title: Cell tracking supports secondary gastrulation in the moon jellyfish Aurelia.
abstract: The moon jellyfish Aurelia exhibits a dramatic reorganization of tissue during its metamorphosis from planula larva to polyp. There are currently two competing hypotheses regarding the fate of embryonic germ layers during this metamorphosis. In one scenario, the original endoderm undergoes apoptosis and is replaced by a secondary endoderm derived from ectodermal cells. In the second scenario, both ectoderm and endoderm remain intact through development. In this study, we performed a pulse-chase experiment to trace the fate of larval ectodermal cells. We observed that prior to metamorphosis, ectodermal cells that proliferated early in larval development concentrate at the future oral end of the polyp. During metamorphosis, these cells migrate into the endoderm, extending all the way to the aboral portion of the gut. We therefore reject the hypothesis that larval endoderm remains intact during metamorphosis and provide additional support for the "secondary gastrulation" hypothesis. Aurelia appears to offer the first and only described case where a cnidarian derives its endoderm twice during normal development, adding to a growing body of evidence that germ layers can be dramatically reorganized in cnidarian life cycles.
authors.affiliation: Department of Ecology and Evolution, University of California, Los Angeles, Los Angeles, CA, 90095, USA.|Division of Biology and Biological Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA, 91125, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Gold
authors.affiliation: Department of Ecology and Evolution, University of California, Los Angeles, Los Angeles, CA, 90095, USA.|Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL, USA.
authors.forename: Nagayasu
authors.initials: N
authors.lastname: Nakanishi
authors.affiliation: Department of Ecology and Evolution, University of California, Los Angeles, Los Angeles, CA, 90095, USA.|Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Nicholai M
authors.initials: NM
authors.lastname: Hensley
authors.affiliation: Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
authors.forename: Volker
authors.initials: V
authors.lastname: Hartenstein
authors.affiliation: Department of Ecology and Evolution, University of California, Los Angeles, Los Angeles, CA, 90095, USA. djacobs@ucla.edu.
authors.forename: David K
authors.initials: DK
authors.lastname: Jacobs
mesh_terms: D000818:Animals; D002465:Cell Movement; D058948:Cell Tracking; D005260:Female; D054262:Gastrulation; D007814:Larva / Q000166:cytology; D037401:Scyphozoa / Q000166:cytology* / Q000254:growth & development*
keywords: Aurelia; Cnidaria; Gastrulation; Moon jellyfish