Nuclear Localization of Ataxin-3 Is Required for the Manifestation of Symptoms in SCA3:In VivoEvidence

Abstract

Spinocerebellar ataxia type 3 (SCA3)is an autosomal dominantly inherited neurodegenerative disorder caused by the expansion of a CAG repeat in the MJD1 gene resulting in an expanded polyglutamine repeat in the ataxin-3 protein. To study the course of the disease, we generated transgenic mice for SCA3 using full-length ataxin-3 constructs containing 15, 70, or 148 CAG repeats, respectively. Control mice (15 CAGs) were phenotypically normal and had no neuropathological findings. However, mice transgenic for ataxin-3 with expanded polyglutamine repeats were severely affected by a strong neurological phenotype with tremor, behavioral deficits, strongly reduced motor and exploratory activity, a hunchback, and premature death at 3 to 6 months of age. Neuropathological examination by immunohistochemical staining revealed ubiquitin-and ataxin-3-positive intranuclear inclusion bodies in a multitude of neurons. Directing ataxin-3 with 148 CAGs to the nucleus revealed an even more pronounced phenotype with more inclusions and earlier death, whereas mice transgenic with the same construct but attached to a nuclear export signal developed a milder phenotype with less inclusions. These studies indicate that nuclear localization of ataxin-3 is required for the manifestation of symptoms in SCA3 in vivo.

Mouse Models of Spinocerebellar Ataxia Type 3 (Machado-Joseph Disease)

“…The fragment was only detected in an enhanced image of the Western blot. 3) In model 3, a reduced turnover rate of dopamine and serotonin is reported [34], which predictably occurs in model 2. Summary of major behaviors/signs, brain distribution of neuronal inclusions, and neurodegeneration quantified by stereology, in mouse models ≤15 months of age.…”

“…For each of the next 7 transgenic mice generated [32][33][34][35][36][37][38]: the transgenic mouse construct, behavior/signs, and pathology are summarized as follows.…”

“…For mouse model 3 [34], ataxin-3 isoform 3c with 70 or 15 CAG are expressed under the control of the mouse prion protein promoter. The vector MoPrP used has 1.14 kb upstream of exon 1, intron 1, and 52 bp of exon 2.…”

“…Mouse model 3 [34], line 70.61 had: 1) low body weight: the animals were described as small; 2) reduced balance and coordination: inability to grab a pen and walk on it at 6 to 8 months; 3) abnormal gait: wide-based footprint pattern at 3 months, and dragged footprint pattern at 6 months; …”

“…Mouse model 3 [34], line 70.61: 1) Intranuclear inclusions in neurons: detected in cerebellar nuclei, pons, granular layer of cerebellum, hippocampus, and cerebral cortex, but not in Purkinje cells. Indeed, it was reported that such inclusions were found in almost all brain regions analyzed.…”