Heterochromatin at mouse pericentromeres: a model for de novo heterochromatin formation and duplication during replication.

How a nuclear domain is formed at specific chromatin loci and maintained throughout multiple cellular divisions is a central question in the field of nuclear organization. Recent efforts have concentrated on understanding how a domain is set during development in a particular cell lineage and then how DNA replication and repair in interphase as well as chromosome dynamics in mitosis deal with chromatin states at specific loci to propagate functional organization. In the latter case, for each of these events, one must not only evaluate the impact in terms of the extent of the disruption and/or modification of chromatin but also determine how and when proper organization can be restored thereafter. Using heterochromatin at mouse pericentromeres as a model, we present how important advances have been made that open avenues for understanding mechanisms involved in de novo heterochromatin formation and its duplication during replication.