Fibronectin is apparently not involved in species-specific reaggregation of cells from the marine sponge geodia cydonium

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Abstract
Experiments were carried out to test the hypothesis that fibronectin is involved in reaggregation of dissociated sponge cells. Cells from the siliceous sponge Geodia cydonium were extracted with urea to solubilize fibronectin from cells of higher multicellular organisms. The crude extract was further fractionated by DNA, heparin, and collagen affinity chromatography; they were termed Geodia fibronectinlike fractions. The fibronectinlike fractions contained a series of proteins with molecular weights different from that of the genuine fibronectin. The Geodia fibronectinlike fractions did not react with antiserum, produced against human fibronectin, under formation of a precipitin line. Using this antiserum the sponge cells could not be specifically labeled with FITC‐anti‐IgG antiserum. Radioimmunoprecipitation experiments revealed that the Geodia fractions contain—if at all—0.1% fibronectin or fibronectinlike protein at the most. In the crucial experiments it was shown that the Geodia fibronectinlike fractions, human fibronectin, and antifibronectin antiserum exerted no influence on adhesion of Geodia cells either in the absence or in the presence of the soluble aggregation factor. Based on these findings, we conclude that fibronectin is apparently not present on Geodia cells and does not play a role in aggregation of this biological system.