Df. Condorelli et al., TISSUE-SPECIFIC DNA METHYLATION PATTERNS OF THE RAT GLIAL FIBRILLARY ACIDIC PROTEIN GENE, Journal of neuroscience research, 39(6), 1994, pp. 694-707
The glial fibrillary acidic protein (GFAP) is an intermediate filament
protein, specific of the cytoskeleton of astrocytes in the central ne
rvous system. In the present work, as a preliminary step to the study
of glial-specific gene expression, we cloned the rat GFAP gene, and we
report the sequence of 1.9 kb of the 5' flanking region, exon 1, and
the majority of the first intron. By digestion with methylation-sensit
ive restriction enzymes followed by Southern blot analysis, the methyl
ation status of various CpG sites was examined in this genomic segment
, We tested whether structural modification of the GFAP gene, such as
DNA methylation, could be related to its tissue-specific transcription
al activity, Therefore, we compared a GFAP-expressing cell population
(primary culture of astroglial cells), a mixed population of GFAP-expr
essing and -nonexpressing cells (adult rat cerebral hemispheres), and
a GFAP-nonexpressing tissue (liver), In the 5' flanking region we iden
tified a CpG site at position -1176 whose level of methylation is inve
rsely correlated to GFAP expression, In primary cultured astrocytes, 7
5% of the GFAP gene alleles were demethylated at this site, while the
corresponding value obtained for the cerebral hemispheres was 45%, and
for liver only 9%. On the basis of the sequence data, a CpG-rich regi
on (putative CpG island) was identified extending from -38 to +347 and
overlapping 80% of the first exon, HhaI and HpaII sites located in th
e putative CpG island showed a relatively high level of methylation in
all the cell populations examined, and did not show any clear correla
tion with the level of GFAP gene expression or with the methylation st
atus of the -1176 site, Further in vivo developmental studies and in v
itro differentiation studies are necessary to better understand the fu
nctional differences of the various methylatable CPG sites in the 5' e
nd of the GFAP gene. (C) 1994 Wiley-Liss, Inc.