The expression and localization of osteopontin in the mouse major salivary glands

The present study investigated the expression and distribution of osteopontin in the mouse major salivary glands. The level of osteopontin expression in the mouse submandibular gland was higher (12.7-fold) than that in parotid and sublingual glands at the mRNA level. By Western blot analysis, intense positive bands were seen at the predicted molecular mass (about 55 kDa) in all the major salivary glands, while an approximately 30 kDa band of osteopontin was detected only in the submandibular gland. Indirect immunofluorescent and immuno-electron microscopy analyses demonstrated the localization of osteopontin in the luminal (apical) membranes of acinar cells in all the salivary glands. Osteopontin was also localized at the lumen of acini in the submandibular gland. These results suggest that the expression of osteopontin in the submandibular gland is different from that in the parotid and sublingual glands and that osteopontin may be degraded in the mouse submandibular gland.