Figure 1.

Methylation changes during early development. The epigenome is a dynamic process where rapid de-methylation occurs immediately post fertilization but is then followed by re-methylation in the blastocyst and early embryo. Developmental stages are shown diagrammatically. During neurulation stages, the direction of neural tube fusion is shown by arrows, resulting in closure of the rostral neuropore (dark shaded area) in the cranial region and the posterior neuropore in the caudal region. Craniorachischisis results from failure to initiate closure of the neural folds, anencephaly and spina bifida from incomplete closure in cranial and caudal regions respectively.