Tissue-specific expression of major urinary protein (MUP) genes in mice: characterization of MUP mRNAs by restriction mapping of cDNA and by in vitro translation.

The major urinary proteins (MUPs) in mice are coded for by a gene family which consists of ca. 30 members. The number of MUP genes that are expressed is not known. Previous studies have shown that MUP mRNAs are present in several secretory tissues in addition to the liver, in which they were originally identified. In this paper we show, through restriction analysis of MUP cDNAs, that distinct sets of MUP mRNAs are synthesized in each of the tissues studied and that these mRNAs are most likely coded for by different genes. As is shown, MUP mRNAs of different tissues are related to an extent that precludes the use of gene-specific probes in differentiating among them. The regions of homology also include the 3' untranslated regions of MUP mRNAs. The question of differential expression was thus investigated by searching for restriction polymorphisms in MUP mRNAs. We demonstrate that subtle differences in the sequences of even scarce mRNAs can be recognized by this particular approach. In addition, it is shown that MUP mRNAs of different tissues code for different, nonoverlapping sets of polypeptides, as determined by gel electrophoresis of in vitro-translated precursors to MUPs. The relevance of these results to models of evolution of tissue-specific regulation in a multigene family is discussed.