Temporal patterns of response to ecdysone and juvenile hormone in the epidermis of the tobacco hornworm, Manduca sexta

Abstract

When abdomens were isolated from larvae during a critical period of the molting cycle, only parts of the abdominal epidermis had seen sufficient ecdysone to render them capable of forming a new cuticle independent of the prothoracic glands. By isolating abdomens at various times, it was found that the epidermis of a segment gains independence according to a reproducible pattern. The pattern of independence seen for a larval molt is roughly the reverse of that seen for a pupal molt. The presence or absence of juvenile hormone commits the epidermis towards the synthesis of larval or pupal cuticle, respectively. Under the influence of juvenile hormone, the pattern by which the various areas of the epidermis become committed to make larval cuticle is very similar to the larval pattern of independence from the prothoracic glands. This commitment to larval differentiation occurs at approximately the time when the epidermis becomes independent. In the absence of JH (in preparation for the pupal molt), the pattern by which the epidermis is committed to synthesis of pupal cuticle is the reverse of that seen for the larval molt. Moreover, the epidermis becomes committed to pupal differentiation 2 days prior to the time that it actually becomes able to secrete a pupal cuticle in the absence of the prothoracic glands.