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.