Background
The calcium-binding protein 4 (
CABP4
) gene is a newly identified epilepsy-related gene that might be associated with a rare type of genetic focal epilepsy; that is, autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE).
In vitro
, mutant CABP4 causes an increased inward flow voltage of calcium ions and a significant increase in the electrical signal discharge in hippocampus neurons; however, the role of
CABP4
in epilepsy has not yet been specifically described, and there is not yet a CABP4 mutant animal model recapitulating the epilepsy phenotype.
Methods
We introduced a human
CABP4
missense mutation into the C57BL/6J mouse genome and generated a knock-in strain carrying a glycine-to-aspartic acid mutation in the gene. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were performed to evaluate the
CABP4
expression level. Slice patch-clamp recording was carried out on pyramidal cells of prefrontal cortex layers II and III.
Results
The
CABP4
G155D/+
mutant mice were viable and born at an expected Mendelian ratio. Surprisingly, the heterozygous (HE) mice did not display either an abnormal appearance or an overt seizure phenotype, and there was no statistically significant difference between the HE and wild-type (WT) mice in terms of overall messenger RNA (mRNA) and protein expression. However, the HE mutant mice showed an imbalance in the amount of protein expressed in the brain regions. Additionally, the patch-clamp recordings from the HE mouse layer II/III cortical pyramidal cells revealed an increase in the frequency of micro-excitatory post-synaptic currents (mEPSCs) but no change in the amplitude was observed.
Conclusions
The findings of this study suggest that the
CABP4
p.G155D mutation might be one of the mechanisms underlying seizure onset.