Spontaneous shaker rat mutant – a new model for X-linked tremor/ataxia

Abstract

The shaker rat is an X-linked recessive spontaneous model of progressive Purkinje cell (PC) degeneration exhibiting a shaking ataxia and wide stance. Generation of Wistar Furth (WF)/Brown Norwegian (BN) F1 hybrids and genetic mapping of F2 sib-sib offspring using polymorphic markers narrowed the candidate gene region to 26 Mbp denoted by the last recombinant genetic marker DXRat21 at 133 Mbp to qter (the end of the long arm). In the WF background, the shaker mutation has complete penetrance, results in a stereotypic phenotype and there is a narrow window for age of disease onset; by contrast, the F2 hybrid phenotype was more varied, with a later age of onset and likely non-penetrance of the mutation. By deep RNA-sequencing, five variants were found in the candidate region; four were novel without known annotation. One of the variants caused an arginine (R) to cysteine (C) change at codon 35 of the ATPase, Ca2+ transporting, plasma membrane 3 (Atp2b3) gene encoding PMCA3 that has high expression in the cerebellum. The variant was well supported by hundreds of overlapping reads, and was found in 100% of all affected replicas and 0% of the wild-type (WT) replicas. The mutation segregated with disease in all affected animals and the amino acid change was found in an evolutionarily conserved region of PMCA3. Despite strong genetic evidence for pathogenicity, in vitro analyses of PMCA3R35C function did not show any differences to WT PMCA3. Because Atp2b3 mutation leads to congenital ataxia in humans, the identified Atp2b3 missense change in the shaker rat presents a good candidate for the shaker rat phenotype based on genetic criteria, but cannot yet be considered a definite pathogenic variant owing to lack of functional changes.

Deep cerebellar stimulation reduces ataxic motor symptoms in the shaker rat

“…Four rats exhibited tremor at 9 to 11 weeks of age, the last 2 having symptom onset at 14 and 19 weeks. These were consistent with previous qualitative determinations that shaker rats first display symptoms between 9 and 20 weeks of age . Whereas qualitative observations noted onset no earlier than 9 weeks, we quantitatively found that shaker rats demonstrated significantly more tremor than WT animals ( bca , p < 0.00001) at all ages from 8 weeks on.…”

“…These were consistent with previous qualitative determinations that shaker rats first display symptoms between 9 and 20 weeks of age. 18 Whereas qualitative observations noted onset no earlier than 9 weeks, we quantitatively found that shaker rats demonstrated significantly more tremor than WT animals (bca, p < 0.00001) at all ages from 8 weeks on. Power spectra of representative 10-week shaker and WT rats are shown (see Fig 2A), along with tremor versus age (see Fig 2B).…”

“…[5][6][7][8][9] Most degenerative ataxias feature Purkinje cell loss, 10,11 resulting in modified inputs to the deep cerebellar nuclei; thus, neuromodulation targeting these deep cerebellar nuclei may succeed in numerous DCAs. 18,19 Symptoms begin at~9 weeks with a full-body tremor, progressing to a severe, shaking ataxia, with frequent falling. Whereas previous work assessed thalamic and basal ganglia stimulation to treat DCAs, 12,13 we targeted stimulation to the dorsal dentate nucleus, because the dentate is immediately downstream from Purkinje cells; furthermore, as the primary cerebellar motor output, it processes the majority of deep cerebellar motor control information.…”

“…Shaker rats progressively lose Purkinje cells but retain an intact overall cerebellar architecture and dentatothalamocortical pathway. 18,19 Symptoms begin at~9 weeks with a full-body tremor, progressing to a severe, shaking ataxia, with frequent falling. The shaker rat's recapitulation of the salient features of DCAs, its large cerebellar targets, and the high-throughput nature of rodent experiments made it ideal for these studies.…”

“…We tested whether dorsal dentate nucleus electrical stimulation reduces degenerative ataxia motor symptoms using the Wistar Furth shaker rat, an x‐linked recessive DCA model. Shaker rats progressively lose Purkinje cells but retain an intact overall cerebellar architecture and dentatothalamocortical pathway . Symptoms begin at ~9 weeks with a full‐body tremor, progressing to a severe, shaking ataxia, with frequent falling.…”