Development Genes and Evolution

, Volume 219, Issue 2, pp 89–101 | Cite as

Axial patterning of the pentaradial adult echinoderm body plan

  • Sharon B. MinsukEmail author
  • F. Rudolf Turner
  • Mary E. Andrews
  • Rudolf A. Raff
Original Article


Adult echinoderms possess a highly diverged, pentaradial body plan. Developmental mechanisms underlying this body plan are completely unknown, but are critical in understanding how echinoderm pentamery evolved from bilateral ancestors. These mechanisms are difficult to study in indirect-developing species; in this study, we use the direct-developing sea urchin Heliocidaris erythrogramma, whose accelerated adult development can be perturbed by NiCl2. We introduce a new nomenclature for the adult echinoderm axes to facilitate discussion of the radially symmetric body plan and the events required to pattern it. In sea urchins, the adult oral–aboral axis is often conflated with the long axes of the five rays; we identify these as distinct body axes, the proximodistal (PD). In addition, we define a circular axis, the circumoral (CO), along which the division into five sectors occurs. In NiCl2-treated larvae, aspects of normal PD pattern were retained, but CO pattern was abolished. Milder treatments resulted in relatively normal juveniles ranging from biradial to decaradial. NiCl2 treatment had no effect either on mesodermal morphology or on the ectodermal gene expression response to an inductive mesodermal signal. This suggests that the mesoderm does not mediate the disruption of CO patterning by NiCl2. In contrast, mesodermal signaling may explain the presence of PD pattern in treated larvae. However, variations in appendage pattern suggest that ectodermal signals are also required. We conclude that CO patterning in both germ layers is dependent on ectodermal events and PD patterning is controlled by mutual ectoderm–mesoderm signaling.


Radial symmetry Mesoderm–ectoderm signaling Axial homologies Echinoderms Body plan patterning 



We thank the Sydney Aquarium and the School of Biological Sciences, University of Sydney for providing resources and for making our work in Australia possible; Gerd Müller and Wolfgang Weninger for the use of equipment; Meg Snoke for help with specimen treatment and transport; and Ulrich Krohs and Ellen Popodi for helpful discussion. We would also like to thank the anonymous reviewers for comments on the manuscript and Javier Capdevila for comments on an earlier draft. New South Wales Fisheries provided collection permits. This work was funded by an NIH Postdoctoral Fellowship to SBM and an NSF research grant to RAR.


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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Sharon B. Minsuk
    • 1
    • 2
    Email author
  • F. Rudolf Turner
    • 1
  • Mary E. Andrews
    • 1
  • Rudolf A. Raff
    • 1
  1. 1.Department of Biology and Indiana Molecular Biology InstituteIndiana UniversityBloomingtonUSA
  2. 2.Department of BiologyMerritt CollegeOaklandUSA

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