TISSUE-SPECIFIC EXPRESSION OF HUMAN SALIVARY MUCIN GENE, MUC7, IN TRANSGENIC MICE

The MUC7 gene encodes the protein core of the low molecular weight hum an salivary mucin (MG2, mucin glycoprotein 2) and is expressed in a ti ssue-specific manner in salivary glands. The purpose of this study was to examine MUC7 expression by transgenic mouse technology. A 16 kb DN A fragment, containing the MUC7 gene (10 kb) and 3 kb of the upstream and 3 kb of the downstream sequences, was used to generate transgenic mice. We have identified five transgenic founder mice which were propa gated as individual transgenic lines and analysed. Tissues of transgen ic offspring from each line were analysed by RT-PCR to determine the s ites of the MUC7 expression. The results indicated that only line 3 an d line 5 expressed the MUC7 gene in salivary glands. The level of MUC7 expression in selected tissues was then determined by northern blot a nalyses. The results showed that line 3 mice contained high levels of MUC7 transcripts in the sublingual glands of both males and females an d indicated low levels of MUC7 transcripts in the submandibular glands of females. No MUC7 expression was detected in this line by northern blot analysis in any other tissue tested. On the other hand, no expres sion of MUC7 was detected in any tissues of line 5 mice examined by no rthern blot analysis. A Southern blot analysis of human and mouse geno mic DNA demonstrated multiple copies of the MUC7 transgene in line 3 a nd a single copy in line 5. Collectively, these results indicate that the regulatory sequences required for the tissue-specific expression o f MUC7 are within the MUC7 transgene. However, the sequences necessary for expression comparable to that of MUC7 in human salivary glands ma y be missing from this construct. Western blot analysis of protein ext racts from different tissues of transgenic mice line 3 showed that MUC 7 gene product was produced in the submandibular-sublingual gland comp lex of both male and female mice and not in the other tissues examined .