 Zebrafish embryos born from mothers that are mutant in IKK-α do not produce a differentiated outer epithelial monolayer.Instead, the outermost cells in these embryos are hyperproliferative and fail to turn on critical epidermal genes.Different domains of the protein are required for this function of IKK-α in zebrafish than in mice, but in neither case does the NF-κB pathway seem to be implicated.