Inhibition of NF-κB activity results in disruption of the apical ectodermal ridge and aberrant limb morphogenesis

In Drosophila, the Dorsal protein establishes the embryonic dorso–ventral axis during development1. Here we show that the vertebrate homologue of Dorsal, nuclear factor-kappa B (NF-κB), is vital for the formation of the proximo–distal organizer of the developing limb bud, the apical ectodermal ridge (AER). Transcription of the NF-κB proto-oncogene c-rel is regulated, in part, during morphogenesis of the limb bud by AER-derived signals such as fibroblast growth factors. Interruption of NF-κB activity using viral-mediated delivery of an inhibitor results in a highly dysmorphic AER, reduction in overall limb size, loss of distal elements and reversal in the direction of limb outgrowth. Furthermore, inhibition of NF-κB activity in limb mesenchyme leads to a reduction in expression of Sonic hedgehog and Twist but derepresses expression of the bone morphogenetic protein-4 gene. These results are the first evidence that vertebrate NF-κB proteins act to transmit growth factor signals between the ectoderm and the underlying mesenchyme during embryonic limb formation.