Cells `remember' their identity by maintaining patterns of transcriptional repression that are established as they differentiate. The Polycomb-group(PcG) proteins are important players in this cellular memory system and their role in Hox gene regulation during embryogenesis has been extensively studied. Now, on p. 1231, Wang and co-workers report that the PcG protein Polyhomeotic (Ph) is required to maintain neuronal diversity during metamorphosis in the Drosophilabrain and that other PcG proteins also function in neuronal development. The researchers used a genetic mosaic screen in adult fly brains to isolate a new ph mutation. In normal fly brains, different neuronal subtypes have characteristic projection patterns and gene expression profiles, but in the absence of ph, neurons acquire aberrant - but apparently uniform -morphologies and cellular identities. This transformation requires a pulse of ecdysone, leading the researchers to speculate that normal steroid hormone signalling (which drives metamorphosis) may have detrimental side effects on neuronal identity when PcG functions are compromised.

© 2006.
2006