The mode of action of juvenile hormone and ecdysone: Towards an epi-endocrinological paradigm? (original) (raw)
Related papers
Insect juvenile hormone: from "status quo" to high society
Brazilian Journal of Medical and Biological Research, 2000
Juvenile hormone (JH) exerts pleiotropic functions during insect life cycles. The regulation of JH biosynthesis by neuropeptides and biogenic amines, as well as the transport of JH by specific binding proteins is now well understood. In contrast, comprehending its mode of action on target organs is still hampered by the difficulties in isolating specific receptors. In concert with ecdysteroids, JH orchestrates molting and metamorphosis, and its modulatory function in molting processes has gained it the attribute status quo hormone. Whereas the metamorphic role of JH appears to have been widely conserved, its role in reproduction has been subject to many modifications. In many species, JH stimulates vitellogenin synthesis and uptake. In mosquitoes, however, this function has been transferred to ecdysteroids, and JH primes the ecdysteroid response of developing follicles. As reproduction includes a variety of specific behaviors, including migration and diapause, JH has come to function as a master regulator in insect reproduction. The peak of pleiotropy was definitely reached in insects exhibiting facultative polymorphisms. In wingdimorphic crickets, differential activation of JH esterase determines wing length. The evolution of sociality in Isoptera and Hymenoptera has also extensively relied on JH. In primitively social wasps and bumble bees, JH integrates dominance position with reproductive status. In highly social insects, such as the honey bee, JH has lost its gonadotropic role and now regulates division of labor in the worker caste. Its metamorphic role has been extensively explored in the morphological differentiation of queens and workers, and in the generation of worker polymorphism, such as observed in ants.
New insights into the roles of juvenile hormone and ecdysteroids in honey bee reproduction
Journal of Insect Physiology, 2013
In workers of the Western honeybee, Apis mellifera, juvenile hormone (JH) and ecdysteroids regulate many aspects of age polyphenism. Here we investigated whether these derived functions in workers have developed by an uncoupling of endocrine mechanisms in adult queens and workers, or whether parallels can be found between the roles of the two hormones in both castes. We looked at yolk protein metabolism as a process central to the physiology of both queens and workers, and at sperm storage as a feature of the queen alone. Queens of differing fertility status (virgin, virgin but CO 2 -treated, inseminated, freshly laying and 1-2 years-old) were compared regarding vitellogenin (Vg), JH and ecdysteroid-titers in their hemolymph, as well as ovarian yolk protein and spermathecal gland composition. Our results showed that hormone titres were unrelated to the composition of spermathecal glands. JH-concentrations in the hemolymph were low in the groups of queens characterized by yolk uptake into the ovaries, and high in pre-vitellogenic queens or animals that were forced to interrupt egg-laying by caging. Ecdysteroidconcentrations were higher in untreated virgins than after insemination or during egg-laying. They were not affected by the caging of queens. These patterns of hormone changes were parallel to those known from worker bees. Together, these findings suggest a conserved role for JH as repressor of vitellogenin uptake into tissues, and for ecdysteroids in preparing tissues for this process. An involvement of the two hormones in the regulation of sperm storage seems unlikely. Our results add to the view that JH and ecdysteroids act similarly on the yolk protein metabolism of both castes of A. mellifera. This may imply that it was the biochemical versatility of Vg rather than that of hormonal regulatory circuits that allowed for the functional separation of the two castes.
Understanding insect endocrine systems: molecular approaches*
Entomologia Experimentalis et Applicata, 2000
Molecular approaches have led to spectacular improvement of our knowledge of insect endocrinology. The present review focuses on two major classes of insect lipidic hormones, ecdysteroids and juvenile hormones. Although the ecdysteroid biosynthetic pathway is not yet fully elucidated, several new steps have been recently characterized, and molecular studies of biosynthetic enzymes are now beginning. It is expected that, thanks to suitable biological models (e.g., ecdysteroid-defective mutants of Drosophila), the entire biosynthetic pathway will be elucidated in the near future. The understanding of the ecdysteroid mode of action has benefited from studies with Drosophila and major developments relate to the cascades of gene activation and the molecular basis for the stage-and tissuespecificity of hormonal effects. The biosynthetic pathway of juvenile hormones is fully known, but molecular studies of enzymes are still in their infancy, and there is some controversy about the nature of juvenile hormone receptors. Within the forthcoming years, molecular tools will allow to characterize all the enzymes involved in hormone biosynthesis and then to analyze the fine regulation of hormone titers. They will also allow comparative studies aimed at investigating the presence of related molecules (hormone biosynthetic enzymes and receptors) among other Invertebrates (Arthropods and non-Arthropods), and thus to propose evolutionary scenarios for their endocrine systems.
Role of Endocrine System in the Regulation of Female Insect Reproduction
Biology, 2021
The proper synthesis and functioning of ecdysteroids and juvenile hormones (JHs) are very important for the regulation of vitellogenesis and oogenesis. However, their role and function contrast among different orders, and even in the same insect order. For example, the JH is the main hormone that regulates vitellogenesis in hemimetabolous insect orders, which include Orthoptera, Blattodea, and Hemiptera, while ecdysteroids regulate the vitellogenesis among the insect orders of Diptera, some Hymenoptera and Lepidoptera. These endocrine hormones also regulate each other. Even at some specific stage of insect life, they positively regulate each other, while at other stages of insect life, they negatively control each other. Such positive and negative interaction of 20-hydroxyecdysone (20E) and JH is also discussed in this review article to better understand the role of these hormones in regulating the reproduction. Therefore, the purpose of the present review is to deeply understand th...
Integration of Endocrine Signals That Regulate Insect Ecdysis
Frontiers in Neuroendocrinology, 2002
The extremely large number of insects and members of allied groups alive today suggests that molting-shedding of an old cuticle-may be one of the most commonly performed behaviors on our planet. Removal of an old cuticle in insects is associated with stereotyped, species-specific patterns of behavior referred to as ecdysis. It has been recognized for decades that the initiation of ecdysis is under hormonal control, but until recently many of the key peptides that regulate ecdysis were unknown. The report in 1996 of a new ecdysis-triggering hormone (ETH) sparked an era of significant advances in our understanding of the regulation of molting. This article summarizes the current model of peptide regulation of ecdysis, a model that is based on a positive feedback loop between ETH and a brain peptide, eclosion hormone. Then the relationship of these regulatory peptides to the neural circuitry that is the ultimate driver of the behavior are described. Because insects can undergo both status quo (larval-larval) and metamorphic (larval-pupal and pupal-adult) molts, differences in ecdysis behavior at different life stages are described and potential sources of these differences are identified. Most of the work described is based on studies of ecdysis in the hawkmoth, Manduca sexta, but results from studies of ecdysis in the fruit fly Drosophila melanogaster are also discussed.
European Journal of Biochemistry, 2004
The IAL-PID2 cells derived from imaginal wing discs of the last larval instar of Plodia interpunctella were responsive to 20-hydroxyecdysone (20E). These imaginal cells respond to 20E by proliferative arrest followed by a morphological differentiation. These 20E-induced late responses were inhibited in presence of juvenile hormone (JH II). From these imaginal wing cells, we have cloned a cDNA sequence encoding a P. interpunctella ecdysone receptor-B1 isoform (PIEcR-B1). The amino acid sequence of PIEcR-B1 showed a high degree of identity with EcR-B1 isoforms of Bombyx mori, Manduca sexta and Choristoneura fumiferana. The pattern of PIEcR-B1 mRNA induction by 20E was characterized by a biphasic response with peaks at 2 h and 18 h. The presence of the protein synthesis inhibitor anisomycin induced a slight reduction in level of PIEcR-B1 mRNA and prevented the subsequent declines observed in 20E-treated cells. Therefore, PIEcR-B1 mRNA was directly induced by 20E and its downregulation depended on protein synthesis. An exposure of imaginal wing cells to 20E in the presence of JH II caused an increased expression of Plodia E75-B and HR3 transcription factors but inhibited the second increase of PIEcR-B1 mRNA. These findings showed that in vitro JH II was able to prevent the 20E-induced differentiation of imaginal wing cells. This effect could result from a JH II action on the 20E-induced genetic cascade through a modulation of EcR-B1, E75-B and HR3 expression.
Journal of Insect Physiology, 2008
During insect development, ecdysteroids and juvenile hormones (JHs) interact to regulate larval growth, metamorphosis and reproduction but the molecular mechanisms by which both hormones influence each other's activity remain unknown. Because of their ease of use and straightforward genetic manipulation, insect cell lines often have been used to clarify the actions and interactions of hormones at the molecular level. Here we report on the use of two insect culture cell lines, Drosophila melanogaster S2 and Bombyx mori Bm5 cells, to investigate two molecular processes in which ecdysteroids and JH have been shown to interact: (1) direct modulation of the activity of the ecdysteroid receptor transcription complex and (2) interference at the level of induction of the primary gene E75. Our data do not support JH analogs (JHAs) acting through the above processes: 'antagonism' of ecdysteroid receptor activity by JHAs correlated with cytotoxicity and induction of E75 expression by JHAs was not demonstrated. However, we confirm previous studies in which it was observed that methoprene can partially reverse the growth inhibition by 20E in S2 cells (but not Bm5 cells). Therefore, the molecular mechanism by which both hormones influence each other's activity to regulate cell growth in S2 cells remains unknown. r
Peptides, 2014
The paradigm saying that release of the brain neuropeptide big prothoracicotropic hormone (PTTH) initiates metamorphosis by activating the Torso-receptor/ERK pathway in larval prothoracic glands (PGs) is widely accepted nowadays. Upon ligand-receptor interaction Ca(2+) enters the PG cells and acts as a secondary messenger. Ecdysteroidogenesis results, later followed by apoptosis. Yet, some data do not fit in this model. In some species decapitated animals can still molt, even repeatedly, and metamorphose. PTTH does not universally occur in all insect species. PGs may also have other functions; PGs as counterpart of the vertebrate thymus? There are also small PTTHs. Finally, PTTH remains abundantly present in adults and plays a role in control of ecdysteroidogenesis (=sex steroid production) in gonads. This is currently documented only in males. This urges a rethinking of the PTTH-PG paradigm. The key question is: Why does PTTH-induced Ca(2+) entry only result in ecdysteroidogenesis ...