Role of nuclear receptors NlHR3 and NlFTZ-F1 in regulating molting and reproduction in Nilaparvata lugens (stål)

RNA interference knockdown of the nuclear receptor HR3 suppresses vitellogenesis in Chilo suppressalis

BACKGROUND

Developmental and reproductive processes are the most critical physiological processes in insects, with the insect hormone 20-hydroxyecdysone (20E, the major active form of ecdysone) playing a central regulatory role in key developmental events such as embryonic development, larval molting, metamorphosis, and reproduction. As an early-late gene within the ecdysone-mediated genetic regulatory network, the orphan nuclear receptor HR3, which exhibits characteristics of both early and late genes, serves as a critical regulator of insect metamorphosis and development. However, the precise molecular mechanisms underlying HR3's function in the reproduction of non-model insects remain poorly understood.

METHODS AND RESULTS

We cloned Chilo suppressalis HR3 (CsHR3) and phylogenetic analysis demonstrates that CsHR3 shares the highest sequence homology with its ortholog in Ostrinia furnacalis. Spatiotemporal expression profiling revealed that CsHR3 expression peaked during day 4 of the female pupal stage, with the highest tissue-specific expression observed in the heads of female pupae. RNA-interference (RNAi) mediated silencing of CsHR3 resulted in delayed oocyte maturation, reduced yolk deposition, and decreased fecundity. Concurrently, transcriptional levels of key genes involved in yolk formation vitellogenin (Vg), 20E and juvenile hormones (JH) signaling pathways, including chitin synthase 1 (CHS1), were significantly downregulated in the CsHR3-knockdown group.

CONCLUSION

These findings collectively demonstrate that CsHR3 plays an essential role in the reproductive regulation of C. suppressalis, potentially mediating transcriptional control of 20E and JH pathway-related genes and chitin biosynthesis-related targets. This study not only advances the understanding of reproductive regulation in Lepidoptera but also highlights HR3 as a potential molecular target for pest management strategies.

BmHR3 Is Essential for Silk Gland Development and Silk Protein Synthesis in Silkworms (Bombyx mori)

The steroid hormone 20-hydroxyecdysone (20E), which is known to regulate insect molting and metamorphosis, is crucial for the normal development of silk glands (SGs) in the silkworm Bombyx mori. However, how the 20E signaling pathway and its core members function in the SG remains largely unclear. Here, we report that the orphan nuclear receptor BmHR3, a 20E-response factor, plays an essential role in regulating SG development and silk protein synthesis. First, we showed that tissue-specific BmHR3 overexpression and knockout result in severe developmental defects in posterior silk glands (PSGs). Second, we revealed that BmHR3 dysfunction in PSGs dramatically represses the transcription of silk fibroin protein-coding genes, thereby inhibiting fibroin protein synthesis. Finally, we confirmed that BmHR3 can regulate fibroin protein-coding gene expression via direct and indirect mechanisms. This study elucidates the vital function of BmHR3 in B. mori SG and provides valuable information for thoroughly understanding the regulatory roles of 20E signaling in specialized insect organs.

Sinuous Is a Claudin Required for Locust Molt in Locusta migratoria

The epidermal cells of insects are polarized epithelial cells that play a pivotal role in the insect's molting process. Sinuous, a pivotal structural protein involved in the formation of septate junctions among epithelial cells, is essential for its physiological function. In this study, to determine whether sinuous participates in the regulation of insect molting, we identified the sinuous gene, Lmsinu, in Locusta migratoria, which encodes a protein belonging to the claudin family and shares 62.6% identity with Drosophila's sinuous protein. Lmsinu is expressed in multiple tissues, and its expression level in the integument significantly increases prior to molting. Knockdown of Lmsinu in L. migratoria results in larval mortality during molting. Furthermore, hematoxylin and eosin and chitin staining demonstrate that the downregulation of Lmsinu led to a prolonged degradation process of the old cuticle during the molting process. Electron microscopy analysis further revealed that knockdown of Lmsinu disrupts the formation of septate junctions among epidermal cells, which are a monolayer of polarized epithelial cells, which may hinder the functionality of epidermal cells during the process of molting. In summary, these findings suggest that Lmsinu plays a role in nymph molting by regulating the formation of septate junctions among epidermal cells.

Buprofezin affects the molting process by regulating nuclear receptors SfHR3 and SfHR4 in Sogatella furcifera

Nuclear receptors play a crucial role in various signaling and metabolic pathways, such as insect molting and development. Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-perhydro-1, 3, 5-thiadiazin-4-one), a chitin synthesis inhibitor, causes molting deformities and slow death in insects by inhibiting chitin synthesis and interfering with their metabolism. This study investigated whether buprofezin affects insect ecdysteroid signaling pathway. The treatment of buprofezin significantly suppressed the transcription levels of SfHR3 and SfHR4, two nuclear receptor genes, in third-instar nymphs of Sogatella furcifera. Meanwhile, the transcription levels of SfHR3 and SfHR4 in first-day fifth-instar nymphs were induced at 12 h after 20E treatment. In addition, the silencing of SfHR3 and SfHR4 genes in first-day fifth-instar nymphs caused severe developmental delay and molting failure, resulting in a significant reduction of survival rates at 7.36% and 2.99% on the eighth day, respectively. Further analysis showed that the silencing SfHR3 and SfHR4 significantly inhibited the transcription levels of chitin synthesis and degradation-related genes. These results indicate that buprofezin can inhibits chitin synthesis and degradation by suppressing the signal transduction of 20E through SfHR3 and SfHR4, leading to molting failure and death. This study not only expands our understanding of the molecular mechanism of buprofezin in pest control but also lays a foundation for developing new control strategies of RNAi by targeting SfHR3 and SfHR4.