CUX2 deficiency causes facilitation of excitatory synaptic transmission onto hippocampus and increased seizure susceptibility to kainate.

CUX2 gene encodes a transcription factor that controls neuronal proliferation, dendrite branching and synapse formation, locating at the epilepsy-associated chromosomal region 12q24 that we previously identified by a genome-wide association study (GWAS) in Japanese population. A CUX2 recurrent de novo variant p.E590K has been described in patients with rare epileptic encephalopathies and the gene is a candidate for the locus, however the mutation may not be enough to generate the genome-wide significance in the GWAS and whether CUX2 variants appear in other types of epilepsies and physiopathological mechanisms are remained to be investigated. Here in this study, we conducted targeted sequencings of CUX2, a paralog CUX1 and its short isoform CASP harboring a unique C-terminus on 271 Japanese patients with a variety of epilepsies, and found that multiple CUX2 missense variants, other than the p.E590K, and some CASP variants including a deletion, predominantly appeared in patients with temporal lobe epilepsy (TLE). The CUX2 variants showed abnormal localization in human cell culture analysis. While wild-type CUX2 enhances dendritic arborization in fly neurons, the effect was compromised by some of the variants. Cux2- and Casp-specific knockout mice both showed high susceptibility to kainate, increased excitatory cell number in the entorhinal cortex, and significant enhancement in glutamatergic synaptic transmission to the hippocampus. CASP and CUX2 proteins physiologically bound to each other and co-expressed in excitatory neurons in brain regions including the entorhinal cortex. These results suggest that CUX2 and CASP variants contribute to the TLE pathology through a facilitation of excitatory synaptic transmission from entorhinal cortex to hippocampus.

A recurrent PJA1 variant in trigonocephaly and neurodevelopmental disorders.

OBJECTIVE: Neurodevelopmental disorders (NDDs) often associate with epilepsy or craniofacial malformations. Recent large-scale DNA analyses identified hundreds of candidate genes for NDDs, but a large portion of the cases still remain unexplained. We aimed to identify novel candidate genes for NDDs. METHODS: We performed exome sequencing of 95 patients with NDDs including 51 with trigonocephaly and subsequent targeted sequencing of additional 463 NDD patients, functional analyses of variant in vitro, and evaluations of autism spectrum disorder (ASD)-like phenotypes and seizure-related phenotypes in vivo. RESULTS: We identified de novo truncation variants in nine novel genes; CYP1A1, C14orf119, FLI1, CYB5R4, SEL1L2, RAB11FIP2, ZMYND8, ZNF143, and MSX2. MSX2 variants have been described in patients with cranial malformations, and our present patient with the MSX2 de novo truncation variant showed cranial meningocele and partial epilepsy. MSX2 protein is known to be ubiquitinated by an E3 ubiquitin ligase PJA1, and interestingly we found a PJA1 hemizygous p.Arg376Cys variant recurrently in seven Japanese NDD patients; five with trigonocephaly and one with partial epilepsy, and the variant was absent in 886 Japanese control individuals. Pja1 knock-in mice carrying p.Arg365Cys, which is equivalent to p.Arg376Cys in human, showed a significant decrease in PJA1 protein amount, suggesting a loss-of-function effect of the variant. Pja1 knockout mice displayed moderate deficits in isolation-induced ultrasonic vocalizations and increased seizure susceptibility to pentylenetetrazole. INTERPRETATION: These findings propose novel candidate genes including PJA1 and MSX2 for NDDs associated with craniofacial abnormalities and/or epilepsy.

Increase in GFAP-positive astrocytes in histone demethylase GASC1/KDM4C/JMJD2C hypomorphic mutant mice.

GASC1, also known as KDM4C/JMJD2C, is a histone demethylase for histone H3 lysine 9 (H3K9) and H3K36. In this study, we observed an increase of GFAP-positive astrocytes in the brain of Gasc1 hypomorphic mutant mice at 2-3 months of age, but not at postnatal day 14 and day 30 by immunohistochemistry. Increases of GFAP-positive astrocytes were widely observed in the forebrain and prominent in such regions as cerebral cortex, caudate putamen, amygdala and diencephalon, but not obvious in hippocampus. Taken together with our observations to be published elsewhere that Gasc1 hypomorphic mutant mice exhibit abnormal behaviors including hyperactivity, persistence and many types of learning and memory deficits and abnormal synaptic functions such as prolonged long-term potentiation, the increase in GFAP-positive astrocytes may help understand their phenotypes, because astrocytes are known to affect synaptic plasticity.