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Mol. Cell. Biol., 03 1997, 1469-1475, Vol 17, No. 3
S Tweedie, J Charlton, V Clark and A Bird
Patterns of DNA methylation in animal genomes are known to vary from an
apparent absence of modified bases, via methylation of a minor fraction of
the genome, to genome-wide methylation. Representative genomes from 10
invertebrate phyla comprise predominantly nonmethylated DNA and (usually
but not always) a minor fraction of methylated DNA. In contrast, all 27
vertebrate genomes that have been examined display genome-wide methylation.
Our studies of chordate genomes suggest that the transition from fractional
to global methylation occurred close to the origin of vertebrates, as
amphioxus has a typically invertebrate methylation pattern whereas
primitive vertebrates (hagfish and lamprey) have patterns that are typical
of vertebrates. Surprisingly, methylation of genes preceded this
transition, as many invertebrate genes have turned out to be heavily
methylated. Methylation does not preferentially affect genes whose
expression is highly regulated, as several housekeeping genes are found in
the heavily methylated fraction whereas several genes expressed in a
tissue-specific manner are in the nonmethylated fraction.
Copyright © 1997, American Society for Microbiology
Methylation of genomes and genes at the invertebrate-vertebrate boundary
Institute of Cell and Molecular Biology, University of Edinburgh, United Kingdom. stweedie@srv0.bio.ed.ac.uk
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