TANAKA, K*; TRUMAN, JW; Univ. of Washington, Seattle; Univ. of Washington, Seattle: Expression of patterning genes in the larval and the adult legs of Manduca sexta

The tobacco hornworm Manduca sexta, like most holometabolous insects, makes two versions of thoracic legs. The simple thoracic legs of the larva are formed during embryogenesis. All the epidermal cells of the larval legs make leg cuticle during the larval molts. In the last larval stage, however, the adult leg primordia, a subset of these epidermal cells, detach from the cuticle and begin rapid proliferation. Eventually, this proliferation, in combination with extensive cell death in the surrounding regions, transforms the larval legs into the more complex adult legs with a radically different morphology. We are interested in the molecular patterning mechanism underlying this biphasic development of the Manduca leg. To this end, we have been focusing on molecular players known to be involved in patterning the proximal-distal axis in insect legs. Here we report on the expression patterns of early genes, distal-less (dll) and dachshund (dac), and a late gene, Bric-a-brac (Bab), during the larval and the adult leg development. During embryogenesis, dll and dac are expressed in patterns comparable to the adult legs of other insects. During adult leg development, dac continues to be expressed in a similar domain. In contrast, the expression domain of dll expands to a much larger area due to growth of the dll- expressing domain and de novo expression in new set of cells. Bab is expressed during embryogenesis, but the mature expression pattern does not develop until metamorphosis. Our results suggest that the remodeling of the leg involves changes in patterning gene expression and that the larval leg morphology is produced, in part, by premature arrest of the adult leg patterning process.