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Zebra fish have turn up to be the outstanding model organism in the study of vertebrate biology. It is the favoured animal model systems in the study of genetics, toxicology, pharmacology, embryogenesis and gene function. It is considered to be a pioneer model as of its transparency during the embryonic development, which countenance the ocular analysis of the early development process. Due to swindle generation times and high fecundity it facilitate genetic analysis. The other favouring factors for the study of developmental biology reckon the conservation of development genes across vertebrates, size and external fertilization. Even the administration of drugs and chemicals are administered by directly adding to the water. Amenability to large scale saturation mutagenesis studied made it unique among the many vertebrate animal models.
It renders a forward genetic set about for assigning function of genes and posing them in the development and disease associated pathways. Genetic screening has determined hundreds of mutant phenotype, legion of which correspond the human clinical disorders. A forward genetic approach is provided by fictive design of screens and by clinically applicable process. A patent approach for acquiring insight to the representing pathophysiology by many of the mutant phenotypes denote in genetic screens which are reminiscent of human disease. In mouse the accessibility of the earlier development process is low due to the reason that it occurs in utero which is quite different in zebra fish that favours for genetic screening as the early development process is clearly panoptic. For analysing the gene regulation and functional determination bioassay is effective and convenient. It has undergone through microsatellite genetic linkage map. (ivan jill 2004).
Zebra fish as a model for human disease :
The understanding of the gene function that modulates the normal embryogenesis process was illustrated by mutant analysis. It is a robust and reliable genetic system is established by identifying the genes that regulate embryogenesis. It has been widely employed in an extensive range of medical and scientific disciplines that may include ophthalmology, cardiology, nephrology, neurology, haematology, toxicology and immunology. Presently manifold novel assays were being evaluated for making zebrafish as hard hitting model of human diseases and this leads to the discovery of novel prospective drug targets.
The zebra fish is susceptible to the studying of particularly HEMATOPOIESIS. Blood circulation was exactly begins by 24hours. Primitive haematopoiesis produced erythroid lineages, and definitive haematopoiesis produced erythriod, monocyte, granulocyte, and thrombocyte lineages. Blood-specific genes of human homologous and many mouse have been cloned in zebra fish. In mammalian over 80 homologous genes have been isolated and 50 mutants in hematopoiesis were identified with defects .Using of zebra fish for human disease model was illustrated by the two hematopoietic mutants :sauternes(sau) this sau mutant is a featured of delaying erythroid mutation and abnormal global expression. Congenital sideroblastic anemia was the result due to the mutation in ALAS2 ( aminolevulinate synthase) in humans. The second mutant is yquem(yqe) contains porphyria syndrome, auto fluorescent blood and lack in uroporiphyrinogen decarboxylase(UROD). The yge fish constitute an animal model which deficient in UROD for studying the human porphyria of pathogenesis. These mutants also effect the hematopoietic stem cell generation; such as spadetail, cloche and moonshine .It results in severe and absence of blood cells in the combination of circulation.
Three weeks gestation of embryo of human heart seems like the embryonic heart of zebra fish. The heart beating begins exactly at 22hpf and peristaltic wave at first at 36 hpf for the atrium and ventricle as a coordinate contractions. The heart function of zebra fish can be evaluate visually hence it is particularly susceptible for the studying of cardiac functions. Mutants of zebra fish effects the particular parts of cardiac development. Producing contraction with imperfection of mutants contains passive aggressive, hal, pickwick. slowmo, tremblor, reggae are rhythmicitically effected. Gridlock mutant in zebra fish is seems like human congenital disorder. Due to low enough blood circulation in tail are the features to the grid lock mutant. This is because of a localized vascular defect where it produces a single dorsal aorta in the place of paired lateral dorsal aorta because of lacking of skill to fuse. This imperfection leads to the collateral blood flow development. The prominent feature of cardiac mutant is that, defects effected on the distinct and separable feature of function.by using cardiac specific molecular markers they have been indicated more than 20 mutants.
The pronepric kidney of zebra fish is a simple part or organ with two nephrons contain paired and fused glomeruli, bilateral nephric ducts. The function and development of kidney of higher vertebrates is identical to that of zebra fish. Development of pronephros are affected by the 18 recessive mutants have been identified in zebra fish. Human autosomal dominant polycystic kidney disorder(ADPKD) are absorbed of several mutants. Initiates of blood filtration are developing as glomerular cysts in the mutant bubble, double. Glomerular basement membranes are being altered and aim of an attack of Na/K ATPase is perceived. Combined renal-retinal dysplasia was displayed by another two mutants fleer and elipsa which are similar to that of human disease Senior-Loken syndrome. These mutants contain two dissimilar genes involved in the same or different pathways which are strongly suggested by the complementation test, to study the components or elements of polycystic kidney.
Various recessive mutations impacting the visual system emphasise the cater of zebra fish as a genetic model for the human congenital defects. Mutation of oval gene, that encodes an intra flagellor transport protein, takes to photoreceptor cell digenesis along with the flee in other sensory receptor cells. This renders just as an example of manifold genetic models to study the primitive cell biology of intra flagellor transport in vertebrate cells as well as facilitating additional imitate for diseases of visual system. It is hypothesised that the future research leads to the identification of diseases causing genes in the early stage. With the entropy attained by the abridgment of the existing mutations in zebra fish, redundant novel screens are necessary to uncover the mutations not analysed by existing assays.
In the zebra fish the snakehead rhabdo virus infection (SHRV) occurred as a result of the kinetics of infection and gross pathology. Through intraperitoneal injection the adult zebra fish were infected by 105 TCID50/ML SHRV. Petechial hemorrhages and redness of the abdomen are exhibited by infected adult fish .Examine of antiviral interferon and Mx levels that allow the positions where it was affected to the virus in both embryos and adults .Adult fish are limited to some infection models they are infectious hematopoietic necrosis virus (IHNV),infectious pancreatic necrosis virus (IPNV),and spring viremia of carp virus (SVCV).To interpret the genetic basis of the disease they established a zebra fish which was effected by spring viremia carp virus .Affected fish were characterized with epidermal petechial hemorrhages and come after death .Not long ago, Lu et al explained that the zebra fish can infected by nervous necrosis virus through injection and leads to the damaging of tissues identical to that of natural fish host.
The embryos of zebra fish were liable to Edwardsiella tarda at 24hpf, when compared to control fish the zebra fish shows 31% of CPM. Rely on the infection dose the adult zebra fish that were exposed to bacteria shows the mortality between 45% and 95%. A model for streptococcus infection were described by Neely et al by consuming of streptococcus iniae and streptococcus pyogenes in zebra fish.This model produced a copy of acute disease caused by the pathogenic infection of streptococcus species in both humans and fish .When the zebra fish was infected by mycobacterium tuberculosis it imitate the symptoms of human tuberculosis that were established by Prouty et al and Davis et al. Menudier et al conducted an experiment were he injected different species of listeria monocytogenes in both mice and zebra fish. When compared to mice the zebra fish shows more resistant to the listeria infection. To encoding the acute-phase proteins the Aeromonas salmonicida, a gram negative bacterium and Staphylococcus aureus induced the genes in zebra fish. Rojo et al,not long ago explained that due to the response of L.anguillarum intraperitoneal injection ,the adult zebra fish expressed inflammatory and immune-response genes.
The best model for the studies of pathogenesis and immune responses related to fish is the zebra fish. Morpholinos, gene specific insertional mutants, and mutant fish lines are the growing and make easier to understand by the obtained genomic information. It facilitates the cloning of genes for other fishes by using the genomic information of zebra fish. The extensive complement reagents such as antibodies and cell lines will be essential for the zebra fish to be developed.
Model for drug delivery:
In vivo assay of zebra fish related to human diseases is help full for the discovery of novel potential drug .Identification and study of mutated gene that lead to human gene can be done using zebra fish as a model organism. Genetic screening is most useful tool for identification of mutation in a gene that lead to human disease or disorder .so many techniques are available for large scale screening of vertebrate organism .some of them are chemical mutagenesis screens, insertional mutagenesis, small molecule screen, screen using antisense molecule ,targeted mutagenesis etc.
In chemical mutagenesis N-ethyl-N-nitrosourea is used induce point mutations in zebra fish and these screen results were used to identify the important loci still now more than 1900 important loci had been discovered. In insertional mutagenesis retroviral insertions are used. Insertional mutagenesis allows rapid cloning of the genes .Large scale experiments has been undergoing in Cambridge by Hopkins group. Using this more than 500 insertional mutation has been identified. Due to limitation in size transposons are used. Transposons provide stable gene transfer .two transposons were developed in zebra fish .the sleeping beauty transposon that belongs to tel/mariner and het transposon belong to tol2
In Small molecule screening chemical compounds are used as ligands to bind to protein blocking their activity the phenotypic changes are studied. The ligand which bind to protein is isolated and purified using chromatography and used for drug design antisense molecular approach is used to know the function of gene .basically there are two type of approach used in this area are antisense knock down and knockout of gene .in both cases gene expression of gene is either reduced or completely removed using the screen results the gene importance are studied.