CDNA CLONING, SEQUENCING AND IN-SITU LOCALIZATION OF A TRANSCRIPT SPECIFIC TO BOTH SUBLINGUAL DEMILUNE CELLS AND PAROTID INTERCALATED DUCT CELLS IN MOUSE SALIVARY-GLANDS

A cDNA clone derived from mouse sublingual gland was isolated from a l ambda-phage cDNA library. Northern blot hybridization indicated that t he transcript from which it was derived was approx. 700 nucleotides in length. This mRNA encoded a protein of about 20 kDa, as determined by hybrid selection and cell-free translation. Conceptual translation of the cDNA clones showed that p20 is 170 amino acids in length. The put ative protein is hydrophobic in nature, is neither a mucin-like protei n nor does its amino acid sequence or composition resemble the other k nown mouse proteins. However, the amino acid sequence of p20 suggests that it may be from a gene or gene family homologous to rat common sal ivary protein 1. The p20 mRNA also appears to share a non-random degre e of sequence homology with the cysteine-rich domains of bovine and po rcine submandibular mucins. The p20 mRNA is abundant in the mouse subl ingual gland, and its expression is approx. nine times greater than in the parotid gland. In situ hybridizations localized the p20 mRNA excl usively in the demilune cells of the sublingual gland and in the inter calated duct cells of the parotid gland. It is detectable in the neona tal and adult submandibular gland at very low levels, but is absent fr om liver, heart, brain, thymus, spleen, lens and lacrimal glands.