DYRK1A maps to the Down syndrome critical region at 21q22. Mutations in this kinase-encoding gene have been reported to cause microcephaly associated with either intellectual disability or autism in humans. Intellectual disability accompanied by microcephaly was recapitulated in a murine model by overexpressing Dyrk1a which mimicked Down syndrome phenotypes. However, given embryonic lethality in homozygous knockout (KO) mice, no murine model studies could present sufficient evidence to link Dyrk1a dysfunction with autism. To understand the molecular mechanisms underlying microcephaly and autism spectrum disorders (ASD), we established an in vivo dyrk1aa KO model using zebrafish. We identified a patient with a mutation in the DYRK1A gene using microarray analysis. Circumventing the barrier of murine model studies, we generated a dyrk1aa KO zebrafish using transcription activator-like effector nuclease (TALEN)-mediated genome editing. For social behavioral tests, we have established a social interaction test, shoaling assay, and group behavior assay. For molecular analysis, we examined the neuronal activity in specific brain regions of dyrk1aa KO zebrafish through in situ hybridization with various probes including c-fos and crh which are the molecular markers for stress response. Microarray detected an intragenic microdeletion of DYRK1A in an individual with microcephaly and autism. From behavioral tests of social interaction and group behavior, dyrk1aa KO zebrafish exhibited social impairments that reproduce human phenotypes of autism in a vertebrate animal model. Social impairment in dyrk1aa KO zebrafish was further confirmed by molecular analysis of c-fos and crh expression. Transcriptional expression of c-fos and crh was lower than that of wild type fish in specific hypothalamic regions, suggesting that KO fish brains are less activated by social context. In this study, we established a zebrafish model to validate a candidate gene for autism in a vertebrate animal. These results illustrate the functional deficiency of DYRK1A as an underlying disease mechanism for autism. We also propose simple social behavioral assays as a tool for the broader study of autism candidate genes.

The microbiota–gut–brain axis (MGBA) is a bidirectional signaling pathway mediating the interaction of the microbiota, the intestine, and the central nervous system. While the MGBA plays a pivotal role in normal development and physiology of the nervous and gastrointestinal system of the host, its dysfunction has been strongly implicated in neurological disorders, where intestinal dysbiosis and derived metabolites cause barrier permeability defects and elicit local inflammation of the gastrointestinal tract, concomitant with increased pro-inflammatory cytokines, mobilization and infiltration of immune cells into the brain, and the dysregulated activation of the vagus nerve, culminating in neuroinflammation and neuronal dysfunction of the brain and behavioral abnormalities. In this topical review, we summarize recent findings in human and animal models regarding the roles of the MGBA in physiological and neuropathological conditions, and discuss the molecular, genetic, and neurobehavioral characteristics of zebrafish as an animal model to study the MGBA. The exploitation of zebrafish as an amenable genetic model combined with in vivo imaging capabilities and gnotobiotic approaches at the whole organism level may reveal novel mechanistic insights into microbiota–gut–brain interactions, especially in the context of neurological disorders such as autism spectrum disorder and Alzheimer’s disease.

A silver nanoparticle is one of the representative engineered nanomaterials with excellent optical, electrical, antibacterial properties. Silver nanoparticles are being increasingly used for medical products, water filters, and cosmetics, etc. However, silver nanoparticles are known to cause adverse effects on the ecosystem and human health. To utilize silver nanoparticles with minimized negative effects, it is important to understand the behavior of silver nanoparticles released to the environment. In this study, we compared toxicity behaviors of citrate-stabilized silver nanoparticles with polyethylene glycol coated silver nanoparticles in two different ionic environments, which are aquatic environments for developing zebrafish embryo. Depending on the composition of the ionic environment, citrate-stabilized silver nanoparticles and polyethylene glycol coated silver nanoparticles exhibited different behaviors in dissolution, aggregation, or precipitation, which governed the toxicity of silver nanoparticles on zebrafish embryos.

Tauopathy, including frontotemporal lobar dementia and Alzheimer’s disease, describes a class of neurodegenerative diseases characterized by the aberrant accumulation of Tau protein due to defects in proteostasis. Upon generating and characterizing a stable transgenic zebrafish that expresses the human TAU^P301L mutant in a neuron-specific manner, we found that accumulating Tau protein was efficiently cleared via an enhanced autophagy activity despite constant Tau mRNA expression; apparent tauopathy-like phenotypes were revealed only when the autophagy was genetically or chemically inhibited. We performed RNA-seq analysis, genetic knockdown, and rescue experiments with clinically relevant point mutations of valosin-containing protein (VCP), and showed that induced expression of VCP, an essential cytosolic chaperone for the protein quality system, was a key factor for Tau degradation via its facilitation of the autophagy flux. This novel function of VCP in Tau clearance was further confirmed in a tauopathy mouse model where VCP overexpression significantly decreased the level of phosphorylated and oligomeric/aggregate Tau and rescued Tau-induced cognitive behavioral phenotypes, which were reversed when the autophagy was blocked. Importantly, VCP expression in the brains of human Alzheimer’s disease patients was severely downregulated, consistent with its proposed role in Tau clearance. Taken together, these results suggest that enhancing the expression and activity of VCP in a spatiotemporal manner to facilitate the autophagy pathway is a potential therapeutic approach for treating tauopathy.

The failure of amyloid beta (Aβ) clearance is a major cause of Alzheimer’s disease, and the brain lymphatic systems play a crucial role in clearing toxic proteins. Recently, brain lymphatic endothelial cells (BLECs), a non-lumenized lymphatic cell in the vertebrate brain, was identified, but Aβ clearance via this novel cell is not fully understood. We established an in vivo zebrafish model using fluorescently labeled Aβ42 to investigate the role of BLECs in Aβ clearance. We discovered the efficient clearance of monomeric Aβ42 (mAβ42) compared to oligomeric Aβ42 (oAβ42), which was illustrated by the selective uptake of mAβ42 by BLECs and peripheral transport. The genetic depletion, pharmacological inhibition via the blocking of the mannose receptor, or the laser ablation of BLECs resulted in the defective clearance of mAβ42. The treatment with an Aβ disaggregating agent facilitated the internalization of oAβ42 into BLECs and improved the peripheral transport. Our findings reveal a new role of BLECs in the differential clearance of mAβ42 from the brain and provide a novel therapeutic strategy based on promoting Aβ clearance.

A comprehensive review has concluded that progenitor cells, which are distributed along the dorsal-ventral axis of the spinal cord in vertebrates, generate distinct types of neuron in each compartment (Briscoe & Ericson, 2001). Our previous study suggested that zebrafish Jagged2 interacts with progenitor cells in the adjacent p3 domain and plays a crucial role in maintaining proliferating neural progenitor cells in this region (Yeo & Chitnis, 2007). It was proposed that Jagged2 might bind to Notch expressed in the neural progenitor cells of the p3 domain, thereby facilitating signal transduction in a contact-dependent manner (Yeo & Chitnis, 2007). While the p3 domain in zebrafish is composed of a single cell layer, the pMN domain is composed of multiple cell layers (Yeo & Chitnis, 2007). Jagged2 is expressed in the pMN domain of the zebrafish, which encompasses neural precursors as well as various types of neurons (Yeo & Chitnis, 2007). Therefore, it can be concluded that Jagged2-mediated Notch signaling does not only occur between neural progenitors in the p3 domain and those in the pMN domain. This study investigates the activation and transmission mechanisms of Jagged2, which has previously been shown to activate the Notch signaling pathway.