From disease genes to behavioural screen in zebrafish: early onset Alzheimer’s as case study

To design prevention strategies and disease-modifying therapies in Alzheimer’s disease, we must discover biological processes which contribute to disease. Genomic studies can point to such causal processes, but their findings are rarely exploited in a systematic, hypothesis-free manner. In this thesis, we present a strategy in zebrafish to link disease-associated genes to likely causal processes. The first step is to inactivate each gene in zebrafish larvae. For this purpose, we developed a rapid CRISPR-Cas9 method capable of converting wild-type eggs directly into knockout larvae for any gene of interest. The method effectively cuts the experimental time from gene to knockout zebrafish from months to one day. The second step is to monitor the behaviour of the mutated larvae. As a case study, we targeted the three genes associated with early-onset Alzheimer’s disease. We found, for example, that larvae with loss-of-function mutations in presenilin 2 are less active during the day. The third step will be to use predictive pharmacology to identify drugs which cause the same phenotype in wild- type animals, thereby pointing to the defective process. This strategy is both scalable thanks to the knockout method and generalisable beyond Alzheimer’s disease. It can now be employed to screen tens or hundreds of genes associated with other conditions, such as schizophrenia or epilepsy