Development 124, 3461-3470 (1997) 3461 Printed in Great Britain © The Company of Biologists Limited 1997 DEV3652 Archenteron precursor cells can organize secondary axial structures in the sea urchin embryo Hélène Benink1, Gregory Wray2 and Jeff Hardin1,3,* 1Department of Zoology and 3Program in Cell and Molecular Biology, University of Wisconsin, Madison, 1117 West Johnson Street, Madison, WI 53706, USA 2Department of Ecology and Evolution, SUNY, Stony Brook, NY 11794, USA *Author for correspondence: (e-mail:
[email protected]) SUMMARY Local cell-cell signals play a crucial role in establishing terning sites within the ectoderm. The ectopic skeletal major tissue territories in early embryos. The sea urchin elements are bilaterally symmetric, and flank the ectopic embryo is a useful model system for studying these inter- archenteron, in some cases resulting in mirror-image, actions in deuterostomes. Previous studies showed that symmetric skeletal elements. Since the induced patterned ectopically implanted micromeres from the 16-cell embryo ectoderm and supernumerary skeletal elements are derived can induce ectopic guts and additional skeletal elements in from the host, the ectopic presumptive archenteron tissue sea urchin embryos. Using a chimeric embryo approach, we can act to ‘organize’ ectopic axial structures in the sea show that implanted archenteron precursors differentiate urchin embryo. autonomously to produce a correctly proportioned and patterned gut. In addition, the ectopically implanted pre- sumptive archenteron tissue induces ectopic skeletal pat- Key words: induction, gastrulation, sea urchin, endoderm INTRODUCTION mapping studies have shown that veg1 descendants contribute tissue to the vegetal regions of the archenteron by the late Progressive refinement of the embryonic body plan via local gastrula stage (Logan and McClay, 1997); by this time veg1 inductive interactions is a common theme among animal and veg2 descendants intermingle within the wall of the archen- embryos.