The embryonic expression pattern of labial, posterior homeotic complex genes and the teashirt homologue in an apterygote insect

During embryogenesis of the fruit fly, Drosophila melanogaster, the homeoti c genes are required to specify proper cell fates along the anterior-poster ior axis of the embryo. We cloned partial cDNAs of homologues of the Drosop hila homeotic gene teashirt and five of the homeotic-complex (HOM-C) genes from the thysanuran insect, Thermobia domestica, and assayed their embryoni c expression patterns. The HOM-C genes we examined were labial, Antennapedi a, Ultrabithorax, abdominal-A and Abdominal-B. As the expression pattern of these HOM-C genes is largely conserved among insects and as Thermobia is a member of a phylogenetically basal order of insects, we were able to infer their ancestral expression patterns in insects. We compare the expression patterns of the Thermobia HOM-C genes with their expression in Drosophila a nd other insects and discuss the potential roles these genes may have playe d in insect evolution. Interestingly, the teashirt homologue shows greater variability between Thermobia and Drosophila than any of the HOM-C genes. I n particular, teashirt is not expressed strongly in the Thermobia abdomen, unlike Drosophila teashirt. We propose that teashirt expression has expande d posteriorly in Drosophila and contributed to a homogenization of the Dros ophila larval thorax and abdomen.