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Mol. Cell. Biol., 03 1997, 1607-1614, Vol 17, No. 3
HG Sutherland, DI Martin and E Whitelaw
Enhancer elements have been shown to affect the probability of a gene
establishing an active transcriptional state and suppress the silencing of
reporter genes in cell lines, but their effect in transgenic mice has been
obscured by the use of assays that do not assess expression on a
cell-by-cell basis. We have examined the effect of a globin enhancer on the
variegation of lacZ expression in erythrocytes of transgenic mice. Mice
carrying lacZ driven by the alpha-globin promoter exhibit
beta-galactosidase (beta-Gal) expression in only a very small proportion of
embryonic erythrocytes. When the transgenic construct also contains the
(alphaHS-40 enhancer, which controls expression of the alpha-globin gene,
expression is seen in a high proportion of embryonic erythrocytes, although
there are variations between transgenic lines which can be attributed to
different sites of integration. Analysis of beta-Gal expression levels
suggests that expressing cells in lines carrying only the alpha-globin
promoter express as much beta-Gal as those in which the transgene also
contains alphaHS-40. A marked decline in transgene expression occurs as
mice age, which is mainly due to a decrease in the proportion of cells
expressing the transgene. Thus, a globin enhancer can act to suppress
variegation of a linked transgene; this result is consistent with a model
in which enhancers act to establish and maintain an active domain without
directly affecting the transcriptional rate.
Copyright © 1997, American Society for Microbiology
A globin enhancer acts by increasing the proportion of erythrocytes expressing a linked transgene
Department of Biochemistry, The University of Sydney, New South Wales, Australia.
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