TOR Pathway-Mediated Juvenile Hormone Synthesis Regulates Nutrient-Dependent Female Reproduction in Nilaparvata lugens (Stål).

Kai Lu,Wen-Ting Liu,Xia Chen,Qiang Zhou

doi:10.3390/ijms17040438

Abstract

The “target of rapamycin” (TOR) nutritional signaling pathway and juvenile hormone (JH) regulation of vitellogenesis has been known for a long time. However, the interplay between these two pathways regulating vitellogenin (Vg) expression remains obscure. Here, we first demonstrated the key role of amino acids (AAs) in activation of Vg synthesis and egg development in Nilaparvata lugens using chemically defined artificial diets. AAs induced the expression of TOR and S6K (S6 kinase), whereas RNAi-mediated silencing of these two TOR pathway genes and rapamycin application strongly inhibited the AAs-induced Vg synthesis. Furthermore, knockdown of Rheb (Ras homologue enriched in brain), TOR, S6K and application of rapamycin resulted in a dramatic reduction in the mRNA levels of jmtN (juvenile hormone acid methyltransferase, JHAMT). Application of JH III on the RNAi (Rheb and TOR) and rapamycin-treated females partially rescued the Vg expression. Conversely, knockdown of either jmtN or met (methoprene-tolerant, JH receptor) and application of JH III had no effects on mRNA levels of Rheb, TOR and S6K and phosphorylation of S6K. In summary, our results demonstrate that the TOR pathway induces JH biosynthesis that in turn regulates AAs-mediated Vg synthesis in N. lugens.

Highlights

Nutrients are key signals regulating reproduction in insects
The cDNA sequences of three key proteins involved in the TOR signaling pathway were identified from N. lugens females: Ras homolog enriched in brain (Rheb), the target of rapamycin (TOR) and S6
In the cockroach B. germanica, systemic depletion of TOR expression by RNA interference (RNAi) dramatically decreased the expression levels of genes coding for 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) synthases and HMG-CoA reductase which was associated with the juvenile hormone (JH) biosynthesis pathway in the corpora allata (CA), and remarkably decreased mRNA levels of Vg in the fat body [17]. These results indicate that the TOR pathway is important to regulate JH synthesis in some kinds of insects by controlling the JH biosynthetic enzyme transcript levels

Summary

Introduction

Nutrients are key signals regulating reproduction in insects. Intake of proteins or amino acids (AAs) is a key trigger for the initiation of vitellogenesis. It is pronounced in most anautogenous insects, in which egg development is arrested until a female takes a blood meal [8,9]. The question of how nutrients are sensed by the insects and transformed into developing eggs is very important and interesting. Both nutritional and hormonal regulation mechanisms are suggested to be involved

Results

Discussion

Conclusion