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Oral–Aboral Axis Specification in the Sea Urchin Embryo

Coffman, James A. and Davidson, Eric H. (2001) Oral–Aboral Axis Specification in the Sea Urchin Embryo. Developmental Biology, 230 (1). pp. 18-28. ISSN 0012-1606. doi:10.1006/dbio.2000.9996.

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In embryos of indirectly developing echinoids, the secondary (oral–aboral) larval axis is established after fertilization by an as yet undiscovered process. One of the earliest manifestations of this axis is an asymmetry in mitochondrial respiration, with the prospective oral side of the embryo exhibiting a higher rate of respiration than the prospective aboral side. We show here that respiratory asymmetry can be experimentally induced within embryos by immobilizing them in tight clusters of four (“rosettes”). Within such clusters a redox gradient is established from the inside to the outside of the rosette. Vital staining of clustered embryos demonstrates that the side of the embryo facing the outside of the rosette (i.e., the most oxidizing) tends to become the oral side, while the side facing the inside tends to become the aboral side. Effective entrainment of the oral–aboral axis requires that the embryos remain immobilized in rosettes until the hatching blastula stage. To begin to investigate the molecular mechanisms underlying this effect we made use of P3A2, a transcriptional regulatory protein whose activity is spatially modulated along the oral–aboral axis. When synthetic mRNA encoding P3A2 fused to the VP16 activation domain is injected into eggs, it activates embryonic expression of a green fluorescent protein reporter gene containing a basal promoter and a single strong P3A2 target site. In embryo rosettes, such activation occurs predominantly on the outside of the rosette, suggesting that the activity of the P3A2 protein is spatially regulated by the respiratory asymmetry established by clustering the embryos. These findings are discussed with reference to earlier work on both oral–aboral axis specification and P3A2 and used to develop a testable model of the mechanism of oral–aboral axis specification in the sea urchin embryo.

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Additional Information:© 2001 Academic Press. Received for publication August 29, 2000. Revised October 26, 2000. Accepted October 26, 2000. Published online January 4, 2001. We thank Dr. Andrew Ransick for technical advice and assistance in the initial stages of this project, for some blind counts of labeled embryos, and for providing a critical review of the manuscript. We are also grateful to Dr. Gaetano Villani for helpful discussions. This research was supported by the Stowers Institute for Medical Research, the Beckman Institute, and the NIH (HD-37105).
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Stowers Institute for Medical ResearchUNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Subject Keywords:oral–aboral axis specification; sea urchin embryos; respiration; P3A2
Issue or Number:1
Record Number:CaltechAUTHORS:20160114-082655875
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Official Citation:James A. Coffman, Eric H. Davidson, Oral–Aboral Axis Specification in the Sea Urchin Embryo: I. Axis Entrainment by Respiratory Asymmetry, Developmental Biology, Volume 230, Issue 1, 1 February 2001, Pages 18-28, ISSN 0012-1606, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63676
Deposited By: Ruth Sustaita
Deposited On:14 Jan 2016 19:37
Last Modified:10 Nov 2021 23:19

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