31.4  Tuesday, Jan. 5  Towards a metamorphic and settlement signaling network in echinoids HODIN, J.*; BISHOP, C.D.; HEYLAND, A.; Hopkins Marine Station, Stanford University; Department of Biology, Dalhousie University; Department of Biology, University of Guelph seastar@stanford.edu

Metamorphosis encompasses both a morphogenetic and behavioral life history transition, and is generally irreversible. As such, the temporal and spatial coordination of this complex process needs precise internal and external regulation. In echinoids, the internal morphogenetic processes begin well before the irreversible transformation occurs, as the bilateral larva transforms to a pentameral body plan over days to weeks or longer. At a certain point, the larva reaches the competent stage, where external signals can initiate the irreversible planktonic-to-benthic transformation. We have been elucidating two signaling systems that are involved, respectively, in the morphogenetic and behavioral aspects of echinoid metamorphosis: thyroid hormones (TH) and nitric oxide (NO). Furthermore, we have shown that these two signaling systems interact in a manner which suggests a mechanism for precise temporal regulation of metamorphosis. While these two signaling systems may be more or less conserved across taxa, the external signals that interact with these internal signaling systems show substantial inter-taxon variation. We interpret these results in the context of hypothesized selective landscapes underlying the evolution of the various conserved and diverged elements of metamorphic regulation in echinoids, and offer possibilities for testing these hypotheses in a comparative manner. Towards this end, we will present our preliminary data on a morpholino technique for disrupting gene function during metamorphic stages in echinoids, and outline a molecular approach for uncovering other signaling components that interact with the TH and NO signaling systems.