Restrictions on the Importation of Zebrafish into Canada Associated with Spring Viremia of Carp Virus.

The zebrafish model system is helping researchers improve the health and welfare of people and animals and has become indispensable for advancing biomedical research. As genetic engineering is both resource intensive and time-consuming, sharing successfully developed genetically modified zebrafish lines throughout the international community is critical to research efficiency and to maximizing the millions of dollars in research funding. New restrictions on importation of zebrafish into Canada based on putative susceptibility to infection by the spring viremia of carp virus (SVCV) have been imposed on the scientific community.

Zebrafish epiboly: Spreading thin over the yolk.

Tissue thinning and spreading, a morphogenetic movement termed epiboly, is used widely during animal development. In zebrafish, epiboly is a prominent cell movement during gastrulation, whereby a squamous epithelium (the enveloping layer), a multi-layer of loosely packed cells (the deep cells), and a yolk nuclear syncytium (the yolk syncytial layer) undergo coordinated expansion to engulf the yolk and close the blastopore. Elucidating the mechanisms that underlie epiboly is important not only for understanding animal development in general, but also for providing insights into fundamental cell behaviors including cell intercalation, cell adhesion, cell signaling, and epithelial morphogenesis.

PAPC mediates self/non-self-distinction during Snail1-dependent tissue separation.

Cleft-like boundaries represent a type of cell sorting boundary characterized by the presence of a physical gap between tissues. We studied the cleft-like ectoderm-mesoderm boundary in Xenopus laevis and zebrafish gastrulae. We identified the transcription factor Snail1 as being essential for tissue separation, showed that its expression in the mesoderm depends on noncanonical Wnt signaling, and demonstrated that it enables paraxial protocadherin (PAPC) to promote tissue separation through two novel functions.

Global identification of Smad2 and Eomesodermin targets in zebrafish identifies a conserved transcriptional network in mesendoderm and a novel role for Eomesodermin in repression of ectodermal gene expression.

Background: Nodal signalling is an absolute requirement for normal mesoderm and endoderm formation in vertebrate embryos, yet the transcriptional networks acting directly downstream of Nodal and the extent to which they are conserved is largely unexplored, particularly in vivo. Eomesodermin also plays a role in patterning mesoderm and endoderm in vertebrates, but its mechanisms of action, and how it interacts with the Nodal signalling pathway are still unclear.

Results: Using a combination of ChIP-seq and expression analysis we identify direct targets of Smad2, the effector of Nodal signalling in blastula stage zebrafish embryos, including many novel target genes.

Dynamin-dependent maintenance of epithelial integrity is essential for zebrafish epiboly.

Epiboly, the thinning and spreading of one tissue over another, is a widely employed morphogenetic movement that is essential for the development of many organisms. In the zebrafish embryo, epiboly describes the coordinated vegetal movement of the deep cells, enveloping layer (EVL) and yolk syncytial layer (YSL) to engulf the yolk cell. Recently, we showed that the large GTPase Dynamin plays a fundamental role in epiboly in the early zebrafish embryo.

Zebrafish Dynamin is required for maintenance of enveloping layer integrity and the progression of epiboly.

Epiboly, the first morphogenetic cell movement that occurs in the zebrafish embryo, is the process by which the blastoderm thins and spreads to engulf the yolk cell. This process requires the concerted actions of the deep cells, the enveloping layer (EVL) and the extra-embryonic yolk syncytial layer (YSL). The EVL is mechanically coupled to the YSL which acts as an epiboly motor, generating the force necessary to draw the blastoderm towards the vegetal pole though actomyosin flow and contraction of the actomyosin ring.

Zebrafish epiboly: mechanics and mechanisms.

Gastrulation involves of a series of coordinated cell movements to organize the germ layers and establish the major body axes of the embryo. One gastrulation movement is epiboly, which involves the thinning and spreading of a multilayered cell sheet. Epiboly plays a prominent role in zebrafish gastrulation and studies of zebrafish epiboly have provided insights into basic cellular properties and mechanisms of morphogenesis that are widely used in animal development.

The tight junction component Claudin E is required for zebrafish epiboly.

Zebrafish epiboly results in the thinning and spreading of the blastoderm to cover the yolk cell and close the blastopore. The extra-embryonic yolk syncytial layer (YSL) tows the blastoderm vegetally during epiboly by means of its tight junction attachments to the enveloping layer (EVL). Claudins are the major transmembrane protein components of tight junctions.

Short- and long-range functions of Goosecoid in zebrafish axis formation are independent of Chordin, Noggin 1 and Follistatin-like 1b.

The organizer is essential for dorsal-ventral (DV) patterning in vertebrates. Goosecoid (Gsc), a transcriptional repressor found in the organizer, elicits partial secondary axes when expressed ventrally in Xenopus, similar to an organizer transplant. Although gsc is expressed in all vertebrate organizers examined, knockout studies in mouse suggested that it is not required for DV patterning.

Characterization and comparative expression of zebrafish calpain system genes during early development.

The classic calpain system has been implicated in regulating a variety of cellular processes including cell adhesion, migration, and intracellular signaling; however, little is known regarding the function of this system in vivo. Two heterodimeric Ca(2+)-dependent cysteine proteases, mu-calpain (CAPN1) and m-calpain (CAPN2), and the endogenous inhibitor calpastatin (CAST) comprise the classic/ubiquitous calpain system in mammals. Recently, knockout of two murine classic calpain genes, Capn2 and Capn4/Capns1, revealed that components of the classic system are indispensable for preimplantation development.

Fog1 is required for cardiac looping in zebrafish.

To further our understanding of FOG gene function during cardiac development, we utilized zebrafish to examine FOG's role in the early steps of heart morphogenesis. We identified fragments of three fog genes in the zebrafish genomic database and isolated full-length coding sequences for each of these genes by using a combination of RT-PCR and 5'-RACE. One gene was similar to murine FOG-1 (fog1), while the remaining two were similar to murine FOG-2 (fog2a and fog2b).

T-box gene eomesodermin and the homeobox-containing Mix/Bix gene mtx2 regulate epiboly movements in the zebrafish.

The T-box gene eomesodermin (eomes) has been implicated in mesoderm specification and patterning in both zebrafish and frog. Here, we describe an additional function for eomes in the control of morphogenesis. Epiboly, the spreading and thinning of an epithelial cell sheet, is a central component of gastrulation in many species; however, despite its importance, little is known about its molecular control.

The maternally expressed zebrafish T-box gene eomesodermin regulates organizer formation.

Early embryonic development in many organisms relies upon maternal molecules deposited into the egg prior to fertilization. We have cloned and characterized a maternal T-box gene in the zebrafish, eomesodermin (eomes). During oogenesis, the eomes transcript becomes localized to the cortex of the oocyte.