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Takahiro Shiotsuki - One of the best experts on this subject based on the ideXlab platform.

  • RNAi-mediated knockdown of SPOOK reduces ecdysteroid titers and causes Precocious Metamorphosis in the desert locust Schistocerca gregaria
    Developmental biology, 2017
    Co-Authors: Ryohei Sugahara, Seiji Tanaka, Takahiro Shiotsuki
    Abstract:

    The Halloween gene SPOOK (SPO) is involved in the production of the active metabolite of ecdysteroid, 20-hydroxyecdysone (20E), in insects. A previous study showed that RNAi-mediated knockdown of SPO in Schistocerca gregaria last instar nymphs markedly reduced the hemolymph 20E titer, but did not affect Metamorphosis. In the present study, the effects of SPO interference on development were re-examined in this locust. Injections of SPO double-stranded RNA (dsSPO) into nymphs at mid and late instars significantly delayed nymphal development and interfered with molting. The 20E levels of dsSPO-treated nymphs were generally low, with a delayed, small peak, suggesting that disturbance of the 20E levels caused the above developmental abnormalities. A small proportion of the dsSPO-injected nymphs metamorphosed Precociously, producing adults and adultoids. Precocious adults were characterized by small body size, short wings with abbreviated venation, and normal reproductive activity. Fourth instar nymphs that Precociously metamorphosed at the following instar exhibited temporal expression patterns of ecdysone-induced protein 93F and the juvenile hormone (JH) early-inducible gene Kruppel homolog 1 similar to those observed at the last instar in normal nymphs. Adultoids displayed mating behavior and adultoid females developed eggs, but never laid eggs. JH injection around the expected time of the 20E peak in the dsSPO-injected nymphs completely inhibited the appearance of adultoids, suggesting that appearance of adultoids might be due to a reduced titer of JH rather than of 20E. These results suggest that SPO plays an important role in controlling morphogenesis, Metamorphosis, and reproduction in S. gregaria.

  • the foxo transcription factor controls insect growth and development by regulating juvenile hormone degradation in the silkworm bombyx mori
    Journal of Biological Chemistry, 2017
    Co-Authors: Baosheng Zeng, Takahiro Shiotsuki, Yuping Huang, Hua Bai, Subba Reddy Palli, Yongping Huang, Anjiang Tan
    Abstract:

    Forkhead box O (FOXO) functions as the terminal transcription factor of the insulin signaling pathway and regulates multiple physiological processes in many organisms, including lifespan in insects. However, how FOXO interacts with hormone signaling to modulate insect growth and development is largely unknown. Here, using the transgene-based CRISPR/Cas9 system, we generated and characterized mutants of the silkworm Bombyx mori FOXO (BmFOXO) to elucidate its physiological functions during development of this lepidopteran insect. The BmFOXO mutant (FOXO-M) exhibited growth delays from the first larval stage and showed Precocious Metamorphosis, pupating at the end of the fourth instar (trimolter) rather than at the end of the fifth instar as in the wild-type (WT) animals. However, different from previous reports on Precocious Metamorphosis caused by juvenile hormone (JH) deficiency in silkworm mutants, the total developmental time of the larval period in the FOXO-M was comparable with that of the WT. Exogenous application of 20-hydroxyecdysone (20E) or of the JH analog rescued the trimolter phenotype. RNA-seq and gene expression analyses indicated that genes involved in JH degradation but not in JH biosynthesis were up-regulated in the FOXO-M compared with the WT animals. Moreover, we identified several FOXO-binding sites in the promoter of genes coding for JH-degradation enzymes. These results suggest that FOXO regulates JH degradation rather than its biosynthesis, which further modulates hormone homeostasis to control growth and development in B. mori In conclusion, we have uncovered a pivotal role for FOXO in regulating JH signaling to control insect development.

  • Synthesis and anti-juvenile hormone activity of ethyl 4-[(6-substituted 2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoates
    Journal of Pesticide Science, 2010
    Co-Authors: Kenjiro Furuta, Norihiro Fujita, Naotaka Yamada, Takahiro Shiotsuki, Tsubasa Ibushi, Eiichi Kuwano
    Abstract:

    Ethyl 4-[(6-substituted 2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoates and their analogues were prepared and the biological activities were evaluated for both anti-juvenile hormone (anti-JH) and JH activity in silkworm larvae, Bombyx mori. Of the compounds tested, ethyl 4-[(6-methoxy-2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoate (3b) showed the most effective Precocious Metamorphosis-inducing activity in 3rd instar larvae and JH activity in allatectomized 4th instar larvae. Furthermore, JH I and 20-hydroxyecdysone (20-E) titers in hemolymph of 3rd instar larvae treated with 3b were measured by liquid chromatography-mass spectrometry (LC-MS) and LC-MS/MS, respectively. The results revealed that compound 3b induced Precocious Metamorphosis by specifically decreasing JH I in hemolymph.

  • juvenile hormone activity of optically active ethyl 4 2 benzylalkyloxy benzoates inducing Precocious Metamorphosis
    Journal of Pesticide Science, 2008
    Co-Authors: Norihiro Fujita, Kiyo Ashibe, Naotaka Yamada, Takahiro Shiotsuki, Makoto Kiuchi, Kenjiro Furuta, Shuhei Yoshida, Eiichi Kuwano
    Abstract:

    A series of ethyl 4-(2-benzylalkyloxy)benzoates possessing Precocious Metamorphosis-inducing activity showed juvenile hormone (JH) activity when topically applied to allatectomized 4th instar larvae of Bombyx mori. Hexyl (KF-13) and heptyl analogs, which induced Precocious Metamorphosis at low doses, had relatively high JH activity. In both compounds, (S)-enantiomers were more active than (R)-enantiomers. A correlation was observed between JH activity and anti-JH activity in the ethyl 4-(2-benzylalkyloxy)benzoate series. Replacement of the 4-ethoxycarbonyl group with a 4-ethyl or 3,4-methylenedioxy group in KF-13 eliminated both JH and anti-JH activity. © Pesticide Science Society of Japan

  • Juvenile hormone activity of ethyl 4-(2-aryloxyhexyloxy)benzoates with Precocious Metamorphosis-inducing activity
    Bioscience biotechnology and biochemistry, 2007
    Co-Authors: Norihiro Fujita, Kiyo Ashibe, Naotaka Yamada, Takahiro Shiotsuki, Makoto Kiuchi, Eiichi Kuwano
    Abstract:

    Ethyl 4-[2-(6-methyl-3-pyridyloxy)hexyloxy]benzoate (1) and ethyl 4-(2-phenoxyhexyloxy)benzoate (2), which induce Precocious Metamorphosis in larvae of Bombyx mori, a clear sign of juvenile hormone (JH) deficiency, showed JH activity when topically applied to allatectomized 4th instar larvae of B. mori. Compounds 1 and 2 induced Precocious Metamorphosis with doses at which they were effective as JH agonists.

Eiichi Kuwano - One of the best experts on this subject based on the ideXlab platform.

  • An anti-juvenile hormone agent, ethyl 4-(2-benzylhexyloxy)benzoate, inhibits juvenile hormone synthesis through the suppression of the transcription of juvenile hormone biosynthetic enzymes in the corpora allata in Bombyx mori.
    Insect biochemistry and molecular biology, 2011
    Co-Authors: Yu Kaneko, Eiichi Kuwano, Kenjiro Furuta, Kiyoshi Hiruma
    Abstract:

    Ethyl 4-[(S)-2-benzylhexyloxy)]benzoate (KF-13S), derived from ethyl 4-[2-(tert-butylcarbonyloxy)butoxy]benzoate (ETB), has strong anti-juvenile hormone (JH) activity which causes Precocious Metamorphosis in Bombyx mori, and the mode of action of this compound was studied. Application of KF-13S inhibited JH biosynthesis by the corpora allata (CA) in a reversible manner, and in vitro culture experiments showed that this inhibition was due to the direct action of this compound on the CA. When mRNA expression of the JH biosynthetic enzymes were studied, KF-13S strongly suppressed those of HMG Co-A synthase and HMG Co-A reductase. mRNA levels of other mevalonate enzymes and JH acid O-methyltransferase were also suppressed but were less sensitive to the compound. These studies showed that KF-13S prevents the transcription of many of the JH biosynthetic enzymes so that JH synthesis is suppressed.

  • Synthesis and anti-juvenile hormone activity of ethyl 4-[(6-substituted 2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoates
    Journal of Pesticide Science, 2010
    Co-Authors: Kenjiro Furuta, Norihiro Fujita, Naotaka Yamada, Takahiro Shiotsuki, Tsubasa Ibushi, Eiichi Kuwano
    Abstract:

    Ethyl 4-[(6-substituted 2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoates and their analogues were prepared and the biological activities were evaluated for both anti-juvenile hormone (anti-JH) and JH activity in silkworm larvae, Bombyx mori. Of the compounds tested, ethyl 4-[(6-methoxy-2,2-dimethyl-2H-chromen-7-yl)methoxy]benzoate (3b) showed the most effective Precocious Metamorphosis-inducing activity in 3rd instar larvae and JH activity in allatectomized 4th instar larvae. Furthermore, JH I and 20-hydroxyecdysone (20-E) titers in hemolymph of 3rd instar larvae treated with 3b were measured by liquid chromatography-mass spectrometry (LC-MS) and LC-MS/MS, respectively. The results revealed that compound 3b induced Precocious Metamorphosis by specifically decreasing JH I in hemolymph.

  • Synthesis and structure-activity relationship of a new series of anti-juvenile hormone agents: Alkyl 4-(2-Benzylhexyloxy)benzoates and ethyl 4-substituted benzoates
    Journal of The Faculty of Agriculture Kyushu University, 2009
    Co-Authors: Shuhei Yoshida, Norihiro Fujita, Kiyo Ashibe, Naotaka Yamada, Kenjiro Furuta, Hiromitsu Shirahashi, Eiichi Kuwano
    Abstract:

    A series of alkyl 4-(2-benzylhexyloxy)benzoates and related compounds were synthesized and investi- gated for their ability to induce Precocious Metamorphosis in larvae of Bombyx mori, a clear sign of JH deficiency in the hemolymph of early larval stages. In the alkyl 4-(2-benzylhexyloxy)benzoate series, the methyl and ethyl (KF-13) esters induced Precocious Metamorphosis at relatively low doses. Replacement of the ester group with an amide, alcohol, oxime, ethyl or 3,4-methylenedioxy group eliminated the activity, indicating that the ester group on the benzene ring is essential for activity. A modification was made between the two benzene rings in KF-13. None of the compounds showed higher activity than KF-13 at low doses. The JH activity of synthesized compounds was assayed using allatectomized 4th instar larvae of B. mori. The aniline analog, which showed stronger Precocious Metamorphosis-inducing activity than KF-13 at higher doses, had obvious JH activity. The n-propyl ester possessing moderate Precocious metamorpho- sis-inducing activity did not show any JH activity. There was some correlation between the ability of com- pounds to cause Precocious Metamorphosis and their JH activity.

  • Ethyl 4-[2-(substituted benzyl)hexyloxy]benzoates: Anti-juvenile hormone agents with juvenile hormone activity
    Journal of The Faculty of Agriculture Kyushu University, 2009
    Co-Authors: Shuhei Yoshida, Norihiro Fujita, Kiyo Ashibe, Naotaka Yamada, Kenjiro Furuta, Seiji Nishikawa, Eiichi Kuwano
    Abstract:

    A large number of ethyl (2-(substituted benzyl)hexyloxy)benzoates and related compounds were pre- pared and their activity to induce Precocious Metamorphosis was evaluated in larvae of Bombyx mori, which was obviously recognized as a juvenile hormone (JH)-deficiency symptom. Introduction of a methyl, chloro or fluoro substituent at the 2-position on the benzene ring increased the activity in comparison with that of ethyl (2-benzylhexyloxy)benzoate (KF-13) in a dose range of 1-40 μg, however, no consistent dose-response relationship was obtained in these compounds as well as KF-13. The 4-methoxybenzyl analog showed strong Precocious Metamorphosis-inducing activity at both low and high doses, while introduction of other substituents such as a methyl, chloro, fluoro or ethyl group at the 3- and 4-position on the benzene ring decreased the activity at low doses. The JH activity of synthesized compounds was examined by bioassay using allatectomized 4th instar larvae. In the ethyl (2-(substituted benzyl)hexyloxy)benzoate series, a cor- relation was observed between JH activity and anti-JH activity; Compounds which induced high percent- ages of Precocious Metamorphosis at lower doses had obvious JH activity. Compounds possessing weak Precocious Metamorphosis-inducing activity showed little JH activity.

  • Ethyl 4-[(1-substituted indol-2-yl)methoxy]benzoates and indoline derivatives: Anti-juvenile hormone and juvenile hormone activities
    Journal of Pesticide Science, 2009
    Co-Authors: Kenjiro Furuta, Norihiro Fujita, Naotaka Yamada, Shuhei Yoshida, Eiichi Kuwano
    Abstract:

    A number of ethyl 4-[(1-substituted indol-2-yl)methoxy]benzoates and indoline derivatives were prepared as rigid congeners of ethyl 4-(2-benzylhexyloxy)benzoate (KF-13), an anti-juvenile hormone (anti-JH) agent, and tested for both anti-JH and JH activities in silkworm larvae. In contrast to KF-13, the Precocious Metamorphosis-inducing activity of which decreased by increasing the applied doses, 1-n-propyl, 1-n-butyl (1c) and 1-benzyl (1d) derivatives were found to induce higher percentages of Precocious Metamorphosis at high doses. Compounds 1c and 1d also exhibited JH activity when topically applied to allatectomized 4th instar larvae. Ethyl 4-[(S)-(1-n-butylindolin-2-yl)methoxy]benzoate, which showed Precocious Metamorphosis-inducing activity at high doses, had no JH activity.

Kenjiro Furuta - One of the best experts on this subject based on the ideXlab platform.

  • Precocious Metamorphosis in the juvenile hormone deficient mutant of the silkworm bombyx mori
    PLOS Genetics, 2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, Precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and Metamorphosis.

  • Precocious Metamorphosis in the Juvenile Hormone–Deficient Mutant of the Silkworm, Bombyx mori
    PLoS genetics, 2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, Precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and Metamorphosis.

  • Precocious Metamorphosis in the juvenile hormone-deficient mutant of the silkworm, Bombyx mori. PLoS Genet 8: e1002486. doi: 10
    2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura, Kazuei Mita
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several ‘‘moltinism’ ’ mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for th

  • A model for JH biosynthetic pathway in the CA of wt and mod silkworms.
    2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    (A) In the B. mori CA, constitutive CYP15C1 expression allows the consistent conversion of homo-FAs to JHAs (predominantly JHA I and II in Lepidoptera). When JHAMT is expressed in CA, JHAs are further converted to JHs, and released from CA, thereby preventing Precocious Metamorphosis. When JHAMT expression is shut off (e.g., in the prepupal stage), JHAs are likely to be released from CA. (B) In CA of the mod strain, homo-FAs are not converted to JHAs because of the loss of CYP15C1, but instead, homo-FAs are converted to ethyl-branched homologs of MF (homo-MFs, i.e., unepoxidized JH I and II) by JHAMT. The loss of CYP15C1 does not allow the conversion of homo-MFs to the authentic JHs. Therefore, neither JHs is synthesized in nor released from CA of the mod strain, thereby causing Precocious Metamorphosis. The synthesized homo-MFs might be released from CA of the mod strain, similar to that of higher dipteran insects [57]. JH I: R1 = R2 = C2H5, JH II: R1 = C2H5, R2 = CH3.

  • Characterization of the mod mutant.
    2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    (A) Precocious Metamorphosis observed in mod larvae. (left panel) Lateral and dorsal views and (middle panel) a magnified view of a larval-pupal intermediate. In intermediate animals, the new head capsule of the next instar (fifth) is formed (arrowhead). Beneath the old cuticles (asterisk), a new exoskeleton with larval eye spot markings (arrows) and brown-colored pupal cuticles are formed. (Right panel) Late-maturing trimolters form small cocoons and are able to develop into small but normal adults with normal fertility. (B) The developmental profiles of two batches of mod larvae (t011 strain). All of the larvae underwent Precocious Metamorphosis in the fourth instar, and no dimolters or tetramolters were observed. Larvae could be classified into two groups (early- and late-maturing trimolters) on the basis of the timing of onset of spinning. The numbers in parentheses indicate the sex of the moths (male/female). (C) Timing of the onset of spinning in mod (red, n = 178) and p50T (black, n = 28) strains after final larval molting. As highlighted by the grey ellipses, spinning was induced at two distinct timings in the mod strain, unlike the p50T strain. (D) Comparison of timings of the onset of spinning among early- and late-maturing trimolters of the mod strain and normal strain larvae that had been allatectomized (CAX) at the beginning of the fourth instar. Data on CAX larvae are from [17]; these larvae were reared at relatively low temperatures (23.0–25.5°C), which delays the timing of the onset of spinning to some extent. (E) Methoprene treatment of mod larvae. Selected doses of methoprene (0.01–10 µg/larva) were topically applied to newly molted third and fourth instar larvae (8–12 h after molting). As highlighted in blue, Precocious pupation could be blocked by methoprene treatment. (F) Measurement of the JH titer in the hemolymph of third instar larvae of p50T and mod strains at 24 h after molting. Hemolymph was collected from ∼400 larvae using a microsyringe and the pooled sample was analyzed. JH in the hemolymph was converted to its corresponding methoxyhydrin derivatives and analyzed by GC-MS. JHs were not detected (ND) in the hemolymph of mod larvae.

Tetsuro Shinoda - One of the best experts on this subject based on the ideXlab platform.

  • Knockout silkworms reveal a dispensable role for juvenile hormones in holometabolous life cycle.
    Proceedings of the National Academy of Sciences of the United States of America, 2015
    Co-Authors: Takaaki Daimon, Miwa Uchibori, Hajime Nakao, Hideki Sezutsu, Tetsuro Shinoda
    Abstract:

    Insect juvenile hormones (JHs) prevent Precocious Metamorphosis and allow larvae to undergo multiple rounds of status quo molts. However, the roles of JHs during the embryonic and very early larval stages have not been fully understood. We generated and characterized knockout silkworms (Bombyx mori) with null mutations in JH biosynthesis or JH receptor genes using genome-editing tools. We found that embryonic growth and morphogenesis are largely independent of JHs in Bombyx and that, even in the absence of JHs or JH signaling, pupal characters are not formed in first- or second-instar larvae, and Precocious Metamorphosis is induced after the second instar at the earliest. We also show by mosaic analysis that a pupal specifier gene broad, which is dramatically up-regulated in the late stage of the last larval instar, is essential for pupal commitment in the epidermis. Importantly, the mRNA expression level of broad, which is thought to be repressed by JHs, remained at very low basal levels during the early larval instars of JH-deficient or JH signaling-deficient knockouts. Therefore, our study suggests that the long-accepted paradigm that JHs maintain the juvenile status throughout larval life should be revised because the larval status can be maintained by a JH-independent mechanism in very early larval instars. We propose that the lack of competence for Metamorphosis during the early larval stages may result from the absence of an unidentified broad-inducing factor, i.e., a competence factor.

  • Importance of juvenile hormone signaling arises with competence of insect larvae to metamorphose.
    Developmental biology, 2014
    Co-Authors: Vlastimil Smykal, Takaaki Daimon, Takumi Kayukawa, Keiko Takaki, Tetsuro Shinoda, Marek Jindra
    Abstract:

    Juvenile hormone (JH) postpones Metamorphosis of insect larvae until they have attained an appropriate stage and size. Then, during the final larval instar, a drop in JH secretion permits a metamorphic molt that transforms larvae to adults either directly (hemimetaboly) or via a pupal stage (holometaboly). In both scenarios, JH precludes Metamorphosis by activating the Kr-h1 gene through a JH receptor, Methoprene-tolerant (Met). Removal of Met, Kr-h1, or JH itself triggers deleterious Precocious Metamorphosis. Although JH is thought to maintain the juvenile status throughout larval life, various methods of depleting JH failed to induce Metamorphosis in early-instar larvae. To determine when does JH signaling become important for the prevention of Precocious Metamorphosis, we chose the hemimetabolous bug, Pyrrhocoris apterus, and the holometabolous silkworm, Bombyx mori. Both species undergo a fixed number of five larval instars. Pyrrhocoris larvae subjected to RNAi-mediated knockdown of Met or Kr-h1 underwent Precocious adult development when treated during the fourth (penultimate) instar, but younger larvae proved increasingly resistant to loss of either gene. The earliest instar developing minor signs of Precocious Metamorphosis was the third. Therefore, the JH-response genes may not be required to maintain the larval program during the first two larval instars. Next, we examined Bombyx mod mutants that cannot synthesize authentic, epoxidized forms of JH. Although mod larvae expressed Kr-h1 mRNA at severely reduced levels since hatching, they only entered Metamorphosis by pupating after four, rarely three instars. Based on findings in Pyrrhocoris and Bombyx, we propose that insect postembryonic development is initially independent of JH. Only later, when larvae gain competence to enter Metamorphosis, JH signaling becomes necessary to prevent Precocious Metamorphosis and to optimize growth.

  • rnai mediated knockdown of juvenile hormone acid o methyltransferase gene causes Precocious Metamorphosis in the red flour beetle tribolium castaneum
    FEBS Journal, 2008
    Co-Authors: Chieka Minakuchi, Toshiki Namiki, Michiyo Yoshiyama, Tetsuro Shinoda
    Abstract:

    Juvenile hormone controls the timing of insect Metamorphosis. As a final step of juvenile hormone biosynthesis, juvenile hormone acid O-methyltransferase (JHAMT) transfers the methyl group from S-adenosyl-l-methionine to the carboxyl group of farnesoic acid and juvenile hormone acid. The developmental expression profiles of JHAMT mRNA in the silkworm Bombyx mori and the fruitfly Drosophila melanogaster suggest that the suppression of JHAMT transcription is critical for the induction of larval–pupal Metamorphosis, but genetic evidence for JHAMT function in vivo is missing. In this study, we identified three methyltransferase genes in the red flour beetle Tribolium castaneum (TcMT1, TcMT2 and TcMT3) that are homologous to JHAMT of Bombyx and Drosophila. Of these three methyltransferase genes, TcMT3 mRNA was present continuously from the embryonic stage to the final larval instar, became undetectable before pupation, and increased again in the adult stage. TcMT3 mRNA was localized in the larval corpora allata. Recombinant TcMT3 protein methylated farnesoic acid and juvenile hormone III acid, but TcMT1 and TcMT2 proteins did not. Furthermore, RNA interference-mediated knockdown of TcMT3 in the larval stage resulted in Precocious larval–pupal Metamorphosis, whereas knockdown of either TcMT1 or TcMT2 showed no visible effects on Metamorphosis. Importantly, Precocious Metamorphosis caused by TcMT3 RNA interference was rescued by an application of a juvenile hormone mimic, methoprene. Together, these results demonstrate that TcMT3 encodes a functional JHAMT gene that is essential for juvenile hormone biosynthesis and for the maintenance of larval status.

Takaaki Daimon - One of the best experts on this subject based on the ideXlab platform.

  • Knockout silkworms reveal a dispensable role for juvenile hormones in holometabolous life cycle.
    Proceedings of the National Academy of Sciences of the United States of America, 2015
    Co-Authors: Takaaki Daimon, Miwa Uchibori, Hajime Nakao, Hideki Sezutsu, Tetsuro Shinoda
    Abstract:

    Insect juvenile hormones (JHs) prevent Precocious Metamorphosis and allow larvae to undergo multiple rounds of status quo molts. However, the roles of JHs during the embryonic and very early larval stages have not been fully understood. We generated and characterized knockout silkworms (Bombyx mori) with null mutations in JH biosynthesis or JH receptor genes using genome-editing tools. We found that embryonic growth and morphogenesis are largely independent of JHs in Bombyx and that, even in the absence of JHs or JH signaling, pupal characters are not formed in first- or second-instar larvae, and Precocious Metamorphosis is induced after the second instar at the earliest. We also show by mosaic analysis that a pupal specifier gene broad, which is dramatically up-regulated in the late stage of the last larval instar, is essential for pupal commitment in the epidermis. Importantly, the mRNA expression level of broad, which is thought to be repressed by JHs, remained at very low basal levels during the early larval instars of JH-deficient or JH signaling-deficient knockouts. Therefore, our study suggests that the long-accepted paradigm that JHs maintain the juvenile status throughout larval life should be revised because the larval status can be maintained by a JH-independent mechanism in very early larval instars. We propose that the lack of competence for Metamorphosis during the early larval stages may result from the absence of an unidentified broad-inducing factor, i.e., a competence factor.

  • Importance of juvenile hormone signaling arises with competence of insect larvae to metamorphose.
    Developmental biology, 2014
    Co-Authors: Vlastimil Smykal, Takaaki Daimon, Takumi Kayukawa, Keiko Takaki, Tetsuro Shinoda, Marek Jindra
    Abstract:

    Juvenile hormone (JH) postpones Metamorphosis of insect larvae until they have attained an appropriate stage and size. Then, during the final larval instar, a drop in JH secretion permits a metamorphic molt that transforms larvae to adults either directly (hemimetaboly) or via a pupal stage (holometaboly). In both scenarios, JH precludes Metamorphosis by activating the Kr-h1 gene through a JH receptor, Methoprene-tolerant (Met). Removal of Met, Kr-h1, or JH itself triggers deleterious Precocious Metamorphosis. Although JH is thought to maintain the juvenile status throughout larval life, various methods of depleting JH failed to induce Metamorphosis in early-instar larvae. To determine when does JH signaling become important for the prevention of Precocious Metamorphosis, we chose the hemimetabolous bug, Pyrrhocoris apterus, and the holometabolous silkworm, Bombyx mori. Both species undergo a fixed number of five larval instars. Pyrrhocoris larvae subjected to RNAi-mediated knockdown of Met or Kr-h1 underwent Precocious adult development when treated during the fourth (penultimate) instar, but younger larvae proved increasingly resistant to loss of either gene. The earliest instar developing minor signs of Precocious Metamorphosis was the third. Therefore, the JH-response genes may not be required to maintain the larval program during the first two larval instars. Next, we examined Bombyx mod mutants that cannot synthesize authentic, epoxidized forms of JH. Although mod larvae expressed Kr-h1 mRNA at severely reduced levels since hatching, they only entered Metamorphosis by pupating after four, rarely three instars. Based on findings in Pyrrhocoris and Bombyx, we propose that insect postembryonic development is initially independent of JH. Only later, when larvae gain competence to enter Metamorphosis, JH signaling becomes necessary to prevent Precocious Metamorphosis and to optimize growth.

  • Precocious Metamorphosis in the juvenile hormone deficient mutant of the silkworm bombyx mori
    PLOS Genetics, 2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, Precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and Metamorphosis.

  • Precocious Metamorphosis in the Juvenile Hormone–Deficient Mutant of the Silkworm, Bombyx mori
    PLoS genetics, 2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Toshiki Namiki, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, Precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and Metamorphosis.

  • Precocious Metamorphosis in the juvenile hormone-deficient mutant of the silkworm, Bombyx mori. PLoS Genet 8: e1002486. doi: 10
    2012
    Co-Authors: Takaaki Daimon, Kenjiro Furuta, Toshinori Kozaki, Ryusuke Niwa, Isao Kobayashi, Keiro Uchino, Yutaka Banno, Susumu Katsuma, Toshiki Tamura, Kazuei Mita
    Abstract:

    Insect molting and Metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent Precocious Metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for Metamorphosis. In the silkworm, Bombyx mori, several ‘‘moltinism’ ’ mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes Precocious Metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious Metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for th