Polycomb group proteins are developmental gene expression regulators that localize to regions of the nucleus called Polycomb bodies. The authors monitored the dynamics at Polycomb bodies during development in Drosophila melanogaster. They showed that Polycomb proteins are gradually recruited to these compartments during embryogenesis. Furthermore, two types of chromosomal movement at Polycomb bodies — a fast, highly constrained motion and a slower, long-range motion that was indicative of chromosome territory movement — decreased through development, suggesting a role for this movement in gene regulation.