The Journal of Cell Biology, Vol 106, 1027-1034, Copyright © 1988 by The Rockefeller University Press
In vivo system for characterizing clonal variation and tissue-specific gene regulatory factors based on function
EC Hardeman, A Minty, P Benton-Vosman, L Kedes and HM Blau
Department of Pharmacology, Stanford University School of Medicine, California 94305-5332.
The inducibility of stably transfected alpha-cardiac actin genes differs
among L cell clones. We examined the ability of muscle-specific factors to
induce the expression of the human muscle alpha-cardiac actin gene promoter
when stably transfected into mouse fibroblast L cells. This promoter is
transcriptionally active in L cells at a low level, 2-5% of that in
transfected muscle cells. Upon fusion with muscle cells to form
heterokaryons, expression of the transfected alpha- cardiac actin gene
promoter can be induced. However, induction is observed with only 10% of
transfected L cell clones and the magnitude of this induction varies
between 5- and 50-fold. These properties of the transfected L cell appear
to be stably inherited. Our results are consistent with the hypothesis that
muscle cells contain factors capable of increasing the transcription of the
transfected gene, but that differences among L cell clones, possibly in the
site of integration in the genome, determine the extent to which the gene
can respond. By fusion into heterokaryons, transfectants with responsive
genes can be identified. Such clones should prove useful in determining the
basis for clonal variation. In addition, they provide an in vivo system for
isolating functionally active tissue-specific transcription factors and the
genes that encode them.
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