Choosing sides : asymmetrical properties of juvenile rudiment formation during the morphogenesis of two species of echinoplutei
Date
2001
Authors
Eaves, Alexandra Anne
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Abstract
The morphogenesis of two species of local echinoid, Strongylocentrotus purpuratus and Dendraster excentricus, was documented and described. Particular emphasis was given to the appearance of a second vestibule (V2). Morphogenesis of V2 was characterized using light micrographs and antibodies directed against the S2amide echinoderm neuropeptide, and the 2D2 antibody directed against the βC integrin subunit of S. purpuratus. V2 is positioned on the right side of the larva, and is bilaterally symmetric to the vestibule that normally gives rise to the juvenile rudiment (V1 ). V2 forms after the onset of juvenile rudiment formation, when V1 and its underlying hydrocoel have contacted.
Populations of larvae were surveyed for the occurrence of V2 relative to the stage of larval development. It was found that V2 became increasingly common in later stage larvae, and contained a juvenile spine immediately prior to metamorphosis. In abnormal larvae of S. purpuratus that possessed two hydrocoels, both V1 and V2 appeared to form a juvenile rudiment. Conversely, in larvae that were devoid of a hydrocoel on both sides, no juvenile rudiment formed. Instead these larvae formed a juvenile spine in both V1 and V2. This observation suggests that the larva may actually be uniformly bilateral, but normally it does not get the cooperation of prospective adult mesodermal tissues to form a rudiment on the right side of the larval body in addition to the one on the left. In an attempt to reliably induce abnormal juvenile rudiment symmetry, embryos were subjected to ...