Multifaceted control of E-cadherin dynamics by Adaptor Protein Complex 1 during epithelial morphogenesis

Intracellular trafficking regulates the distribution of transmembrane proteins including the key determinants of epithelial polarity and adhesion. The Adaptor Protein 1 (AP-1) complex is the key regulator of vesicle sorting, which binds many specific cargoes. We examined roles of the AP-1 complex in epithelial morphogenesis, using the Drosophila wing as a paradigm. We found that AP-1 knockdown leads to ectopic tissue folding, which is consistent with the observed defects in integrin targeting to the basal cell–extracellular matrix adhesion sites. This occurs concurrently with an integrin-independent induction of cell death, which counteracts elevated proliferation and prevents hyperplasia. We discovered a distinct pool of AP-1 that localizes at the subapical adherens junctions. Upon AP-1 knockdown, E-cadherin is hyperinternalized from these junctions and becomes enriched at the Golgi and recycling endosomes. We then provide evidence that E-cadherin hyperinternalization acts upstream of cell death in a potential tumor-suppressive mechanism. Simultaneously, cells compensate for elevated internalization of E-cadherin by increasing its expression to maintain cell–cell adhesion.     

Zebrafish as a model for systems biology

Zebrafish offer a unique vertebrate model for research areas such as drug development, disease modeling and other biological exploration. There is significant conservation of genetics and other cellular networks among zebrafish and other vertebrate models, including humans. Here we discuss the recent work and efforts made in different fields of biology to explore the potential of zebrafish. Along with this, we also reviewed the concept of systems biology. A biological system is made up of a large number of components that interact in a huge variety of combinations. To understand completely the behavior of a system, it is important to know its components and interactions, and this can be achieved through a systems biology approach. At the end of the paper we present a concept of integrating zebrafish into the systems biology approach.     

Zebrafish as a cancer model

The zebrafish has developed into an important model organism for biomedical research over the last decades. Although the main focus of zebrafish research has traditionally been on developmental biology, keeping and observing zebrafish in the lab led to the identification of diseases similar to humans, such as cancer, which subsequently became a subject for study. As a result, about 50 articles have been published since 2000 in which zebrafish were used as a cancer model. Strategies used include carcinogenic treatments, transplantation of mammalian cancer cells, forward genetic screens for proliferation or genomic instability, reverse genetic target-selected mutagenesis to inactivate known tumor suppressor genes, and the generation of transgenics to express human oncogenes. Zebrafish have been found to develop almost any tumor type known from human, with similar morphology and, according to gene expression array studies, comparable signaling pathways. However, tumor incidences are relatively low, albeit highly comparable between different mutants, and tumors develop late in life. In addition, tumor spectra are sometimes different when compared with mice and humans. Nevertheless, the zebrafish model has created its own niche in cancer research, complementing existing models with its specific experimental advantages and characteristics. Examples of these are imaging of tumor progression in living fish by fluorescence, treatment with chemical compounds, and screening possibilities not only for chemical modifiers but also for genetic enhancers and suppressors. This review aims to provide a comprehensive overview of the state of the art of zebrafish as a model in cancer research. (Mol Cancer Res 2008;6(5):685-94).     

Zebrafish as a model system for biomedical studies

Zebrafish (Danio rerio) is now firmly recognized as a powerful research model for many areas of biology and medicine. Here, we review some achievements of zebrafish-based assays for modeling human diseases and for drug discovery and development. For drug discovery, zebrafish is especially valuable during the earlier stages of research as its represents a model organism to demonstrate a new treatment’s efficacy and toxicity before more costly mammalian models are used. This review considers some examples of known compounds which exhibit both physiological activity and toxicity in humans and zebrafish. The major advantages of zebrafish embryos consist in their permeability to small molecules added to their incubation medium and chorion transparency that enables the easy observation of the development. Assay of acute toxicity (LC₅₀ estimation) in embryos can also include the screening for developmental disorders as an indicator of teratogenic effects. We have used the zebrafish model for toxicity testing of new drugs based on phospholipid nanoparticles (e.g. doxorubicin). Genome organization and the pathways involved into control of signal transduction appear to be highly conserved between zebrafish and humans and therefore zebrafish may be used for modeling of human diseases. The review provides some examples of zebrafish application in this field.     

Zebrafish as a model for developmental neurotoxicity testing

BACKGROUND: To establish zebrafish as a developmental toxicity model, we used 7 well-characterized compounds to examine several parameters of neurotoxicity during development. METHODS: Embryos were exposed by semistatic immersion from 6 hrs postfertilization (hpf). Teratogenicity was assessed using a modified method previously developed by Phylonix. Dying cells in the brain were assessed by acridine orange staining (these cells are likely to be apoptotic). Motor neurons were assessed by antiacetylated tubulin staining and catecholaminergic neurons were visualized by antityrosine hydroxylase staining. RESULTS: Atrazine, dichlorodiphenyltrichloroethane (DDT), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were primarily teratogenic and not specifically neurotoxic. 2,4-dichlorophenoxyacetic acid (2,4-D), dieldrin, and nonylphenol showed specific neurotoxicity; dieldrin and nonylphenol were specifically toxic to catecholaminergic neurons. Malathion, although not teratogenic, showed some nonspecific toxicity. CONCLUSIONS: Teratogenicity measured in 96-hpf zebrafish is predictive of mammalian teratogenicity and is useful in determining whether a compound causes specific neurotoxicity or general developmental toxicity. Induction of apoptosis or necrosis is an indicator of neurotoxicity. An effect on motor neurons in the caudal third of the embryo correlates with expected defects in motility. Overall, our results showed a strong correlation with mammalian data and suggest that zebrafish is a predictive animal model for neurotoxicity screening.     

Zebrafish as a model for hearing and deafness

The zebrafish is an especially attractive model for the study of the development and function of the vertebrate inner ear. It combines rapid and accessible embryogenesis with a host of genetic and genomic tools for systematic gene discovery and analysis. A large collection of mutations affecting development and function of the ear and a related sensory system, the lateral line, have been isolated; several of these have now been cloned, and at least five provide models for human deafness disorders. Disruption of multiple genes, using both forward and reverse genetic approaches, has established key players--both signaling molecules and autonomous factors--responsible for induction and specification of the otic placode. Vestibular and auditory defects have been detected in adult animals, making the zebrafish a useful system in which to tackle the genetic causes of late onset deafness and vestibular disease.     

Zebrafish heart as a model for human cardiac electrophysiology

The zebrafish (Danio rerio) has become a popular model for human cardiac diseases and pharmacology including cardiac arrhythmias and its electrophysiological basis. Notably, the phenotype of zebrafish cardiac action potential is similar to the human cardiac action potential in that both have a long plateau phase. Also the major inward and outward current systems are qualitatively similar in zebrafish and human hearts. However, there are also significant differences in ionic current composition between human and zebrafish hearts, and the molecular basis and pharmacological properties of human and zebrafish cardiac ionic currents differ in several ways. Cardiac ionic currents may be produced by non-orthologous genes in zebrafish and humans, and paralogous gene products of some ion channels are expressed in the zebrafish heart. More research on molecular basis of cardiac ion channels, and regulation and drug sensitivity of the cardiac ionic currents are needed to enable rational use of the zebrafish heart as an electrophysiological model for the human heart.     

Zebrafish as a model for normal and malignant hematopoiesis

Zebrafish studies in the past two decades have made major contributions to our understanding of hematopoiesis and its associated disorders. The zebrafish has proven to be a powerful organism for studies in this area owing to its amenability to large-scale genetic and chemical screening. In addition, the externally fertilized and transparent embryos allow convenient genetic manipulation and in vivo imaging of normal and aberrant hematopoiesis. This review discusses available methods for studying hematopoiesis in zebrafish, summarizes key recent advances in this area, and highlights the current and potential contributions of zebrafish to the discovery and development of drugs to treat human blood disorders.     

Zebrafish as a new animal model for movement disorders

The zebrafish, long recognized as a model organism for the analysis of basic developmental processes, is now also emerging as an alternative animal model for human diseases. This review will first provide an overview of the particular characteristics of zebrafish in general and their dopaminergic nervous system in particular. We will then summarize all work undertaken so far to establish zebrafish as a new animal model for movement disorders and will finally emphasize its particular strength – amenability to high throughput in vivo drug screening.     

模式生物斑马鱼在微量元素代谢研究中的应用

微量元素如铁、锌、铜等对维持生物体代谢和健康至关重要,其含量失衡会造成代谢异常甚至死亡,因此生物体存在复杂机制维持这些微量元素的稳态代谢平衡（homeostasis）。近年来国际上一些实验室尝试用模式脊椎生物斑马鱼来开展该领域的研究,展示出斑马鱼的特有优势。特别是大规模正向遗传学筛选的成功开展,一系列微量元素代谢异常的突变体（如：weissherbst、chardonnay、chianti、shiraz、gavi、calamity和catastrophe）相继发现,为研究离子代谢调控机制和相关疾病的发病机理,提供了整体动态的活体模型。铁代谢相关基因加,2J和grx5都己在斑马鱼中成功定位克隆,斑马鱼铜载体基因atp7a突变体calamity的深入研究,进一步阐明了Menkes病的发病机理。利用斑马鱼的优势,结合小鼠模型和人群来研究微量元素的体内稳态代谢平衡将是微量元素代谢机制研究的新方向。     

Zebrafish as a model for infectious disease and immune function

The zebrafish, Danio rerio, has come to the forefront of biomedical research as a powerful model for the study of development, neurobiology, and genetics of humans. In recent years, use of the zebrafish system has extended into studies in behaviour, immunology and toxicology, retaining the concept that it will serve as a model for human disease. As one of the most thoroughly studied teleosts, with a wealth of genetic and genomic information available, the zebrafish is now being considered as a model for pathogen studies in finfishes. Its genome is currently being sequenced and annotated, and gene microarrays and insertional mutants are commercially available. The use of gene-specific knockdown of translation through morpholino oligonucleotides is widespread. As a result, several laboratories have developed bacterial and viral disease models with the zebrafish to study immune responses to infection. Although many of the zebrafish pathogen models were developed to address human infectious disease, the results of these studies should provide important clues for the development of effective vaccines and prophylactic measures against bacterial and viral pathogens in economically important fishes. In this review, the capabilities and potential of the zebrafish model system will be discussed and an overview of information on zebrafish infectious disease models will be presented.     

Hydra as a model organism for the study of morphogenesis

Pattern formation in hydra is controlled by two sets of morphogens: an activator and an inhibitor o f head and bud formation, and an activator and an inhibitor o f foot formation.     

Epimorphin: a mesenchymal protein essential for epithelial morphogenesis.

A novel 150 kd protein expressed on the surface of mesenchymal cells of mouse embryonic tissues was identified. A monoclonal antibody to this molecule inhibited various processes of epithelial morphogenesis, such as hair follicle growth and lung epithelial tubular formation, in organ cultures of these tissues. Sequence analysis of cDNA encoding this protein revealed that it had 289 amino acids with a hydrophobic stretch at the C-terminus. NIH 3T3 cells transfected with the cDNA of this protein expressed the exogenous 150 kd protein on their surface. When lung epithelial cells were cocultured with these transfected cells, they showed normal tubular morphogenesis, but not with untransfected NIH 3T3 cells. These results indicate that this protein, termed epimorphin, plays a central role in epithelial-mesenchymal interactions.     

Zebrafish as a genomics model for human neurological and polygenic disorders

Whole exome sequencing and, to a lesser extent, genome-wide association studies, have provided unprecedented advances in identifying genes and candidate genomic regions involved in the development of human disease. Further progress will come from sequencing the entire genome of multiple patients and normal controls to evaluate overall mutational burden and disease risk. A major challenge will be the interpretation of the resulting data and distinguishing true pathogenic mutations from rare benign variants.While in model organisms such as the zebrafish,mutants are sought that disrupt the function of individual genes, human mutations that cause, or are associated with, the development of disease, are often not acting in a Mendelian fashion, are frequently of small effect size, are late onset, and may reside in noncoding parts of the genome. The zebrafish model is uniquely poised for understanding human coding- and noncoding variants because of its sequenced genome, a large body of knowledge on gene expression and function, rapid generation time, and easy access to embryos. A critical advantage is the ease of zebrafish transgenesis, both for the testing of human regulatory DNA driving expression of fluorescent reporter proteins, and the expression of mutated disease-associated human proteins in specific neurons to rapidly model aspects of neurological disorders. The zebrafish affords progress both through its model genome and it is rapidly developing transparent model vertebrate embryo.