Molecular cloning and structural analysis of 3-hydroxy-3-methylglutaryl coenzyme A reductase of the moth Agrotis ipsilon

Identification and characterization of genes involving the early step of Juvenile Hormone pathway in Helicoverpa armigera

Juvenile hormones (JHs) are crucial regulators for multiple physiological processes in insects. In the current study, 10 genes in mevalonate pathway involved in JH biosynthesis were identified from Helicoverpa armigera. Tissue-specific expression analysis showed that six genes were highly expressed in the head which contained the JH biosynthetic gland (corpora allata). Temporal expression pattern showed that 10 of 12 genes were highly transcribed in the late 2^nd-instar when the in vivo JH titer reached the peak, indicating a tight correlation between JH titer and the transcription of JH synthetic pathway genes. Moreover, ingestion of methoprene, a JH analogue, significantly suppressed the transcription of nine JH biosynthetic genes and caused a feedback upregulation of the JH degradation enzyme. Particularly, the Acetoacetyl CoA thiolase (HaAce) and Farnesyl diphosphate synthase gene 4 (HaFpps4) showed high transcript abundance, and their temporal expressions keep pace with JH fluctuations. Further study by RNAi showed that knockdown of HaFpps4 caused the decrease of JH titer, led to a negative effect on the transcript levels of other genes in JH pathway, and resulted in molting disturbance in larvae. Altogether, these results contribute to our understanding of JH biosynthesis in H. armigera and provide target genes for pest control based on JH-dependent regulation.

Juvenile Hormone Biosynthesis in Insects: What Is New, What Do We Know, and What Questions Remain?

Our understanding of JH biosynthesis has significantly changed in the last years. In this review I would like to discuss the following topics: (1) the progresses in understanding the JH biosynthesis pathway. Access to genome sequences has facilitated the identification of all the genes encoding biosynthetic enzymes and the completion of comprehensive transcriptional studies, as well as the expression and characterization of recombinant enzymes. Now the existence of different flux directionalites, feed-back loops and pathway branching points in the JH biosynthesis pathways can be explored; (2) the new concepts in the modulation of JH synthesis by allatoregulators. The list of putative JH modulators is increasing. I will discuss their possible role during the different physiological states of the CA; (3) the new theoretical and physiological frameworks for JH synthesis analysis. I will discuss the bases of the flux model for JH biosynthesis. JH plays multiple roles in the control of ovary development in female mosquitoes; therefore, the CA presents different physiological states, where JH synthesis is altered by gating the flux at distinctive points in the pathway; (4) in the final section I will identify new challenges and future directions on JH synthesis research.

RNAi silencing of the HaHMG-CoA reductase gene inhibits oviposition in the Helicoverpa armigera cotton bollworm

RNA interference (RNAi) has considerable promise for developing novel pest control techniques, especially because of the threat of the development of resistance against current strategies. For this purpose, the key is to select pest control genes with the greatest potential for developing effective pest control treatments. The present study demonstrated that the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase; HMGR) gene is a potential target for insect control using RNAi. HMGR is a key enzyme in the mevalonate pathway in insects. A complete cDNA encoding full length HMGR (encoding an 837-aa protein) was cloned from Helicoverpa armigera (Lepidoptera: Noctuidae). The HaHMGR (H. armigera HMGR) knockdown using systemic RNAi in vivo inhibited the fecundity of the females, effectively inhibited ovipostion, and significantly reduced vitellogenin (Vg) mRNA levels. Moreover, the oviposition rate of the female moths was reduced by 98% by silencing HaHMGR compared to the control groups. One-pair experiments showed that both the proportions of valid mating and fecundity were zero. Furthermore, the HaHMGR-silenced females failed to lay eggs (approximate 99% decrease in oviposition) in the semi-field cage performance. The present study demonstrated the potential implications for developing novel pest management strategies using HaHMGR RNAi in the control of H. armigera and other insect pests.

Juvenile hormone acid methyl transferase is a key regulatory enzyme for juvenile hormone synthesis in the Eri silkworm, Samia cynthica ricini

During the period of adult emergence in the Eri silkworm, Samia cynthia ricini, the corpora allata (CA) are apparently reactivated in females, but not males. This creates a significant sexual dimorphism in juvenile hormone (JH) synthesis by CA. To determine the underlying molecular mechanisms in this process, we cloned cDNAs of two enzymes involved in the JH synthesis pathway: 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and juvenile hormone acid methyl transferase (JHAMT). Both Samcri-HMGR and -JHAMT mRNAs were detected in CA almost exclusively. However, their expression patterns were different from each other. During the period of adult emergence, Samcri-HMGR was expressed in CA at a constantly high level suggesting it plays little role for the regulation of JH synthesis. In contrast, the patterns of both Samcri-JHAMT mRNA level and enzyme activity were closely correlated with the patterns of JH synthesis, CA reactivation, and sexual dimorphism of JH synthesis. In addition, JHAMT mRNA levels were paralleled JH synthesis in the fifth-instar larvae of S. cynthia ricini and the pharate adults of the silkworm Bombyx mori. We infer from these results that JHAMT is a key regulatory enzyme for JH synthesis in the Eri silkworm.

Isolation, endocrine regulation and mRNA distribution of the 3-hydroxy-3-methylglutaryl coenzyme A synthase (HMG-S) gene from the pine engraver, Ips pini (Coleoptera: Scolytidae)

We isolated a full-length cDNA encoding 3-hydroxy-3-methylglutaryl coenzyme A synthase (HMG-S) from the pine engraver beetle, Ips pini (Say), and examined its genomic structure. The intron-less gene has a predicted 460 amino acid cytosolic protein product with 73% identity to HMG-S from Dendroctonus jeffreyi, and high identity (58-64%) with other insect HMG-Ss. Topically applied juvenile hormone (JH) III induced HMG-S mRNA levels up to 6.5-fold in both sexes, mostly in the anterior midgut, though there were differences between males and females in the timing, sensitivity to JH III dose and tissue distribution of HMG-S mRNA. These data further validate the coordinate regulation of mevalonate pathway genes for de novo isoprenoid pheromone production in bark beetles.

Neurodegenerative mutants in Drosophila: a means to identify genes and mechanisms involved in human diseases?

There are 50 ways to leave your lover (Simon 1987) but many more to kill your brain cells. Several neurodegenerative diseases in humans, like Alzheimer's disease, have been intensely studied but the underlying cellular and molecular mechanisms are still unknown for most of them. For those syndromes where associated gene products have been identified their biochemistry and physiological as well as pathogenic function is often still under debate. This is in part due to the inherent limitations of genetic analyses in humans and other mammals and therefore experimentally accessible invertebrate in vivo models, such as Caenorhabditis elegans and Drosophila melanogaster, have recently been introduced to investigate neurodegenerative syndromes. Several laboratories have used transgenic approaches in Drosophila to study the human genes associated with neurodegenerative diseases. This has added substantially to our understanding of the mechanisms leading to neurodegenerative diseases in humans. The isolation and characterization of Drosophila mutants, which display a variety of neurodegenerative phenotypes, also provide valuable insights into genes, pathways, and mechanisms causing neurodegeneration. So far only about two dozen such mutants have been described but already their characterization reveals an involvement of various cellular functions in neurodegeneration, ranging from preventing oxidative stress to RNA editing. Some of the isolated genes can already be associated with human neurodegenerative diseases and hopefully the isolation and characterization of more of these mutants, together with an analysis of homologous genes in vertebrate models, will provide insights into the genetic and molecular basis of human neurodegenerative diseases.

The mevalonate pathway and the synthesis of juvenile hormone in insects

The mevalonate pathway in insects has two important peculiarities, the absence of the sterol branch and the synthesis of juvenile hormone (JH), that may have influenced the mechanisms of regulation. The data available on these mechanisms indicate that cholesterol does not play a regulatory role and that JH modulates transcript levels of a number of genes of the mevalonate pathway or can influence the translatability and/or stability of the transcripts themselves. These data suggest that the mevalonate pathway in insects can best be interpreted in terms of coordinated regulation, in which regulators act in parallel to a number of enzymes, as occurs in the cholesterol-driven pathway in vertebrates.

The lobster mandibular organ produces soluble and membrane-bound forms of 3-hydroxy-3-methylglutaryl-CoA reductase

In a previous study [Li, Wagner, Friesen and Borst (2003) Gen. Comp. Endocrinol. 134, 147-155], we showed that the MO (mandibular organ) of the lobster Homarus americanus has high levels of HMGR (3-hydroxy-3-methylglutaryl-CoA reductase) and that most (approx. 75%) of the enzyme activity is soluble. In the present study, we report the biochemical and molecular characteristics of this enzyme. HMGR had two forms in the MO: a more abundant soluble form (66 kDa) and a less abundant membrane-bound form (72 kDa). Two cDNAs for HMGR were isolated from the MO. A 2.6-kb cDNA encoded HMGR1, a 599-amino-acid protein (63 kDa), and a 3.2-kb cDNA encoded HMGR2, a 655-amino-acid protein (69 kDa). These two cDNAs had identical 3'-ends and appeared to be products of a single gene. The deduced amino acid sequences of these two proteins revealed a high degree of similarity to other class I HMGRs. Hydropathy plots indicated that the N-terminus of HMGR1 lacked a transmembrane region and HMGR2 had a single transmembrane segment. Recombinant HMGR1 expressed in Sf9 insect cells was soluble and had kinetic characteristics similar to native HMGR from the MO. Treatment with phosphatase did not affect HMGR activity, consistent with the observation that neither HMGR1 nor HMGR2 has a serine at position 490 or 546, the position of a conserved phosphorylation site found in class I HMGR from higher eukaryotes. Other lobster tissues (i.e. midgut, brain and muscles) had low HMGR activities and mRNA levels. MO with higher HMGR activities had higher HMGR mRNA levels, implying that HMGR is regulated, in part, at the transcription level.

3-hydroxy-3-methylglutaryl-coenzyme A reductase in the lobster mandibular organ: regulation by the eyestalk

The mandibular organ (MO) of the lobster, Homarus americanus, produces the isoprenoid methyl farnesoate (MF), a compound related to insect juvenile hormone (JH). To better understand the synthesis and regulation of MF, we studied 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGR), the rate-limiting enzyme in isoprenoid biosynthesis. Lobster HMGR had a Km of 11.4 microM for HMG-CoA, a Km of 14.8 microM for NADPH, and was at least 2000-fold more selective for this cofactor than for NADH. Lovastatin and mevalonic acid inhibited HMGR, with KI values of 1.3 nM and 25.3 microM, respectively, whereas MF, farnesoic acid, cholesterol, 20-hydroxyecdysone, and progesterone had no effect. Approximately 75% of the HMGR activity in lobster MO was soluble. Similar levels of HMGR activity were observed in all regions of the MO. Eyestalk removal increased MF synthesis and the activity of farnesoic acid O-methyltransferase (FAOMeT, the final step in MF synthesis) in the MO by 10.7- and 5.7-fold, respectively, and caused a 3.1-fold increase of HMGR activity. Injection of the eyestalk ablated lobsters with an extract of two sinus glands (SG), a neuroendocrine organ in the eyestalk, decreased MF synthesis, FAOMeT activity and HMGR activity to 3, 8, and 20%, respectively, of the levels observed in saline-treated animals. The regulation of crustacean HMGR by the SG suggests that the lobster MO is a useful model system for investigating the cellular regulation of HMGR activity.

Inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase lower fecundity in the German cockroach: correlation between the effects on fecundity in vivo with the inhibition of enzymatic activity in embryo cells

The enzyme 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase is crucial to insect development and reproduction, as revealed by the sterilising properties of some specific inhibitors of it. In the present paper, we study the sterilising effects of a number of HMG-CoA reductase inhibitors on the German cockroach, Blattella germanica (L). The inhibitors tested were naringenin, lovastatin, mevastatin, simvastatin, atorvastatin and fluvastatin. The first two compounds were ineffective or scarcely effective as HMG-CoA reductase inhibitors. The most active compounds in vivo were fluvastatin and atorvastatin, followed by simvastatin and mevastatin. They were equally ranked when tested as HMG-CoA reductase inhibitors in the B germanica embryonic derived cell line UM-BGE-1. This suggests that this cell line may be an appropriate tool for testing HMG-CoA reductase inhibitors and so to predict their properties as insect sterilising agents with insecticide potential.

The neurodegeneration mutant löchrig interferes with cholesterol homeostasis and Appl processing

The novel Drosophila mutant löchrig (loe) shows progressive neurodegeneration and neuronal cell death, in addition to a low level of cholesterol ester. loe affects a specific isoform of the gamma-subunit of AMP-activated protein kinase (AMPK), a negative regulator of hydroxymethylglutaryl (HMG)-CoA reductase and cholesterol synthesis in vertebrates. Although Drosophila cannot synthesize cholesterol de novo, the regulatory role of fly AMPK on HMG-CoA reductase is conserved. The loe phenotype is modified by the level of HMG-CoA reductase and suppressed by the inhibition of this enzyme by statin, which has been used for the treatment of Alzheimer patients. In addition, the degenerative phenotype of loe is enhanced by a mutation in amyloid precursor protein-like (APPL), the fly homolog of the human amyloid precursor protein involved in Alzheimer's disease. Western analysis revealed that the loe mutation reduces APPL processing, whereas overexpression of Loe increases it. These results describe a novel function of AMPK in neurodegeneration and APPL/APP processing which could be mediated through HMG-CoA reductase and cholesterol ester.

Ovarian 3-hydroxy-3-methylglutaryl-CoA reductase in Blattella germanica (L.): pattern of expression and critical role in embryogenesis

In the ovary of adult Blattella germanica, the enzyme 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) is highly expressed in mid-late vitellogenesis, suggesting a functional link of the mevalonate pathway with choriogenesis. The inhibitor of HMG-CoA reductase, fluvastatin, applied in females in late vitellogenesis, inhibits the activity of the enzyme in the ovary and in the developing embryos within the ootheca. This does not affect choriogenesis or ootheca formation but reduces the number of larvae per ootheca. Our results suggest that fluvastatin is incorporated into the oocytes and has delayed inhibitory effects on the oviposited eggs. HMG-CoA reductase is essential for embryogenesis, but not for chorion formation.

Effects of hypocholesterolaemic agents on the expression and activity of 3-hydroxy-3-methylglutaryl-CoA reductase in the fat body of the German cockroach

In the fat body of adult Blattella germanica females, the expression of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) during the first reproductive cycle is parallel to that of vitellogenin, suggesting a functional link between the mevalonate pathway, and vitellogenesis and reproduction. We have studied the effects of compactin and fluvastatin, two inhibitors of HMG-CoA reductase, on the expression and activity of the enzyme in the fat body, and on the ootheca formation, ootheca viability, and number of larvae per viable ootheca. Short-term assays showed that both compounds reduce the protein levels and enzymatic activity of HMG-CoA reductase, and long-term experiments revealed that fluvastatin impairs embryo development.