Search

Many age-related neurological diseases still lack effective treatments, making their understanding a critical and urgent issue in the globally aging society. To overcome this challenge, an animal model that accurately mimics these diseases is essential. To date, many mouse models have been developed to induce age-related neurological diseases through genetic manipulation or drug administration. These models help in understanding disease mechanisms and finding potential therapeutic targets. However, some age-related neurological diseases cannot be fully replicated in human pathology due to the different aspects between humans and mice. Although zebrafish has recently come into focus as a promising model for studying aging, there are few genetic zebrafish models of the age-related neurological disease. This review compares the aging phenotypes of humans, mice, and zebrafish, and provides an overview of age-related neurological diseases that can be mimicked in mouse models and those that cannot. We presented the possibility that reproducing human cerebral small vessel diseases during aging might be difficult in mice, and zebrafish has potential to be another animal model of such diseases due to their similarity of aging phenotype to humans.

The brain is an essential organ that controls various biological activities via the nervous system. The cerebral blood vessels supply oxygen and nutrients to neuronal cells and carry away waste products, which is essential in maintaining brain functions. Aging affects cerebral vascular function and decreases brain function. However, the physiological process of age-dependent cerebral vascular dysfunction is not fully understood. In this study, we examined aging effects on cerebral vascular patterning, vascular function, and learning ability in adult zebrafish. We found that the tortuosity of the blood vessels was increased, and the blood flow rate was reduced with aging in the zebrafish dorsal telencephalon. Moreover, we found cerebral blood flow positively correlated with learning ability in middle-old-aged zebrafish, as in aged humans. In addition, we also found that the elastin fiber decreased in the middle-old-aged fish brain vessel, suggesting a possible molecular mechanism underlying vessel dysfunction. Therefore, adult zebrafish may serve as a useful model for studying the aging-dependent decline in vascular function and human diseases such as vascular dementia.

BMP signaling is critical for many biological processes. Therefore, small molecules that modulate BMP signaling are useful for elucidating the function of BMP signaling and treating BMP signaling-related diseases. Here, we performed a phenotypic screening in zebrafish to examine the in vivo effects of N-substituted-2-amino-benzoic acid analogs NPL1010 and NPL3008 and found that they affect BMP signaling-dependent dorsal–ventral (D–V) patterning and bone formation in zebrafish embryos. Furthermore, NPL1010 and NPL3008 suppressed BMP signaling upstream of BMP receptors. BMP1 cleaves Chordin, an antagonist of BMP, and negatively regulates BMP signaling. Docking simulations demonstrated that NPL1010 and NPL3008 bind BMP1. We found that NPL1010 and NPL3008 partially rescued the disruptions in the D–V phenotype caused by bmp1 overexpression and selectively inhibited BMP1-dependent Chordin cleavage. Therefore, NPL1010 and NPL3008 are potentially valuable inhibitors of BMP signaling that act through selective inhibition of Chordin cleavage.

Polypyrrole-based polyamides are used as sequence-specific DNA probes. However, their cellular uptake and distribution are affected by several factors and have not been extensively studied in vivo. Here, we generated a series of fluorescence-conjugated polypyrrole compounds and examined their cellular distribution using live zebrafish and cultured human cells. Among the evaluated compounds, Py3-FITC was able to visualize collagen-rich tissues, such as the jaw cartilage, opercle and bulbus arteriosus, in early-stage living zebrafish embryos. Then, we stained cultured human cells with Py3-FITC and found that the staining became more intense as the amount of collagen was increased. In addition, Py3-FITC-stained HR cells, which represent a type of ionocyte on the body surface of living zebrafish embryos. Py3-FITC has low toxicity, and collagen-rich tissues and ionocytes can be visualized when soaked in Py3-FITC solution. Therefore, Py3-FITC may be a useful live imaging tool for detecting changes in collagen-rich tissue and ionocytes, including their mammalian analogues, during both normal development and disease progression.

Glucocorticoid-induced osteoporosis (GIOP) is a major cause of secondary osteoporosis, and the pathogenic mechanisms of GIOP remain to be elucidated. Here, we show a rapid dexamethasone-induced osteoporosis animal model using zebrafish scales. Intraperitoneal injection of dexamethasone over a 5-day period suppressed the regeneration of scales. Furthermore, the circularity of the newly formed regenerated scales was also slightly reduced compared to that of the control group on day 5. The changes in bone-related enzymes, such as cathepsin K, tartrate-resistant acid phosphatase (TRAP) for bone resorption, and alkaline phosphatase (ALP) for bone formation, provide insight into the progression of bone diseases; therefore, we further developed a method to measure the activities of cathepsin K, TRAP, and ALP using zebrafish scales. We found that a lysis buffer with detergent at neutral pH under sonication efficiently helped extract these three enzymes with high activity levels. Interestingly, treatment with a dexamethasone injection produced considerably higher levels of cathepsin K activity and a lower Ca/P ratio than those in the control group, suggesting that dexamethasone increased osteoclast activity, with no significant changes in the activities of TRAP and ALP. Our GIOP model and enzyme assay method could help to design better treatments for GIOP.

The zebrafish endoderm begins to develop at gastrulation stages as a monolayer of cells. The behaviour of the endoderm during gastrulation stages is well understood. However, knowledge of the morphogenic movements of the endoderm during somitogenesis stages, as it forms a mesenchymal rod, is lacking. Here we characterise endodermal development during somitogenesis stages, and describe the morphogenic movements as the endoderm transitions from a monolayer of cells into a mesenchymal endodermal rod. We demonstrate that, unlike the overlying mesoderm, endodermal cells are not polarised during their migration to the midline at early somitogenesis stages. Specifically, we describe the stage at which endodermal cells begin to leave the monolayer, a process we have termed ‘midline aggregation’. The planar cell polarity (PCP) signalling pathway is known to regulate mesodermal and ectodermal cell convergence towards the dorsal midline. However, a role for PCP signalling in endoderm migration to the midline during somitogenesis stages has not been established. In this report, we investigate the role for PCP signalling in multiple phases of endoderm development during somitogenesis stages. Our data exclude involvement of PCP signalling in endodermal cells as they leave the monolayer.

The Mindbomb E3 ubiquitin protein ligase (Mib) family of proteins, Mib1 and Mib2, are RING finger ubiquitin ligases that share specific substrates. Mib1 is known to play essential roles in Notch signalling by ubiquitinating Notch ligands in vivo. Conversely, the functions of Mib2 in vivo are not fully understood, although Mib2 ubiquitinates multiple substrates, including Notch ligands, in vitro. To determine the Notch-dependent and Notch-independent functions of Mib2 in vivo, we generated mutant alleles of zebrafish mib2 using transcription activator-like effector nucleases (TALENs). We found that mib2 homozygous mutants were viable and fertile. Notch-mediated functions, such as early neurogenesis, somitogenesis, and pigment cell development, were not affected in mib2 mutant embryos. The lack of Notch-deficient phenotypes in mib2 mutants was not due to compensation by a mib2 maternal gene product because mib2 maternal-zygotic mutants also did not exhibit a distinct phenotype. We also showed that Mib2 does not redundantly act with Mib1 because the genetic ablation of mib2 neither enhanced mibtfi91-null phenotypes nor did it alleviate antimorphic mibta52b phenotypes. Furthermore, the postulated Notch-independent roles of Mib2 in maintaining muscular integrity and N-methyl-D-aspartate receptor (NMDAR) activity were not evident: mib2 mutants did not show phenotypes different from that of the control embryos. These observations suggest that Mib2 is dispensable for embryonic development and does not have redundant functions with Mib1 in Notch signalling at least during early development stages in zebrafish.

In the vertebrate ventral spinal cord, p2 progenitors give rise to two interneuron subtypes: excitatory V2a interneurons and inhibitory V2b interneurons. In the differentiation of V2a and V2b cells, Notch signaling promotes V2b fate at the expense of V2a fate. Later, V2b cells extend axons along the ipsilateral side of the spinal cord and express the inhibitory transmitter GABA. Notch signaling has been reported to inhibit the axonal outgrowth of mature neurons of the central nervous system; however, it remains unknown how Notch signaling modulates V2b neurite outgrowth and maturation into GABAergic neurons. Here, we have investigated neuron-specific Notch functions regarding V2b axon growth and maturation into zebrafish GABAergic neurons. We found that continuous neuronspecific Notch activation enhanced V2b fate determination but inhibited V2b axonal outgrowth and maturation into GABAergic neurons. These results suggest that Notch signaling activation is required for V2b fate determination, whereas its downregulation at a later stage is essential for V2b maturation. Accordingly, we found that a Notch signaling downstream gene, her15.1, showed biased expression in V2 linage cells and downregulated expression during the maturation of V2b cells, and continuous expression of her15.1 repressed V2b axogenesis. Our data suggest that spatiotemporal control of Notch signaling activity is required for V2b fate determination, maturation and axogenesis. [ABSTRACT FROM AUTHOR]

Persistent directional cell migration is involved in animal development and diseases. The small GTPase Rac1 is involved in F-actin and focal adhesion dynamics. Local Rac1 activity is required for persistent directional migration, whereas global, hyperactivated Rac1 enhances random cell migration. Therefore, precise control of Rac1 activity is important for proper directional cell migration. However, the molecular mechanism underlying the regulation of Rac1 activity in persistent directional cell migration is not fully understood. Here, we show that the ubiquitin ligase mind bomb 1 (Mib1) is involved in persistent directional cell migration. We found that knockdown of MIB1 led to an increase in random cell migration in HeLa cells in a wound-closure assay. Furthermore, we explored novel Mib1 substrates for cell migration and found that Mib1 ubiquitinates Ctnnd1. Mib1-mediated ubiquitination of Ctnnd1 K547 attenuated Rac1 activation in cultured cells. In addition, we found that posterior lateral line primordium cells in the zebrafish mib1ta52b mutant showed increased random migration and loss of directional F-actin-based protrusion formation. Knockdown of Ctnnd1 partially rescued posterior lateral line primordium cell migration defects in the mib1ta52b mutant. Taken together, our data suggest that Mib1 plays an important role in cell migration and that persistent directional cell migration is regulated, at least in part, by the Mib1-Ctnnd1-Rac1 pathway. [ABSTRACT FROM AUTHOR]