Insights into the Molecular Basis of the Hormonal Control of Molting and Metamorphosis from Manduca Sexta and Drosophila Melanogaster

This short review summarizes our current knowledge about the role of transcription factors regulated by ecdysteroids and juvenile hormone (JH) in larval molting and metamorphosis in the tobacco hornworm, Manduca sexta, and Drosophila melanogaster. We show new evidence that EcR-A/USP-2 and E75A contribute to the down-regulation of MHR3 after the peak of ecdysteroid. Also, there is suggestive evidence that both MHR4 and betaFTZ-F1 may regulate the expression of dopa decarboxylase as the ecdysteroid titer declines. We summarize the regulation by JH of the Broad transcription factor that normally appears in the epidermis in the final larval instar and specifies pupal cuticle formation at the metamorphic molt. Premature expression of different Broad isoforms also is shown to cause precocious degeneration of the prothoracic glands as well as to prevent ecdysteroid release during its presence.