Secretion of chondroitin sulfate from embryonic epidermal cells in Xenopus laevis.

We examined proteoglycans (PGs) in amphibian epidermal cells by immunofluorescence microscopy. Immunoelectron microscopy with pre- and post-embedding methods, combined with HRP- or gold-conjugated secondary antibody, revealed ultrastructural localization of glycosaminoglycans (GAGs). Embryonic epidermis secretion granules in Xenopus laevis contained chondroitin 6-sulfate and unsulfated chondroitin. Immature secretion granules were also labeled with anti-chondroitin 6-sulfate and anti-chondroitin. A step-wise digestion experiment on chondroitinase ABC revealed that fine filaments in the secretion granules were chondroitin sulfate chains. Inhibition experiments with brefeldin A revealed that the life of a secretion granule was 5-10 hr, suggesting that GAG secretion from embryonic epidermis is routed through a regulated pathway.

A neonatal secretory protein associated with secretion granule membranes in developing rat salivary glands.

In the perinatal submandibular gland, the secretion granules of Type I cells contain protein C (89 KD) and those of Type III cells have Bl-immunoreactive proteins (Bl-IP, 23.5-27.5 KD). In this report we used immunocytochemistry at the light and electron microscopic levels to describe the developmental distribution and localization of protein D (175 KD), which is secreted by both Type I and Type III cells. At its first appearance in Type I cells at 18 days and in Type III cells at 19 days post conception, protein D immunoreactivity (D-IR) is associated with secretion granule membranes; this is more pronounced in Type I than in Type III cells. In early postnatal life the label remains membrane associated, but as Type III cells differentiate into seromucous acinar cells, the lower level of label present in these cells is found in the granule content. Label is found associated with the membrane in secretion granules of Type I cells as long as these cells are identifiable in acini, and subsequent to this similarly labeled cells are seen in intercalated ducts. In the sublingual gland (SLG), D-IR is membrane associated in secretion granules of serous demilune cells, and is present in the secretion granule content in mucous acinar cells. D-IR is also found in the lingual serous (von Ebner's) glands, lacrimal gland, and tracheal glands, primarily in the ducts, where it is localized in the content of secretion granules.