MARTINDALE, M. Q.; PANG, K; MATUS, D.Q.; FINNERTY, J.R.; Univ. Hawai’i; Univ. Hawai’i; Univ. Hawai’i; Boston University: Expression of �mesodermal� genes in the anthozoan Nematostella vectensis.

The starlet sea anemone Nematostella vectensis is quickly becoming a new model system for understanding the evolution of metazoan development. It is an anthozoan cnidarian, the sister group to bilaterian metazoans, and as a diploblastic, radially symmetrical organim, holds promise for understanding not only the origins of the anterior-posterior and dorso-ventral axes of bilaterians, but also in the origin of the �middle� germ layer, mesoderm. We have cloned a number of genes implicated in mesodermal or mesendodermal development in bilaterians to determine their pattern of expression in embryos of this direct developing cnidarian. Here we report the pattern of expression of transcripts by in situ hybridization for over 20 orthologs of such genes: GATA, Twist, snail (1-2), 4 nk-class homeodomain genes (tinman, bagpipe, vax, and sax), mox (1-2), krox, mlim, sox, tropomyosin, m-actin, mef2, otx, eve, dpp, and five forkhead genes. While each of these genes has a unique and dynamic spatio-temporal pattern of expression, virtually all of them (except for mef2, Krox, sax, and eve) are expressed in the gastrodermis or presumptive gastrodermis. These data suggest that there is a great deal of patterning at the molecular level that is not readily apparent at the morphological level and that these genes may reveal the precursors of a mesendodermal network of gene activity.