Identification of an enhancer required for the expression of a mouse major urinary protein gene in the submaxillary gland.

The MUP1.5b gene was previously found to be expressed specifically in the submaxillary gland and at high levels when introduced into mice as a transgene including 4.7 kb of 5'-flanking DNA and 0.3 kb of 3'-flanking DNA. To localize regulatory elements responsible for this tissue-specific pattern of expression, we tested the expression of three additional MUP1.5b transgenes including various amounts of 5'-flanking DNA. These experiments indicated that sequences between -1.85 and -3.46 kb from the transcription initiation site were required for high-level expression in the submaxillary gland. The presence of regulatory elements in this region was also suggested by the detection of a DNase I-hypersensitive site, seen only in submaxillary gland nuclei, at position -2.5 kb upstream from the MUP1.5a gene, a member of the same MUP gene subfamily and virtually identical to the MUP1.5b gene. Further evidence for enhancer activity was provided by the ability of the 1.6-kb DNA fragment including sequences between -1.85 and -3.46 kb to stimulate the expression of an otherwise inactive MUP1.5b-chloramphenicol acetyltransferase fusion gene specifically in the submaxillary gland. The nucleotide sequence of this 1.6-kb DNA fragment was found to be identical for the MUP1.5a and MUP1.5b genes. Together, these results provide the first localization of a cis-acting regulatory sequence involved in the differential tissue-specific expression of the MUP gene family.