Predominant transgene expression in exocrine pancreas directed by the CMV promoter

The enhancer/promoter of the human cytomegalovirus gene encoding the major immediate-early protein (CMVp) is reputed to be one of the strongest and mo st promiscuous regulatory elements for directing transcription of heterolog ous genes in vitro. However, transgene expression under the promoter in adu lt transgenic mice is often more restricted. We selected a CMVp segment fro m position -350 to +59 to control expression of transgenes for two secretor y fusion proteins. Expression was analyzed by immunohistology staining and quantified by Northern blot, Western blot, and ELISA of secretions from exp lanted tissues. In all six lines of transgenic mice, the highest expression of transgenes at the mRNA and protein level was observed in the exocrine t issue of the pancreas, although the levels of expression varied among the l ines. The results indicate not only that CMVp is not a universal promoter i n vivo but indeed that it can be relatively specific for the exocrine pancr eas, where expression of the gene it controlled was consistently very high.