Expression of juvenile hormone acid O‐methyltransferase and juvenile hormone synthesis in Blattella germanica

Abstract

Juvenile hormone (JH), a sesquiterpenoid synthetized by the insect corpora allata (CA), plays critical roles in metamorphosis and reproduction. Penultimate or last step of JH synthesis is catalyzed by juvenile hormone acid O-methyltransferase (JHAMT). Here we report the cloning and expression analysis of the JHAMT orthologue in the cockroach, Blattella germanica (L.) (BgJHAMT). BgJHAMT is mainly expressed in CA, with only expression traces in ovary. Three different isoforms, differing in the 3'-UTR sequence, were identified. Isoform A shows between 35 and 65 times higher expression than B and C in CA from penultimate nymphal instar and adult females. RNAi-triggered knock down of BgJHAMT produces a dramatic reduction of JH synthesis, concomitant with a decrease of fat body vitellogenin expression and basal follicle length. BgJHAMT mRNA levels in CA of females along the gonadotrophic cycle parallel, with a slight advancement, JH synthesis profile. BgJHAMT mRNA levels were reduced in starved females and in females in which we reduced nutritional signaling by knocking down insulin receptor and target of rapamycin (TOR). Results show that conditions that modify JH synthesis in adult B. germanica females show parallel changes of BgJHAMT mRNA levels and that the JH-specific branch of the JH synthesis pathway is regulated in the same way as the mevalonate branch. Furthermore, we demonstrate that nutrition and its signaling through the insulin receptor and TOR pathways are essential for activating BgJHAMT expression, which suggests that this enzyme can be a checkpoint for the regulation of JH production in relation to nutritional status.

Juvenile hormone signaling in short germ-band hemimetabolan embryos

“…We chose the following interference targets from downstream to upstream of the signaling axis (Jindra et al, 2015a,b): Krüppel homolog 1 (Kr-h1), the main transducer of the JH signal during metamorphosis, Met and JHAMT. The three genes have been structurally and functionally characterized in B. germanica (Dominguez and Maestro, 2017;Belles, 2011, 2014).…”

Juvenile hormone mediates the positive effects of nitrogen fertilization on weight and reproduction in pea aphid

“…Enhanced transcription of TOR and increased phosphorylation of TOR/S6K have been shown to indicate enhanced TOR activity. 17, TOR activation has been shown to promote JH biosynthesis in various insect species . Thus, the enhanced amino acid content in pea aphid likely caused the enhanced transcription of TOR, which indicates enhanced activation of JH biosynthesis in aphids at the fourth instar and adult stage under nitrogen fertilization.…”

“…17,32,45 TOR activation has been shown to promote JH biosynthesis in various insect species. 16,19,32,45 Thus, the enhanced amino acid content in pea aphid likely caused the enhanced transcription of TOR, which indicates enhanced activation of JH biosynthesis in aphids at the fourth instar and adult stage under nitrogen fertilization. In addition to the TOR pathway, the neuropeptides allatotropin and allatostatin released from the brain, which result in the activation or inhibition of JH biosynthesis, can also be affected by nutritional signals.…”

“…Numerous studies with artificial diet suggest that juvenile hormone (JH) coordinates dietary nutrition with insect performance . In the adult stage, JH biosynthesis and JH titre are often positively related to nutrition, as revealed by experiments with limited diets or starvation . Enhanced JH biosynthesis in well‐nourished insects has been shown to be mediated by target of rapamycin (TOR) signalling, a core component of the nutrient‐sensing pathway, because depletion of TOR caused a dramatic reduction in nutrient‐induced JH biosynthesis .…”

“…15 In the adult stage, JH biosynthesis and JH titre are often positively related to nutrition, as revealed by experiments with limited diets or starvation. 16,17 Enhanced JH biosynthesis in well-nourished insects has been shown to be mediated by target of rapamycin (TOR) signalling, a core component of the nutrient-sensing pathway, because depletion of TOR caused a dramatic reduction in nutrient-induced JH biosynthesis. 18,19 Moreover, increased JH promotes ovary growth and reproduction in several insect species, and is accompanied by greater weight under well-nourished conditions.…”