Developmental changes in hemolymph ecdysteroid level and prothoracicotropic hormone activity during the fifth larval instar of the Eri silkworm, Samia cynthia ricini (original) (raw)
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Regulation and significance of ecdysteroid titre fluctuations in lepidopterous larvae and pupae
Journal of Insect Physiology, 1981
The last larval moult of GaNeria mellonella is induced by an elevation of ecdysteroid titre to more than 200 rig/g.. After ecdysis the titre remains very low until 70 hr of the last-instar when a slight elevation in ecdysteroid concentration initiates the onset of metamorphosis. An ecdysteroid peak (275 ng/g), which occurs between 108 and 144 hr. is associated with wandering and cocoon spinning. Pupal ecdysis follows about 20 hr after a large ecdysteroid peak (780 rig/g)) with a maximum in slowly-mobile prepupae (160 hr of the last larval instar). The ecdysteroid decrease between the two peaks coincides with the period when the larvae exposed to unfavourable conditions enter diapause. The pupal-adult moult is initiated by a high ecdysteroid peak (1500-2500 rig/g)) in early pupae and imaginal cuticle is secreted in response to a smaller peak (ca. 500 rig/g)) in the middle of pupal instar.
Regulation of ecdysteroidogenesis in prothoracic glands of the tobacco hornworm Manduca sexta
The Journal of experimental zoology, 1989
Ecdysteroidogenesis in Manduca sexta prothoracic glands is regulated by a set of bioregulatory molecules, including prothoracicotropic hormone (PTTH) and a protein factor present in larval hemolymph, and by the competence of the glands to synthesize ecdysteroids in response to those molecules. A larval molting bioassay was used to assess the in vivo activity of Manduca PTTHs. Crude PTTH, big PTTH, and small PTTH each elicited a larval molt in head-ligated larvae. However, big PTTH was approximately 10-fold more potent than crude PTTH, which was, in turn, several orders of magnitude more potent than small PTTH. When big and small PTTH were combined, the molting response was similar to that elicited with crude PTTH. The chemical nature of the hemolymph protein factor was also investigated. Injection of [3H]cholesterol into last-instar larvae and fractionation of the radiolabeled hemolymph by gel filtration chromatography revealed three peaks of radioactivity. One peak eluted in fracti...
Journal of Insect Physiology, 1995
Fluctuations in hemolymph ecdysteroid titer are part of a complex mechanism that regulates pupal-adult development. The amount of ecdysteroid produced in z&-o by prothoracic glands from female Lymantria dispar (L.) (Lepidoptera: Lymantriidae) pupae and pharate adults, as well as the competency of these glands to respond to a prothoracicotropic hormone (PTTH) stimulus in uitro, each correspond temporally with hemolymph ecdysteroid titers. Based on studies of gland kinetics and dose-responses to brain extract using prothoracic glands from different female pupal and pharate adult ages, an in vitro bioassay for the quantification of PTTH activity was developed using glands from day 2 females incubated without stimulus for 1 h followed by a 3 h incubation with stimulus. Only extracts of brains and corpora allata from pupae and pharate adults possess a PTTH factor. This factor is heat stable and can be separated on high performance size exclusion chromatography into two molecular sizes of 13.75 and 3.2 kDa. Ecdysone and 3-dehydroecdysone are produced in vitro by prothoracic glands from all ages of female L.. dispar pupae and pharate adults tested. The amount of ecdysone produced by these glands exceeds that of 3-dehydroecdysone production after 4 h of incubation.
Diversity in Factors Regulating Ecdysteroidogenesis in Insects
2000
Ecdysteroid synthesis in insects was long considered as an exclusive feature of the ecdysial glands in larvae, and control of molting and metamorphosis was long thought to be the only function of ecdysteroids. The ‘classical dogma’ (Delbecque et al., 1990) of insect endocrinology states that ecdysteroids are produced by the prothoracic glands (PGs) (or analogs: ventral glands and ring glands),
Archives of Insect Biochemistry and Physiology, 2007
Larvae of Sesamia nonagrioides developing under long day (LD) conditions pupate in the 5th or 6th instar, whereas under the short day (SD) conditions, they undergo several supernumerary larval molts and are regarded as diapausing. The development in early larval instars occurs in the LD larvae at a moderate and in the SD larvae at a high juvenile hormone (JH) titer; ecdysteroid titer cycles similarly under both conditions. The transformation to pupa is initiated by a burst of ecdysteroids at undetectable JH levels, whereas extra larval molts in the diapausing larvae are associated with moderate JH titer and irregular rises of ecdysteroids. Application of 0.2 ppm RH-2485 to the diet of the 6th instar larvae promotes hormonal changes supporting metamorphosis in the LD larvae and slightly accelerates larval molts in the diapausing SD larvae. The 0.5-and 1ppm doses revert these patterns of endocrine regulations to a mode typical for early larval instars. Particularly dramatic is a JH titer increase provoked within 24 h in the LD larvae. After the treatment, both the LD and SD larvae undergo a series of larval molts, suggesting that hormonal programming of the larval development has been stabilized. A few insects receiving 1 ppm RH-2485, and a high proportion of those fed with 5 ppm RH-2485, deposit two cuticles within a single apolysis and die. Arch. Insect Biochem. Physiol. 65:74-84, 2007. Abbreviations used: E = ecdysone; ELISA = enzyme-linked immunosorbent assay; HPLC = high performance liquid chromatography; HRP = horse radish peroxidase; 20E = 20-hydroxyecdysone; JH = juvenile hormone(s); LD = long day; MA = makisterone A; SD = short day; 2dE = 2-deoxyecdysone; 2d20E = 2-deoxy-20-hydroxyecdysone; 20,26E = 20,26-dihydroecdysone.
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.
Presence and function of ecdysteroids in adult insects
Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 1984
1. Ecdysteroids have been found in both male a 2. In Diptera vitellogenin synthesis is primarily controllq synthesis can easily be induced by ecdysone and 20-OH ecdy do not directly control vitellogenin synthesis in the fat bot 3. In vivo the ovary readily takes up [3H]ecdysone from 1 releases ecdysteroids. 4. A high ecdysteroid peak was found in non-reproducing 5. Ecdysteroids do occur in adult males but the titre in tl that found in females.
Archives of Insect Biochemistry and Physiology, 1987
In vivo biosynthesis of ecdysteroids during t h e last larval instar of Pieris brassicae was investigated by administering [3H] cholesterol followed byhighperformance liquid chromatography analysis of t h e resulting [3H] ecdysteroids. The demonstration that t h e specific activity of t h e ecdysteroids synthesized at a given time is always identical with that of cholesterol indicates that t h e cholesterol pool is uniformly labeled, and this allows us to easily calculate t h e amounts of ecdysteroids produced by animals. The total amount of ecdysone produced throughout the last larval instar was measured as 1.17 nmol/insect. This quantity is more than three-fold the maximal level of molting hormones (ecdysone + 20-hydroxyecdysone) reached during t h e instar (0.37 nmollanimal) because a high catabolic activity occurs at the-beginning of t h e hormone production period. Larvae thus differ from pupae, where catabolism is minimal when ecdysone synthesis takes place, resulting in a more "economical" system.