A Hereditary Spastic Paraplegia Mouse Model Supports a Role of ZFYVE26/SPASTIZIN for the Endolysosomal System

Hereditary spastic paraplegias (HSPs) are characterized by progressive weakness and spasticity of the legs because of the degeneration of cortical motoneuron axons. SPG15 is a recessively inherited HSP variant caused by mutations in the ZFYVE26 gene and is additionally characterized by cerebellar ataxia, mental decline, and progressive thinning of the corpus callosum. ZFYVE26 encodes the FYVE domain-containing protein ZFYVE26/SPASTIZIN, which has been suggested to be associated with the newly discovered adaptor protein 5 (AP5) complex. We show that Zfyve26 is broadly expressed in neurons, associates with intracellular vesicles immunopositive for the early endosomal marker EEA1, and co-fractionates with a component of the AP5 complex. As the function of ZFYVE26 in neurons was largely unknown, we disrupted Zfyve26 in mice. Zfyve26 knockout mice do not show developmental defects but develop late-onset spastic paraplegia with cerebellar ataxia confirming that SPG15 is caused by ZFYVE26 deficiency. The morphological analysis reveals axon degeneration and progressive loss of both cortical motoneurons and Purkinje cells in the cerebellum. Importantly, neuron loss is preceded by accumulation of large intraneuronal deposits of membrane-surrounded material, which co-stains with the lysosomal marker Lamp1. A density gradient analysis of brain lysates shows an increase of Lamp1-positive membrane compartments with higher densities in Zfyve26 knockout mice. Increased levels of lysosomal enzymes in brains of aged knockout mice further support an alteration of the lysosomal compartment upon disruption of Zfyve26. We propose that SPG15 is caused by an endolysosomal membrane trafficking defect, which results in endolysosomal dysfunction. This appears to be particularly relevant in neurons with highly specialized neurites such as cortical motoneurons and Purkinje cells.     

Expression and Electrophysiological Function of Actin in Chick Cerebellar Neurons

Among several monoclonal antibodies obtained by immunizing Balb/c mice with cerebellar synaptic membrane fractions from E20 chick embryos, the antibody, named M35, suppressed Ca-spikes in immature cultured chick cerebellar neurons. M35 immunoprecipitated 43kDa protein from a ¹²⁵I-labeled embryonic crude cerebellar membrane fraction. Immunohistochemically, the M35 antigen was expressed most intensively in Purkinje cells, but its expression was limited to highly motile structures at developmental neuronal remodeling. Electrophysiologically, M35 facilitated current responses to AMPA and inhibited the responses to GABA in cultured cerebellar Purkinje neurons. The several peptides derived from the affinity-purified 43kDa protein were found to have homologous amino acid sequences to non-muscle actins. These results suggest that the antigen recognized by M35 may play an essential role probably as membrane ion channels modulating synaptic functions in not only the development and growth but also the neuronal activity of chick cerebellar Purkinje cells.     

Mitochondrial dysfunction driven by the LRRK2-mediated pathway is associated with loss of Purkinje cells and motor coordination deficits in diabetic rat model

Diabetic neuropathy develops on a background of hyperglycemia and an entangled metabolic imbalance. There is increasing evidence of central nervous system involvement in diabetic neuropathy and no satisfactory treatment except maintenance of good glycemic control, thereby highlighting the importance of identifying novel therapeutic targets. Purkinje cells are a class of metabolically specialized active neurons, and degeneration of Purkinje cells is a common feature of inherited ataxias in humans and mice. However, whether Purkinje cells are implicated in diabetic neuropathy development under metabolic stress remains poorly defined. Here, we revealed a novel leucine-rich repeat kinase 2 (LRRK2)-mediated pathway in Purkinje cells that is involved in the pathogenesis of diabetic neuropathy from a 24-week long study of streptozotocin (STZ)-diabetic rats. We found that hyperglycemia, cerebellum proinflammatory cytokines, and chemokines increased markedly in 24-week STZ-diabetic rats. Furthermore, we demonstrated that degeneration of Purkinje cells is characterized by progressive swellings of axon terminals, no autophagosome formation, the reduction of LC3II/LC3I and Lamp2, and accumulation of p62 puncta in 24-week STZ-diabetic rats. Importantly, a higher expression level of LRRK2-mediated hyperphosphorylation of tau along with increased mitochondrial dynamin-like protein (mito-DLP1) was demonstrated in 24-week STZ-diabetic rats. This effect of LRRK2 overexpression induced mitochondrial fragmentation, and reduced mitochondrial protein degradation rates were confirmed in vitro. As a consequence, 24-week STZ-diabetic rats showed mitochondrial dysfunction in cerebellar Purkinje neurons and coordinated motor deficits evaluated by rotarod test. Our findings are to our knowledge the first to suggest that the LRRK2-mediated pathway induces mitochondrial dysfunction and loss of cerebellar Purkinje neurons and, subsequently, may be associated with motor coordination deficits in STZ-diabetic rats. These data may indicate a novel cellular therapeutic target for diabetic neuropathy.     

ATP-Dependent Glutamate Uptake into Synaptic Vesicles from Cerebellar Mutant Mice

The ATP-dependent glutamate uptake system in synaptic vesicles prepared from mouse cerebellum was characterized, and the levels of glutamate uptake were investigated in the cerebellar mutant mice, staggerer and weaver, whose main defect is the loss of cerebellar granule cells, and the nervous mutant, whose main defect is the loss of Purkinje cells. The ATP-dependent glutamate uptake is stimulated by low concentrations of chloride, is insensitive to aspartate, and is inhibited by agents known to dissipate the electrochemical proton gradient. These properties are similar to those of the glutamate uptake system observed in the highly purified synaptic vesicles prepared from bovine cortex. The ATP-dependent glutamate uptake system is reduced by 68% in the staggerer and 57-67% in the weaver mutant; these reductions parallel the substantial loss of granule cells in those mutants. In contrast, the cerebellar levels of glutamate uptake are not altered significantly in the nervous mutant, which has lost Purkinje cells, but not granule cells. In view of evidence that granule cells are glutamatergic neurons and Purkinje cells are GABAergic neurons, these observations support the notion that the ATP-dependent glutamate uptake system is present in synaptic vesicles of glutamatergic neurons.     

Gene transfer into Purkinje cells using herpesviral amplicon vectors in cerebellar cultures

Purkinje cells play a crucial role in sensory motor coordination since they are the only output projection neurons in the cerebellar cortex and are affected in most spinocerebellar ataxias. They stand out in the central nervous system due to their large size and their profusely branched dendritic arbor. However, molecular and cellular studies on Purkinje cells are often hampered by the difficulty of maintaining these cells in culture. Here we report an easy, robust and reproducible method to obtain Purkinje-enriched mixed cerebellar cell cultures from day 16 mouse embryos using papain digestion and a semi-defined culture medium, being the composition of the culture approximately 20% Purkinje cells, 70% non-Purkinje neurons and 10% glial cells. We demonstrate that efficient gene transfer into Purkinje cells (as well as into other cerebellar populations) is possible using herpes simplex virus-1 (HSV-1)-derived vectors. Indeed, up to 50% of the Purkinje cells can be transduced and gene expression may persist for at least 14 days. As a result, this procedure permits functional gene expression studies to be carried out on cultured Purkinje neurons. To demonstrate this, we show that the expression of a dominant-negative form of glycogen synthase kinase-3 protects Purkinje neurons against cell death triggered by a chemical inhibitor of phosphatidylinositol-3 kinase. In summary, we have established reproducible and reliable cerebellar cell cultures enriched for Purkinje cells which enables gene transfer studies to be carried out using herpesviral vectors.     

Heat Shock Protein Beta-1 Modifies Anterior to Posterior Purkinje Cell Vulnerability in a Mouse Model of Niemann-Pick Type C Disease

Selective neuronal vulnerability is characteristic of most degenerative disorders of the CNS, yet mechanisms underlying this phenomenon remain poorly characterized. Many forms of cerebellar degeneration exhibit an anterior-to-posterior gradient of Purkinje cell loss including Niemann-Pick type C1 (NPC) disease, a lysosomal storage disorder characterized by progressive neurological deficits that often begin in childhood. Here, we sought to identify candidate genes underlying vulnerability of Purkinje cells in anterior cerebellar lobules using data freely available in the Allen Brain Atlas. This approach led to the identification of 16 candidate neuroprotective or susceptibility genes. We demonstrate that one candidate gene, heat shock protein beta-1 (HSPB1), promoted neuronal survival in cellular models of NPC disease through a mechanism that involved inhibition of apoptosis. Additionally, we show that over-expression of wild type HSPB1 or a phosphomimetic mutant in NPC mice slowed the progression of motor impairment and diminished cerebellar Purkinje cell loss. We confirmed the modulatory effect of Hspb1 on Purkinje cell degeneration in vivo, as knockdown by Hspb1 shRNA significantly enhanced neuron loss. These results suggest that strategies to promote HSPB1 activity may slow the rate of cerebellar degeneration in NPC disease and highlight the use of bioinformatics tools to uncover pathways leading to neuronal protection in neurodegenerative disorders.     

In Vivo Evidence for Lysosome Depletion and Impaired Autophagic Clearance in Hereditary Spastic Paraplegia Type SPG11

Hereditary spastic paraplegia (HSP) is characterized by a dying back degeneration of corticospinal axons which leads to progressive weakness and spasticity of the legs. SPG11 is the most common autosomal-recessive form of HSPs and is caused by mutations in SPG11. A recent in vitro study suggested that Spatacsin, the respective gene product, is needed for the recycling of lysosomes from autolysosomes, a process known as autophagic lysosome reformation. The relevance of this observation for hereditary spastic paraplegia, however, has remained unclear. Here, we report that disruption of Spatacsin in mice indeed causes hereditary spastic paraplegia-like phenotypes with loss of cortical neurons and Purkinje cells. Degenerating neurons accumulate autofluorescent material, which stains for the lysosomal protein Lamp1 and for p62, a marker of substrate destined to be degraded by autophagy, and hence appears to be related to autolysosomes. Supporting a more generalized defect of autophagy, levels of lipidated LC3 are increased in Spatacsin knockout mouse embryonic fibrobasts (MEFs). Though distinct parameters of lysosomal function like processing of cathepsin D and lysosomal pH are preserved, lysosome numbers are reduced in knockout MEFs and the recovery of lysosomes during sustained starvation impaired consistent with a defect of autophagic lysosome reformation. Because lysosomes are reduced in cortical neurons and Purkinje cells in vivo, we propose that the decreased number of lysosomes available for fusion with autophagosomes impairs autolysosomal clearance, results in the accumulation of undegraded material and finally causes death of particularly sensitive neurons like cortical motoneurons and Purkinje cells in knockout mice.     

Ischemia deteriorates the spike encoding of rat cerebellar Purkinje cells by raising intracellular Ca2+

Ischemia-induced excitotoxicity at cerebellar Purkinje cells is presumably due to a persistent glutamate action. To the fact that they are more vulnerable to ischemia than other glutamate-innervated neurons, we studied whether additional mechanisms are present and whether cytoplasm Ca²⁺ plays a key role in their ischemic excitotoxicity. Ischemic changes in the excitability of Purkinje cells were measured by whole-cell recording in cerebellar slices of rats with less glutamate action. The role of cytoplasm Ca²⁺ was examined by two-photon cellular imaging and BAPTA infusion in Purkinje cells. Lowering perfusion rate to cerebellar slices deteriorated spike timing and raised spike capacity of Purkinje cells. These changes were associated with the reduction of spike refractory periods and threshold potentials, as well as the loss of their control to spike encoding. Ischemia-induced functional deterioration at Purkinje neurons was accompanied by cytoplasm Ca²⁺ rise and prevented by BAPTA infusion. Therefore, the ischemia destabilizes the spike encoding of Purkinje cells via raising cytoplasm Ca²⁺ without a need for glutamate, which subsequently causes their excitotoxic death.     

Nna1 mediates Purkinje cell dendritic development via lysyl oxidase propeptide and NF-κB signaling

The molecular pathways controlling cerebellar Purkinje cell dendrite formation and maturation are poorly understood. The Purkinje cell degeneration (pcd) mutant mouse is characterized by mutations in Nna1, a gene discovered in an axonal regenerative context, but whose actual function in development and disease is unknown. We found abnormal development of Purkinje cell dendrites in postnatal pcd(Sid) mice and linked this deficit to a deletion mutation in exon 7 of Nna1. With single cell gene profiling and virus-based gene transfer, we analyzed a molecular pathway downstream to Nna1 underlying abnormal Purkinje cell dendritogenesis in pcd(Sid) mice. We discovered that mutant Nna1 dramatically increases intranuclear localization of lysyl oxidase propeptide, which interferes with NF-κB RelA signaling and microtubule-associated protein regulation of microtubule stability, leading to underdevelopment of Purkinje cell dendrites. These findings provide insight into Nna1's role in neuronal development and why its absence renders Purkinje cells more vulnerable.     

Accumulation of DNA damage and reduced levels of nicotine adenine dinucleotide in the brains of Atm-deficient mice.

Ataxia-telangiectasia (A-T) is a human genetic disorder caused by mutational inactivation of the ATM gene. A-T patients display a pleiotropic phenotype, in which a major neurological feature is progressive ataxia due to degeneration of cerebellar Purkinje and granule neurons. Disruption of the mouse Atm locus creates a murine model of A-T that exhibits most of the clinical and cellular features of the human disease, but the neurological phenotype is barely expressed. We present evidence for the accumulation of DNA strand breaks in the brains of Atm(-/-), supporting the notion that ATM plays a major role in maintaining genomic stability. We also show a perturbation of the steady state levels of pyridine nucleotides. There is a significant decrease in both the reduced and the oxidized forms of NAD and in the total levels of NADP(T) and NADP(+) in the brains of Atm(-/-) mice. The changes in NAD(T), NADH, NAD(+), NADP(T), and NADP(+) were progressive and observed primarily in the cerebellum of 4-month-old Atm(-/-) mice. Higher rates of mitochondrial respiration were also recorded in 4-month-old Atm(-/-) cerebella. Taken together, our findings support the hypothesis that absence of functional ATM results in continuous stress, which may be an important cause of the degeneration of cerebellar neurons in A-T.     

Dual Transgene Expression in Murine Cerebellar Purkinje Neurons by Viral Transduction In Vivo

Viral-vector mediated gene transfer to cerebellar Purkinje neurons in vivo is a promising avenue for gene therapy of cerebellar ataxias and for genetic manipulation in functional studies of animal models of cerebellar disease. Here, we report the results of experiments designed to identify efficient methods for viral transduction of adult murine Purkinje neurons in vivo. For these analyses, several lentiviral and an adeno-associated virus (AAV), serotype 1, vector with various promoter combinations were generated and compared for in situ transduction efficiency, assayed by fluorescent reporter protein expression in Purkinje neurons. Additional experiments were also conducted to identify the optimal experimental strategy for co-expression of two proteins in individual Purkinje neurons. Of the viruses tested, AAV1 with a CAG promoter exhibited the highest specificity for Purkinje neurons. To deliver two proteins to the same Purkinje neuron, several methods were tested, including: an internal ribosome entry site (IRES), a 2A sequence, a dual promoter vector, and co-injection of two viruses. Efficient expression of both proteins in the same Purkinje neuron was only achieved by co-injecting two AAV1-CAG viruses. We found that use of an AAV1-CAG virus outperformed similar lentivirus vectors and that co-injection of two AAV1-CAG viruses could be used to efficiently deliver two proteins to the same Purkinje neuron in adult mice. AAV1 with a CAG promoter is highly efficient and selective at transducing adult cerebellar Purkinje neurons and two AAV-CAG viruses can be used to efficiently express two proteins in the same neuron in vivo.     

Lysosomal dysfunction in neurodegeneration

Neuronal homeostasis and survival critically depend on an efficient autophagy-lysosomal degradation pathway, especially since neurons cannot reduce the concentration of misfolded proteins and damaged organelles by cell division. While increasing evidence implicates lysosomal dysfunction in the pathogenesis of neurodegenerative disorders, the molecular underpinnings of the role of lysosomes in neurodegeneration remain largely unknown. To this end, studies of neurodegenerative disorders caused by mutations in lysosomal proteins offer an opportunity to elucidate such mechanisms and potentially identify specific therapeutic targets. One of these disorders is Kufor-Rakeb syndrome, caused by mutations in the lysosomal protein ATP13A2/PARK9 and characterized by early-onset Parkinsonism, pyramidal degeneration and dementia. We found that loss of ATP13A2 function results in impaired lysosomal function and, consequently, accumulation of SNCA/α-synuclein and neurotoxicity. Our results suggest that targeting of ATP13A2 to lysosomes to enhance lysosomal function may result in neuroprotection in Kufor-Rakeb syndrome. From a broader perspective, these findings, together with other recent studies of lysosomal dysfunction in neurodegeneration, suggest that strategies to upregulate lysosomal function in neurons represent a promising therapeutic approach for neurodegenerative disorders.     

Lysosomal dysfunction in neurodegeneration: The role of ATP13A2/PARK9

Neuronal homeostasis and survival critically depend on an efficient autophagy-lysosomal degradation pathway, especially since neurons cannot reduce the concentration of misfolded proteins and damaged organelles by cell division. While increasing evidence implicates lysosomal dysfunction in the pathogenesis of neurodegenerative disorders, the molecular underpinnings of the role of lysosomes in neurodegeneration remain largely unknown. To this end, studies of neurodegenerative disorders caused by mutations in lysosomal proteins offer an opportunity to elucidate such mechanisms and potentially identify specific therapeutic targets. One of these disorders is Kufor-Rakeb syndrome, caused by mutations in the lysosomal protein ATP13A2/PARK9 and characterized by early-onset Parkinsonism, pyramidal degeneration and dementia. We found that loss of ATP13A2 function results in impaired lysosomal function and, consequently, accumulation of SNCA/α-synuclein and neurotoxicity. Our results suggest that targeting of ATP13A2 to lysosomes to enhance lysosomal function may result in neuroprotection in Kufor-Rakeb syndrome. From a broader perspective, these findings, together with other recent studies of lysosomal dysfunction in neurodegeneration, suggest that strategies to upregulate lysosomal function in neurons represent a promising therapeutic approach for neurodegenerative disorders.     

Cerebellar Nuclear Neurons Use Time and Rate Coding to Transmit Purkinje Neuron Pauses

Neurons of the cerebellar nuclei convey the final output of the cerebellum to their targets in various parts of the brain. Within the cerebellum their direct upstream connections originate from inhibitory Purkinje neurons. Purkinje neurons have a complex firing pattern of regular spikes interrupted by intermittent pauses of variable length. How can the cerebellar nucleus process this complex input pattern? In this modeling study, we investigate different forms of Purkinje neuron simple spike pause synchrony and its influence on candidate coding strategies in the cerebellar nuclei. That is, we investigate how different alignments of synchronous pauses in synthetic Purkinje neuron spike trains affect either time-locking or rate-changes in the downstream nuclei. We find that Purkinje neuron synchrony is mainly represented by changes in the firing rate of cerebellar nuclei neurons. Pause beginning synchronization produced a unique effect on nuclei neuron firing, while the effect of pause ending and pause overlapping synchronization could not be distinguished from each other. Pause beginning synchronization produced better time-locking of nuclear neurons for short length pauses. We also characterize the effect of pause length and spike jitter on the nuclear neuron firing. Additionally, we find that the rate of rebound responses in nuclear neurons after a synchronous pause is controlled by the firing rate of Purkinje neurons preceding it.     

Neuronal autophagy: going the distance to the axon

Autophagy, a regulated cellular degradation process responsible for the turnover of long-lived proteins and organelles, has been increasingly implicated in neurological disorders. Although autophagy is mostly viewed as a stress-induced process, recent studies have indicated that it is constitutively active in central nervous system (CNS) neurons and is protective against neurodegeneration. Neurons are highly specialized, post-mitotic cells that are typically composed of a soma (cell body), a dendritic tree and an axon. The detailed process of autophagy in such a highly differentiated cell type remains to be characterized. To elucidate the physiological role of neuronal autophagy, we generated mutant mice containing a neural cell type-specific deletion of Atg7, an essential gene for autophagy. Establishment of these mutant mice allowed us to examine cell-autonomous events in cerebellar Purkinje cells deficient in autophagy. Our data reveal the indispensability of autophagy in the maintenance of axonal homeostasis and the prevention of axonal dystrophy and degeneration. Furthermore, our study implicates dysfunction of axonal autophagy as a potential mechanism underlying axonopathy, which is linked to neurodegeneration associated with numerous human neurological disorders. Finally, our study has raised a possibility that "constitutive autophagy" in neurons involves processes that are not typical of autophagy in other cell types, but rather is highly adapted to local physiological function in the axon, which is projected in a distance from one neuron to another for transducing neural signals.     

STIM and ORAI proteins in the nervous system

Stromal interaction molecules (STIM) 1 and 2 are sensors of the calcium concentration in the endoplasmic reticulum. Depletion of endoplasmic reticulum calcium stores activates STIM proteins which, in turn, bind and open calcium channels in the plasma membrane formed by the proteins ORAI1, ORAI2, and ORAI3. The resulting store-operated calcium entry (SOCE), mostly controlled by the principal components STIM1 and ORAI1, has been particularly characterized in immune cells. In the nervous system, all STIM and ORAI homologs are expressed. This review summarizes current knowledge on distribution and function of STIM and ORAI proteins in central neurons and glial cells, i.e. astrocytes and microglia. STIM2 is required for SOCE in hippocampal synapses and cortical neurons, whereas STIM1 controls calcium store replenishment in cerebellar Purkinje neurons. In microglia, STIM1, STIM2, and ORAI1 regulate migration and phagocytosis. The isoforms ORAI2 and ORAI3 are candidates for SOCE channels in neurons and astrocytes, respectively. Due to the role of SOCE in neuronal and glial calcium homeostasis, dysfunction of STIM and ORAI proteins may have consequences for the development of neurodegenerative disorders, such as Alzheimer's disease.     

STIM and ORAI proteins in the nervous system

Stromal interaction molecules (STIM) 1 and 2 are sensors of the calcium concentration in the endoplasmic reticulum. Depletion of endoplasmic reticulum calcium stores activates STIM proteins which, in turn, bind and open calcium channels in the plasma membrane formed by the proteins ORAI1, ORAI2, and ORAI3. The resulting store-operated calcium entry (SOCE), mostly controlled by the principal components STIM1 and ORAI1, has been particularly characterized in immune cells. In the nervous system, all STIM and ORAI homologs are expressed. This review summarizes current knowledge on distribution and function of STIM and ORAI proteins in central neurons and glial cells, i.e. astrocytes and microglia. STIM2 is required for SOCE in hippocampal synapses and cortical neurons, whereas STIM1 controls calcium store replenishment in cerebellar Purkinje neurons. In microglia, STIM1, STIM2, and ORAI1 regulate migration and phagocytosis. The isoforms ORAI2 and ORAI3 are candidates for SOCE channels in neurons and astrocytes, respectively. Due to the role of SOCE in neuronal and glial calcium homeostasis, dysfunction of STIM and ORAI proteins may have consequences for the development of neurodegenerative disorders, such as Alzheimer''s disease.     

The abnormal cerebellar organization of Weaver and reeler mice does not affect the cellular distribution of three neuronal mRNAs

We used in situ hybridization of 35S-labeled antisense RNAs to study the cellular distribution of three neuronal mRNAs. We compared the expression of these RNAs in cerebellar Purkinje neurons in wild-type (C57Bl-6J) mice and in two mutants (Weaver and reeler) known to have abnormal cerebellar morphologies. In normal mice, GAD mRNA is present in four sets of neurons in the cerebellar cortex while calbindin mRNA is present only in Purkinje neurons. Proenkephalin mRNA is present in Golgi II neurons as well as in a set of neurons in the deep part of the molecular layer. Despite the dramatic differences in structural organization and inputs of Purkinje neurons in the cerebella of adult Weaver and reeler mice, the expression of these RNAs appears unchanged. These results support the hypothesis that Purkinje cell cytodifferentiation proceeds autonomously after its inception in early embryonic life.     

A novel inhibitor rescues cerebellar defects in a zebrafish model of Down syndrome–associated kinase Dyrk1A overexpression

The highly conserved dual-specificity tyrosine phosphorylation–regulated kinase 1A (Dyrk1A) plays crucial roles during central nervous system development and homeostasis. Furthermore, its hyperactivity is considered responsible for some neurological defects in individuals with Down syndrome. We set out to establish a zebrafish model expressing human Dyrk1A that could be further used to characterize the interaction between Dyrk1A and neurological phenotypes. First, we revealed the prominent expression of dyrk1a homologs in cerebellar neurons in the zebrafish larval and adult brains. Overexpression of human dyrk1a in postmitotic cerebellar Purkinje neurons resulted in a structural misorganization of the Purkinje cells in cerebellar hemispheres and a compaction of this cell population. This impaired Purkinje cell organization was progressive, leading to an age-dependent dispersal of Purkinje neurons throughout the cerebellar molecular layer with larval swim deficits resulting in miscoordination of swimming and reduced exploratory behavior in aged adults. We also found that the structural misorganization of the larval Purkinje cell layer could be rescued by pharmacological treatment with Dyrk1A inhibitors. We further reveal the in vivo efficiency of a novel selective Dyrk1A inhibitor, KuFal194. These findings demonstrate that the zebrafish is a well-suited vertebrate organism to genetically model severe neurological diseases with single cell type specificity. Such models can be used to relate molecular malfunction to cellular deficits, impaired tissue formation, and organismal behavior and can also be used for pharmacological compound testing and validation.