Developmental expression of rat torsinA transcript and protein

RNAi blocks DYT1 mutant torsinA inclusions in neurons

Early onset generalized dystonia is a dominantly inherited movement disorder caused by neuronal dysfunction without an apparent loss of neurons. The same single mutation (GAG deletion) causes most cases and results in loss of a glutamic acid (E) in the carboxy terminal region of torsinA (Delta302/303). To model the neuronal involvement, adult rat primary sensory dorsal root ganglion neurons in culture were infected with lentivirus vectors expressing human wild-type or mutant torsinA. Expression of the mutant protein resulted in formation of torsinA-positive perinuclear inclusions. When the cells were co-infected with lentivirus vectors expressing the mutant torsinA message and a shRNA selectively targeting this message, inclusion formation was blocked. Vector-delivered siRNAs have the potential to decrease the adverse effects of this mutant protein in neurons without affecting wild-type protein.

Caytaxin deficiency causes generalized dystonia in rats

The genetically dystonic rat (SD-dt:JFL) is an autosomal recessive model of generalized dystonia. Without cerebellectomy, the dt rat dies prior to Postnatal Day 40. The dt locus was mapped to a 4.2 Mb region on Chr 7q11 and candidate genes were screened with semi-quantitative RT-PCR. Then, Southern blotting and genomic DNA sequencing identified the 3'-long terminal repeat portion of an intracisternal A particle element inserted into Intron 1 of Atcay, the gene which encodes caytaxin. Northern and Western blotting and quantitative real-time RT-PCR defined the Atcay allele in dt rats (Atcay(dt)) as hypomorphic. To establish a framework for functional studies of caytaxin, the developmental expression of rat Atcay transcript was analyzed with Northern blotting, relative quantitative multiplex real-time RT-PCR (QRT-PCR) and in situ hybridization. With a multiple tissue Northern blot, three Atcay transcripts were identified in brain but none were present in heart, spleen, lung, liver, muscle, kidney or testis. With a multiple time-point Northern blot, the same three transcripts were present in cerebellum at Embryonic Day (E15), Postnatal Day 1 (P1), P7, P14, P36 and 8 months. During early development (E15 to P14), the relative proportion of the smallest transcript was increased. QRT-PCR was performed with total RNA from cerebral cortex, striatum, thalamus, hippocampus and cerebellum. Transcript levels peaked at P7 in hippocampus, increased linearly from P1 to P36 in cerebellum, and showed minimal developmental regulation in cerebral cortex. Radioactive in situ hybridization localized Atcay transcript to seemingly all neuronal populations in brain. In cerebellum, Atcay transcript was present in the molecular, Purkinje and granular layers; transcript density in the molecular layer peaked at P14. In the background of previous biochemical, behavioral and electrophysiological studies in the dt rat, our data are compatible with a vital role for caytaxin in the development and neurophysiology of cerebellar cortex.

Transgenic mouse model of early-onset DYT1 dystonia

Early-onset dystonia is an autosomal dominant movement disorder associated with deletion of a glutamic acid residue in torsinA. We generated four independent lines of transgenic mice by overexpressing human DeltaE-torsinA using a neuron specific enolase promoter. The transgenic mice developed abnormal involuntary movements with dystonic-appearing, self-clasping of limbs, as early as 3 weeks after birth. Animals also showed hyperkinesia and rapid bi-directional circling. Approximately 40% of transgenic mice from each line demonstrated these severe behavioral abnormalities. Neurochemical analyses revealed decreases in striatal dopamine in affected transgenic mice, although levels were increased in those that had no behavioral changes. Immunohistochemistry demonstrated perinuclear inclusions and aggregates that stained positively for ubiquitin, torsinA and lamin, a marker of the nuclear envelope. Inclusions were detected in neurons of the pedunculopontine nucleus and in other brain stem regions in a pattern similar to what has been described in DYT1 patients. This transgenic mouse model demonstrates behavioral and pathologic features similar to patients with early-onset dystonia and may help to better understand the pathophysiology of this disorder and to develop more effective therapies.