Variations on a theme? Polyp and medusa development in Podocoryna carnea

The life cycles of many cnidarian species are notable for including two stages with very different morphologies – sessile polyp and swimming medusa. Cnidarians thus provide an opportunity to study the developmental bases of differences in body organization without the need to compare organisms of different taxa. Information about the two life cycle stages suggests the following questions about differences in their development. (1) Are the mouth and tentacle-bearing region (bell margin) specified using any of the same molecular mechanisms as in the polyp? (2) Has the oral-aboral axis of the medusa been truncated relative to that of the polyp by elimination of molecular processes specifying aboral tissue identity? (3) Is the elongated region between the hydrozoan medusa mouth and tentacle ring (the manubrium) patterned using processes that pattern the entire oral-aboral axis in the polyp? We describe how data on their expression of FoxA, NK-2, and Emx genes during polyp and medusa development, together with reagents targeting specific signaling pathways, could be used to address these questions. We have isolated portions of a FoxA2 homologue, an NK-2 gene, and two Emx genes from Podocoryna carnea Sars, an experimentally tractable hydrozoan with both polyp and medusa stages. Phylogenetic analyses indicate that the two P. carnea Emx genes are the result of a gene duplication.

Key words: emx, forkhead, NK-2, Podocoryne, Cnidaria