Alcohol-induced methylation alterations in chromosomes containing a large number of imprinted genes and genes prone to silencing were observed (Fig. 6 and Table 3). Chromosome 7 is known to contain clusters of imprinted genes (e.g., Igf2, Ube3a) that mediate embryonic growth and development. Increased methylation of a large number of genes in alcohol-treated embryos with more severe neural tube defects (i.e., ALC-NTO as compared to ALC-NTC) was particularly evident in Chromosome 10 and the X chromosome. A remarkable ~15-fold increase in methylated genes in the X chromosome was observed when neural tube development was compromised by alcohol treatment. While already containing many silenced genes,58 our data indicates further DNA methylation-mediated repression of the X chromosome, perhaps suggesting a compelling new hypothesis that large-scale alcohol-induced methylation changes in the X chromosome contributes to neural tube defects.
