The Short antennae gene of Tribolium is required for limb development and encodes the orthologue of the Drosophila Distal-less protein

Insects bear a stereotyped set of limbs, or ventral body appendages. In the highly derived dipteran Drosophila melanogaster, the homeodomain transcrip tion factor encoded by the Distal-less (Dll) gene plays a major role in est ablishing distal limb structures. We have isolated the DEI orthologue (TcDl l) from the beetle Tribolium castaneum, which, unlike Drosophila, develops well-formed limbs during embryogenesis, TcDll is initially expressed at the sites of limb primordia formation in the young embryo and subsequently in the distal region of developing legs, antennae and mouthparts except the ma ndibles. Mutations in the Short antennae (Sa) gene of Tribolium delete dist al limb structures, closely resembling the Dll phenotype in Drosophila, TcD ll expression is severely reduced or absent in strong So alleles, Genetic m apping and molecular analysis of Sa alleles also support the conclusion tha t TcDll corresponds to the So gene. Our data indicate functional conservati on of the Dll gene in evolutionarily distant insect species. Implications f or evolutionary changes in limb development are discussed.