Tremor dominant Kyoto (Trdk) rats carry a missense mutation in the gene encoding the SK2 subunit of small-conductance Ca2+-activated K+ channel.

Tremor dominant Kyoto (Trdk) is an autosomal dominant mutation that appeared in F344/NSlc rats mutagenized with N-ethyl-N-nitrosourea (ENU). In this study, we characterized and genetically analyzed F344-Trdk/+ heterozygous rats. The rats exhibited a tremor that was especially evident around weaning but persisted throughout life. The tremors of F344-Trdk/+ rats were attenuated by drugs effective against essential tremor (ET) but not drugs used to treat Parkinson's disease-related tremor, indicating that the pharmacological phenotype of F344-Trdk/+ rats was similar to human ET. Using positional candidate approach, we identified the Trdk mutation as a missense substitution (c. 866T>A, p. I289N) in Kcnn2, which encodes the SK2 subunit of the small-conductance Ca2+-activated K+ channel. In vitro electrophysiological studies revealed that the I289N mutation diminished SK2 channel activity. These findings demonstrate that F344-Trdk/+ rats represent a novel model of ET, and strongly suggest that Kcnn2 is the causative gene for the tremor phenotype in F344-Trdk/+ rats.

Involvement of aspartoacylase in tremor expression in rats.

Essential tremor (ET) is a common movement disorder with a poorly understood etiology. The TRM/Kyo mutant rat, showing spontaneous tremor, is an animal model of ET. Recently, we demonstrated that tremors in these rats emerge when two mutant loci, a missense mutation in the hyperpolarization-activated cyclic nucleotide-gated potassium channel 1 (Hcn1) and the tremor (tm) deletion, are present simultaneously. However, we did not identify which gene within the tm deletion causes tremor expression in TRM/Kyo rats. A strong candidate among the 13 genes within the tm deletion is aspartoacylase (Aspa), because some Aspa-knockout mouse strains show tremor. Here, we generated Aspa-knockout rats using transcription activator-like effector nuclease technology and produced Aspa/Hcn1 double-mutant rats by crossing Aspa-knockout rats with Hcn1-mutant rats. The Aspa-knockout rats carried nonsense mutations in exon 4; and ASPA proteins were not detectable in their brain extracts. They showed elevated levels of N-acetyl-L-aspartate (NAA) in urine and spongy vacuolation and abnormal myelination in the central nervous system, but no tremor. By contrast, Aspa/Hcn1 double-mutant rats spontaneously showed tremors resembling those in TRM/Kyo rats, and the tremor was suppressed by drugs therapeutic for ET but not for parkinsonian tremor. These findings indicated that the lack of the Aspa gene caused tremor expression in TRM/Kyo rats. Our animal model suggested that the interaction of NAA accumulation due to ASPA deficiency with an unstable neuronal membrane potential caused by HCN1 deficiency was involved in tremor development.

Atopic dermatitis-like skin lesions with IgE hyperproduction and pruritus in KFRS4/Kyo rats.

BACKGROUND: Rats showing spontaneous atopic dermatitis (AD)-like skin lesions were observed in the Kyoto Fancy Rat Stock 4 (KFRS4) strain breeding colony. OBJECTIVE: To establish the KFRS4 rat as a model of AD. METHODS: The clinical symptoms of AD-like skin lesions were assessed by scoring the degree of dermatitis and examining scratching behavior. The transepidermal water loss was measured to evaluate skin barrier function. Cells infiltrating the skin lesions were identified using histological and immunohistological analyses. IgE and cytokine levels were measured to examine immune status. An ointment treatment experiment was carried out to characterize dermatitis in the KFRS4 rats. RESULTS: Dermatitis initially appeared around 4 months of age and rapidly worsened from 6 to 8 months of age. The skin lesions accompanied scratching behavior and were predominantly observed in females. The increased transepidermal water loss indicated skin barrier dysfunction. Extensive infiltration of eosinophils, mast cells and lymphocytes was observed in the skin lesions. The plasma IgE level increased in accord with increasing severity of dermatitis. The Th2 and Th17 cytokine mRNA levels were significantly higher in the skin-draining lymph nodes than those in the non-skin-draining lymph nodes. It was demonstrated that betamethasone improved the symptoms of dermatitis. These findings demonstrated that dermatitis in the KFRS4 rats closely resembled that seen in human AD. CONCLUSION: Female KFRS4 rats have the potential to serve as an animal model of human AD.

A rat model of hypohidrotic ectodermal dysplasia carries a missense mutation in the Edaradd gene.

BACKGROUND: Hypohidrotic ectodermal dysplasia (HED) is a congenital disorder characterized by sparse hair, oligodontia, and inability to sweat. It is caused by mutations in any of three Eda pathway genes: ectodysplasin (Eda), Eda receptor (Edar), and Edar-associated death domain (Edaradd), which encode ligand, receptor, and intracellular adaptor molecule, respectively. The Eda signaling pathway activates NF-κB, which is central to ectodermal differentiation. Although the causative genes and the molecular pathway affecting HED have been identified, no curative treatment for HED has been established. Previously, we found a rat spontaneous mutation that caused defects in hair follicles and named it sparse-and-wavy (swh). Here, we have established the swh rat as the first rat model of HED and successfully identified the swh mutation. RESULTS: The swh/swh rat showed sparse hair, abnormal morphology of teeth, and absence of sweat glands. The ectoderm-derived glands, meibomian, preputial, and tongue glands, were absent. We mapped the swh mutation to the most telomeric part of rat Chr 7 and found a Pro153Ser missense mutation in the Edaradd gene. This mutation was located in the death domain of EDARADD, which is crucial for signal transduction and resulted in failure to activate NF-κB. CONCLUSIONS: These findings suggest that swh is a loss-of-function mutation in the rat Edaradd and indicate that the swh/swh rat would be an excellent animal model of HED that could be used to investigate the pathological basis of the disease and the development of new therapies.

Genetic analyses of fancy rat-derived mutations.

To collect rat mutations and increase the value of the rat model system, we introduced fancy-derived mutations to the laboratory and carried out genetic analyses. Six fancy rats were shipped from a fancy rat colony in the USA and used as founders. After initial crosses with a laboratory strain, TM/Kyo or PVG/Seac, inbreeding started and 6 partially inbred lines, including 2 sublines, were produced as Kyoto Fancy Rat Stock (KFRS) strains. During inbreeding, we isolated 9 mutations: 5 coat colors, American mink (am), Black eye (Be), grey (g), Pearl (Pel), siamese (sia); 1 coat pattern, head spot (hs); 2 coat textures, Rex (Re), satin (sat); and an ear pinnae malformation, dumbo (dmbo). Genetic analyses mapped 7 mutations to particular regions of the rat chromosomes (Chr): am to Chr 1, sia to Chr 1, sat to Chr 3, Re to Chr 7, g to Chr 8, dmbo to Chr 14, and hs to Chr 15. Candidate gene analysis revealed that a missense mutation in the tyrosinase gene, Ser79Pro, was responsible for sia. From mutant phenotypes and mapping positions, it is likely that all mutations isolated in this study were unique to the fancy rat. These findings suggest that fancy rat colonies are a good source for collecting rat mutations. The fancy-derived mutations, made available to biomedical research in the current study, will increase the scientific value of laboratory rats.