The establishment and maintenance of DNA methylation patterns in mouse somatic cells

Somatic cell DNA methylation patterns in mammals are established during emb ryonic development and are then maintained somewhat faithfully for the rema inder of the individual's lifetime. Pattern formation can be divided into a series of linked steps that include demethylation, de novo methylation, me thylation spreading, methylation blocking, and maintenance methylation. In this review, these str;Ds will be combined to present a model for the forma tion and maintenance of a methylation pattern in the 5' region of the mouse Aprt gene. This model suggests that an apparently 'stable' methylation pat tern results from a dynamic equilibrium between forces that promote and inh ibit methylation spreading.