Geometric locations of differentiated cells in sponges are totally unrelated to spatial signals to differentiate

Albert KĀ Harris
Professor of Biology
UNC-Chapel Hill
Presented in the Embryo Physics Course, January 16, 2013


Sponge cells constantly rearrange, just as much from one day to the next as when their cells are mechanically separated from each other. H. V. Wilson discovered the ability of sponge and coral cells to rearrange into normal patterns. Calhoun Bond and Albert Harris discovered the constant rearrangement phenomenon, while making time lapse videos of sponges living in the equivalent of “ant farms”, i.e. between parallel glass slides. Their mesenchymal cells move the fastest, which is twice a cell length per minute. Extracellular skeletal rods (“spicules”, made of silicon oxide) are temporarily assembled into the mechanical equivalents of tent poles, and glued together with collagen. Within a few days or hours, spicules are detached from each other and carried to new locations for reassembly. Special kinds of epithelial cells, which lack basal membranes, form the outside surfaces of sponges, and also internal canals through which water is pumped out by flagellated cells called choanocytes, which pull water between each other, as occurs in nephridial kidneys of many phyla. By looking only at dead, fixed sections through sponges, textbooks and specialists have misinterpreted nearly every aspect of their anatomy, which leaves many opportunities for biophysical research to determine which properties of individual cells cause continual reformation of their same histological patterns.





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