TANAKA, K.*; TRUMAN, J.W.; University of Washington, Seattle: Molecular patterning of the larval and the adult legs in the tobacco hornworm Manduca sexta

Insect leg development can be classified into three major types. The first type is found in direct developing insects where a leg of the adult form is made during embryogenesis. Insects with distinct larval and adult forms show the other two. In the second type of leg development, novel larval legs are formed during embryogenesis. These legs are then transformed into the adult form during metamorphosis. Finally, in insects whose larvae lack externally visible thoracic legs, adult legs are simply formed during metamorphosis. Most of our knowledge of insect leg development comes from Drosophila whose leg development is of the last kind. We are interested in determining how the leg patterning mechanism of Drosophila is modified in the insects with the second type of leg development. To this end, we study the leg development in the tobacco hornworm Manduca sexta, which posses distinct larval and adult legs. Molecular players in the proximal-distal patterning of the insect legs are well known from the studies in Drosophila and few other non-model insects. We have been characterizing the expression patterns of some of these molecules during the larval and adult leg development in Manduca. They include the early patterning genes, Distalless, Extradenticle and dacshund, as well as downstream genes such as Aristaless and Bric-a-brac. Our preliminary data suggest that Manduca may be prematurely arresting the adult leg patterning in order to generate the larval form.