Hox genes typically display a high level of functional specificity during the formation of the vertebrate axial skeleton. To date, most studies have focused on understanding the mechanism responsible for Hox functional specificity, and thus little is known regarding the potential function of Hox proteins beyond their well-established roles. In this issue (p. ), Moisés Mallo and colleagues uncover an interesting role for Hoxb6, distinct from its involvement in rib formation. The authors show that forced expression of Hoxb6 in the paraxial mesoderm produces non-rib-related malformations due to problems in somitogenesis and anterior-posterior somite patterning, which result from dysregulated expression of the oscillator gene Lfng. Dysregulated Lfng expression was restricted to regions posterior to the hindlimb, suggesting that the mechanisms of paraxial segmentation are not uniform along the main body axis as previously thought. These data provide a mechanistic connection between Hoxb6 expression and the mammalian segmentation clock and convincingly demonstrate functional differences in somitogenesis before and after the trunk-to-tail transition. The authors postulate that their data suggest the existence of yet-to-be-identified differential mechanisms operating during development of the trunk or tail areas of the body axis.
