Lectin histochemistry and ultrastructure of microgranular cells in Cinachyra tarentina (Porifera, Demospongiae)

A histochemical study is described that characterizes microgranular cells o f the demosponge Cinachyra tarentina (C. tarentina) with the use of routine staining methods for mucosubstances, lectin histochemistry and electron mi croscopy. Microgranular cells are rare or absent in other species of sponge s, but abundant in this species. Microgranular cells are present in both ec tosome and mesohyl, particularly along the canal of the aquiferous system a nd around spicule holes. Inclusions of microgranular cells and the extracel lular matrix were particularly positive for acidic glycoproteins with abund ant sulfated ester groups and glycosidic residues containing GalNAc and Gal beta 1,3GalNAc. Terminal L-fucose bound to the penultimate GalNAc residues and/or difucosylated oligosaccharides were present as well. Our results su ggest that soybean lectin (SBA), peanut lectin (PNA), and winged pea lectin (WPA) are valuable markers for identifying microgranular cells of C. taren tina. Electron microscopy revealed some of the microgranular cells to conta in small smooth cytoplasmic vesicles originating from the Golgi complex and few electron-dense granules, others were characterized by numerous secreto ry granules and vacuoles formed by vesicle fusion and connected with the pl asma membrane. Our results suggest that microgranular cells in C. tarentina contribute to the synthesis of glycoprotein components of the extracellula r matrix.