Cap’n’collar differentiates the mandible from the maxilla in the beetle Tribolium castaneum

Our analyses show that Tc-cnc is required for specification of the identity of the mandibular segment of Tribolium and differentiates the mandible from maxillary identity. Loss of Tc-cnc function results in a transformation of the mandible to maxillary identity as well as deletion of the labrum. Tc-Dfd and the Tribolium homolog of proboscipedia (Tc-mxp？=？maxillopedia), Hox genes that are required to pattern the maxillary appendage, are expressed in a maxilla-like manner in the transformed mandible. Tribolium homologs of paired (Tc-prd) and Distal-less (Tc-Dll) that are expressed in the endites and telopodites of embryonic appendages are also expressed in a maxilla-like manner in the transformed mandible.We also show that Tc-Dfd is required to activate the collar of Tc-cnc expression in the mandibular segment but not the cap expression in the labrum. Tc-Dfd is also required for the activation of Tc-prd in the endites of the mandible and maxillary appendages.Tc-cnc is necessary for patterning the mandibular segment of Tribolium. Together, Tc-cnc and Tc-Dfd cooperate to specify mandibular identity, as in Drosophila. Expression patterns of the homologs of cnc and Dfd are conserved in mandibulate arthropods suggesting that the mandible specifying function of cnc is likely to be conserved across the mandibulate arthropods.The arthropod mandible is an appendage adapted for biting and chewing and is present in three arthropod groups, the insects and crustaceans (collectively the Pancrustacea) and the myriapods (millipedes and centipedes). The mandibulate arthropods, commonly grouped together in the monophyletic Mandibulata, constitute the majority of animals both in terms of numbers of species and biomass on this planet. The mandible is therefore an evolutionary novelty of particular interest.There are many different types of mandible, but the characteristic that most mandibles share, and which differentiates it from other arthropod appendages, is the presence of a function