Identification of Candidate Genes for Generalized Tonic–Clonic Seizures in Noda Epileptic Rat

Abstract

The Noda epileptic rat (NER) exhibits generalized tonic-clonic seizures (GTCS). A genetic linkage analysis identified two GTCS-associated loci, Ner1 on Chr 1 and Ner3 on Chr 5. The wild-type Ner1 and Ner3 alleles suppressed GTCS when combined in double-locus congenic lines, but not when present in single-locus congenic lines. Global expression analysis revealed that cholecystokinin B receptor (Cckbr) and suppressor of tumorigenicity 5 (St5), which map within Ner1, and PHD finger protein 24 (Phf24), which maps within Ner3, were significantly downregulated in NER. De novo BAC sequencing detected an insertion of an endogenous retrovirus sequence in intron 2 of the Phf24 gene in the NER genome, and PHF24 protein was almost absent in the NER brain. Phf24 encodes a G-interacting protein involved in GABA receptor signaling pathway. Based on these findings, we conclude that Cckbr, St5, and Phf24 are strong candidate genes for GTCS in NER.

Role of Astrocytic Inwardly Rectifying Potassium (Kir) 4.1 Channels in Epileptogenesis

“…Specifically, Kir4.1 expression was significantly reduced in Noda epileptic rats (NER), a hereditary epilepsy model ( Table 1) (89). NER exhibited frequent spontaneous GTCSs associated with two genetic loci, chromosome (Chr) 1q32-33 and Chr5q22, including cholecystokinin B receptor (Cckbr), suppressor of tumorigenicity 5 (St5), and PHD finger protein 24 (Phf24) (90)(91)(92)(93)(94)(95). In NER, Kir4.1 expression was region-specifically reduced in the amygdala, where the expression of Fos protein, a biological marker of neural excitation, significantly elevated (89).…”

Comparative genomic analysis of inbred rat strains reveals the existence of ancestral polymorphisms

“…We used the genomic sequences corresponding to the coding regions of 25 inbred rat strains (DDBJ Sequence Read Archive accession number: DRA004543; DDBJ/EMBL/ GenBank accession number: PRJDB4648) obtained from our previous studies (Yoshihara et al 2016a, b;Kuramoto et al 2017) (Table 1). These 25 strains were selected according to the following three categories: representative inbred strains (F344/DuCrlCrlj, F344/Jcl, F344/NSlc, and F344/ Stm), those originating from wild populations (BN/SsNSlc, DOB/Oda, IS/Kyo, IS-Tlk/Kyo, LE/Stm, LEC/Tj, and NIG-III/Hok), and disease models derived from selective breeding (BDIX/NemOda, BDIX.Cg-Tal/NemOda, BUF/ MNa, HTX/Kyo, HWY/Slc, KFRS3B/Kyo, KFRS4/Kyo, NER/Kyo, PVG/Seac, RCS/Kyo, WTC/Kyo, WTC-swh/ Kyo, ZF, and ZFDM).…”

“…The advent of genome editing technologies, however, has enabled the genetic manipulation of rats (Mashimo et al 2013), and genetic analyses in rats will be greatly advanced in the future. Currently, more than 800 inbred rat strains are registered in the National BioResource Project-Rat (NBRP-Rat) at Kyoto University, one of the largest repositories for rat strains, as live animals, embryos, or sperm (Serikawa et al 2009), and we have determined the protein coding genes and non-coding conserved sequences of some representative rat strains registered in NBRP-Rat (Yoshihara et al 2016a, b;Kuramoto et al 2017).…”

“…In this study, using the genomic sequences of all protein coding genes of 25 inbred rat strains that we recently sequenced (Yoshihara et al 2016a, b;Kuramoto et al 2017), we first analyzed the phylogenetic relationship among them, and then comprehensively identified variant sites that showed discordant mutation patterns. We found that discordant sites are not uniformly distributed along chromosomes, but are concentrated at certain genomic loci.…”

PHF24 is expressed in the inhibitory interneurons in rats

“…Three candidate genes were identified to contribute to the epileptogenesis of NER [5,6]. PHD finger protein 24 (Phf24) was identified as a major candidate gene; lack of PHF24 expression was considered to be related to epileptogenesis of NER [6]. PHF24 is a key modulator of peripherally evoked GABAB-receptor signaling [7].…”