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Hum Mol Genet. 2019 Jan 2. doi: 10.1093/hmg/ddy445. [Epub ahead of print]

The phenotypic landscape of a Tbc1d24 mutant mouse includes convulsive seizures resembling human early infantile epileptic encephalopathy.

Author information

1
Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, Porter Neuroscience Research Center, National Institutes of Health, Bethesda, MD, USA.
2
Department of Otolaryngology, Head and Neck Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
3
Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, USA.
4
Quantitative Medical Imaging Section, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA.
5
Advanced Imaging Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA.
6
Division of Veterinary Resources, National Institutes of Health, Bethesda, MD, USA.
7
Mouse Auditory Testing Core Facility, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA.
8
Genomics and Computational Biology Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA.
9
Rodent Behavioral Core, National Institute of Mental Health, Porter Neuroscience Research Center, National Institutes of Health, Bethesda, MD, USA.
10
Mouse Imaging Facility, In vivo NMR Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
11
Section on Behavioral Neuroscience, National Institute of Mental Health, Porter Neuroscience Research Center, National Institutes of Health, Bethesda, MD, USA.
12
Genetic Engineering Core, National Eye Institute, National Institutes of Health, Bethesda, MD, USA.

Abstract

Epilepsy, deafness, onychodystrophy, osteodystrophy and intellectual disability are associated with a spectrum of mutations of human TBC1D24. The mechanisms underlying TBC1D24-associated disorders and the functions of TBC1D24 are not well understood. Using CRISPR-Cas9 genome editing, we engineered a mouse with a premature translation stop codon equivalent to human S324Tfs*3, a recessive mutation of TBC1D24 associated with early infantile epileptic encephalopathy (EIEE). Homozygous S324Tfs*3 mice have normal auditory and vestibular functions but show an abrupt onset of spontaneous seizures at postnatal day 15 recapitulating human EIEE. The S324Tfs*3 variant is located in an alternatively spliced micro-exon encoding six perfectly conserved amino acids incorporated postnatally into TBC1D24 protein due to a micro-exon utilization switch. During embryonic and early postnatal development, S324Tfs*3 homozygotes produce predominantly the shorter wild-type TBC1D24 protein isoform that omits the six residues encoded by the micro-exon. S324Tfs*3 homozygotes show an abrupt onset of seizures at P15 that correlates with a developmental switch to utilization of the micro-exon. A mouse deficient for alternative splice factor SRRM3 impairs incorporation of the Tbc1d24 micro-exon. Wild-type Tbc1d24 mRNA is abundantly expressed in the hippocampus using RNAscope in situ hybridization. Immunogold electron microscopy using a TBC1D24-specific antibody revealed that TBC1D24 is associated with clathrin-coated vesicles and synapses of hippocampal neurons, suggesting a crucial role of TBC1D24 in vesicle trafficking important for neuronal signal transmission. This is the first characterization of a mouse model of human TBC1D24-associated EIEE that can now be used to screen for antiepileptogenic drugs ameliorating TBCID24 seizure disorders.

PMID:
30602030
DOI:
10.1093/hmg/ddy445

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