R. Huber et al., DNA methylation in transcriptional repression of two differentially expressed X-linked genes, GPC3 and SYBL1, P NAS US, 96(2), 1999, pp. 616-621
Citations number
27
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Methylation of CpG islands is an established transcriptional repressive mec
hanism and is a feature of silencing in X chromosome inactivation, Housekee
ping genes that are subject to X inactivation exhibit differential methylat
ion of their CpG islands such that the inactive alleles are hypermethylated
, In this report, we examine two contrasting X-linked genes with CpG island
s for regulation by DNA methylation: SYBL1, a housekeeping gene in the Xq p
seudoautosomal region, and GPC3, a tissue-specific gene in Xq26 that is imp
licated in the etiology of the Simpson-Golabi-Behmel overgrowth syndrome. W
e observed that in vitro methylation of either the SYBL1 or the GPC3 promot
er resulted in repression of reporter constructs. In normal contexts, we fo
und that both the Y and inactive X alleles of SYBL1 are repressed and hyper
methylated, whereas the active X allele is expressed and unmethylated. Furt
hermore, the Y and inactive X alleles of SYBL1 were derepressed by treatmen
t with the demethylating agent azadeoxycytidine, GPC3 is also subject to X
inactivation, and the active X allele is unmethylated in nonexpressing leuk
ocytes as well as in an expressing cell line, suggesting that methylation i
s not involved in the tissue-specific repression of this allele. The inacti
ve X allele, however, is hypermethylated in leukocytes, presumably reflecti
ng early X inactivation events that become important for gene dosage in exp
ressing lineages. These and other data suggest that all CPG islands on Xq,
including the pseudoautosomal region, are subject to X inactivation-induced
meth ylation, Additionally, methylation of SYBL1 on Yq may derive from a p
rocess related to X inactivation that targets large chromatin domains for t
ranscriptional repression.