Characterization of common salivary protein 1, a product of rat submandibular, sublingual, and parotid glands.

We have isolated and characterized cDNA clones derived from a developmentally regulated neonatal rat submandibular gland salivary protein gene called "common salivary protein 1" (CSP1). Identical clones were also identified in cDNA libraries from adult male parotid, submandibular, and sublingual glands. CSP1 transcripts are at least 10-fold more abundant in the sublingual gland than in the submandibular or parotid glands. In situ hybridization and immunocytochemical localization demonstrated the presence of CSP1 transcripts and proteins in sublingual gland serous demilune cells, parotid and submandibular gland intercalated duct cells, and in the type III (proacinar) cells of the neonatal submandibular gland. This cell-type distribution is similar to that described by Ball and colleagues (Ball, W. D., Hand, A. R., and Johnson, A. O. (1988) Dev. Biol. 125, 265-279) for the developmentally regulated submandibular gland B1-immunoreactive proteins. Immunoblotting of salivary secretion identified proteins of M(r) 20,000 in sublingual, 16,000 in submandibular and 22,000 and 16,000 in parotid gland. The M(r) 20,000 sublingual and 22,000 parotid proteins represent N-glycosylated forms of a M(r) 16,000 apoprotein, suggesting that these salivary proteins arise by post-translational modification of a common precursor.