Cellular reorganization based on active cell motility and adhesion is the major means of morphogenesis in animal embryos, and is particularly elaborated in vertebrates. Nowhere is this fact more clearly shown than in the dorsal mesoderm of gastrulating zebrafish embryos. Here, occurring in the company of both cellular internalization at the blastoderm margin (Carmany-Rampey and Schier, 2001) (R...

Fragments of Hensen's node or head process were implanted into the primitive streak 0-8 mm behind the node. The posterior region was isolated from all influences emanating from the anterior part of the blastoderm, either by cutting off a large rectangular piece just in front of the implant or by explanting the region combined with the notochord implant into the area opaca. As controls, correspo...

An extracellular signaling molecule acts on several types of cells, evoking characteristic and different responses depending on intrinsic factors in the signal-receiving cells. In ascidian embryos, notochord and mesenchyme are induced in the anterior and posterior margins, respectively, of the vegetal hemisphere by the same FGF signal emanating from endoderm precursors. The difference in the re...

Anatomical details of the ontogeny of the notochord of the european lancelet (ˆ amphioxus), Branchiostoma lanceolatum, are described, based on complete series of alternating thin and semithin sections for light and transmission electron microscopy of early neurula and larval stages, as well as observation of living specimens. The notochord is formed by the outgrowth of dorsal medial cells of th...

Previously, we reported a zebrafish iroquois gene, ziro3, and its expression during early embryogenesis (Mech. Dev. 87 (1999) 165). In the present study, we have isolated two novel zebrafish iroquois genes, ziro1 and ziro5, homologs of mouse Irx1 and mouse Irx5, respectively. The expression of both genes is initiated in dorsal neuroectoderm and mesoderm during gastrulation. Later, their express...

Eph receptors have been implicated in cell-to-cell interaction during embryogenesis. We generated EphA2 mutant mice using a gene trap method. Homozygous mutant mice developed short and kinky tails. In situ hybridization using a Brachyury probe found the notochord to be abnormally bifurcated at the caudal end between 11.5 and 12.5 days post coitum. EphA2 was expressed at the tip of the tail noto...

We analysed the role of Notch signalling during the specification of the dorsal midline in Xenopus embryos. By activating or blocking the pathway we found that Notch expands the floor plate domain of sonic hedgehog and pintallavis and represses the notochordal markers chordin and brachyury, with a concomitant reduction of the notochord size. We propose that within a population of the early orga...

To elucidate the precise roles of axial structures in the myogenic differentiation of the somite, we have examined the effects of the axial organs' precise spatial position during migration and differentiation of somitic cells by using in vivo transplantation of the neural tube and of the notochord directly into the paraxial mesoderm. Differentiation of myotomal cells was identified through the...

Nodal activity in the left lateral plate mesoderm is a conserved sign of irreversible left-right asymmetry at early somite stages of the vertebrate embryo. An earlier, paraxial nodal domain accompanies the emergence and initial extension of the notochord and is either left-sided, as in the chick and pig, or symmetrical, as in the mouse and rabbit; intriguingly, this interspecific dichotomy is m...

Sodium metam (NaM), a dithiocarbamate, is a general agricultural biocide applied prior to planting for the elimination of nematodes, soil pathogens, and weeds. There is a remarkable paucity of information about the mechanism of action and the risk that dithiocarbamates may pose to developing vertebrates. We have characterized NaM toxicity during early life stage exposure in zebrafish. Zebrafish...