Genetic Modeling of the Neurodegenerative Disease Spinocerebellar Ataxia Type 1 in Zebrafish

Abstract

Dominant spinocerebellar ataxias (SCAs) are progredient neurodegenerative diseases commonly affecting the survival of Purkinje cells (PCs) in the human cerebellum. Spinocerebellar ataxia type 1 (SCA1) is caused by the mutated ataxin1 (Atx1) gene product, in which a polyglutamine stretch encoded by CAG repeats is extended in affected SCA1 patients. As a monogenetic disease with the Atx1-polyQ protein exerting a gain of function, SCA1 can be genetically modelled in animals by cell type-specific overexpression. We have established a transgenic PC-specific SCA1 model in zebrafish coexpressing the fluorescent reporter protein mScarlet together with either human wild type Atx1[30Q] as control or SCA1 patient-derived Atx1[82Q]. SCA1 zebrafish display an age-dependent PC degeneration starting at larval stages around six weeks postfertilization, which continuously progresses during further juvenile and young adult stages. Interestingly, PC degeneration is observed more severely in rostral than in caudal regions of the PC population. Although such a neuropathology resulted in no gross locomotor control deficits, SCA1-fish with advanced PC loss display a reduced exploratory behaviour. In vivo imaging in this SCA1 model may help to better understand such patterned PC death known from PC neurodegeneration diseases, to elucidate disease mechanisms and to provide access to neuroprotective compound characterization in vivo.

Purkinje cells located in the adult zebrafish valvula cerebelli exhibit variable functional responses

“…Though the Purkinje cell layer continues seamlessly from the corpus to the valvula, these structures form cerebellar functional subcompartments built from different combinations of common and specific Purkinje cell subtypes. Recent evidence from the zebrafish genetic model of Spinocerebellar Ataxia Type 1 (SCA1) revealed an apparent preferential regional vulnerability of Purkinje cells that affected significant the exploratory behavior but not the animal’s locomotion 28 , supporting further the presence of regional specific Purkinje cell contributions to different cerebellar functions. Hence, our findings further suggest that multiple functionally diverse classes of Purkinje cells are essential for dividing the labor of the demanding computational duties of the cerebellum to process numerous and diverse locomotor and non-locomotor functions.…”

Advances in Modeling Polyglutamine Diseases Using Genome Editing Tools

“…Additionally, the models explore genetic pathways and mechanisms underlying disease development such as expansions, aberrant splicing, repeat-associated non-AUG (RAN) translation and RNA frameshifting. By using methods such as lentiviral transduction, microinjection with mRNA and transposase-mediated recombination, transgenic models were generated in yeast [87,88], human embryonic kidney (HEK) 293T cells [89][90][91], C. elegans [92][93][94][95], D. melanogaster [96][97][98], zebrafish [99][100][101][102], the mouse [27,[103][104][105][106][107][108][109][110][111][112][113], rat [83,114], sheep [115], pig [116,117] and monkey [118][119][120][121]. Additionally, patient-derived cells were reprogrammed into iPSCs and used to model polyQ diseases [122][123][124][125][126][127][128].…”

“…Among the simplest models that favored the study of polyQ diseases in the context of the whole organism were those made in Caenorhabditis elegans (nematode), Drosophila melanogaster (fruit fly) and Danio rerio (zebrafish). These models, with the full gene [95,102] or with a truncated gene, were used with the expanded CAG repeat tract [96][97][98]. They convincingly showed pathogenic features of polyQ diseases including aggregate formation, the toxicity of the mutant proteins, neurotransmission defects and progressive neuronal degeneration [92,[96][97][98]102,[165][166][167].…”

“…These models, with the full gene [95,102] or with a truncated gene, were used with the expanded CAG repeat tract [96][97][98]. They convincingly showed pathogenic features of polyQ diseases including aggregate formation, the toxicity of the mutant proteins, neurotransmission defects and progressive neuronal degeneration [92,[96][97][98]102,[165][166][167]. Additionally, they are excellent models with which to study the mechanisms underlying polyQ disease symptoms, find potential targets for therapeutic interventions, search for new interactomes and verify findings from other models or patients [95][96][97]101,167].…”

Lifelong regeneration of cerebellar Purkinje neurons after induced cell ablation in zebrafish

“…Hence, PC degeneration in humans results in severe neurological symptoms like ataxia, altered locomotor activity, but also anxiety and social disabilities. These diseases can be genetically modeled in zebrafish PCs (Elsaey et al, 2021; Hsieh et al, 2020; K. Namikawa et al, 2019; Kazuhiko Namikawa et al, 2019; Watchon et al, 2017), but it has remained elusive so far whether such PC degeneration can be counteracted by regeneration to slow down and mitigate disease progression.…”