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J. Cell Biol.,
Volume 145, Number 6, June 14, 1999 1133-1143
* Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208; and The cell nucleus is organized as discrete domains, often associated with specific events involved in
chromosome organization, replication, and gene expression. We have examined the spatial and functional
relationship between the sites of heat shock gene transcription and the speckles enriched in splicing factors in primary human fibroblasts by combining immunofluorescence and fluorescence in situ hybridization (FISH).
The hsp90 DyOGen, INSERM U309, Institut Albert Bonniot, Domaine de la Merci, 38706 La Tronche cedex, France
and hsp70 genes are inducibly regulated by
exposure to stress from a low basal level to a high rate
of transcription; additionally the hsp90 gene contains
10 introns whereas the hsp70 gene is intronless. At
37°C, only 30% of hsp90 transcription sites are associated with speckles whereas little association is detected
with the hsp70 gene, whose constitutive expression is
undetectable relative to the hsp90 gene. Upon exposure of cells to heat shock, the heavy metal cadmium, or
the amino acid analogue azetidine, transcription at the
hsp90 and hsp70 gene loci is strongly induced, and
both hsp transcription sites become associated with
speckles in >90% of the cells. These results reveal a
clear disconnection between the presence of intervening sequences at specific gene loci and the association
with splicing factor-rich regions and suggest that subnuclear structures containing splicing factors are associated with sites of transcription.
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