Cnidarian Evo-Devo Research

Our second focus in diploblast research is on the evolution and development of cnidarians, because, like placozoans, they represent a key transition in animal complexity - from a sac-like bauplan with an oral-aboral axis and only two germ layers to the oral-aboral axis and three germ layers in triploblasts. Our model system is the hydrozoan Eleutheria dichotoma which was the first cnidarian representative in which Hox-like genes were identified [1,2]⁠. Subsequent research on Eleutheria homeobox genes gave valuable insights about the evolution of the Hox system and the developmental role of homeobox genes in cnidaria [3–5]⁠. In the future we plan to sequence the estimated 500 Mb genome of Eleutheria dichotoma because it would ideally complement the cnidarian genomes already sequenced or planned to sequence: Eleutheria not only represents a typical cnidarian in having both polyp and medusa life cycle stages, but it also has some distinguishing features like internal fertilization, a brood pouch where planula develop, a crawling medusa and the possession of ocelli.

In collaboration with Professor David Miller from the James Cook University, Townsville, Australia, we are also interested in the developmental signaling pathway of fibroblast growth factors in Cnidaria. In animals the FGF and FGF-related signaling pathway is important for cell-cell communication during development and it is now clear that these important genes emerged early during metazoan evolution [6]⁠. Recent findings about FGF signalling in Nematostella vectensis [7]⁠ and Hydra vulgaris [8]⁠ gave first clues about the evolution and function of FGF genes in cnidarians. While Hydra represents a highly diverged hydrozoan representative, molecular and functional data from Eleutheria and other cnidarians will certainly improve our knowledge about the FGF signaling pathway in early metazoan evolution.

[1] Schierwater B, Murtha M, Dick M, Ruddle FH, Buss LW. Homeoboxes in cnidarians. J Exp Zool 1991;260:413–6. doi:10.1002/jez.1402600316.
[2] Kuhn K, Streit B, Schierwater B. Homeobox Genes in the CnidarianEleutheria dichotoma:Evolutionary Implications for the Origin ofAntennapedia-Class (HOM/Hox) Genes. Mol Phylogenet Evol 1996;6:30–8. doi:10.1006/mpev.1996.0055.
[3] Kamm K, Schierwater B, Jakob W, Dellaporta SL, Miller DJ. Axial patterning and diversification in the cnidaria predate the Hox system. Curr Biol 2006;16:920–6. doi:10.1016/j.cub.2006.03.036.
[4] Jakob W, Schierwater B. Changing hydrozoan bauplans by silencing Hox-like genes. PLoS One 2007;2:e694. doi:10.1371/journal.pone.0000694.
[5] Kamm K, Schierwater B. Ancient linkage of a POU class 6 and an anterior hox-like gene in cnidaria: implications for the evolution of homeobox genes. J Exp Zool Part B Mol Dev Evol 2007;308B:777–84. doi:10.1002/jez.b.21196.
[6] Bertrand S, Iwema T, Escriva H. FGF signaling emerged concomitantly with the origin of Eumetazoans. Mol Biol Evol 2014;31:310–8. doi:10.1093/molbev/mst222.
[7] Rentzsch F, Fritzenwanker JH, Scholz CB, Technau U. FGF signalling controls formation of the apical sensory organ in the cnidarian Nematostella vectensis. Development 2008;135:1761–9. doi:10.1242/dev.020784.
[8] Lange E, Bertrand S, Holz O, Rebscher N, Hassel M. Dynamic expression of a Hydra FGF at boundaries and termini. Dev Genes Evol 2014;224:235–44. doi:10.1007/s00427-014-0480-1.

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