Early death and neuronal abnormalities in depdc5 loss-of-function mosaic zebrafish models

DEPDC5 (DEP domain-containing protein 5) encodes a repressor of the mTORC1 signaling pathway. Variants in DEPDC5 are associated with a range of focal epilepsies, including mosaic variants associated with focal cortical dysplasia (FCD) and other focal brain malformations with brain-only somatic mosaic variants. To investigate the role of DEPDC5 in human epilepsy related to mosaic variants, we have generated mosaic depdc5 loss-of-function zebrafish models using homology-based constructs acutely targeting depdc5 and labeled with tdTomato to allow for visualization of the degree of mosaicism. The resulting mosaic depdc5 CRISPants demonstrated early larval death, with ~50% of CRISPants (vs. 10% of controls) dead by 7 days post fertilization (dpf), analogous to the early death sometimes associated with human DEPDC5-related epilepsy. We compared depdc5 CRISPants with uninjected and scrambled controls from the same clutches. Body and head size were reduced in the depdc5 CRISPants. Analysis of swimming behavior showed a striking reduction in distance traveled and maximum velocity in the depdc5 CRISPants vs. controls. Based on visual confirmation of mutational load, we categorized CRISPants into depdc5+ vs. depdc5++, reflecting weak vs. strong tdTomato fluorescence. We observed that depdc5++ CRISPants had increased episodes of posture loss, suggesting increased seizure-like behavior related to higher percentages of mutant cells. Local field potential recordings revealed increased neuronal hyperexcitability in depdc5 CRISPants vs. controls. Acridine orange staining demonstrated early apoptosis in the CRISPants vs. controls. Our mosaic depdc5 CRISPants provide a clinically relevant model to study the role of mosaic DEPDC5-related epilepsy and early death.