Expression of Tc-en and Tc-Dfd in wildtype and Tc-kni RNAi embryos. The antennal Tc-en stripe (marked by white arrowhead in wildtype panels A, D, G, J, M) is missing in all Tc-kni RNAi embryos. The mandibular Tc-en stripe (marked by black arrow) forms within the Tc-Dfd expression domain, but is broken (panels B, C, E, H, K, L, N) and often missing (panels F, I, O) in Tc-kni RNAi embryos. Tc-en expression in the intercalary segment (black asterisk in panels J-L, N-O; hidden by antenna in panel M) appears at a variable time point in mid-elongation stage embryos at the anterior border of the Tc-Dfd expression domain in both wildtype and Tc-kni RNAi embryos. Tc-en expression associated with structures at the base of the antenna is evident in late Tc-kni RNAi embryos (red arrows in panels K-O). Head lobes appear reduced in size (panels A’-C’), and the Tc-Dfd domain slightly narrower (panels G-O) in Tc-kni RNAi embryos, consistent with a failure to specify and form posterior antennal and mandibular tissue. Black arrowheads in panels D-O mark the maxillary Tc-en stripe. Ventral views, and anterior towards the top, in all panels.