Changes in DNA methylation and histone modification during epigenetic transitions

Aberrant epigenetic silencing is a major mechanism of tumor suppressor gene inactivation, yet the early events that trigger this process are not well defined. This work demonstrates that transient reductions in gene activation can initiate stable epigenetic silencing, producing chromatin changes similar to those seen at silenced tumor suppressor genes in cancer. Using an inducible transgene system and analysis of endogenous Aprt alleles, the study shows that silencing initiation depends on histone deacetylases, while DNA methylation primarily stabilizes later stages. The findings reveal distinct early and late silencing events and identify a heritable, DNA‑methylation–independent repressive state that limits stable reactivation.