Epigenetic plasticity of hematopoietic cells.

In recent years significant evidence was provided for the concept that the developmental potential is engraved in the chromatin of stem cells. This is indicated by low-level expression of lineage specific genes and also by epigenetic alterations that occur prior to gene locus activation. Hence, cell lineage specification involves not only the activation, but also the epigenetic silencing of different genetic programmes. In this article, I summarize recent data from my laboratory that indicate that (i) at the epigenetic level developmental processes occur in a step-wise fashion and (ii) that developmental windows exist, which are associated with a specific chromatin structure, in which such decisions can be reversed.