A cassette for high-level expression in the mouse salivary glands

Expression in the mouse salivary glands may be used as a model system for studies involving oral cavity delivery of gene products. Previously, sequences from the mouse Psp gene were used to build a minigene construct denoted 'Lama'. This construct was used as a cassette for expression of human factor VIII light chain in mouse saliva. However, whereas the endogenous Psp mRNA is the most abundant protein-coding transcript in the parotid glands, the Lama mRNA was expressed below 1% of the level of Psp mRNA in these glands. Here, we show that a 25-kb cosmid-derived DNA fragment (PspX25) carrying the structural gene and large flanking areas of Psp is expressed in all 14 analysed lines in the parotid glands. The average level of transgene expression was estimated to be 45% of that of the endogenous Psp gene. More importantly, it was possible to transfer PspX25's ability for high-level parotid gland expression to the Lama construct.