RESUMO
Juvenile hormone (JH) controls key events in the honey bee life cycle, viz. caste development and age polyethism. We quantified transcript abundance of 24 genes involved in the JH biosynthetic pathway in the corpora allata-corpora cardiaca (CA-CC) complex. The expression of six of these genes showing relatively high transcript abundance was contrasted with CA size, hemolymph JH titer, as well as JH degradation rates and JH esterase (jhe) transcript levels. Gene expression did not match the contrasting JH titers in queen and worker fourth instar larvae, but jhe transcript abundance and JH degradation rates were significantly lower in queen larvae. Consequently, transcriptional control of JHE is of importance in regulating larval JH titers and caste development. In contrast, the same analyses applied to adult worker bees allowed us inferring that the high JH levels in foragers are due to increased JH synthesis. Upon RNAi-mediated silencing of the methyl farnesoate epoxidase gene (mfe) encoding the enzyme that catalyzes methyl farnesoate-to-JH conversion, the JH titer was decreased, thus corroborating that JH titer regulation in adult honey bees depends on this final JH biosynthesis step. The molecular pathway differences underlying JH titer regulation in larval caste development versus adult age polyethism lead us to propose that mfe and jhe genes be assayed when addressing questions on the role(s) of JH in social evolution.
Assuntos
Abelhas/genética , Corpora Allata/metabolismo , Hormônios Juvenis/biossíntese , Larva/genética , RNA Mensageiro/metabolismo , Animais , Abelhas/crescimento & desenvolvimento , Abelhas/metabolismo , Hidrolases de Éster Carboxílico/genética , Hidrolases de Éster Carboxílico/metabolismo , Corpora Allata/crescimento & desenvolvimento , Ácidos Graxos Insaturados/metabolismo , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Hemolinfa/química , Hormônios Juvenis/genética , Larva/crescimento & desenvolvimento , Larva/metabolismo , Oxigenases/antagonistas & inibidores , Oxigenases/genética , Oxigenases/metabolismo , RNA Mensageiro/genética , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Transcrição GênicaRESUMO
Juvenile hormones (JHs) play key roles in regulating metamorphosis and reproduction in insects. The last two steps of JH synthesis diverge depending on the insect order. In Lepidoptera, epoxidation by a P450 monooxygenase precedes esterification by a juvenile hormone acid methyltransferase (JHAMT). In Orthoptera, Dictyoptera, Coleoptera and Diptera epoxidation follows methylation. The aim of our study was to gain insight into the structural basis of JHAMT's substrate recognition as a means to understand the divergence of these pathways. Homology modeling was used to build the structure of Aedes aegypti JHAMT. The substrate binding site was identified, as well as the residues that interact with the methyl donor (S-adenosylmethionine) and the carboxylic acid of the substrate methyl acceptors, farnesoic acid (FA) and juvenile hormone acid (JHA). To gain further insight we generated the structures of Anopheles gambiae, Bombyx mori, Drosophila melanogaster and Tribolium castaneum JHAMTs. The modeling results were compared with previous experimental studies using recombinant proteins, whole insects, corpora allata or tissue extracts. The computational study helps explain the selectivity toward the (10R)-JHA isomer and the reduced activity for palmitic and lauric acids. The analysis of our results supports the hypothesis that all insect JHAMTs are able to recognize both FA and JHA as substrates. Therefore, the order of the methylation/epoxidation reactions may be primarily imposed by the epoxidase's substrate specificity. In Lepidoptera, epoxidase might have higher affinity than JHAMT for FA, so epoxidation precedes methylation, while in most other insects there is no epoxidation of FA, but esterification of FA to form MF, followed by epoxidation to JH III.
Assuntos
Aedes/enzimologia , Proteínas de Insetos/química , Proteínas de Insetos/metabolismo , Hormônios Juvenis/biossíntese , Metiltransferases/química , Metiltransferases/metabolismo , Aedes/química , Aedes/genética , Aedes/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Ácidos Graxos Insaturados/metabolismo , Proteínas de Insetos/genética , Insetos/química , Insetos/enzimologia , Insetos/genética , Isomerismo , Hormônios Juvenis/química , Metiltransferases/genética , Modelos Moleculares , Dados de Sequência Molecular , Processamento de Proteína Pós-Traducional , Alinhamento de Sequência , Especificidade por SubstratoRESUMO
We investigated the relationship among nutritional reserves, previtellogenic ovary development and juvenile hormone (JH) synthesis in Aedes aegypti female mosquitoes. By raising larvae under different nutritional regimes, two adult phenotypes (large and small females) were generated, which differed significantly in size at eclosion (measured by wing length). We measured the total amount of protein, lipids and glycogen in newly emerged (teneral) large and small females. Teneral reserves were significantly lower in small females. Maximum previtellogenic ovary development occurred only if enough teneral nutrients were present. Maximum previtellogenic ovary development was stimulated in small females with low teneral nutrients by topically applying a JH analog. The biosynthetic activity of Ae. aegypti corpora allata (CA) was studied in vitro using a radiochemical method. JH synthesis was significantly reduced in females emerged with low teneral reserves and stimulated by sugar feeding. These results establish that the CA synthesizes enough JH to activate ovary maturation only in the presence of large nutrient reserves.
Assuntos
Aedes/crescimento & desenvolvimento , Fenômenos Fisiológicos da Nutrição Animal , Hormônios Juvenis/biossíntese , Ovário/crescimento & desenvolvimento , Fenótipo , Aedes/metabolismo , Análise de Variância , Animais , Pesos e Medidas Corporais , Corpora Allata/metabolismo , Feminino , Glicogênio/metabolismo , Metabolismo dos Lipídeos , Proteínas/metabolismo , RadioquímicaRESUMO
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 wing-dimorphic 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.
Assuntos
Insetos/fisiologia , Hormônios Juvenis/fisiologia , Animais , Abelhas/fisiologia , Comportamento Animal/fisiologia , Feminino , Insetos/genética , Hormônios Juvenis/biossíntese , Hormônios Juvenis/química , Masculino , Metamorfose Biológica/fisiologia , Polimorfismo Genético , Reprodução , Caracteres SexuaisRESUMO
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 wing-dimorphic 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