Low levels of GRP-Ca expression in transgenic mice

The GRP-Ca gene of the rat encodes a member of the glutamine/glutamic-acid- rich protein (GRP) family. This gene is expressed in a highly tissue-specif ic fashion, with transcription being found only in the acinar cells of the submandibular gland (SMG). To begin to define the cis-acting elements gover ning GRP-Ca expression, we constructed transgenic mice containing the rat G RP-Ca gene plus 9.5 kb of 5' genomic sequence and 1 kb of 3' genomic sequen ce. Expression of GRP-Ca was detectable in progeny from only 1 of 3 indepen dent founders. Expression levels of the transgenic GRP-Ca were much lower t han the native GRP-Ca found in the rat SMG. Furthermore, GRP-Ca in transgen ic mice was not tissue-specifically expressed, being found in both the SMG/ SLG complex and the liver. These results indicate that the genomic region o f GRP-Ca included in these transgenic mice is not sufficient to confer the high levels of tissue-specific expression seen in the rat.