Posted by: Dan | November 15, 2006

Axis Formation in Animal Development

Science‘s Signal Transduction Knowledge Environment (STKE) has a great perspectives piece on a canonical pathway – the Wnt/beta-catenin pathway in establishment of the dorso-ventral axis in animal development, including insights from the recently published sea urchin genome. This pathway governs cell-cell interactions, which are critical for coordinated organization of cells.

Cell-matrix interactions are important too, of course. I’m most familiar with the roles of fibronectin fibrillogenesis, which establishes the direction of mesoderm involution in gastrulation, and morphogenesis of epithelial and endothelial tisssues. These developmental processes occur via migration of sheets of cells, hence the role of cell-cell contacts – the topic of the STKE piece.

The Emergence of Pattern in Embryogenesis: Regulation of beta-Catenin Localization During Early Sea Urchin Development: Mechanisms by which localized signaling molecules specify axis formation during development show species-specific differences. Abstract, below the fold:

The accumulation of beta-catenin in the nuclei of blastomeres at one pole of the early embryo is a highly conserved and essential feature of animal development. In the sea urchin, beta-catenin accumulates in the nuclei of vegetal blastomeres during early cleavage and activates gene regulatory networks that drive mesoderm and endoderm formation. Measurements of beta-catenin half-life in vivo have demonstrated a gradient in stability along the animal-vegetal axis. Dishevelled (Dsh), a protein that regulates beta-catenin turnover, is localized in the vegetal cortex, where it has an essential role in stabilizing beta-catenin and activating endomesodermal gene networks. Two motifs of Dsh are required for targeting to the vegetal cortex. Overexpression of Dsh in animal blastomeres does not alter their fate, which suggests that a localized activator of Dsh may be missing in these cells. Wnt signaling may be localized in the early sea urchin embryo, as it is in Xenopus, but findings point to possible differences in the initial polarizing signal in amphibians and echinoderms. Further studies will be required to determine the extent to which mechanisms that control beta-catenin nuclearization in early embryogenesis have been conserved during animal evolution.


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