Purchase this article with an account.
S. S. Deeb, L. Fu; Epigenetic Control of the Human L-and M-photoreceptor Opsin Genes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2746.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To investigate whether methylation of a CpG island, located about 6 kb upstream of L-pigment gene promoter and 3 kb upstream of the locus control region, contributes to L and M gene expression. Methylation of the C nucleotide in CpG rich islands usually causes inhibition of expression of the target genes.
The pattern and extent of methylation of the CpG island upstream of the L- and M-pigment genes was compared between the human retinoblastoma cell line WERI that expresses the L-and M-pigment genes and other cell lines that do not. DNA isolated from these cells was first treated with bisulfite to convert unmethylated C-nucleotides to T-nucleotides. The CpG region (250 nucleotides in length) was then PCR amplified and cloned into plasmids. The inserts in about 40 individual clones from each cell line were sequenced to determine the ratio between methylated and unmethylated CpGs.
The tested CpG island was previously found to be hypersensitive to DNase I digestion in WERI cells, suggesting that it may play a role in setting up the proper conformation for gene expression. This region also contains a highly conserved sequence motif that is typically found in insulators of gene expression. We found that the pattern and extent of methylation of this CpG island in WERI cells are significantly different from those in lymphocyte and lymphoblastoid cell lines that do not express the opsin genes. A much smaller number (8 out of 40 clones) had methylated CpGs within, and in the vicinity of the insulator motif in WERI cells, compared to 36/40 in lymphocytes.
Demethylation of the insulator motif in the CpG island that is hypersensitive to DNase I in WERI cells is potentially associated with turning on expression of the L and M opsin genes by inducing an open chromatin conformation.
This PDF is available to Subscribers Only