..................................................................................................................... 5 List of publications ...................................................................................................... 7 General introduction ................................................................................................... 8 The notochord .................

The anterior aspect of the mouse primitive streak resembles the organizer of Xenopus and chick in terms of its developmental fate, ability to alter pattern in the chick limb bud and with respect to the repertoire of genes that its constituent cells express. However, until now there has been no direct evidence that the mouse node organizes pattern during gastrulation, nor that the exceptionally ...

The dynamic behaviour of cells during formation of the notochord in the ascidian, Ciona intestinalis, was examined by means of Differential Interference Contrast (DIC) microscopy and time-lapse videorecording. The initial rudiment is formed in part as a consequence of the pattern of mitotic divisions as the blastopore shifts posteriorly. Vertical and horizontal rearrangements produce an elongat...

Cell shape changes and proliferation are two fundamental strategies for morphogenesis in animal development. During embryogenesis of the simple chordate Ciona intestinalis, elongation of individual notochord cells constitutes a crucial stage of notochord growth, which contributes to the establishment of the larval body plan. The mechanism of cell elongation is elusive. Here we show that althoug...

The establishment of the floor plate at the ventral midline of the CNS is dependent on an inductive signaling process mediated by the secreted protein Sonic hedgehog (Shh). To understand molecularly how floor plate induction proceeds we identified a Shh-responsive regulatory element that directs transgene reporter expression to the ventral midline of the CNS and notochord in a Shh-like manner a...

We performed in vivo experiments in chick embryos that examined whether application of an exogenous source of Shh protein mimics the ability of the notochord to induce ectopic floor plate cells in the neural tube. Shh cannot act alone to induce a floor plate. However, coapplication of Shh and chordin, a BMP antagonist normally coexpressed with Shh in the notochord, results in a marked switch fr...

In vertebrates, the medial moieties of the somites give rise to the vertebrae and epaxial muscles, which develop in close relationship with the axial organs, neural tube and notochord. The lateral moieties contribute to the ribs and to limb and body wall muscles (hypaxial muscles) after a phase of lateral and ventral migration. Surgical ablation of the neural tube and notochord in the chick emb...

Caveolae have been linked to diverse cellular functions and to many disease states. In this study we have used zebrafish to examine the role of caveolin-1 and caveolae during early embryonic development. During development, expression is apparent in a number of tissues including Kupffer's vesicle, tailbud, intersomite boundaries, heart, branchial arches, pronephric ducts and periderm. Particula...

We present evidence that the embryo of the ascidian, Ciona intestinalis, is an easily manipulated system for investigating the establishment of basic chordate tissues and organs. Ciona has a small genome, and simple, well-defined embyronic lineages. Here, we examine the regulatory mechanisms underlying the differentiation of the notochord. Particular efforts center on the regulation of a notoch...

The pattern of growth and morphogenesis of the cranial neural epithelium of rat embryos during neurulation is described. Transverse sections of the midbrain/hindbrain neural epithelium at different stages (0-14 somites) show a constant area and cell number throughout neurulation, even though there is a high level of mitosis. Mitotic spindles are orientated parallel to the long axis of the embry...