Development Genes and Evolution

, Volume 214, Issue 4, pp 170–175 | Cite as

The Trox-2 Hox/ParaHox gene of Trichoplax (Placozoa) marks an epithelial boundary

  • Wolfgang Jakob
  • Sven Sagasser
  • Stephen Dellaporta
  • Peter Holland
  • Kerstin Kuhn
  • Bernd SchierwaterEmail author
Original Article


Hox and ParaHox genes are implicated in axial patterning of cnidarians and bilaterians, and are thought to have originated by tandem duplication of a single “ProtoHox” gene followed by duplication of the resultant gene cluster. It is unclear what the ancestral role of Hox/ParaHox genes was before the divergence of Cnidaria and Bilateria, or what roles the postulated ProtoHox gene(s) played. Here we describe the full coding region, spatial expression and function of Trox-2, the single Hox/ParaHox-type gene identified in Trichoplax adhaerens (phylum Placozoa) and either a candidate ProtoHox or a ParaHox gene. Trox-2 is expressed in a ring around the periphery of Trichoplax, in small cells located between the outer margins of the upper and lower epithelial cell layers. Inhibition of Trox-2 function, either by uptake of morpholino antisense oligonucleotides or by RNA interference, causes complete cessation of growth and binary fission. We speculate that Trox-2 functions within a hitherto unrecognized population of possibly multipotential peripheral stem cells that contribute to differentiated cells at the epithelial boundary of Trichoplax.


Trichoplax Placozoa RNAi Morpholino ProtoHox 



This work was supported by the German Science Foundation, (DFG Schi 277/10-2), the Human Frontier Science Program (HFSP RGP0221/2001-M), and the Graduiertenförderung Niedersachsen (fellowship to W.J.). We are grateful to Jutta Bunnenberg for technical assistance, and two anonymous reviewers for valuable and constructive comments.


  1. Blackstone NW, Jasker BD (2003) Phylogenetic considerations of clonality, coloniality, and mode of germline development in animals. J Exp Zool Part B Mol Dev Evol 297:35–47Google Scholar
  2. Bosch TC, David CN (1984) Growth regulation in Hydra: relationship between epithelial cell cycle length and growth rate. Dev Biol 104:161–171PubMedGoogle Scholar
  3. Brooke NM, Garcia-Fernandez J, Holland PWH (1998) The ParaHox gene cluster is an evolutionary sister of the Hox gene cluster. Nature 392:920–922CrossRefPubMedGoogle Scholar
  4. Cartwright P, Bowsher J, Buss LW (1999) Expression of a Hox gene, Cnox-2, and the division of labor in a colonial hydroid. Proc Natl Acad Sci USA 96:2183–2186CrossRefPubMedGoogle Scholar
  5. Ender A, Schierwater B (2003) Placozoa are not derived cnidarians: evidence from molecular morphology. Mol Biol Evol 20:130–134CrossRefPubMedGoogle Scholar
  6. Ferrier DE, Holland PWH (2001) Sipunculan ParaHox genes. Evol Dev 3:263–270CrossRefPubMedGoogle Scholar
  7. Ferrier DE, Holland PWH (2002) Ciona intestinalis ParaHox genes: evolution of Hox/ParaHox cluster integrity, developmental mode, and temporal colinearity. Mol Phylogenet Evol 24:412–417CrossRefPubMedGoogle Scholar
  8. Finnerty JR, Martindale MQ (1999) Ancient origins of axial patterning genes: Hox genes and ParaHox genes in the Cnidaria. Evol Dev 1:16–23CrossRefPubMedGoogle Scholar
  9. Finnerty JR, Paulson D, Burton P, Pang K, Martindale MQ (2003) Early evolution of a homeobox gene: the parahox gene Gsx in the Cnidaria and the Bilateria. Evol Dev 5:331–345PubMedGoogle Scholar
  10. Gauchat D, Mazet F, Berney C, Schummer M, Kreger S, Pawlowski J, Galliot B (2000) Evolution of Antp-class genes and differential expression of Hydra Hox/paraHox genes in anterior patterning. Proc Natl Acad Sci USA 97E:4493–4498CrossRefGoogle Scholar
  11. Grell KG (1972) Eibildung und Furchung von Trichoplax adhaerens F.E. Schulze (Placozoa). Z Morphol Tiere 73:297–314Google Scholar
  12. Grell KG (1983) Ein neues Kulturverfahren für Trichoplax adhaerens F.E. Schulze. Z Naturforsch 38c:1072Google Scholar
  13. Gröger H, Callaerts P, Gehring WJ, Schmid V (1999) Gene duplication and recruitment of a specific tropomyocin to striated muscle cells in the jellyfish, Podocoryne carnea. J Exp Zool 285:378–386CrossRefPubMedGoogle Scholar
  14. Kuhn K, Streit B, Schierwater B (1999) Isolation of Hox genes from the scyphozoan Cassiopeia xamachana: implications for the early evolution of Hox genes. J Exp Zool 285:63–75CrossRefPubMedGoogle Scholar
  15. Li YX, Farrell MJ, Liu R, Mohanty N, Kirby ML (2000) Double-stranded RNA injection produces null phenotypes in zebrafish. Dev Biol 217:394–405CrossRefPubMedGoogle Scholar
  16. Martinelli C, Spring J (2003) Distinct expression patterns of the two T-box homologues Brachyury and Tbx2/3 in the placozoan Trichoplax adhaerens. Dev Genes Evol 213:492–499PubMedGoogle Scholar
  17. Morcos PA (2001) Achieving efficient delivery of Morpholino oligos in cultured cells. Genesis 30:94–102CrossRefPubMedGoogle Scholar
  18. Müller P, Yanze N, Schmid V, Spring J (1999) The homeobox gene Otx of the jellyfish Podocoryne carnea: role of a head gene in striated muscle and evolution. Dev Biol 216:582–593PubMedGoogle Scholar
  19. Partridge M, Vincent A, Matthews P, Puma J, Stein D, Summerton J (1996) A simple method for delivering morpholino antisense oligos into the cytoplasm of cells. Antisense Nucleic Acid Drug Dev 169Google Scholar
  20. Pearse VB, Uehara T, Miller RL (1994) Birefringent granules in placozoans (Trichoplax adhaerens). Trans Am Microsc Soc 113:385–389Google Scholar
  21. Plaza S, Prince F, Jaeger J, Kloter U, Flister S, Benassayag C, Cribbs D, Gehring WJ (2001) Molecular basis for the inhibition of Drosophila eye development by Antennapedia. Embo J 20:802–811CrossRefPubMedGoogle Scholar
  22. Rassat J, Ruthmann A (1979) Trichoplax adhaerens F.E. Schulze (Placozoa) in the scanning electron microscope. Zoomorphology 93:59–72Google Scholar
  23. Rokas A, King N, Finnerty J, Carroll SB (2003) Conflicting phylogenetic signals at the base of the metazoan tree. Evol Dev 5:346–359PubMedGoogle Scholar
  24. Ronshaugen M, McGinnis N, McGinnis W (2002) Hox protein mutation and macroevolution of the insect body plan. Nature 415:914–917CrossRefPubMedGoogle Scholar
  25. Sarkar IN, Thornton JW, Planet PJ, Figurski DH, Schierwater B, DeSalle R (2002) An automated phylogenetic key for classifying homeoboxes. Mol Phylogenet Evol 24:388–399CrossRefPubMedGoogle Scholar
  26. Schierwater B, Desalle R (2001) Current problems with the zootype and the early evolution of Hox genes. J Exp Zool 291:169–174CrossRefPubMedGoogle Scholar
  27. Schierwater B, Kuhn K (1998) Homology of Hox genes and the zootype concept in early metazoan evolution. Mol Phylogenet Evol 9:375–381CrossRefPubMedGoogle Scholar
  28. Schierwater B, Dellaporta S, DeSalle R (2002) Is the evolution of Cnox-2 Hox/ParaHox genes “multicolored” and “polygenealogical?” Mol Phylogenet Evol 24:374–378Google Scholar
  29. Schuchert P (1993) Trichoplax adhaerens (phylum Placozoa) has cells that react with antibodies against the neuropeptide RFamide. Acta Zool (Stockholm) 74:115–117Google Scholar
  30. Schwartz V (1984) Das radiopolare Differenzierungsmuster bei Trichoplax adhaerens F.E. Schulze (Placozoa). Z Naturforsch 39c:818–832Google Scholar
  31. Shenk MA, Bode HR, Steele RE (1993) Expression of Cnox-2, a HOM/HOX homeobox gene in hydra, is correlated with axial pattern formation. Development 117:657–667PubMedGoogle Scholar
  32. Summerton J, Weller D (1997) Morpholino antisense oligomers: design, preparation and properties. Antisense Nucleic Acid Drug Dev 187Google Scholar
  33. Summerton J, Stein D, Huang SB, Matthews P, Weller D, Partridge M (1997) Morpholino and phosphorothioate antisense oligomers compared in cell-free and cell-system. Antisense Nucleic Acid Drug Dev 63Google Scholar
  34. Syed T, Schierwater B (2002) Trichoplax adhaerens: discovered as a missing link, forgotten as a hydrozoan, re-discovered as a key to metazoan evolution. Vie Milieu 52:177–187Google Scholar
  35. Yanze N, Spring J, Schmidli C, Schmid V (2001) Conservation of Hox/ParaHox-related genes in the early development of a cnidarian. Dev Biol 236:89–98PubMedGoogle Scholar

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Wolfgang Jakob
    • 1
  • Sven Sagasser
    • 1
  • Stephen Dellaporta
    • 2
  • Peter Holland
    • 3
  • Kerstin Kuhn
    • 4
  • Bernd Schierwater
    • 1
    • 2
    Email author
  1. 1.ITZ, Ecology and EvolutionTiHo HannoverHannoverGermany
  2. 2.MCDBYale UniversityNew HavenUSA
  3. 3.Department of ZoologyUniversity of OxfordOxfordUK
  4. 4.Ecology and EvolutionJ.W. Goethe-UniversitätFrankfurtGermany

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