Embryonic expression of Tc-kni and the Tc-kni head cuticle phenotype. A-M: Expression of Tc-kni during blastoderm (A-H’) and early germband stages (I-M). See text for a detailed description. Panels A’-H’ show inverted DAPI images of the embryos in panels A-H respectively. Black arrows in panels D-M mark Tc-kni expression at the anterior border of one or both head lobes. Black arrowheads in panels D-M indicate the stripe of Tc-kni expression marking the anterior compartment of the mandibular segment. White arrowheads in panels E-M mark the posterior domain of Tc-kni expression which first becomes visible within the primitive pit as it forms (E-I) and later resolves into a stripe marking segment A1 (J-M). Anterior is to the left in panels A-H’ and to the top in panels I-M. Panel B shows a dorso-lateral view, panels D, E and G show ventro-lateral views, panel C and F lateral views, and panels H-M are all ventral views. N-O: In contrast to wildtype (N), antennaless mutant first instar larvae (O) lack antennae (black arrows in panel N) and mandibles (black arrowhead in panel N). All lateral and dorsal head bristles are however present.