In the Lepidoptera, the order is as given here; ester cleavage preceding epoxide hydration. Either one terminates the activity of the hormone. JH diol acid, the product of both enzymes, is acted on by JH diol kinase to increase the solubility for excretion. The biosynthesis of JH is similar to that of cholesterol in animals. Cholesterol biosynthesis has been exhaustively studied in animals.
All steps occur in the cytosol. The starting material is citrate, which is exported by the mitochondrion when metabolic fuels are high. This enzyme has 8 helical domains anchoring it in the Golgi membrane of the ER;  the catalytic domain is in the cytosol. It is strongly inhibited by the statins , a class of drugs based on a mold metabolite which, at least at one time, were the largest selling class of drugs in the world. Mevalonate is acted of by a series of 3 kinases to give the highly labile 1,2-diphosphomevalonatephosphate, which is acted on by a lyase to give phosphate, CO 2 , and isopentenyl diphosphate.
Isopentenyl diphosphate isomerase converts the latter to the less stable dimethylallyl diphosphate. There are a large number of additional steps to generate cholesterol from IPP, the ubiquitous precursor of all isoprenoids. It appears that the biosyntheis of JH III is identical to that of cholesterol, from production of IPP to FPP, although there appear to be no studies on export of citrate or other metabolites from the mitochondrion into the cytosol , or formation of acetyl-CoA.
All parts of the carbon skeleton comes from IPP. Then it does the same thing to geranyl diphosphate, giving farnesyl diphosphate C This reaction appears to be the only known enzymatic reaction involving the coupling of two molecules with a carbocation. The free electron pair adds to the double bond of IPP, also isomerizing IPP so that the product is an allylic diphosphate. Thus, this part of the isoprenoid pathway appears nearly identical with that of cholesterol with the exception of the insect specific homoisoprenoid units.
Absolute configuration of homomevalonate and 3-hydroxyethylglutaryl and 3-hydroxymethylglutaryl coenzyme a, produced by cell-free extracts of insect corpora allata. A cautionary note on prediction of absolute stereochemistry based on liquid chromatographic elution order of diastereomeric derivatives. However, at this point these pathways diverge. Subsequent work has shown that the enzyme is highly specific for trans allylic alcohols with at least three isoprene units,  and to also be present in mosquitoes. The next steps of JH biosynthesis differ between orders.
In Lepidoptera and mosquitoes farnesoic acid or its homologs is epoxidized by a P dependent farnesoic acid methyl epoxidase, then it is methylated by a JH acid methyl transferase  In most orders, farnesoic acid is methylated by farensoic acid methyl transferase, and then is epoxidized by a P dependent methyl transferas. A recent publication by Nouzova et al. This is a very logical control mechanism for JH biosynthesis. From Wikipedia, the free encyclopedia. See also: Bee learning and communication.
General considerations and premetamorphic actions". Advances in Insect Physiology. Roles of Juvenile Hormone in Adult Insects". Insect Hormones. Princeton: Princeton University Press. Angewandte Chemie International Edition. Bibcode : PNAS Bibcode : Sci Manville; T. Sahota April Canadian Journal of Chemistry. Identification of an allatostatin from the tobacco hornworm Manduca sexta. Biochemical and Biophysical Research Communications.
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Biol Cell — Google Scholar. A laboratory manual. Nature Lond — Google Scholar. Riski TM The circulatory system and associated cells and tissues. The early recognized prominent integrative role of JH in the morphological differentiation of the queen and worker caste and the paradigm of JH as a regulator of female fertility in insects in general has strongly influenced the direction of research activities on reproduction and division of labor in social insects, and particularly in honey bees. The reproductive physiology of adult honey bee queens differs from that of workers in two important respects, the rate and amount of vitellogenin synthesis and the production of queen pheromone.
Workers are thus principally capable of producing and laying eggs haploid eggs giving rise to males as well, but are repressed to do so in the presence of a dominant queen. The queen inhibits ovary activation and follicle development in workers by her pheromones principally E oxodecenoic acid. Under queenless conditions and in the absence of young larvae, however, egg laying by workers can frequently be observed. Indeed, JH plays only a very subtle role in the reproductive physiology of female honey bees, and it clearly does not stimulate vitellogenin synthesis. Rather it appears to serve as an integrative element in social behavior and colony function for review, see Ref.
Elevated JH levels are associated with periods of flight activity in queens and workers, and also in drones 50 , the only difference being that the flights of queens and drones occur early in adult life and are associated with mating activities, whereas flight activities in workers initiate much later and serve to collect nectar, pollen, and water. JH application or allatectomy affected the onset of flight activities, thus demonstrating a general requirement for JH in flight activities in all three honey bee morphs 51, In the case of workers, the onset of flight activity for foraging is controlled by age and colony conditions, and stands within the context of division of labor and age-dependent performance of different tasks age polyethism.
Recent studies have shown that the transition from intranidal activities to foraging is accompanied by a significant increase in CA activity, and that this modulation of CA activity depends on the age structure of a colony, i. Modulation of CA activity appears to require full physical contact and the possibility for exchange of age-characteristic signals in such worker-worker encounters This JH-mediated transition to foraging activity does not only involve behavioral changes, but rather has, once more, pleiotropic effects. It results in degeneration and functional changes in the larval food-producing hypopharyngeal glands, a decrease in vitellogenin synthesis, and in restructuring of the protocerebral mushroom bodies reviewed in Ref.
These latter changes are a prime example of JH-mediated neuronal plasticity occurring in concert with changes in behavior. The transition from a nurse bee to a forager, thus evidently involves structural changes as the bee expands its learning capacity When foraging, a bee has to know the location of the hive, learn the location of the food source, and has to communicate the latter via an elaborate dance language.
Behavioral integration of a honey bee colony does not only depend on encounters of workers of different age cohorts, but also involves genetic predisposition to certain tasks 56 and the signal of presence of a functional queen. As mentioned above, the queen suppresses worker fertility via a queen pheromone, but this queen pheromone is also a relevant indicator that colony reproduction is running at full speed. In this sense, the repressor action of queen pheromone components on CA activity in young bees can be interpreted as a regulator of colony demography guaranteeing an adequate cohort of nurse bees in colony reproduction.
This primer effect of queen pheromone on workers apparently delays their behavioral ontogeny without affecting typical behavioral responses of workers to queen pheromone, such as retinue formation Interestingly, biogenic amines appear to play a transmitter role in this context. These results are in accordance with the general view that external and colony conditions affect the levels of biogenic amines in the CNS of honey bee workers, and that these levels, in turn, may adjust task performance of individual workers by modulating their JH titers. It is interesting to note that in this highly social context, as exemplified by behavioral integration in a honey bee colony, JH has acquired two new functions.
Firstly, elevated JH titers have become associated with flight activity and JH has apparently lost its gonadotropic role. This represents a dissociation of the "oogenesis-flight syndrome" as described above. Secondly, JH has become a key element in social integration. I decided to describe the dissociation of JH from reproductive functions other than mating flights as a loss of function because in bumble bees and polistine wasps, JH still retains such a function. In contrast to the highly social species where reproductive dominance is by and large a matter of "chemical control", the hierarchies of reproductive dominance in colonies of primitively social species are strongly based on and established by aggressive behavioral interactions, especially oophagy.
In the subfamily Polistini, colonies are founded by single females which are soon joined by cofoundresses. Caste differences are virtually absent in the paper wasps genus Polistes of temperate climates. All females present in such incipient colonies are mated and capable of egg laying. A single female, however, will eventually become dominant and monopolize reproduction. She signals her status of dominance to subordinate females by antennal tapping, and whenever she encounters eggs laid by other females on the comb she removes them.
At the endocrine level, this hierarchy is reflected by elevated JH titers in the dominant females, and by low titers and low CA activity in the subordinate females for review, see Ref. High JH titers in these wasps are associated with activated ovaries and progressing oogenesis, and ovariectomy often leads to a reduction in JH titer and dominance status. Colony organization in the subtropical and tropical subfamilies Ropalidini and Polybiini is more complex. Incipient morphological caste characteristics have been postulated for Ropalidia marginata.
Hormonal control mechanisms, however, have not yet been investigated.
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The advanced social polybiines already exhibit a system of age polyethism in their large colonies. In Polybia occidentalis , this age polyethism could be accelerated by JH application with effects strongly reminiscent of JH effects in honey bees The interactions of JH titers, progressing follicle development, and reproductive dominance appear to have been extensively exploited in social evolution, as exemplified by the bumble bees.
The colony cycle in these predominantly temperate climate species initiates with colony foundation by a single queen. Once the first brood is reared and workers emerge, these aid the queen in the next brood cycles until the queen starts to lay haploid eggs giving rise to males switch point. Subsequently, queens are frequently challenged by workers over the production of unfertilized, male-producing eggs competition point , and soon afterwards the colonies disintegrate.
Thus, at the end of the colony cycle the dominant queen appears to lose her dominant status which she had previously maintained by dominant behavior and a pheromone, and some of the workers of an "elite" group become egg layers as well for review, see Ref. Egg laying and the establishment of dominance hierarchies are also observed under conditions of queen loss.
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Thus, in the bumble bees, oogenesis and egg laying have apparently become dissociated within the context of social organization. Follicle development initiates in ovaries of workers, both in the presence and absence of the queen, but in the presence of the queen and dominant workers, these follicles are resorbed in the subdominant workers. Follicle development in workers generally starts 5 days after emergence and may be observed during much of their life span, quite different from the narrow temporal window for egg development in honey bee workers.
Late stages of follicle development, however, were mainly observed in bumble bee workers belonging to the "elite" group after the competition point of the colony cycle. Ovary activation was also observed in experimental groups of queenless workers which were put together before their respective colonies had reached the competition point JH enters as a key player at several points in the regulation of dominance and egg development in bumble bees. JH titers were found to be high in egg-laying queens, and these high levels are considered to be required for vitellogenesis 61, Elevated CA activity and corresponding JH titers were also observed in queenless workers which exhibited significantly more advanced levels of oogenesis than queenright workers 63, Ovariectomy, however, did not affect CA activity in dominant workers, indicating that the dominance status, which appears to be established by aggressive interactions with fellow workers and possibly also by the production of a dominance-indicating pheromone in these workers at the competition point of the colony cycle, can be dissociated from their egg-laying capacity The existence of a worker-produced dominance pheromone was also hypothesized from analyses of JH synthesis in young workers introduced into queenless groups established from colonies before and after the competition point The role of JH in colony organization of the more primitively social bumble bees exhibits striking differences from the role it plays in the highly social honey bees: a JH is associated with dominance and reproduction vitellogenesis in the former but not the latter, b age polyethism and division of labor among workers is not affected by JH in bumble bees 65 , c foraging workers in bumble bee colonies have lower JH titers than workers that perform tasks within the nest, and d mating flight activity of virgin queens is not affected by JH in bumble bees An interesting parallel for JH function in primitively and highly social bees, though, becomes apparent when JH titers during the larval stages of prospective queens and workers are compared.
Even though bumble bees do not have morphologically but only physiologically differentiated castes, CA activity in penultimate-instar queen larvae of Bombus terrestris is much higher than that detected in prospective workers These incipient differences in levels of hormone synthesis, however, appear to be suppressed again during the prepupal phase 67 , and thus apparently do not permit the development of morphological caste differences.
From these observations we can propose a dichotomy for the role of JH in social organization of hymenopteran colonies. In the primitively social wasps and bumble bees, JH still exerts a gonadotropic function and, in addition, becomes associated with the dominance status of individual females. The dominance status evidently is still tightly connected with reproduction.
In the highly social honey bees, and possibly also in the stingless bees and in highly social wasps, the fixation of morphological caste differences has liberated JH from these functions.
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Egg production by queens in such colonies reaches levels far beyond the capacities of a bumble bee queen and requires very high and constant levels of vitellogenin synthesis by the fat body. This eliminates the need for cyclic regulation of oogenesis by JH, so that egg production can now also occur at low JH titers. Evidently, in at least some of the highly social Hymenoptera this "old" hormone has been coopted for a fundamentally new function, which can only become apparent in a highly social context, namely division of labor based on age polyethism.
In this context, JH even affects the organization of elementary brain structures. In highly social insects, the originally gonadotropic function of JH has thus been transformed into an integrator of colony function colony reproduction , whereas its metamorphic function has been preserved and even been expanded to generate polymorphic castes. This metamorphic function of JH has reached its summit in the ants, where JH orchestrates not only the differentiation of the queen and worker castes, but also guides the formation of morphologically distinct worker morphs.
This role of JH has been investigated in detail in the genus Pheidole where production of the strongly dimorphic soldiers and workers depends on differences in JH levels during the late larval stages, whereas the queen-worker decision is made much earlier in larval development Developmental rules underlying the production of these secondary castes have been outlined as JH-mediated modulation of allometric growth parameters in the different imaginal discs Only few ant species have been studied with regard to a putative gonadotropic role of JH, and rather equivocal results were obtained.
Whereas JH treatment stimulates shedding of the wings and oogenesis in newly emerged virgin queens of the fire ant, Solenopsis invicta 70 , JH titers in reproductives of the ponerine ant Diacamma sp were consistently low In Diacamma , JH titers were found to be positively correlated with worker age, suggesting a role for JH in division of labor, much like the picture emerging in the honey bee.
The evolution of insect polymorphisms, including the complex caste systems of social insects, has been reviewed under premises of phenotypic plasticity 23, The driving forces towards sociality in the Hymenoptera appear to have been a the haplodiploid system of sex determination generating asymmetries in the relatedness among offspring, and b the tendency of females to return and reuse the parental nest.
The subsequent chain of effects probably did not require genetic change. It included the formation of groups, establishment of reproductive dominance by aggressive interactions between nestmates, and care for larvae by non-ovipositing females. All these traits can be seen as derived from species that do not nest socially and are interpretable as behavioral trait amplification.
Adaptive phenotypes could then have originated by minor genetic changes via correlated shifts in the expression of phenotypically plastic traits. The pleiotropic functions of JH in insect development and reproductive physiology in general made this hormone system an ideal integrator for caste development and social organization. During social evolution, the gonadotropic role of JH has apparently suffered a striking transformation from its original function in egg production and dominance rank to a behavioral pacemaker in division of labor among workers Methylfarnesoate derivatives made their appearance in arthropod evolution as "supporting actors" in the ecdysteroid-regulated molting process.
In the larval and pupal stages of insect life cycles, JH is now known to modify the expression patterns of ecdysteroid-regulated genes, creating the possibility for an insect to express different types of cuticles, and in particular to develop from a larval form to an adult form through a complex metamorphosis. Complete metamorphosis, as observed in the holometabolous insects, is the key to the intraspecific separation of ecological niches occupied by larvae and adults, and undoubtedly has played a major role in the tremendous ecological and evolutionary radiation of holometabolous insects.
The multiple functions of JH during preimaginal development may have been a preadaptation for its implication in the regulation of reproductive processes, where the primary functions appear to have been the synchronization of vitellogenin synthesis by the fat body and vitellogenin uptake by developing oocytes during distinct reproductive cycles. Diversification of life and reproductive cycles, together with the necessity to avoid conditions unfavorable for reproduction, have added ever more facets to JH function.
One of the most intriguing new facets is the recent discovery that sex peptides produced by the male accessory glands cause a complex behavioral switch in mated females, from mate-seeking to mate-rejection and oviposition behavior. A synthetic Drosophila sex peptide has now been shown to modulate JH biosynthesis levels in the CA of different insect species. Life cycle complexity in insects is further increased in species exhibiting facultative polymorphism, such as wing dimorphism in crickets, phase polymorphism in desert locusts and aphids, and the castes of social insects.
In social evolution, JH seems to have first been implicated in the coupling of oogenesis to status in a dominance hierarchy. This is a reflection of the early steps of socioevolution where colonies are established by the joining of sisters or unrelated females. All of these females are mated and thus can function as potential egg layers, but in general one of these will effectively monopolize reproduction and suppress oviposition by the others, mainly by antagonistic behavior.
In these primitively social insects, high JH titers generally exhibit a high correlation with dominance status and follicle development in the ovaries. In the populous colonies of highly social insects, one or more reproductively dominant females reign by means of pheromones. These elicit behavioral responses in the workers, guaranteeing colony cohesion and suppressing follicle development in the ovaries of workers.
JH is involved in several aspects of the life cycle in such highly social species, and its multiple roles are currently best understood in the honey bee. First of all, JH titers exhibit caste-specific modulation during critical developmental periods in the larval instars. These titer differences eventually lead to the expression of different alternative developmental programs in the ovaries and in other target tissues.
JH has thus gained a key function in the generation of polymorphic castes. Secondly, JH has lost its association with oogenesis, and thus, could be coopted into other functions in adult bees. It now coordinates mating flight activities in newly emerged queens and drones, and serves as a behavioral pacemaker in workers. This latter function represents a new and fascinating facet in JH pleiotropy which allows to integrate colony demography and colony needs with the age-related performance of specific tasks by each individual worker bee.
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