Meeting Abstract

P2.88  Saturday, Jan. 5  Metamorphosis in the Demosponge Amphimedon queenslandica NAKANISHI, N*; SOGABE, S; DEGNAN, B; University of Queensland n.nakanishi@uq.edu.au

We examined the pattern of cell proliferation, differentiation, migration and death during metamophosis from a free-swimming larva into a juvenile in the demosponge Amphimedon queenslandica. Our experimental approach combined immunohistochemistry (e.g. anti-phosphorylated histone H3), dye labeling (e.g. DiI), EdU pulse and chase experiments, TUNEL assay, and confocal and electron microscopy. The free-swimming larva consists of a ciliated outer epithelium, a subepithelial layer of cells, and an innermost group of mesenchymal cells referred to as the inner cell mass. In larvae, cell proliferation is restricted to archeocytes in the inner cell mass, while apoptosis is limited to epithelial cuboidal cells at the anterior-most (with respect to the swimming direction) region. During metamorphosis into a juvenile, spherulous cells of subepithelial and/or inner cell mass origin emigrate and form an outer layer that encloses the larval epithelial cells. A large fraction of the larval epithelial cells undergo programmed cell death, and their apoptotic bodies are taken up by the surrounding cells, including the migratory archeocytes of the larval origin. Non-apoptotic, ciliated larval epithelial cells migrate and differentiate into such cell types as the pinacocyte in the outer layer pinacoderm, the archeocyte in mesohyl, and the choanocyte in the inner layer epithelium that constitutes feeding structures known as the choanocyte chambers. Also, larval archeocytes give rise to a set of differentiated cell types including the pinacocyte. Cell proliferation is prominent in developing choanocyte chambers, indicating that the chambers grow by mitosis of choanocytes. A single choanocyte chamber does not always originate from a single precursor cell; multiple precursor cells are often involved in forming a single chamber.