Acid phosphatase activity in mature secretory granules of the salivary gland of Bradysia hygida

Abstract

It is uncommon to find acid phosphatase activity in mature secretory granules. This paper demonstrates by light and electron microscope cytochemistry an acid phosphatase in mature secretory granules in the cells of one region of the salivary gland of Bradysia hygida (Diptera, Sciaridae). These secretory granules increase in number during larval development up to the beginning of the pre-pupal period when they undergo massive exocytosis. Biochemical assays show that upon exocytosis of the majority of the granules the total acid phosphatase activity in the granular gland region drops to 10% of the maximum reached before exocytosis. During and after exocytosis, two other acid phosphatases, eletrophoretically different and much weaker in activity, become increasingly detectable in all gland regions. At the same time, in whole mount preparations, numerous tiny acid phosphatase-positive granules (probably secondary lysosomes) become evident in all major cell types of the salivary gland. These results indicate that the S2 region of the salivary gland has mature secretory granules containing an acid phosphatase destined for exocytosis which is different in molecular properties from other acid phosphatases (likely lysosomal) made by the gland.

Immunocharacterization of the DNA puff BhC4-1 protein of Bradysia hygida (Diptera: Sciaridae)

“…The BhC4-1 protein was detected neither in the cytoplasm nor in secretory granules in the frozen sections of the S2 region (results not shown, Table 1). The ultra-structure of S2 cells reveals an abundant and morphologically distinct type of secretory granule, which has been previously described as having an acid phosphatase-rich peripheral ring (Laicine et al, 1991). The results from the immunolocalization of BhC4-1 protein at the ultrastructural level in the different gland regions are in agreement with the observation that the BhC4-1 protein is only detected in immunoblots of the S1 and S3 region extracts (Fig.…”

“…This suggestion is in accord with the demonstration that the S2 is the only gland region in which secretory granules that stain positive for acid phosphatase are detected (Laicine et al, 1991). In B. hygida, salivary gland region specific differences have also been observed at the DNA puff level.…”

“…Furthermore, at E7 þ 4 h the 43 kDa polypeptide is detected both in the saliva and in extracts of the salivary gland regions S1 and S3 (Fig. 2B,C) but not in gland extracts from the S2 region where the DNA puff C4 is not formed (Laicine et al, 1991).…”

“…The secreted saliva is employed to build the cocoon in which the larvae pupates and is insoluble which suggests that further modifications of the secreted polypeptydes must occur in the lumen of the gland or during its passage through the secretory duct. In this context it is possible that the acid phosphatase, which is present in the gland secretion at the time the cocoon is being build (Laicine et al, 1991), plays a role in modifying the secreted salivary gland polypeptides to render them insoluble. Fig.…”

A 28-fold increase in secretory protein synthesis is associated with DNA puff activity in the salivary gland of Bradysia hygida (Diptera, Sciaridae)

“…However, it was shown that S2 produces and secretes special acid phosphatases that may play an important role in the polymerization of the cocoon protein meshwork (33).…”