CHANGES IN FINE STRUCTURE DURING SILK PROTEIN PRODUCTION IN THE AMPULLATE GLAND OF THE SPIDER ARANEUS SERICATUS

Abstract

The ampullate silk gland of the spider, Araneus sericatus, produces the silk fiber for the scaffolding of the web . The fine structure of the various parts of the gland is described . The distal portion of the duct consist of a tube of epithelial cells which appear to secrete a substance which forms the tunica intima of the duct wall. At the proximal end of the duct there is a region of secretory cells . The epithelium of the sac portion contains five morphologically distinct types of granules . The bulk of the synthesis of silk occurs in the tail of the gland, and in this region only a single type of secretory droplet is seen in the epithelium . Protein synthesis can be stimulated by the injection of 1 mg/kg acetylcholine into the body fluids . 10 min after injection, much of the protein stored in the cytoplasm of the epithelial cells has been secreted into the lumen . 20 min after stimulation, the ergastoplasmic sacs form large whorls in the cytoplasm . Protein, similar in electron-opacity to protein found in the lumen, begins to form in that portion of the cytoplasm which is enclosed by the whorls . The limiting membrane of these droplets is formed by ergastoplasmic membranes which lose their ribosomes .

Fine structural analysis of secretory silk production in the black widow spider,Latrodectus mactans

“…However, the exact functions of these two kinds of silks for web building are still not known sufficiently, either for this species or for any other species of genus Latrodectus. Cytologic aspects of spider silk elaboration have been studied only in the case of the ampullate glands of Araneus (Peakall, 1965;Bell and Peakall, 1969;Tillinghast and Townley, 1986) and Nephila (Tillinghast and Christenson, 1984;. It has been noted in these reports that the two kinds of ampullate glands (major and minor) produce different types of silk materials.…”

“…The regulation of secretory protein release in the ampullate silk glands has been frequently considered (Peakall, 1965;Bell and Peakall, 1969;Tillinghast and Townley, 1986). In this experiment, we have examined two distinct specimens: before and after extrusion of its luminal contents of silk materials.…”

“…The secretory precursors are produced as separated vesicles via well-oriented rER of the glandular epithelial cells, and no Golgi complex has been found in these cells characteristically. It was reported by Bell and Peakall (1969) that the epithelial cells of the silk gland have developed a somewhat unique method for rapid production of protein. These cells apparently bypass the concentration and packaging steps in the Golgi complex, which is known to be a common process in secretory cells including the silk gland cells of Bombyx mori (Sasaki and Tashiro, 1976;Sasaki et al, 1981).…”

Fine structure of the glandular epithelium during secretory silk production in the black widow spiderlatrodectus mactans

“…Among these major silk glands, the ampullate gland is present in all spiders (FoeIk, 1982), and are responsible for the production of dry silk used in dragline (Nentwig and Heimer, 1987). Following the observations by Peakall (1964) on silk synthesis in Araneus diadematus, regulation of secretory protein release in the ampullate silk glands has been frequently considered (Peakall, 1965;Bell and Peakall, 1969;Tillinghast and Townley, 1986).…”

“…However, exact functions are still not known sufficiently. Cytologic aspects of spider silk elaboration have been studied onfy in the case of the ampullate glands of Araneus (Peakall, 1965;Bell and Peakall, 1969;Tillinghast and Townley, 1986) and Nephib (Tillinghast and Christenson, 1984;Moon et al, 1988).…”