ABSTRACT
De novo methylation mostly occurs in embryonic development, responsible for genomic imprinting, X-inactivation and transposon suppression in mammals. Aberrant de novo methylation of the CpG islands in the promoters of growth regulatory genes occurs frequently in human cancers. Maize root tissues undergo genome-wide demethylation when the seedlings are exposed to cold stress. Homeostatic imbalance of the components, such as folate, methionine and S-adenosylmethionine, in the biosynthetic pathways for DNA and histone methylation may precede disorder. A time-ordered microarray measurement of the evolving pattern of DNA methylation, monitoring the fate of 5′ cytosines, helps elucidate the regulatory program of the epigenetic machinery.
