Conservation of a DPP/BMP signaling pathway in the nonbilateral cnidarian Acropora millepora

Members of the TGF-beta superfamily of signaling molecules are widespread in metazoans, but the evolutionary origin of particular subclasses of signaling mechanisms is poorly defined. The DPP/BMP class, for example, is implicated in dorsal-ventral patterning, neural patterning, and limb development. Here we report the presence of several components of a DPP/BMP-specific signal transduction cascade in a nonbilateral animal, the coral Acropora millepora. The discovery of these components, a putative type I receptor and two putative receptor-activated Smads, suggests that DPP/BMP signaling predates both dorsal-ventral pattern formation and limb development. We postulate that an ancestral role in neuroepithelial patterning may account for the high level of conservation between DPP/BMP signaling components found in this nonbilateral animal and the more complex triploblastic organisms of the arthropod and chordate phyla.