Lack of correlation between DNA methylation and transcriptional inactivation: the chicken lysozyme gene

We have analyzed the methylation state of all nine CpG sites in the transcription start region (-420 to +250 base pairs) of the chicken lysozyme gene by genomic sequencing. One of these sites, at -81, lies within the promoter, seven are clustered within the first exon, and the last is in the first intron. Five cell types and tissues have been investigated to study the relationship between methylation level and gene expression. For each cell type used, the majority of CpG sites showed a similar level of methylation. Of two gene-nonexpressing tissues, erythrocytes are hypomethylated, whereas liver is methylated at most of its CpG sites. For gene-expressing tissues, oviduct is completely unmethylated, whereas HD-11 culture cells are methylated. Thus no correlation is observed between degree of CpG methylation and level of expression of the lysozyme gene. The observed methylation patterns are discussed in terms of possible features of the local chromatin structure.