Time out: developmental regulation of heterochromatic silencing in Drosophila.

Transcriptional silencing by heterochromatin represents a model for developmental gene silencing. Current models of heterochromatin envision DNA-protein complexes that prevent access by euchromatic transcription factors. Here, we summarize the evidence that heterochromatin acts at the chromatin level to silence genes and the status of current models of heterochromatin silencing, and we highlight some recent progress in understanding the composition and regulation of heterochromatin in Drosophila.