DNA methylation pattern changes during development of a sea urchin.

Cytosine methylation of developmentally regulated genes of the sea urchin Strongylocentrotus purpuratus was studied by using restriction-endonuclease digestion and Southern blotting. The single-copy bindin gene, the family of five cytoplasmic actin genes and the 400-fold-repeated set of five early histone genes were mostly unmethylated, but some sites exhibited partial methylation that varied throughout development. This shows that in echinoderms the methylation of DNA is not confined to the non-transcribed portion of the genome, as previously believed [Bird, Tagart & Smith (1979) Cell 17, 889-901], and may play a role in transcriptional regulation.