Almost all animal species use Hox genes to determine developmental cell fate and morphology, and on , Cameron and co-workers investigate how Hox genes regulate programmed cell death. The C. elegans Hox gene mab-5 is required for the programmed death of two related cells in the posterior ventral nerve cord: P11.aaap and P12.aaap. Programmed cell death in C. elegans requires the BH3-domain gene egl-1, and the researchers found that, in the P11.aaap cell, MAB-5 (together with its cofactor CEH-20)activates egl-1 transcription by directly interacting with a consensus binding site in the egl-1 regulatory sequence (although,remarkably, the death of P12.aaap is determined in a different fashion). This is the first time that a cell biological effector gene - rather than a transcription factor - has been found to be directly regulated by Hox proteins in C. elegans. Together with similar findings from Drosophila, this indicates that non-homeotic targets of Hox proteins,including targets that control programmed cell death, might be more common than previously thought.
