Identification of 20-hydroxyecdysone-inducible genes from larval brain of the silkworm, Bombyx mori, and their expression analysis

Adenosine Monophosphate-Activated Protein Kinase (AMPK) Phosphorylation Is Required for 20-Hydroxyecdysone Regulates Ecdysis in Apolygus lucorum

The plant mirid bug Apolygus lucorum is an omnivorous pest that can cause considerable economic damage. The steroid hormone 20-hydroxyecdysone (20E) is mainly responsible for molting and metamorphosis. The adenosine monophosphate-activated protein kinase (AMPK) is an intracellular energy sensor regulated by 20E, and its activity is regulated allosterically through phosphorylation. It is unknown whether the 20E-regulated insect's molting and gene expression depends on the AMPK phosphorylation. Herein, we cloned the full-length cDNA of the AlAMPK gene in A. lucorum. AlAMPK mRNA was detected at all developmental stages, whereas the dominant expression was in the midgut and, to a lesser extent, in the epidermis and fat body. Treatment with 20E and AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AlCAR) or only AlCAR resulted in activation of AlAMPK phosphorylation levels in the fat body, probed with an antibody directed against AMPK phosphorylated at Thr172, enhancing AlAMPK expression, whereas no phosphorylation occurred with compound C. Compared to compound C, 20E and/or AlCAR increased the molting rate, the fifth instar nymphal weight and shortened the development time of A. lucorum in vitro by inducing the expression of EcR-A, EcR-B, USP, and E75-A. Similarly, the knockdown of AlAMPK by RNAi reduced the molting rate of nymphs, the weight of fifth-instar nymphs and blocked the developmental time and the expression of 20E-related genes. Moreover, as observed by TEM, the thickness of the epidermis of the mirid was significantly increased in 20E and/or AlCAR treatments, molting spaces began to form between the cuticle and epidermal cells, and the molting progress of the mirid was significantly improved. These composite data indicated that AlAMPK, as a phosphorylated form in the 20E pathway, plays an important role in hormonal signaling and, in short, regulating insect molting and metamorphosis by switching its phosphorylation status.

Vrille is required for larval moulting and metamorphosis of Helicoverpa armigera (Lepidoptera: Noctuidae)

Vrille (Vri), a basic leucine zipper transcription factor, plays important roles in insect circadian clock regulation, tracheal development, proliferation, flight and metamorphosis. Here, Helicoverpa armigera was used as a model to investigate the role of Vri in larval moulting and metamorphosis. Sequence analysis results revealed that H. armigera Vri (HaVri) shares a high amino acid identity with other Lepidoptera Vri homologues. Spatial-temporal expression pattern data showed that HaVri expression was highly abundant in larval moulting and metamorphosis stages and was mainly expressed in the midgut and Malpighian tubule during metamorphosis. HaVri knockdown by RNA interference in the fourth-instar larvae prevented larval moulting, and HaVri knockdown in the fifth-instar larvae suppressed midgut remodelling and delayed or blocked metamorphosis. Further studies confirmed that 20-hydroxyecdysone (20E) activated HaVri expression via its heterodimer receptors, ecdysone receptor (EcRB1) and ultraspiracle protein (USP1), whereas methoprene [juvenile hormone analogue (JHA)] promoted HaVri expression via its intracellular receptor methoprene-tolerant (Met1). However, 20E and JHA can counteract each other in the activation of HaVri expression. Together, the present results suggested that HaVri was involved in larval moulting and metamorphosis and was regulated by 20E and JHA in H. armigera.

Pupal diapause termination in Bactrocera minax: an insight on 20-hydroxyecdysone induced phenotypic and genotypic expressions

The Chinese citrus fruit fly, Bactrocera minax, is an economically important pest of citrus. It exhibits pupal diapause from November to May to combat harsh environmental conditions. Such a long pupal diapause is a barrier for laboratory rearing and development of control strategies against this pest. In the present study, 20-hydroxyecdysone (20E) was used to break pupal diapause of B. minax by topical application. After diapause termination by 20E treated, the pupal ontogenetic processes were observed along the temporal trajectory. The pupal response time to 20E was estimated by detecting the relative expression of 20E responsive genes at different times after 20E-treatment. Results revealed that 20E could effectively terminate the pupal diapause in a dose-dependent manner and significantly shorten the time for 50% adult emergence (Et50). 20E response genes, including ecr, broad and foxo, were up-regulated within 72h, indicating these genes are involved in pupal metamorphosis and diapause termination processes. Morphological changes showed the pupal metamorphosis began ~7 days after 20E-treatment at 22 °C. This study does not only pave the way for artificial rearing in the laboratory through manipulating of pupal diapause termination, but also deepens our understanding of the underlying pupal diapause termination mechanism of B. minax.

Serotonin receptor B may lock the gate of PTTH release/synthesis in the Chinese silk moth, Antheraea pernyi; a diapause initiation/maintenance mechanism?

The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTRA and B). 5HTRA-, and 5HTRB-like immunohistochemical reactivities (-ir) were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL). Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA(5HTRB) responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTRA was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA(5HTRB) resulted in early diapause termination, whereas that of dsRNA(5HTRA) did not affect the rate of diapause termination. The injection of dsRNA(5HTRB) induced PTTH accumulation, indicating that 5HTRB binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTRB may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.