Vertebrate hox gene regulation: clustering and/or colinearity?

The relationship between the clustered organization of vertebrate Hox genes and their coordinate transcription in space and time is still lacking a convincing mechanistic explanation. Recent work on the regulatory interactions within Hox complexes suggests some reasons why these genes have remained clustered. Although these results do not address the puzzling issue of colinearity directly, they nevertheless add novel important input to the debate.