Knockout of the epilepsy gene Depdc5 in mice causes severe embryonic dysmorphology with hyperactivity of mTORC1 signalling

Abstract

DEPDC5 mutations have recently been shown to cause epilepsy in humans. Evidence from in vitro studies has implicated DEPDC5 as a negative regulator of mTORC1 during amino acid insufficiency as part of the GATOR1 complex. To investigate the role of DEPDC5 in vivo we generated a null mouse model using targeted CRISPR mutagenesis. Depdc5 homozygotes display severe phenotypic defects between 12.5-15.5 dpc, including hypotrophy, anaemia, oedema, and cranial dysmorphology as well as blood and lymphatic vascular defects. mTORC1 hyperactivity was observed in the brain of knockout embryos and in fibroblasts and neurospheres isolated from knockout embryos and cultured in nutrient deprived conditions. Heterozygous mice appeared to be normal and we found no evidence of increased susceptibility to seizures or tumorigenesis. Together, these data support mTORC1 hyperactivation as the likely pathogenic mechanism that underpins DEPDC5 loss of function in humans and highlights the potential utility of mTORC1 inhibitors in the treatment of DEPDC5-associated epilepsy.

Depdc5 knockdown causes mTOR‐dependent motor hyperactivity in zebrafish

“…While the Depdc5 heterozygous animals presented mTORC1 hyperactivation, they did not display any spontaneous seizures,12, 16 suggesting that in these constitutive Depdc5 KO rodent models a functional compensation could partially mask the proepileptic effect of DEPDC5 loss of function. In the acute knockdown experiments presented here the possibility of functional compensation is strongly reduced.…”

“…Two other components of the GATOR1 complex, NPRL2 and 3 have been shown to be mutated in familial focal epilepsy with or without focal cortical dysplasia,5, 13, 14, 15 suggesting hyperactivation of mTORC1 as a major cause of epileptic syndromes. Rodent models of Depdc5 confirm the essential role played by this mTOR regulator in development 12, 16. DEPDC5 homozygous null mutations cause embryonic lethality at midgestation due to a range of abnormalities such as general hypoplasia, cranial dysplasia and cardiovascular defects.…”

“…Recent rodent knockout models of Depdc5 highlight the essential role of DEPDC5 during embryonic development, as constitutive null mutations result in embryonic lethality 12, 16. While the Depdc5 heterozygous animals presented mTORC1 hyperactivation, they did not display any spontaneous seizures,12, 16 suggesting that in these constitutive Depdc5 KO rodent models a functional compensation could partially mask the proepileptic effect of DEPDC5 loss of function.…”

“…In both mouse and rat models, Depdc5 loss‐of‐function was associated with increased mTOR activity. Constitutive DEPDC5 heterozygous null animals were viable and presented subtle alterations of electrographic activity12; however, they lacked overt behavioral phenotypes and seizures,12, 16 highlighting the complexity of the Depdc5 loss‐of‐function phenotype.…”

mTOR pathway somatic variants and the molecular pathogenesis of hemimegalencephaly

“…The study by Marsan and colleagues showed that mTORC1 is hyperactivated in DEPDC5 knockout mice and that a single prenatal injection of rapamycin could avoid its overall growth delay, demonstrating that embryonic lethality is caused by hyperactivation of mTORC1. Hughes et al (2017) corroborated these findings and reported blood vascular defects, as well as cortical and lymphatic developmental malformations underlying embryonic lethality in DEPDC5 knockout rats …”