M. Lucarelli et al., The dynamics of myogenin site-specific demethylation is strongly correlated with its expression and with muscle differentiation, J BIOL CHEM, 276(10), 2001, pp. 7500-7506
The molecular mechanisms underlying the activation of tissue-specific genes
have not yet been fully clarified. We analyzed the methylation status of s
pecific CCGG sites in the 5'-flanking region and exon 1 of myogenin gene, a
very important myogenic differentiation factor. We demonstrated a loss of
methylation, at the onset of C2C12 muscle cell Line differentiation, limite
d to the CCGG site of myogenin 5'-flanking region, which was strongly corre
lated with the transcriptional activation of this gene and with myogenic di
fferentiation. The same CCGG site was also found to be hypomethylated, in v
ive, in embryonic mouse muscle (a myogenin-expressing tissue), as opposed t
o nonmuscle (nonexpressing) tissues that had a fully methylated site. In a
C2C12-derived clone with enhanced myogenic ability, demethylation occurred
within 2 h of induction of differentiation, :suggesting the involvement of
some active demethylation mechanism(s) that occur in the absence of DNA rep
lication. Exposure to drugs that inhibit DNA methylation by acting on the S
-adenosylmethionine metabolism produced a further reduction, to a few minut
es, in the duration of the demethylation dynamics, These effects suggest th
at the final site-specific DNA methylation pattern of tissue-specific:genes
is defined through a continuous, relatively fast interplay between active
DNA demethylation and re-methylation mechanisms.