Abstract
Juvenile Hormone (JH) represses metamorphosis of young instars in insects. One of the main players in hormonal signalling is Methoprene-tolerant (Met), which plays the role of JH receptor. Using the Polyneopteran insect Blattella germanica as the model and RNAi for transcript depletion, we have confirmed that Met transduces the antimetamorphic signal of JH in young nymphs and plays a role in the last nymphal instar moult in this species. Previously, the function of Met as the JH receptor had been demonstrated in the Eumetabola clade, with experiments in Holometabola (in the beetle Tribolium castaneum) and in their sister group Paraneoptera (in the bug Pyrrhocoris apterus). Our result shows that the function of Met as JH receptor is also conserved in the more basal Polyneoptera. The function of Met as JH transducer might thus predate the evolutionary innovation of metamorphosis. Moreover, expression of Met was also found in last nymphal instar of B. germanica, when JH is absent. Depletion of Met in this stage provoked deficiencies in wing growth and ecdysis problems in the imaginal moult. Down-regulation of the ecdysone-inducible gene E75A and Insulin-Like-Peptide 1 in these Met-depleted specimens suggest that Met is involved in the ecdysone and insulin signalling pathways in last nymphal instar, when JH is virtually absent.
Highlights
Insect metamorphosis is regulated by the interplay of two hormones, 20-hydroxyecdysone (20E), which triggers the successive moults throughout the life cycle, and juvenile hormone (JH), which represses the transition to the adult stage [1]
From an evolutionary point of view, it is worth noting that this essential endocrine regulation is conserved in the species closest to the ancestral state, where juvenile stages are similar to the adult, as well as in more derived species, where juvenile stages can be extremely divergent with respect to the adult stage [1]
B. germanica Met is the first Met sequence reported in Dictyoptera, a Polyneopteran within the Pterygota subclass of hemimetabolan insects
Summary
Insect metamorphosis is regulated by the interplay of two hormones, 20-hydroxyecdysone (20E), which triggers the successive moults throughout the life cycle, and juvenile hormone (JH), which represses the transition to the adult stage [1]. From an evolutionary point of view, it is worth noting that this essential endocrine regulation is conserved in the species closest to the ancestral state, where juvenile stages are similar to the adult (hemimetabolan insects), as well as in more derived species, where juvenile stages can be extremely divergent with respect to the adult stage (holometabolan insects) [1]. While molecular mechanisms regulating the action of 20E have largely been unveiled, those underlying the action of JH have remained almost a complete mystery until recent years, when the transcription factor Methoprene-tolerant (Met) has been proclaimed as the JH receptor [2]. Met was identified as a member of the basic helix-loop-helix Per-ARNT-Sim (bHLH-PAS) family of transcription factors [4], which are critical regulators of gene expression networks underlying many essential physiological and developmental processes [5]. Miura et al [6] showed that
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