© 1993 by The Society for Integrative and Comparative Biology
Hormone Receptors and the Regulation of Insect Metamorphosis1
Department of Zoology, University of Washington Seattle, Washington 98195
SYNOPSIS. Studies of hormone receptors and the transcription factors that they induce are providing new insights into the control of growth and metamorphosis of insects. The epidermis and the nervous system are used to illustrate the power of these new approaches. Many aspects of a tissue's response to the molting hormone are encoded at the level of the ecdysteroid receptor (EcR) itself. For example, there is a correlation between the presence of EcR and a particular tissue's response to ecdysteroids during larval molts. In preparation for metamorphosis around the time of commitment, all tissues express high levels of EcR as they are losing their larval identities and preparing to transform into the adult. Different forms of EcR are then associated with different programs of differentiation during the subsequent adult development.
Tissue- and cell-specific aspects of responses to ecdysteroid are presumably also reflected in quantitative and qualitative alterations in the cascade of transcription factors that the hormone elicits. In Manduca sexta the ecdysteroid-induced transcription factor MHR3 shows a regionspecific onset of expression in the epidermis that mirrors the spread of competence to form a new cuticle in response to the rise of ecdysteroid.
Juvenile hormone (JH) prevents metamorphosis by modulating ecdysteroid action during the molt and thus may also influence the levels and forms of the EcR and the ecdysteroid-induced transcription factors. Studies of a putative nuclear receptor for JH have shown that its expression is influenced by both the ecdysteroid and JH titers.