For all animals, the formation of the embryonic axes is an important developmental milestone. Now, on p. , Akiyama-Oda and Oda report that in spiders Decapentaplegic (Dpp) is essential for the transformation of a radially symmetrical embryo to one with axial symmetry. They also report that Short gastrulation (Sog) is required for ventral patterning. In Drosophila embryos, Sog functions antagonistically with Dpp in dorsoventral pattern formation. To investigate the function of these two proteins in house spider embryos, the researchers used RNAi knockdown. Depletion of dpp stopped the embryos losing their radial symmetry; depletion of sog led to nearly complete loss of ventral structures, including the central nervous system. The researchers note that this mechanism for ventral specification is much more similar to that of vertebrates than to that of evolutionarily distant arthropods, like Drosophila, in which Sog makes only minor contributions to the development of ventral structures. Future studies in spider embryos could,therefore, provide new insights into the evolution of early development.
