Analysis of genomic methylation patterns at cytogenetic scale. (A) Methylated and unmethylated DNA was isolated from control and ICF syndrome fibroblasts, labeled with contrasting fluorophores, and hybridized against normal human metaphase chromosomes. Satellite 3 on chromosome 9 can be seen to be methylated in the control (top) and unmethylated in ICF syndrome DNA (bottom). Methylated DNA is labeled in green, unmethylated DNA in red. (B) As in A, except that DNA was from normal human brain and all chromosomes are shown. Dense methylation is seen as green and is present at classical and α satellite DNA; demethylation is most conspicuous at rDNA repeats on acrocentric short arms. The regions of most intense labeling with both methylated and unmethylated probes correspond to tandem repeat sequences that are not part of current genome assemblies.
