Meeting Abstract

P2.178  Monday, Jan. 5  Thyroid hormone signaling in echinoderms: Comparative genomics, cross-kingdom signaling and life history evolution HEYLAND, A*; REITZEL, A; HODIN, J; U. of Guelph, Canada; WHOI, USA; Hopkins Marine Station, USA aheyland@uoguelph.ca

Hormones orchestrate life history transitions in animals and non-animals, canonically via environmental inputs that directly or indirectly regulate internal (endogenous) hormonal release and/or response. Less well studied are cases in which the sources of the hormones themselves are external (exogenous). One such example is echinoderms, where thyroid hormones (THs) regulate metamorphic timing. In planktotrophic echinoderm larvae (i.e. those that need to feed to complete metamorphosis), the primary source of THs appears to be exogenous: they are derived from the unicellular algae that these larvae consume. By contrast, lecithotrophic echinoderm larvae (i.e. those that need not feed) apparently have a greater capacity for endogenous TH synthesis. We have proposed that such variation in internal hormone synthesis capacity may bias the evolutionary origin of lecithotrophy, a developmental mode that has evolved repeatedly in echinoderms. First, we will review what we know about THs in echinoderm development and evolution, in the context of a general discussion of hormones and life history evolution in multicellular eukaryotes. We will also report on our ongoing measurements of THs from sea urchin developmental stages and unicellular algae using HPLC coupled mass spectrometry. Lastly, we will discuss the current state of knowledge regarding invertebrate TH signaling. Comparative genomics and EST analyses have confirmed that many TH signaling components are conserved among deuterostomes, and that orthologs of vertebrate TH receptors are identifiable throughout the Bilateria. We will describe our current research on TH signaling modalities and metabolism in echinoids (sea urchins and sand dollars).