Abstract
Heterozygous and rare homozygous mutations in PRoline-Rich Transmembrane protein 2 (PRRT2) underlie a group of paroxysmal disorders including epilepsy, kinesigenic dyskinesia episodic ataxia and migraine. Most of the mutations lead to impaired PRRT2 expression and/or function. Recently, an important role for PRTT2 in the neurotransmitter release machinery, brain development and synapse formation has been uncovered. In this work, we have characterized the phenotype of a mouse in which the PRRT2 gene has been constitutively inactivated (PRRT2 KO). β-galactosidase staining allowed to map the regional expression of PRRT2 that was more intense in the cerebellum, hindbrain and spinal cord, while it was localized to restricted areas in the forebrain. PRRT2 KO mice are normal at birth, but display paroxysmal movements at the onset of locomotion that persist in the adulthood. In addition, adult PRRT2 KO mice present abnormal motor behaviors characterized by wild running and jumping in response to audiogenic stimuli that are ineffective in wild type mice and an increased sensitivity to the convulsive effects of pentylentetrazol. Patch-clamp electrophysiology in hippocampal and cerebellar slices revealed specific effects in the cerebellum, where PRRT2 is highly expressed, consisting in a higher excitatory strength at parallel fiber-Purkinje cell synapses during high frequency stimulation. The results show that the PRRT2 KO mouse reproduces the motor paroxysms present in the human PRRT2-linked pathology and can be proposed as an experimental model for the study of the pathogenesis of the disease as well as for testing personalized therapeutic approaches.
Highlights
Proline-rich transmembrane protein 2 (PRRT2)1 is the causative gene for a variety of paroxysmal neurological disorders that can be⁎ Corresponding author at: Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy.To date, some 1500 patients with 70 different PRRT2 mutations have been reported, 78% of which carrying the same frameshift mutation (c.649dupC)
We have characterized the phenotype of a mouse in which the PRRT2 gene has been constitutively inactivated (PRRT2 KO). β-galactosidase staining allowed to map the regional expression of PRRT2 that was more intense in the cerebellum, hindbrain and spinal cord, while it was localized to restricted areas in the forebrain
After the demonstration that successful homologous recombination had occurred in our PRRT2 mice by PCR (Fig. S1B), we confirmed the creation of a null allele for PRRT2 by analyzing the expression of PRRT2 protein in various brain areas in adult WT, HET and KO mice by quantitative immunoblotting (Fig. S1C)
Summary
Some 1500 patients with 70 different PRRT2 mutations have been reported, 78% of which carrying the same frameshift mutation (c.649dupC). In addition to this frequent mutation, about 75% of all reported PRRT2 mutations involve the insertion of a precocious stop codon, leading to an unstable mRNA and/or a truncated protein that is degraded or mistargeted (Chen et al, 2011; Lee et al, 2012; Li et al, 2015; Liu et al, 2016; Valtorta et al, 2016). The noticeable pleiotropy of the phenotypes associated with PRRT2 mutations is not reflected by specific genotype-phenotype correlations (Ebrahimi-Fakhari et al, 2015; Gardiner et al, 2015; Heron and Dibbens, 2013; Valtorta et al, 2016)
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