Depdc5 knockdown causes mTOR‐dependent motor hyperactivity in zebrafish

Abstract

Objective DEPDC5 was identified as a major genetic cause of focal epilepsy with deleterious mutations found in a wide range of inherited forms of focal epilepsy, associated with malformation of cortical development in certain cases. Identification of frameshift, truncation, and deletion mutations implicates haploinsufficiency of DEPDC5 in the etiology of focal epilepsy. DEPDC5 is a component of the GATOR1 complex, acting as a negative regulator of mTOR signaling.MethodsZebrafish represents a vertebrate model suitable for genetic analysis and drug screening in epilepsy‐related disorders. In this study, we defined the expression of depdc5 during development and established an epilepsy model with reduced Depdc5 expression.ResultsHere we report a zebrafish model of Depdc5 loss‐of‐function that displays a measurable behavioral phenotype, including hyperkinesia, circular swimming, and increased neuronal activity. These phenotypic features persisted throughout embryonic development and were significantly reduced upon treatment with the mTORC1 inhibitor, rapamycin, as well as overexpression of human WT DEPDC5 transcript. No phenotypic rescue was obtained upon expression of epilepsy‐associated DEPDC5 mutations (p.Arg487* and p.Arg485Gln), indicating that these mutations cause a loss of function of the protein.InterpretationThis study demonstrates that Depdc5 knockdown leads to early‐onset phenotypic features related to motor and neuronal hyperactivity. Restoration of phenotypic features by WT but not epilepsy‐associated Depdc5 mutants, as well as by mTORC1 inhibition confirm the role of Depdc5 in the mTORC1‐dependent molecular cascades, defining this pathway as a potential therapeutic target for DEPDC5‐inherited forms of focal epilepsy.

GATORopathies: The role of amino acid regulatory gene mutations in epilepsy and cortical malformations

“…A number of Depdc5 transgenic strains have been described in several species. For example, a zebrafish model generated with antisense morpholino oligonucleotides causing depdc5 loss‐of‐function KD exhibits hyperkinesia, circular swimming, and increased neuronal activity . These phenotypic features were reduced upon treatment with rapamycin.…”

Phenotypic Characterization of Larval Zebrafish (Danio rerio) with Partial Knockdown of the cacna1a Gene

“…In the last decade, zebrafish (Danio rerio) has emerged as a new, attractive species for modeling human brain disorders. With regard to epilepsy research, the utility of zebrafish to mimic aspects of this human disorder has been demonstrated for Dravet syndrome (i.e., SCN1A mutations) [22,23], pyridoxine-dependent epilepsy (ALDH7A1 and PLPBP) [24,25], focal seizures (DEPDC5) [26], or in CHD2-mediated epileptic encephalopathies [27,28]. More recently, Samarut et al [29], using CRISPR/Cas9 technology, generated a new gabra1 −/− mutant zebrafish line in order to unravel the epileptogenic mechanisms underlying gabra1 deficiency and this study undoubtedly confirmed the potential of zebrafish for elucidating mechanisms underlying the process of epileptogenesis.…”

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

“…To record global activity, 28 hpf zebrafish embryos in their chorion were placed on a plastic mesh, submerged in embryo water, and imaged at the frequency of 30 fps as previously described. 37 Activity parameters were quantified using an automatized Zebralab system (ViewPoint, France). Analysis of variance (ANOVA) was performed using the SigmaStat software (California) and data were reported as significant when p<0.05.…”