Constitutive genomic methylation during embryonic development of Xenopus

Methylation of CpG dinucleotides is a predominant modification of genomic D NA in many species, especially in vertebrates. This modification, generally associated with transcriptional repression, is rapidly and globally lost d uring mammalian pre-implantation development. This loss of methylation is g radually reversed during subsequent stages of development. Here we show tha t the amphibian Xenopus laevis maintains high levels of DNA methylation dur ing early embryonic development. The methylation status of specific loci is independent of the temporal expression profile. The observations have prof ound implications for the regulation of early embryonic gene regulation and genome function. (C) 2001 Elsevier Science B.V. All rights reserved.