New twists on embryonic patterning. EMBO workshop: embryonic organizer signaling: the next frontiers.

Abstract

The EMBO workshop ‘Embryonic organizer signaling: the next frontiers’ was held at the European Molecular Biology Laboratory in Heidelberg, Germany, April 28–30, 2001. ![][1] The term ‘organizer’ was coined by Hans Spemann and Hilde Mangold in 1924, based on the seminal observation that a small region of the amphibian gastrula, the dorsal lip, when transplanted to an ectopic location, had the ability to induce, or organize, the formation of a twinned embryo, recruiting neighboring cells from the host into a variety of cell differentiation pathways. The gastrula organizer has been reviewed in extenso recently (special issue of Int. J. Dev. Biol. , 45 ). It has become apparent that organizing centers, which secrete signals that pattern adjacent regions, are a recurring theme in developmental biology. Organizing centers function during neural tube formation in vertebrates, compartment boundary formation in Drosophila , limb development and the establishment of left–right asymmetry. Intercellular signaling is effected through a surprisingly small number of cell surface receptor‐mediated signaling pathways, in particular Hedgehog, Wnt, FGF, Delta/Notch and TGF‐β family members. Molecular and genetic studies on the various organizing centers have revealed that these signaling pathways are highly modulated, by agonist and antagonist signals and a variety of post‐translational modifications, to generate the intricate patterns observed in developing embryos. The complexity, mechanisms of action and the conceptual convergence/divergence of distinct embryonic organizer centers was discussed at the EMBO workshop on ‘Embryonic organizer signaling: the next frontiers’ held at the EMBL on April 28–30, 2001 in Heidelberg. In this review, we highlight some of the salient themes that emerged. ### Secreted antagonists, inhibitory modulation of growth factor activity A major conclusion to emerge in recent years is that embryonic patterning is controlled to a large extent by the modulatory action of secreted antagonists or agonists (Figure 1). For example, Chordin and Noggin are antagonists secreted by the gastrula organizer, which … [1]: /embed/graphic-1.gif