Remodelling of a homeobox gene cluster by multiple independent gene reunions in Drosophila.

Genome clustering of homeobox genes is often thought to reflect arrangements of tandem gene duplicates maintained by advantageous coordinated gene regulation. Here we analyse the chromosomal organization of the NK homeobox genes, presumed to be part of a single cluster in the Bilaterian ancestor, across 20 arthropods. We find that the ProtoNK cluster was extensively fragmented in some lineages, showing that NK clustering in Drosophila species does not reflect selectively maintained gene arrangements.