ABSTRACT
The origin of the pentaradial body plan of echinoderms from a bilateral ancestor is one of the most enduring zoological puzzles1,2. Because echinoderms are defined by morphological novelty, even the most basic axial comparisons with their bilaterian relatives are problematic. To revisit this classical question, we used conserved anteroposterior axial molecular markers to determine whether the highly derived adult body plan of echinoderms masks underlying patterning similarities with other deuterostomes. We investigated the expression of a suite of conserved transcription factors with well-established roles in the establishment of anteroposterior polarity in deuterostomes3-5 and other bilaterians6-8 using RNA tomography and in situ hybridization in the sea star Patiria miniata. The relative spatial expression of these markers in P. miniata ambulacral ectoderm shows similarity with other deuterostomes, with the midline of each ray representing the most anterior territory and the most lateral parts exhibiting a more posterior identity. Strikingly, there is no ectodermal territory in the sea star that expresses the characteristic bilaterian trunk genetic patterning programme. This finding suggests that from the perspective of ectoderm patterning, echinoderms are mostly head-like animals and provides a developmental rationale for the re-evaluation of the events that led to the evolution of the derived adult body plan of echinoderms.
Subject(s)
Body Patterning , Echinodermata , Animals , Body Patterning/genetics , Gene Expression Regulation, Developmental , Transcription Factors/metabolism , Echinodermata/embryology , Echinodermata/genetics , Biological EvolutionABSTRACT
Ni++ and Co++ concentrations from 10 minus 3M to 10 minus 6M were added to rat peritoneal mast cells. These metal ions, at the concentrations indicated, did not cause histamine release from the mast cells, and did not inhibit the histamine release mediated by compound 48/80. On the basis of these studies, anaphylactoid edema of the rat following injection of i++ or Co++ is on a basis other than a direct effect of the m-tal ion on mast cells.
