Tissue-specific expression of kallikrein family transgenes in mice and rats

To define the regulatory strategy for the transcriptional control of the kallikrein multigene family, we analyzed the expression of several kallikrein/SV40 T-antigen (TAg) fusion genes in transgenic mice and rats. Kallikrein family members are normally expressed at a high level in the submandibular gland and are expressed in a wide range of tissues that vary among individual family members. A total of 1.7 kb of proximal 5'-flanking DNA from the tissue kallikrein gene (rKlk1) was sufficient to confer much of the correct tissue-specific pattern on a TAg reporter gene. TAg mRNA was detectable in tissues that normally express rKlk1 and TAg-induced tumors arose in brain and pancreas. However, absolute levels of transgene mRNA were very low relative to the expression of the normal endogenous tissue kallikrein gene. In particular, expression in the salivary glands, normally very high for endogenous rKlk1, was either low or absent. An intact rKlk1 transgene with extensive flanking DNA (4.5 kb 5' and 4.7 kb 3') and complete intragenic (4 kb) sequences was expressed similarly to the fusion transgene, demonstrating that regulatory elements necessary for comprehensively correct expression are not contained within these additional gene regions. Two additional kallikrein/SV40 fusion transgenes were derived from other family members, one from the rKlk2 gene, which encodes tonin, and another from the rKlk8 gene, which encodes a prostate kallikrein. Whereas the endogenous rKlk2 and rKlk8 genes normally are expressed at high levels in rat salivary glands, they were not expressed in the salivary glands as transgenes. The results for these transgenes of three different family members indicate that control elements that direct the particular nonsalivary gland expression pattern characteristic of each family member may be present within the proximal 5'-flanking region of each gene, whereas regulatory sequences necessary for normal levels of expression in these tissues and for maximal salivary gland expression are not. We propose that the gene-associated regulatory sequences are complemented by a dominant control region that imposes salivary gland expression on the extended kallikrein family locus.