Expression analysis of GSK-3β in diapause pupal brains in the cotton bollworm, Helicoverpa armigera

Low GSK3β activity is required for insect diapause through responding to ROS/AKT signaling and down-regulation of Smad1/EcR/HR3 cascade

Glycogen synthase kinase 3β (GSK3β) plays important roles in gene transcription, metabolism, apoptosis, development, and signal transduction. However, its role in the regulation of pupal diapause remains unclear. In this paper, we find that low GSK3β activity in brains of diapause-destined pupae of Helicoverpa armigera is caused by elevated AKT activity. In response to ROS, AKT phosphorylates GSK3β to decrease its activity. In developing pupal brains, GSK3β can activate the transcription factor Smad1, which binds to the promoter region of the ecdysone receptor (EcR) gene and increases its expression. In the presence of 20-hydroxyecdysone (20E), EcR can bind to USP and increase the expression of 20E-response genes, including HR3, for pupal-adult development. In contrast, high levels of ROS in brains of diapause-destined pupae up-regulate p-AKT, which in turn decreases GSK3β activity. Low GSK3β activity causes low expression of EcR/HR3 via down-regulation of Smad1 activity, leading to diapause initiation. These results suggest that low GSK3β activity plays a key role in pupal diapause via ROS/AKT/GSK3β/Smad/EcR/HR3 signaling.

Smurf participates in Helicoverpa armigera diapause by regulating the transforming growth factor-β signaling pathway

Diapause, an important strategy used by insects to avoid adverse environments, is regulated by various cell signaling pathways. The results of our previous studies demonstrated that the transforming growth factor-β (TGF-β) signaling pathway regulated pupal diapause in Helicoverpa armigera, which was accompanied by downregulation of proteins in TGF-β signaling. However, to date the mechanism underlying this phenomenon remains unknown. Here, we cloned the E3 ubiquitin ligases gene Smurf. In vitro experiments showed that Smurf directly bound to TGF-β receptor type I (TGFβRI) and Smad2. Overexpressing Smurf promoted ubiquitination of TGFβRI and Smad2, thereby downregulating their protein levels. Conversely, silencing of the Smurf gene suppressed ubiquitination of TGFβRI and Smad2 thereby increasing their protein levels. Results from in vivo co-immunoprecipitation assays revealed that the binding of Smurf to TGFβRI or Smad2 was stronger in diapause pupae than in nondiapause pupae. Injection of Smurf inhibitor A01 into diapause pupae markedly upregulated expression of TGFβRI and Smad2 proteins, leading to resumption of development in diapause pupae. Taken together, these findings suggested that ubiquitin ligase E3 Smurf participated in H. armigera diapause by regulating TGF-β signaling, and thus could be playing a crucial role in insect diapause.

Regulatory Functions of Nilaparvata lugens GSK-3 in Energy and Chitin Metabolism

Glucose metabolism is a biologically important metabolic process. Glycogen synthase kinase (GSK-3) is a key enzyme located in the middle of the sugar metabolism pathway that can regulate the energy metabolism process in the body through insulin signaling. This paper mainly explores the regulatory effect of glycogen synthase kinase on the metabolism of glycogen and trehalose in the brown planthopper (Nilaparvata lugens) by RNA interference. In this paper, microinjection of the target double-stranded GSK-3 (dsGSK-3) effectively inhibited the expression of target genes in N. lugens. GSK-3 gene silencing can effectively inhibit the expression of target genes (glycogen phosphorylase gene, glycogen synthase gene, trehalose-6-phosphate synthase 1 gene, and trehalose-6-phosphate synthase 2 gene) in N. lugens and trehalase activity, thereby reducing glycogen and glucose content, increasing trehalose content, and regulating insect trehalose balance. GSK-3 can regulate the genes chitin synthase gene and glucose-6-phosphate isomerase gene involved in the chitin biosynthetic pathway of N. lugens. GSK-3 gene silencing can inhibit the synthesis of chitin N. lugens, resulting in abnormal phenotypes and increased mortality. These results indicated that a low expression of GSK-3 in N. lugens can regulate the metabolism of glycogen and trehalose through the insulin signal pathway and energy metabolism pathway, and can regulate the biosynthesis of chitin, which affects molting and wing formation. The relevant research results will help us to more comprehensively explore the molecular mechanism of the regulation of energy and chitin metabolism of insect glycogen synthase kinases in species such as N. lugens.

Alternative splicing and expression analysis of HSF1 in diapause pupal brains in the cotton bollworm, Helicoverpa armigera

BACKGROUND

Diapause is the arrest of the development of insects and can be used for the development of effective agricultural pest management strategies. Heat shock protein 70 (Hsp70) is reported to be up-regulated during diapause to maintain survival in some insect species. However, its regulatory mechanism is unknown.

RESULTS

Expression of hsp70 in Helicoverpa armigera was found to be up-regulated in diapause pupal brains. To elucidate the molecular regulatory mechanisms of hsp70, we focused our attention on its transcription factor, heat shock factor 1 (HSF1). Four alternative splicing variants of HSF1 from pupal brains of H. armigera were identified, and subcellular localization analysis indicated that these variants were exclusively expressed in the nucleus. Real-time PCR analysis showed that all of these variants were up-regulated in diapause pupal brains, and their expression patterns were consistent with that of hsp70. Finally, promoter activity assay and Western blotting detection demonstrated that hsp70 was activated and up-regulated by these variants.

CONCLUSION

Expression of hsp70 in H. armigera during diapause is regulated by multiple alternatively spliced isoforms of HSF1. The results of this study may provide important information for understanding the regulatory mechanisms of hsps during insect diapause. © 2018 Society of Chemical Industry.