Zebrafish has emerged as an important vertebrate model for studying hematopoiesis and its genetic and chemical modifiers. The zebrafish embryos are unique in their optical transparency, ease of maintenance and high fecundity. They are also amendable to genetic and pharmacological perturbation at high throughput. As a result, the embryos are suitable for various experimental techniques and have a high efficiency in large-scale drug screening. Recently, zebrafish has also emerged as a model for the study of human disease. In this model organism, primitive hematopoiesis is transitory and it occurs in the intermediate cells mass and comprises primarily erythroid cells. Definitive hematopoiesis arises from the ventral wall of dorsal aorta and moves to the caudal hematopoietic tissues, thence the kidney, where life-long and multi-lineage differentiation occurs. The chemical screening platform comprises O-dianisidine staining for hemoglobin containing cells (erythroid) during primitive hematopoiesis. Positive hits were validated based on flow cytometry of dissociated transgenic Tg(gata1:GFP) embryos and whole-mount in-situ hybridization (WISH) for hematopoietic genes. Gene knock-down was conducted by morpholinos (MO) injected into zebrafish embryos at 1-4 cell stage and the effects on hematopoietic development evaluated by WISH and quantitative real-time PCR. Chemical screening of 74 compounds has been performed. These compounds were obtained from a chemical library comprising 879 compounds from NIH (National Institutes of Health) and pre-screened by their effects on cancer cell lines. Four compounds (Tin(IV), chlorotriphenyl [1-(4-ethoxyphenyl)- 3-cyanoureato]-hydrogen,triethylamine, Nogamycin, N,N-Dibenzyldaunorubicin hydrochloride and Allyl 2,3,4-tri-O-benzyl-6-O-(tert-butyldimethylsilyl)-α- D-gluco-Pyranoside) which significantly reduced O-dianisidine staining were identified of which one (Allyl 2,3,4-tri-O-benzyl-6-O-(tert-butyldimethylsilyl) -α-D-glucopyranoside was shown to reduce GFP+ population in Tg(gata1:GFP) population Another chemical (2-Propanol,1,1'-[(1-methylethylidene)bis(4, 1-phenyleneoxy)]bis[3-[(1,1,3,3-tetramethylbutyl)amino]-,dihydrochloride]) was shown to reduce c-myb (marker of definitive hematopoiesis) expression in the ventral wall of dorsal aorta. I also attempted gene knock in zebrafish embryos based on anti-sense morpholino microinjection. A gene encoding for arl4ab was examined, as it was shown to be expressed in hematopoietic tissue in zebrafish embryos but its function is entirely unknown. Knock-down of arl4ab significantly reduced c-myb and runx1 expression in the ventral wall of dorsal aorta and it can be reversed by co-injecting arl4ab mRNA. scl and gata1 expression as well as GFP expression in transgenic Tg(flk1:GFP) embryos that represented vascular development was unaffected. In summary, a zebrafish platform for the study of chemical and genetic modifiers was established. The results have provided important leads for further study into the mechanisms whereby these modifiers regulate hematopoiesis in the zebrafish embryos. / published_or_final_version / Medicine / Master / Master of Medical Sciences

Zebrafish has emerged as an important model for the study of embryonic hematopoiesis. It is a well-characterized model with numerous advantages. Large amount of embryos can be produced by a single pair of zebrafish and the optically transparent embryos allow direct visualization and manipulation of embryonic processes. Large-scale chemical screening using zebrafish embryos can be developed for robust screening of chemical libraries. The zebrafish hematopoiesis resembles that of mammals and occurs in two successive waves, primitive and definitive hematopoiesis. High-throughput read-outs are available to study the effects of different chemicals and genetic modifications on hematopoiesis. In first part of this study, an initial screening using O-dianisidine staining and whole-mount in-situ hybridization as read-out for chemicals that might perturb the regulation of hematopoiesis was conducted. Positive hit was further evaluated by flow cytometry of dissociated transgenic Tg(gata1:GFP) zebrafish embryos. A total of 50 compounds were screened from the "Mechanistic set" chemical libraries obtained from Developmental Therapeutics Program of the National Cancer Institute. One compound, "NSC 643834" was shown to reduce O-dianisidine staining at different concentrations tested. The second part of this study was performed to investigate the role of inca2 in zebrafish hematopoiesis. inca2 was found to be upregulated in chordin morphant zebrafish in which primitive hematopoiesis was expanded. The spatial expression of inca2 was examined by whole mount in-situ hybridization of embryos at different developmental stages. Furthermore the function of inca2 was investigated by gene knockdown using inca2 anti-sense morpholino. Primitive hematopoiesis was perturbed, suggesting that inca2 might play an important role in the regulation of this process. In conclusion, the present study demonstrated the distinct advantages and feasibility of using zebrafish as a platform of high throughput chemical screening and genetic manipulation. The result provided important ground to investigate the regulatory mechanisms of embryonic hematopoiesis. / published_or_final_version / Medicine / Master / Master of Research in Medicine

Although much more work needs to be done to elucidate the functional roles of FSH and LH in fish reproduction, the preset study provides a relatively comprehensive study for us to understand the potential roles of FSH and LH during ovarian development in fish, especially the importance of FSH. / At the same time, functional studies were carried out to examine and compare bioactivities of the CHO-derived zfFSH and zfLH in zebrafish ovary, which is the major part of the present project. The following aspects were covered to investigate the actions of zfFSH and zfLH: steroidogenesis and folliculogenesis. / Both recombinant zfGTHs stimulated activin betaA expression but slightly suppressed activin betaB expression. During short-term treatment, zfFSH and zfLH exhibited similar stimulatory effects on activin betaA expression; the effect of zfLH became more prominent after 24 h treatment while zfFSH had little effect. / Previously, our laboratory had established two stable Chinese hamster ovary (CHO) cell lines expressing recombinant zebrafish FSH (zfFSH) and LH (zfLH). However, the production yields are very low. Therefore, the present study tried to adopt the yeast Pichia pastoris as another bioreactor to produce recombinant zfFSH and zfLH. Two different forms of expression vectors for a native form and a fusion form carrying a His-tag, respectively, were constructed for each hormone. Their bioactivities were monitored and confirmed by receptor-based reporter gene assays as well as ovarian fragment incubation. As expected, the native form exhibited much higher activities than the fusion form. / The pituitary gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are the key hormones controlling vertebrate reproduction. Although the two gonadotropins have been characterized in numerous teleost species, our understanding of their biological functions remains rather limited. This is largely due to the lack of pure form of homologous gonadotropins and inadequate understanding of gonadal physiology in most species studied as well as species variation of hormone actions. The present study aims at systematically investigating the functional roles of FSH and LH in the ovary using zebrafish as the model. Zebrafish is becoming more and more popular as the model of reproductive and developmental studies due to several advantages. First, though its body size is small, its ovary is relatively large and available all the year around. Second, zebrafish spawns everyday and its development is fast. Last but not least, its bioinformatics information is tremendous compared to other fish models. / We investigated the effects of zfFSH and zfLH on steroidogenesis by examining the regulation of aromatase by these two hormones. Aromatase catalyzes the conversion of androgens into estrogens during steroidogenesis. Both recombinant zfGTHs stimulated the aromatase expression during short-term treatment (8 h) in ovarian fragment culture, with zfFSH much more potent than zfLH. However, zfFSH continued to exhibit powerful effect on aromatase expression after 24 h treatment while zfLH had little effect at all. The stimulatory effect of zfFSH on aromatase expression was time-, dose- and stage-dependent and was also confirmed by in vivo study. Furthermore, it was also zfFSH but not zfLH that significantly stimulated StAR protein expression during short-term treatment. StAR protein is critical to steroidogenesis by facilitating the movement of cholesterol across the mitochondrial membrane. / zfLH was found to be able to induce GVBD in zebrafish, as demonstrated in other fish species. However, our preliminary data showed that zfFSH was also involved in this process. To our knowledge, this is the first time to demonstrate that homologous FSH induces GVBD in teleosts. / Yu, Xiaobin. / Adviser: Wei Ge. / Source: Dissertation Abstracts International, Volume: 70-09, Section: B, page: . / Thesis submitted in: December 2008. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 152-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Foodborne toxins include a variety of biologically produced toxins and process-induced toxicants. Among them, marine algal toxins in polluted seafood can induce serious harmful effects on human, while heat-induced toxicants remain in a wide range of food and chronically affect health. In this present study, several representative toxins from these two categories were selected and studied, they are, brevetoxins (PbTxs), saxitoxin (STX) and acrolein (ACR). During past decades, the molecular actions of these toxins have been well studied, however, their effects and mechanisms corresponding to their sublethal toxicity in vivo still need more investigation. Therefore, in our current study, we adopted medaka fish (Oryzias melastigma) and zebrafish (Danio rerio) as models to study the toxicological responses and pathways of these selected toxins at the molecular and cellular level. In the first part of study, the targeted organs of medaka fish, gills and brains, were studied in medaka fish after exposure to the sublethal level of PbTx-1, the most potent neurotic shellfish poisoning (NSP) toxin. Facilitated by the two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ ionization tandem time-of-flight mass spectrometry (MALDI TOF/TOF MS), proteins affected by PbTx-1 in these organs were identified, including myosin like proteins, aldose reductase, gelsolin and keratin. Collectively, the proteins altered after exposure suggested the altered calcium ion binding process, and dysfunction in cytoskeleton assembly and metabolism. After successfully applying the fish model and proteomic approaches in the NSP toxin study, we put emphasis on the developmental toxicity of foodborne toxins, as children are more sensitive and vulnerable to foodborne toxins. Among the marine algal toxins, paralytic shellfish poisoning (PSP) toxins are the commonest and most lethal ones with STX as the most potent PSP toxin. Therefore, we examined the developmental effects of STX using medaka model. By exposing medaka embryos from the early blastula stage onwards, which covered the main developmental stage of the central nervous system and somites, we found newly hatched medaka fish exhibit abnormal growth with longer body length and relatively smaller yolk sac size. High cell proliferation, neuron development, and metabolism were confirmed by whole-mount immunostaining and 2-DE. In summary, STX disturbs the normal growth of medaka embryos probably by affecting the metabolic rate in the exposed medaka embryos. Opposite to STX, after exposure to ACR, a pollutant that ubiquitously exists in food and environment, the zebrafish exhibited delayed development. ACR is a known glutathione (GSH) depleting factor and oxidative stress inducer. Apart from developmental retardance, increased reactive oxygen species (ROS) and inflammation were found in newly hatched zebrafish, suggesting the developmental delay may be partly related to the ACR-induced oxidative stress. In summary, findings from the present study highlighted the molecular responses and possible pathways of some selected foodborne toxins. Developmental effects and toxicity were also found after exposing to both the biologically produced toxin and the heat-produced toxicant. Our current study makes contributions to the knowledge on the hazardous effects of foodborne toxins in vivo, and provides useful information for the further study on the human health. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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Zebrafish (Brachydanio rerio) are small, freshwater teleost fishes in the family Cyprinidae, the true minnows. They are native to the tropical latitudes of India, but have become widespread through their use as aquarium fish and as models for several branches of biological research. Their ease of rearing, short generation time, year-around egg laying potential, brief developmental period, and embryo transparency have made them especially desirable as models for developmental biology, genetics, and neurobiology. Because of their popularity, they were also the first small aquarium fish to be used as test organisms for carcinogenesis in the early 1960's. For reasons that have never been stated, their use as a model for carcinogenesis research did not continue. Due to the number of positive characteristics that this species has, the goal of this research effort was to systematically evaluate the potential of zebrafish for use as an environmental monitor, to evaluate the toxicology and carcinogenesis of surface and/or ground waters. The overall project was multidisciplinary in nature, but the focus of this thesis research was on the whole animal, dose-response to a number of well-known carcinogens, administered by multiple exposure routes, and the pathological description of the resulting lesions. Exposure to N-nitrosodiethylamine (DEN) and N-nitrosodimethylamine (DMN) in the diet was ineffective, but static water bath exposure of fry and embryos to these nitrosamines resulted in neoplasms, primarily in the liver. Embryo exposure to DEN resulted in a low response of neoplasms in several other organs as well. Dietary exposure of zebrafish to aflatoxin B₁ resulted in few hepatic neoplasms, revealing a marked resistance to this carcinogen. Dietary exposure to methylazoxymethanol acetate (MAM-Ac) produced mostly liver tumors, as did both fry and embryo water bath exposures. Each water bath exposure also produced neoplasms at other tissue and organ sites, but the embryo stage produced the greatest variety. These results demonstrate a relative resistance to neoplastic development compared to the well-known rainbow trout model. But in one comparative trial, zebrafish were similar to Japanese medaka in their response to dietary MAM-Ac. The major limitation of this species, that will prevent its use as a model for environmental monitoring, however, is its narrow range of temperature tolerance. Temperatures below 15°C produce marked sluggishness, and below 10-12°C cause anesthesia and death. Therefore, this research indicates that this species is not as versatile as some other small fish species for laboratory and especially field monitoring of environmental carcinogenic hazards. / Graduation date: 1997

Thesis (Ph.D.) - University of St Andrews, May 2010.