or formation? In this proposal, we aim to identify the molecules and pathways that link gene mutation in one of these 'regulator genes' to changes in synapse function, in a part of the brain that is well known to be affected in autism, the prefrontal cortex. We will focus on a specific gene called Chd8, which is one of the highest confidence risk genes for autism, and where we have already identified a robust synaptic phenotype in prefrontal cortex. In particular, there is increasing evidence that the effects of missing a copy of Chd8 (and other autism risk genes) depends critically on which type of cell is affected. We will use transgenic technology to selectively delete a copy of Chd8 from excitatory neurons or different types of inhibitory neurons and find out exactly how synapse function and/or formation is affected. We will then collect individual cells of each type - excitatory and inhibitory - and use single nuclei sequencing to discover which genes show either increased or decreased expression when that cell type is missing a copy of Chd8. While this kind of approach usually results in many different genes that show changes, we will focus on those that we already know are involved in synaptic function / formation. We will carry out extensive validation of potential targets, including testing whether simply increasing or decreasing expression of the candidate in cortical neurons in a dish leads to the expected alteration to synaptic phenotype. Finally, we will take advantage of recent advances in CRISPR/Cas9 technology (the so-called genetic 'scissors' that allow researchers to edit DNA) to bring expression levels of candidate genes back to normal in the living brain, and see whether this can rescue the synaptic phenotypes.This will allow us to work out the molecules and pathways that link the original genetic mutation to changes in cell and synapse function, thereby helping to fill a major gap in our understanding of this disorder. These molecules and pathways may provide novel targets for therapeutic intervention, potentially opening up new avenues in the effort to develop new treatments.