Meeting Abstract

35.2  Jan. 5  Embryogenesis and metamorphosis of Aurelia aurita HARTENSTEIN, Volker*; YUAN, David; NAKANISHI, Nagayasu; JACOBS, David K.; UCLA; UCLA; UCLA; UCLA; UCLA volkerh@mcdb.ucla.edu

We observed morphogenesis of the Aurelia aurita from embryogenesis, through the planula to early polyp using markers for nuclei (sytox), actin/myofibrils (phalloidin), neurons (Tyrosinated tubulin, FMRFamide, 5HT), dividing cells (Phosphohistone) cell death (Caspase 3) and TEM. Early embryos form a mono-layered blastula. At gastrulation, the future endoderm invaginates through the blastopore as a coherent epithelium. Endoderm then forms a solid inner mass of large vacuolated cells and the former blastopore is lost. Ectoderm develops as a pseudostratified epithelium, separated from the endoderm by a pronounced basement membrane with no interstitial cells. Cell division occurs in all embryonic tissues until shortly after gastrulation. FMRF-positive nerve cells differentiate within the ectoderm of the planula; they have T-shaped axons which extend at the endoderm-ectoderm boundary in antero-posterior direction. Neurons are located at the aboral pole and a cylindrical domain in the anterior half of the planula. At the onset of metamorphosis, neurons degenerate and are taken up into the endoderm, which also undergoes apoptosis. At the same stage, a secondary �blastopore� surrounded by four, later 8 tentacle buds appears at the oral pole of the metamorphosing animal. Secondary endoderm giving rise to the gastral cavity and the solid cellular stands filling the interior of the tentacles arise at the secondary blastopore, through invagination and delamination from the deep layers of the former planula ectoderm. Cell division occurs at the base of the tentacle buds, but not the extending tentacles themselves. A new set of intraepithelial neurons also arises at the tentacle base. Our data provide the anatomical framework for ongoing studies of gene expression and function in Aurelia development. The apoptosis of larval neurons and endoderm are novel observations.