A DNAzyme based knockdown model for Fragile-X syndrome in zebrafish reveals a critical window for therapeutic intervention.

Introduction: FXS is the leading cause of intellectual disabilities in males and a major monogenic cause of ASD (Autism spectrum disorders). It occurs due to the loss of FMRP, whose role in early development is not well understood. In this study, we have used a novel DNAzyme based approach to create a larval model of FXS in zebrafish with specific focus on the early developmental window.

Methods: Fmr1specific DNAzymes were electroporated into embryos to create the knockdown. Changes in RNA and protein levels of FMRP and relevant biomarkers were measured in the 0-7dpf window. Behavioral tests to measure anxiety, cognitive impairments and irritability in the larvae were conducted at the 7dpf stage. Drug treatment was carried out at various time points in the 0-7dpf window to identify the critical window for pharmacological intervention.

Results: The DNAzyme based knockdown approach led to a significant knockdown of FMRP in the zebrafish embryos, accompanied by increased anxiety, irritability and cognitive impairments at 7dpf, thus creating a robust larval model of FXS. Treatment with the Mavoglurant was able to rescue the behavioral phenotypes in the FXS larvae, and found to be more efficacious in the 0-3dpf window.

Discussion: The results from this study have revealed that a) a DNAzyme based knockdown approach can be used to create robust larval zebrafish model of disease, in a high-throughput manner and b) optimal window for therapeutic intervention for FXS as well as other pediatric diseases with a monogenic cause can be identified using such a model.