Androgenetic development of X- and Y-chromosome bearing haploid rainbow trout embryos

Haploid fish embryos are important in studies regarding role of the recessive traits during early ontogeny. In fish species with the male heterogamety, androgenetic haploid embryos might be also useful tool in studies concerning role of the sex chromosomes during an embryonic development. Morphologically differentiated X and Y chromosomes have been found in a limited number of fish species including rainbow trout (Oncorhynchus mykiss Walbaum 1792). To evaluate role of the sex chromosomes during rainbow trout embryonic development, survival of the androgenetic haploids in the presence of X or Y sex chromosomes has been examined. Androgenetic haploid rainbow trout were produced by fertilization of X-irradiated eggs with spermatozoa derived from the normal males (XY) and neomales, that is, sex-reversed females (XX) to produce X- and Y-bearing haploids, and all X-bearing haploids, respectively. Survival rates of the androgenetic progenies of normal males and neomales examined during embryogenesis and at hatching did not differ significantly. However, all haploids died within next few days after hatching. Cytogenetic analysis of the androgenetic embryos confirmed their haploid status. Moreover, apart from the intact paternal chromosomes, residues of the irradiated maternal chromosomes observed as chromosome fragments were identified in some of the haploids. Provided results suggested that rainbow trout X and Y chromosomes despite morphological and genetic differences are at the early stage of differentiation and still share genetic information responsible for the proper embryonic development.

Inbred strains of zebrafish exhibit variation in growth performance and myostatin expression following fasting

Although the zebrafish (Danio rerio) has been widely utilized as a model organism for several decades, there is little information available on physiological variation underlying genetic variation among the most commonly used inbred strains. This study evaluated growth performance using physiological and molecular markers of growth in response to fasting in six commonly used zebrafish strains [AB, TU, TL, SJA, WIK, and petstore (PET) zebrafish]. Fasting resulted in a standard decrease in whole blood glucose levels, a typical vertebrate glucose metabolism pattern, in AB, PET, TL, and TU zebrafish strains. Alternatively, fasting did not affect glucose levels in SJA and WIK zebrafish strains. Similarly, fasting had no effect on myostatin mRNA levels in AB, PET, TU, and WIK zebrafish strains, but decreased myostatin-1 and -2 mRNA levels in SJA zebrafish. Consistent with previous work, fasting increased myostatin-2 mRNA levels in TL zebrafish. These data demonstrate that variation is present in growth performance between commonly used inbred strains of zebrafish. These data can help future research endeavors by highlighting the attributes of each strain with regard to growth performance so that the most fitting strain may be utilized.

Stages in the development of a model organism as a platform for mechanistic models in developmental biology: Zebrafish, 1970-2000

Model organisms became an indispensable part of experimental systems in molecular developmental and cell biology, constructed to investigate physiological and pathological processes. They are thought to play a crucial role for the elucidation of gene function, complementing the sequencing of the genomes of humans and other organisms. Accordingly, historians and philosophers paid considerable attention to various issues concerning this aspect of experimental biology. With respect to the representational features of model organisms, that is, their status as models, the main focus was on generalization of phenomena investigated in such experimental systems. Model organisms have been said to be models for other organisms or a higher taxon. This, however, presupposes a representation of the phenomenon in question. I will argue that prior to generalization, model organisms allow researchers to built generative material models of phenomena - structures, processes or the mechanisms that explain them - through their integration in experimental set-ups that carve out the phenomena from the whole organism and thus represent them. I will use the history of zebrafish biology to show how model organism systems, from around 1970 on, were developed to construct material models of molecular mechanisms explaining developmental or physiological processes.

Zebrafish genomic instability mutants and cancer susceptibility

Somatic loss of tumor suppressor gene function comprising the second hit of Knudson's two-hit hypothesis is important in human cancer. A genetic screen was performed in zebrafish (Danio rerio) to find mutations that cause genomic instability (gin), as scored by Streisinger's mosaic-eye assay that models this second hit. The assay, based on a visible test for loss of wild-type gene function at a single locus, golden, is representative of genomewide events. Twelve ENU-induced genomic instability (gin) mutations were isolated. Most mutations showed weak dominance in heterozygotes and all showed a stronger phenotype in homozygotes. Trans-heterozygosity for 7 of these mutations showed greatly enhanced instability. A variety of spontaneous tumors were found in heterozygous adults from all gin lines, consistent with the expectation that genomic instability (mutator) mutations can accelerate carcinogenesis. The incidence of spontaneous cancer at 30-34 months was increased 9.6-fold in heterozygotes for the mutant with the strongest phenotype, gin-10. Tumors were seen in skin, colon, kidney, liver, pancreas, ovary, testis, and neuronal tissues, with multiple tumors in some fish. The study of these mutants will add to our understanding of the mechanisms of somatic loss of gene function and how those mechanisms contribute to cancer susceptibility.

A gynogenetic screen to isolate naturally occurring recessive mutations in Xenopus tropicalis

In the rapidly developing, diploid amphibian Xenopus tropicalis, genetics can be married to the already powerful tools of the amphibian system to overcome a disability that has hampered Xenopus laevis as a model organism: the difficulties inherent in conducting genetic analyses in a tetraploid organism with a longer generation time. We describe here a gynogenetic screen to uncover naturally occurring recessive mutations in wild X. tropicalis populations, a procedure that is both faster and easier than conventional genetic screens traditionally employed in model organisms to dissect early developmental pathways. During the first round of our screen, gynogenetic diploids from over 160 females comprising four different wild-caught populations were examined. Forty-two potential mutant phenotypes were isolated during this round of gynogenesis. From this group, we describe 10 lines that have genetically heritable recessive mutations. A wide range of developmental defects were obtained in this screen, encompassing effects limited to individual organs as well phenotypes characterized by more global changes in tadpole body morphology. The frequency of recessive mutations detected in our screen appears lower than that seen in other vertebrate genetic screens, but given constraints on the screening procedure used here, is likely to be consistent with rates seen in other animals, and clearly illustrates how wild-caught animals can be a productive source of developmental mutations for experimental study. The development of genetic strategies for the Xenopus system, together with new genomic resources, existing technologies for transgenesis, and other means for manipulating gene expression, as well as the power of performing embryonic manipulations, will provide an impressive set of tools for resolving complex cell and developmental phenomena in the future.

High-throughput non-heme iron assay for animal tissues

Iron has been widely studied in nearly every realm of biology. However, current methodologies, such as genetic mapping or mutation screening, have been difficult to apply due to the lack of robust high-throughput methods for quantifying iron levels from cells or tissues. The measurement of total iron levels in tissues, usually done with atomic absorption spectroscopy, is impractical for large numbers of samples and includes the contribution of heme iron from hemoglobin contained in red blood cells. The measurement of non-heme iron by reaction with a bathophenanthroline reagent, a commonly used assay reported more than 30 years ago, is also not feasible for large-scale analyses because it is cuvette-based. We therefore have modified this method to a microplate format that will facilitate large-scale analysis. The microplate assay is highly sensitive and specific, and is a simple and effective method for the measurement of non-heme iron for animal tissues that will enable the application of high-throughput of genetic methodologies.

Histology-based screen for zebrafish mutants with abnormal cell differentiation

The power of histology to define states of cell differentiation was used as the basis of a mutagenesis screen in zebrafish. In this screen, 7-day-old parthenogenetic half-tetrad larvae from potential carrier females were screened for mutations affecting cell differentiation in hematoxylin and eosin-stained tissue sections. Seven, noncomplementing, recessive mutations were found. Two mutations affect only the retina: segmented photoreceptors (spr) show a discontinuous photoreceptor cell layer; vestigial outer segments (vos) has fewer photoreceptor cells and degenerated outer segments within this cell layer. Three mutants have gut-specific defects: the epithelial cells of kirby (kby) are replaced by ballooned cells; the intestines of stuffy (sfy) and stuffed (sfd) contain increased luminal mucus. Two mutations affect multiple organs: disordered neural retina (dnr) has disrupted retinal layering and mild nuclear abnormalities in the gut and liver; and in huli hutu (hht), the retinal cell layers are disorganized and multiple organs have mild to severe nuclear abnormalities that are reminiscent of the atypia of human neoplasia. Each mutation appears to be homozygous lethal. This screen is proof of principle for the feasibility of histologic screens to yield novel mutations, including potential models of human disease. The throughput for this type of screen may be enhanced by automation.

Functional genomic dissection of multimeric protein families in zebrafish

The study of multimeric protein function in the postgenomicera has become complicated by the discovery of multiple isoforms for each subunit of those proteins. A correspondingly large number of potential isoform combinations offer the multicellular organism a constellation of protein assemblies from which to generate a variety of functions across different cells, tissues, and organs. At the same time, the multiplicity of potential subunit isoform combinations presents a significant challenge when attempting to dissect the functions of particular isoform combinations. Biochemical and cell culture methods have brought us to a significant state of understanding of multimeric proteins but are unable to answer questions of function within the context of the many tissues and developmental stages of the multicellular organism. Answering those questions can be greatly facilitated in model systems in which expression can be determined over time, in the context of the whole organism, and in which hypomorphic function of each subunit can be studied individually and in combination. Fortunately, the potential for high-throughput in situ hybridization studies and antisense-based reverse genetic knockdowns in zebrafish offers exciting opportunities to meet this challenge. Some of these opportunities, along with cautions of interpretation and gaps in the existing technologies, are discussed in the context of ongoing investigations of the dimeric Na,K-ATPases and heterotrimeric G proteins.

Mosaic Eyes, Genomic Instability Mutants, and Cancer Susceptibility

We now know that genomic instability contributes to cancer. The zebrafish mosaic eye assay developed by George Streisinger takes advantage of the organism's transparency to provide an excellent assay for detecting somatic mutation. This assay allowed us to identify zebrafish mutants with increased frequencies of somatic mutation and spontaneous cancer. Here, we have described details of mutagenesis, the basis and practical use of the mosaic eye assay, and the histological methods used to study genomic instability mutants and cancer susceptibility. These techniques should prove useful to other zebrafish researchers, as they are broadly applicable to many other biological investigations of embryos, larvae, and adult zebrafish.

Comparative aspects of zebrafish (Danio rerio) as a model for aging research

The zebrafish has emerged over the past decade as a major model system for the study of development due to its invertebrate-like advantages coupled with its vertebrate biology. These features also make it a potentially valuable organism for gerontological research. The main advantages of zebrafish include its economical husbandry, small yet accessible size, high reproductive capacity, genetic tractability, and a large and growing biological database. Although zebrafish life span is longer than rodents, it shares the feasibility of large-scale mutational analysis with the extremely short-lived invertebrate models. This review compares zebrafish with the more widely used model organisms used for aging research, including yeast, worms, flies, mice, and humans.

Zebrafish-Mycobacterium marinum model for mycobacterial pathogenesis

We report here the development of a pathogenesis model utilizing Mycobacterium marinum infection of zebrafish (Danio rerio) for the study of mycobacterial disease. The zebrafish model mimics certain aspects of human tuberculosis, such as the formation of granuloma-like lesions and the ability to establish either an acute or a chronic infection based upon inoculum. This model allows the genetics of mycobacterial disease to be studied in both pathogen and host.

Cancer genetics and drug discovery in the zebrafish

Fish have a long history of use in cancer toxicology studies, because they develop neoplasms that are histologically similar to human cancers. Because of considerable progress in zebrafish genetics and genomics over the past few years, the zebrafish system has provided many useful tools for studying basic biological processes. These tools include forward genetic screens, transgenic models, specific gene disruptions and small-molecule screens. By combining carcinogenesis assays, genetic analyses and small-molecule screening techniques, the zebrafish is emerging as a powerful system for identifying novel cancer genes and for cancer drug discovery.

The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations

The zebrafish (Danio rerio) is now the pre-eminent vertebrate model system for clarification of the roles of specific genes and signaling pathways in development. The zebrafish genome will be completely sequenced within the next 1-2 years. Together with the substantial historical database regarding basic developmental biology, toxicology, and gene transfer, the rich foundation of molecular genetic and genomic data makes zebrafish a powerful model system for clarifying mechanisms in toxicity. In contrast to the highly advanced knowledge base on molecular developmental genetics in zebrafish, our database regarding infectious and noninfectious diseases and pathologic lesions in zebrafish lags far behind the information available on most other domestic mammalian and avian species, particularly rodents. Currently, minimal data are available regarding spontaneous neoplasm rates or spontaneous aging lesions in any of the commonly used wild-type or mutant lines of zebrafish. Therefore, to fully utilize the potential of zebrafish as an animal model for understanding human development, disease, and toxicology we must greatly advance our knowledge on zebrafish diseases and pathology.

A call to fins! Zebrafish as a gerontological model

Among the wide variety of model organisms commonly used for studies on aging, such as worms, flies and rodents, a wide research gap exists between the invertebrate and vertebrate model systems. In developmental biology, a similar gap has been filled by the zebrafish (Danio rerio). We propose that the zebrafish is uniquely suited to serve as a bridge model for gerontology. With high fecundity and economical husbandry requirements, large populations of zebrafish may be generated quickly and cheaply, facilitating large-scale approaches including demographic studies and mutagenesis screens. A variety of mutants identified in such screens have led to modelling of human disease, including cardiac disorders and cancer. While zebrafish longevity is at least 50% longer than in commonly used mouse strains, as an ectothermic fish species, its life span may be readily modulated by caloric intake, ambient temperature and reproductive activity. These features, coupled with a growing abundance of biological resources, including an ongoing genome sequencing project, make the zebrafish a compelling model organism for studies on aging.

Life spans and senescent phenotypes in two strains of Zebrafish (Danio rerio)

Zebrafish have become a widely used model organism in developmental biology research. In order to initiate an experimental foundation for aging studies, we have determined some basic gerontological parameters for populations of outbred zebrafish, and the golden sparse strain. Outbred zebrafish manifested a mean life span of about 42 months, with the longest living individual surviving for 66 months. The golden sparse populations had a mean life span of 36 months and a maximum longevity of 58 months. Skeletal length at death increased with age, suggestive of indeterminate growth. A common age-related phenotype was spinal curvature. Radiographic analysis excluded bony changes as the cause of the spinal curvature, suggesting muscle abnormalities as a primary mechanism. These data and a growing abundance of related biological resources suggest that the zebrafish may be a compelling model organism for studies on aging.