Molecular Mechanisms of Transcription Activation by Juvenile Hormone: A Critical Role for bHLH-PAS and Nuclear Receptor Proteins.

Travis J Bernardo,Edward B Dubrovsky

doi:10.3390/insects3010324

Abstract

Juvenile hormone (JH) is responsible for controlling many biological processes. In several insect species JH has been implicated as a key regulator of developmental timing, preventing the premature onset of metamorphosis during larval growth periods. However, the molecular basis of JH action is not well-understood. In this review, we highlight recent advances which demonstrate the importance of transcription factors from the bHLH-PAS and nuclear receptor families in mediating the response to JH.

Highlights

The insect life cycle is regulated by two major hormones whose balance determines the course of development
With nanomolar affinity, an observation that is consistent with the requirement of MET for preventing premature metamorphosis in Tribolium [4] and for the induction of Juvenile hormone (JH) target genes including the antimetamorphic transcription factor Krüppel homolog 1 (Kr-h1) [23,24]
The molecular mechanisms underlying JH action are gradually being elucidated, a critical question remains: what is the role of JH in the broader context of insect development? This question has grown increasingly complex with the observation that JH signaling involves more than one pathway [13,14]

Summary

Introduction

The insect life cycle is regulated by two major hormones whose balance determines the course of development. JH is pleiotropic and controls development and sexual behavior, pheromone production, caste determination, diapause, migration, and the synthesis of female yolk proteins and male accessory gland proteins [9] In regulating these diverse processes JH appears to utilize multiple pathways, some of which involve the activation of gene expression [10,11,12] while others are transcription-independent [13,14]. There has been much progress in understanding the molecular basis of JH signaling In this short review, we highlight significant advances that have been made in the past two years that demonstrate the importance of transcription factors, including basic-helix-loop-helix Per/Arnt/Sim (bHLH-PAS) and nuclear receptor proteins, in mediating the antimetamorphic activity of JH. We emphasize several unresolved issues, including how JH is integrated into the broader array of signaling pathways and the mechanisms which allow JH to operate distinctly in different insect species

MET as a JH Receptor

JH-Dependent Transcription Mediated by bHLH-PAS and Nuclear Receptor Proteins

Structural Elements of MET Involved in JH Reception and Function

Crosstalk between JH and Ecdysone

Conclusions