Ultrastructural Effects of a Non-Steroidal Ecdysone Agonist, RH-5992, on the Sixth Instar Larva of the Spruce Budworm, Choristoneura fumiferana (original) (raw)
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Insect Moulting Hormones: A Study of 4-En-3-one Steroids as Possible Ecdysteroid Precursors
Australian Journal of Chemistry, 1979
The trienol ether (15) of cholesta-4,7-dien-3-one (4) is oxidized with peroxy acid mainly to the 6-hydroxy derivatives (6) and (7) and the corresponding cholesta-4,7-diene-3,6-dione (8). However, the biosynthesis of ecdysteroids may not proceed by a similar pathway since the labelled keto diene (5) was not incorporated into 20-hydroxyecdysone (10) in Calliphora stygia. None of the possible 4-en-3-one ecdysteroid precursors synthesized (6), (7), (8), (18) were active in the Calliphora assay.
Role of ecdysone in larval metamorphosis
Parasitologists United Journal
Larvae of almost all insects and nematodes have to undergo a cycle of molting for growing and further development, and with the final molt, adults emerge (complete metamorphosis). In insects, it seems that complete metamorphosis takes place through a dormant stage (pupa), in which all larval cells (muscles, salivary glands, gut, etc.) disintegrate by apoptosis. That is why adult forms appear completely different from their pre-pupa larval stages. In contrast, adult nematodes resemble their final larval stages because dormant pupa stages are absent. In insects, molting with or without pupation requires a pro-thoracicotropic hormone (PTTH) secreted by two pairs of cells in the larval brain. This hormone activates prothoracic glands to secrete a steroid hormone, known as the ecdysone. Also by these glands, sufficient production of the juvenile hormone (JH), promotes larva molting. In case of lower JH production, steroid hormones promote pupation, while complete loss of JH leads to direct formation of the adult from the last final larval molt [1]. Steroid hormones have an essential role on the physiological development and behavior of various organisms. Ecdysone is a major steroid hormone that directs major transitions during developmental stages in the life cycle of some helminth and almost all insects by coordinating larval molting and metamorphosis. Ecdysteroid is produced by the prothoracic gland of all insects as 20-hydroxyecdysone. Increase of ecdysteroid induces the expression of genes controlling protein production for larval development. In adult female insects, ecdysone signaling is critical for reproduction as it mediates egg-chamber maturation during oogenesis, whereas in adult males, ecdysteroids have a role in sperm maturation. It is also present in several plants to protect them from agricultural insects. The ecdysone receptor (EcR) is a nuclear receptor found in the cells of reproduction in all insects, and is activated through binding with ecdysteroid. Once activated, it leads to activation of several genes responsible for physiological changes leading to larval ecdysis (molting). EcR is a non-covalent heterodimer of two proteins; EcR protein and ultraspiracle protein (USP), which are homologous to the mammalian farnesoid X receptor (FXR) and retinoid X receptor (RXR) proteins, respectively. The term USP is usually used for the EcR partner from dipteran and lepidopteran insects, while RXR is applied in other insects. This means that EcR consists of EcR protein and USP for dipteran and lepidopteran insects, whereas it consists of EcR protein and RXR for other insects [2-5]. EcR is mainly applied to control gene expression with two uses; for gene therapy in medical and agricultural fields, and for drug development and vector control in Parasitology researches. The present editorial aims to throw light on the second application.
Effect of RH-5992 on adult development in the spruce budworm, Choristoneura fumiferana
Insect Biochemistry and Molecular Biology, 2002
The effect of RH-5992 (tebufenozide), a non-steroidal ecdysone agonist, on adult development of the spruce budworm, Choristoneura fumiferana, was investigated by administering the compound intrahemocoelically to pupae on days 1-6 after pupal ecdysis. At concentrations of 200 ng/pupa there was significant mortality but at doses of 50-100 ng/pupa, the emerging adults displayed wing deformities which reduced their ability to mate and oviposit. Light microscopy of the pupal wings revealed that there was degeneration of the epithelial cells, reduction in the number of veins, precocious cuticle formation and inhibition of growth of normal wing scales. Injection of RH-5992 into pupae resulted in a dose dependent induction of mRNA for ecdysone-induced transcription factor, Choristoneura hormone receptor 3 (CHR3). These results suggest that the pupae respond to RH-5992 in a manner similar to larvae. However, the effects are not expressed overtly and are camouflaged by the pharmacological effects.
Insect Moulting Hormones: The Synthesis of Possible Ecdysone Precursors for Metabolic Studies
Australian Journal of Chemistry, 1974
The possible biological precursors of ecdysones, 3β-hydroxy-5β-cholest-7-en-6-one (2) and 3β,14α-dihydroxy-5β-cholest-7-en-6-one (3), are prepared from 7-dehydrocholesterol through their 5α-epimers.The corresponding 3α-[3H] derivatives of high specific activity are prepared in a similar way via 5α-cholest-7-ene-3β,6α-diol[3α-3H] 6-acetate which is obtained by reducing the corresponding 3-keto derivative with sodium borotritide.
1999
Larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), that were orally treated with RH-0345 at 0.1 mg l −1 , RH-5849 at 10 and 50 mg l −1 , tebufenozide at 2 g l −1 , and 20-hydroxyecdysone at 2 g l −1 , showed symptoms of premature moulting, followed by inhibition of ecdysis. In addition, fresh weight gain and total protein content were blocked. The effects on haemolymphal and cuticular polypeptides after PAGE were linked with premature, new epicuticle deposition as was observed under the electron microscope. These observations support the concept that the ecdysteroid-mimicking action of the three nonsteroidal molecules is specific.
Insect Biochemistry and Molecular Biology, 2005
The non-steroidal ecdysone agonist, RH-5992, exhibits ecdysteroid activities in vivo as well as in vitro more effectively than 20hydroxyecdysone (20E). Using the IAL-PID2 cells derived from imaginal wing discs of last larval instar of Plodia interpunctella, we investigated the action of RH-5992 in the control of cell growth. Its effects on the proliferative activity of IAL-PID2 cells, the induction level in G2/M arrest and on the expression rate of Plodia B cyclin (PcycB), ecdysone B1-isoform (PIEcR-B1) and Ultraspiracle-2 isoform (PIUSP-2) were examined. From these cellular and molecular assays, our results brought evidence that RH-5992, like 20E, induced an inhibition on cell proliferation by blocking IAL-PID2 cells in G2/M phase. Moreover, this G2/M arrest was preceded by a decrease in the expression level of PcycB and a high induction of PIEcR-B1, PIUSP-2 mRNAs. Dose-response experiments revealed that RH-5992 was even more potent than 20E. On these parameters, we therefore suggest that the differential observed in the expression level of USP and EcR by RH-5992 and 20E could contribute to the difference observed for the biological potency of these two compounds.
Reproduction Nutrition Development, 1986
Injection of ecdysone can break diapause in Pieris brassicae pupae. The purpose of this study was to investigate whether the injected hormone acts directly on the target tissues, promoting adult morphogenesis, or through a reactivation of the neuroendocrine system, leading to a neosynthesis of ecdysone. A dose of 500 ng/pupa was sufficient to obtain synchronous adult development. Ecdysone injected either in whole or in decapitated pupae induced a neosynthesis of ecdysone, starting on day 5 after treatment, and the onset of imaginal development. Thus, we suggest that ecdysone can act independently of the brain, and that its stimulatory action on ecdysone neosynthesis is probably indirect, according to the long delay (5 days) necessary for this reactivation. In addition, isolated abdomens from diapausing pupae injected with the same dose of ecdysone also developed, but did not synthesize any ecdysteroid. This suggests that the injected hormone has also a direct morphogenetic effect on target tissues. The significance of this ecdysone neosynthesis is discussed. Introduction. The development of many Insect species can be delayed in response to environmental conditions : this diapause state is a strategy for surviving during unfavourable climatic conditions. The white cabbage butterfly, Pieris brassicae (Lepidoptera) presents such an arrest of development at the pupal stage, induced by short photoperio.ds (L 8 : D 16, for example) during the fourth and early fifth larval stages (Claret, 1972). The pupal diapause appears to be due to a deficiency of the circulating moulting hormones : ecdysone (E) and 20-hydroxyecdysone (20E) (Williams, 1946 ; Williams, 1952). In non-diapausing animals, E is synthesized by the prothoracic glands (Chino et al., 1974 ; King et al., 1974) and released in the hemolymph. It is then hydroxylated in peripheral tissues into 20E (King and Sidall, 1969 ; Bergamasco and Horn, 1980) which is generally considered as the active