Formation of the A/B cis ring junction of ecdysteroids in the locust, Schistocerca gregaria

Transcriptome analysis of abscisic acid induced 20E regulation in suspension Ajuga lobata cells

Ajuga lobata D. Don is a medicinal plant rich in 20-hydroxyecdysone (20E), alkaloids, and other active substances. In this study, the cell suspension was incubated for 7 days, followed by the analysis on the effects of abscisic acid (ABA) on the regulation of 20E synthesis. Then A. lobata suspension cells treated with 0.15 mg/l ABA were used as material, with the Illumina technology applied for transcriptome sequencing. Digital analysis on the gene expression profile was carried out on ABA treated and control samples, respectively. Finally, transcriptomics was applied to assess the molecular response of A. lobata induced by ABA through applying transcriptomics by evaluating differentially expressed genes. The results suggested that ABA promoted 20E accumulation, while longer processing time caused cell browning. A total of 154 genes were significantly regulated after ABA treatment, with 99 up-regulated and 55 down-regulated, respectively. In addition to 20E-related pathways, the genes belonged to the ko00900 (terpenoid backbone biosynthesis) pathway (six differentially expressed genes [DEGs]), ko00100 (steroid biosynthesis) pathway (four DEGs), and ko00140 (steroid hormone biosynthesis) pathway (six DEGs). Providing a better understanding of the 20E biosynthetic pathway and its regulation, in particular in plants, this study is necessary.

Characterization of candidate intermediates in the Black Box of the ecdysone biosynthetic pathway in Drosophila melanogaster: Evaluation of molting activities on ecdysteroid-defective larvae

Early steps of the biosynthetic pathway of the insect steroid hormone ecdysone remains the "Black Box" wherein the characteristic ecdysteroid skeleton is built. 7-Dehydrocholesterol (7dC) is the precursor of uncharacterized intermediates in the Black Box. The oxidation step at C-3 has been hypothesized during conversion from 7dC to 3-oxo-2,22,25-trideoxyecdysone, yet 3-dehydroecdysone is undetectable in some insect species. Therefore, we first confirmed that the oxidation at C-3 occurs in the fruitfly, Drosophila melanogaster using deuterium-labeled cholesterol. We next investigated the molting activities of candidate intermediates, including oxidative products of 7dC, by feeding-rescue experiments for Drosophila larvae in which an expression level of a biosynthetic enzyme was knocked down by the RNAi technique. We found that the administration of cholesta-4,7-dien-3-one (3-oxo-Δ^4,7C) could overcome the molting arrest of ecdysteroid-defective larvae in which the expression level of neverland was reduced. However, feeding 3-oxo-Δ^4,7C to larvae in which the expression levels of shroud and Cyp6t3 were reduced inhibited molting at the first instar stage, suggesting that this steroid could be converted into an ecdysteroid-antagonist in loss of function studies of these biosynthetic enzymes. Administration of the highly conjugated cholesta-4,6,8(14)-trien-3-one, oxidized from 3-oxo-Δ^4,7C, did not trigger molting of ecdysteroid-defective larvae. These results suggest that an oxidative product derived from 7dC is converted into ecdysteroids without the formation of this stable conjugated compound. We further found that the 14α-hydroxyl moiety of Δ⁴-steroids is required to overcome the molting arrest of larvae in loss of function studies of Neverland, Shroud, CYP6T3 or Spookier, suggesting that oxidation at C-14 is indispensable for conversion of these Δ⁴-steroids into ecdysteroids via 5β-reduction.

Biosynthesis of 20-hydroxyecdysone in plants: 3β-hydroxy-5β-cholestan-6-one as an intermediate immediately after cholesterol in Ajuga hairy roots

3β-Hydroxy-5β-cholestan-6-one was identified in the EtOAc extract of Ajuga hairy roots by micro-analysis using LC-MS/MS in the multiple reaction mode (MRM). Furthermore, administration of (2,2,4,4,7,7-(2)H6)- and (2,2,4,4,6,7,7-(2)H7)-cholesterols to the hairy roots followed by LC-MS/MS analysis of the EtOAc extract of the hairy roots indicated that cholesterol was converted to the 5β-ketone with hydrogen migration from the C-6 to the C-5 position. These findings, in conjunction with the previous observation that the ketone was efficiently converted to 20-hydroxyecdysone, strongly suggest that the 5β-ketone is an intermediate immediately formed after cholesterol during 20-hydroxyecdysone biosynthesis in Ajuga sp. In addition, the mechanism of the 5β-ketone formation from cholesterol is discussed.

Gonadal ecdysteroidogenesis in arthropoda: occurrence and regulation

Ecdysteroids are multifunctional hormones in male and female arthropods and are stored in oocytes for use during embryogenesis. Ecdysteroid biosynthesis and its hormonal regulation are demonstrated for insect gonads, but not for the gonads of other arthropods. The Y-organ in the cephalothorax of crustaceans and the integument of ticks are sources of secreted ecdysteroids in adults, as in earlier stages, but the tissue source is not known for adults in many arthropod groups. Ecdysteroid metabolism occurs in several tissues of adult arthropods. This review summarizes the evidence for ecdysteroid biosynthesis by gonads and its metabolism in adult arthropods and considers the apparent uniqueness of ecdysteroid hormones in arthropods, given the predominance of vertebrate-type steroids in sister invertebrate groups and vertebrates.

Expansion and evolution of insect GMC oxidoreductases

Background

The GMC oxidoreductases comprise a large family of diverse FAD enzymes that share a homologous backbone. The relationship and origin of the GMC oxidoreductase genes, however, was unknown. Recent sequencing of entire genomes has allowed for the evolutionary analysis of the GMC oxidoreductase family.

Results

Although genes that encode enzyme families are rarely linked in higher eukaryotes, we discovered that the majority of the GMC oxidoreductase genes in the fruit fly (D. melanogaster), mosquito (A. gambiae), honeybee (A. mellifera), and flour beetle (T. castaneum) are located in a highly conserved cluster contained within a large intron of the flotillin-2 (Flo-2) gene. In contrast, the genomes of vertebrates and the nematode C. elegans contain few GMC genes and lack a GMC cluster, suggesting that the GMC cluster and the function of its resident genes are unique to insects or arthropods. We found that the development patterns of expression of the GMC cluster genes are highly complex. Among the GMC oxidoreductases located outside of the GMC gene cluster, the identities of two related enzymes, glucose dehydrogenase (GLD) and glucose oxidase (GOX), are known, and they play major roles in development and immunity. We have discovered that several additional GLD and GOX homologues exist in insects but are remotely similar to fungal GOX.

Conclusion

We speculate that the GMC oxidoreductase cluster has been conserved to coordinately regulate these genes for a common developmental or physiological function related to ecdysteroid metabolism. Furthermore, we propose that the GMC gene cluster may be the birthplace of the insect GMC oxidoreductase genes. Through tandem duplication and divergence within the cluster, new GMC genes evolved. Some of the GMC genes have been retained in the cluster for hundreds of millions of years while others might have transposed to other regions of the genome. Consistent with this hypothesis, our analysis indicates that insect GOX and GLD arose from a different ancestral GMC gene than that of fungal GOX.

Biosynthesis of 20-hydroxyecdysone in Ajuga hairy roots: the possibility of 7-ene introduction at a late stage

Administration of [3alpha-2H]-3beta-hydroxy-5beta-cholestan-6-one to hairy roots of Ajuga reptans var. atropurpurea followed by 2H-NMR spectroscopic analysis of the resulting 20-hydroxyecdysone so formed revealed that the substrate was efficiently incorporated into the latter. Additionally, [5beta,7alpha,7beta-2H3]-2beta,3beta-dihydroxy-+ ++5beta-cholestan-6-one was converted into 20-hydroxyecdysone. These findings clearly indicate that Ajuga hairy roots are capable of introducing a double bond at the 7-position at a late stage of 20-hydroxyecdysone biosynthesis, suggesting the possibility of an alternative biosynthetic pathway which does not involve 7-dehydrocholesterol as an obligatory intermediate.

Biosynthesis of sterols and ecdysteroids in Ajuga hairy roots

Hairy roots of Ajuga reptans var. atropurpurea produce clerosterol, 22-dehydroclerosterol, and cholesterol as sterol constituents, and 20-hydroxyecdysone, cyasterone, isocyasterone, and 29-norcyasterone as ecdysteroid constituents. To better understand the biosynthesis of these steroidal compounds, we carried out feeding studies of variously 2H- and 13C-labeled sterol substrates with Ajuga hairy roots. In this article, we review our studies in this field. Feeding of labeled desmosterols, 24-methylenecholesterol, and 13C2-acetate established the mechanism of the biosynthesis of the two C29-sterols and a newly accumulated codisterol, including the metabolic correlation of C-26 and C-27 methyl groups. In Ajuga hairy roots, 3alpha-, 4alpha-, and 4beta-hydrogens of cholesterol were all retained at their original positions after conversion into 20-hydroxyecdysone, in contrast to the observations in a fern and an insect. Furthermore, the origin of 5beta-H of 20-hydroxyecdysone was found to be C-6 hydrogen of cholesterol exclusively, which is inconsistent with the results in the fern and the insect. These data strongly support the intermediacy of 7-dehydrocholesterol 5alpha,6alpha-epoxide. Moreover, 7-dehydrocholesterol, 3beta-hydroxy-5beta-cholest-7-en-6-one (5beta-ketol), and 3beta,14alpha-dihydroxy-5beta-cholest-7-en-6-one (5beta-ketodiol) were converted into 20-hydroxyecdysone. Thus, the pathway cholesterol-->7-dehydrocholesterol-->7-dehydrocholesterol 5alpha,6alpha-epoxide-->5beta-ketol-->5beta-k etodiol is proposed for the early stages of 20-hydroxyecdysone biosynthesis. 3beta-Hydroxy-5beta-cholestan-6-one was also incorporated into 20-hydroxyecdysone, suggesting that the introduction of a 7-ene function is not necessarily next to cholesterol. C-25 Hydroxylation during 20-hydroxyecdysone biosynthesis was found to proceed with ca. 70% retention and 30% inversion. Finally, clerosterol was shown to be a precursor of cyasterone and isocyasterone.

Biosynthesis of 20-hydroxyecdysone in Ajuga hairy roots: fate of 6alpha- and 6beta-hydrogens of lathosterol

The fate of 6alpha- and 6beta-hydrogens of lathosterol during the transformation into 20-hydroxyecdysone was chased by feeding [3alpha,6beta-2H2]- and [3alpha,6alpha-2H2]-lathosterols to hairy roots of Ajuga reptans var. atropurpurea. The behavior of 6beta-hydrogen, which mostly migrated to the C-5 position of 20-hydroxyecdysone, was in agreement with that of C-6 hydrogen of cholesterol. The results strongly supported the view that cholesterol and lathosterol are first metabolized into 7-dehydrocholesterol, which is then converted into 20-hydroxyecdysone via 7-dehydrocholesterol 5alpha,6alpha-epoxide in the hairy roots.

Purification and characterisation of haemolymph 3-dehydroecdysone 3 beta-reductase in relation to ecdysteroid biosynthesis in the cotton leafworm Spodoptera littoralis

The in vitro secretion of ecdysteroids from the prothoracic glands of last instar larvae of Spodoptera littoralis was detected and analysed by HPLC-RIA. The primary product was identified as 3-dehydroecdysone (approximately 82%), with lesser amounts of ecdysone (approximately 18%). Interconversion of ecdysone and 3-dehydroecdysone by prothoracic glands was not detectable. 3-Dehydroecdysone 3 beta-reductase activity was demonstrated in the haemolymph. Ecdysone, the endproduct, was characterised by reverse-phase and adsorption HPLC, chemical transformation into ecdysone 2, 3-acetonide, and mass spectrometry. The conditions for optimal activity were determined. The enzyme requires NADPH or NADH as cofactor and Km values for NADPH and NADH were determined to be 0.94 microM, and 22.8 microM, respectively. Investigation of the kinetic properties of the enzyme, using either NADPH or NADH as cofactor, revealed that it exhibits maximal activity at low 3-dehydroecdysone substrate concentrations, with a drastic inhibition of activity at higher concentrations (> 5 microM). The results suggest that the 3-dehydroecdysone 3 beta-reductase has a high-affinity (low Km) binding site for 3-dehydroecdysone substrate, together with a lower-affinity inhibition site. The 3 beta-reductase enzyme was purified to homogeneity using a combination of poly(ethylene glycol) 6000 precipitation and successive FPLC fractionation on Mono-Q, phenyl Superose (twice), and hydroxyapatite columns. The native enzyme was shown to be a monomer with molecular mass of 36 kDa by SDS/PAGE and gel-filtration chromatography. Furthermore, the activity of the enzyme during the last larval instar was found to reach a peak prior to that of the haemolymph ecdysteroid titre, supporting a role for the enzyme in development.

Evidence for the involvement of 3-oxo-delta 4 intermediates in ecdysteroid biosynthesis

Although the involvement of 3-oxo-delta 4 compounds as intermediates in arthropod ecdysteroid biosynthesis has been postulated for a long time, it has not yet been directly demonstrated. In the present study, 3-oxo-delta 4-steroids have been synthesized and incubated in vitro with dissociated moulting gland cells from the crab Carcinus maenas. The tritiated compounds were converted into 3-dehydroecdysone, ecdysone and/or 25-deoxyecdysone, i.e. final ecdysteroids. This means that the 3-oxo-delta 4 compounds had undergone a 5 beta-reduction, to give the 5 beta-conformation of ecdysteroids. Our results suggest that the 3-oxo-delta 4-steroid 4,7-cholestadien-14 alpha-ol-3,6-dione may be an intermediate in the biosynthetic pathway. The 5 beta-reduction reaction involves a cytosolic enzyme which requires NADPH as electron donor and seems specific for 3-oxo-delta 4 substrates. This reaction was the most active in crab Y-organs, as compared with other tissues. The characteristics of the 5 beta-reductase (subcellular localization, substrate and cofactor requirements) appear similar to those of the vertebrate 3-oxo-delta 4-steroid 5 beta-reductase involved in steroid hormone catabolism and bile acid biosynthesis.

[New studies on 3-dehydroecdysteroids in the biosynthetic pathway of ecdysone in Locusta migratoria]

Prothoracic glands of the locust, Locusta migratoria, incubated in vitro, converted in the same manner 3-dehydroketodiol (14 alpha-hydroxy-5 beta-cholest-7-en-3,6-dione) tritiated either on the side chain (22,23,24,25)3H4 or on the nucleus (1,2)3H2. Conversion products always appeared in two forms: one oxidized at C-3 corresponding with 3-dehydroecdysteroids, and the other corresponding with "classical" ecdysteroids which are usually obtained by conversion of ketodiol. All the different intermediate ecdysteroids between ketodiol and ecdysone are presents. A non-hemolymphatic reductase is conceivably responsible for the conversion of 3-dehydroecdysteroids at one or several places in the course of the biosynthetic pathway. Quantitatively the two forms (oxidized or hydroxylated at C-3) appeared in changeable ratios according to the different ecdysteroids but with a prevailing tendency to 1:1. The specificity of the conversion from nucleus-tritiated-dehydroketodiol depended on an enormous production of polar degradation products (more than 50% of total radioactivity). Consequently the quantities of 3-dehydro- and 3-hydroxy-ecdysteroids were lower than those which could be obtained after the conversion of side-chain-tritiated-3-dehydroketodiol. By means of an incubation with locust-larval-hemolymph, each 3-dehydroecdysteroid was totally (or at least in a great part: 3-dehydro-2-deoxyecdysone) converted into the corresponding reduced ecdysteroid. This fact confirms the reducing function of the hemolymph.(ABSTRACT TRUNCATED AT 250 WORDS)

[Involvement of 3-dehydroecdysteroids in the ecdysone biosynthetic pathway in Locusta migratoria, in vitro]

Prothoracic glands of the locus, Locusta migratoria, incubated in vitro converted tritiated 3-dehydrocetodiol (22,23,24,25 3H4-14 alpha-hydroxy-5 beta-cholest-7-en-3,6-dione) into ecdysteroids and 3-dehydroecdysteroids as far as the final products of the two series, ecdysone and 3-dehydroecdysone. In the two series, the different compounds are formed in the same quantities, except for 2,22-desoxy-products, the nature of which could not have been determined. Converted 3-dehydroecdysone issued from 3-dehydrocetodiol is transformed into ecdysone after several hours incubation with Locusta last instar larvae hemolymph. Till now is has been impossible to determine if the reduction of 3-dehydroecdysteroids took place into the prothoracic glands or in the incubation medium. In no case is 3-dehydrocetodiol converted into cetodiol. Conversion rates of the different compounds, either issued from cetodiol or from 3-dehydrocetodiol as precursors, are of same importance, so that a weak specificity of the hydroxylation enzymes must be considered.

Elimination of C-6-hydrogen during the formation of ecdysteroids from cholesterol in Locusta migratoria ovaries

Being administered to Locusta migratoria adult females, [6-3H, 4-14C]cholesterol was incorporated into ecdysone and 2-deoxyecdysone. The ratio of 3H/14C of the two ecdysteroids isolated from newly laid eggs revealed that C-6-hydrogen of cholesterol was eliminated during the conversion to ecdysteroids in the ovaries of the insects. Thus, a hypothetical mechanism involving migration of the C-6-hydrogen to the C-5 position in the formation of A/B cis junction turned out to be less likely.

Mechanism of hydroxylation at C-2 during the biosynthesis of ecdysone in ovaries of the locust, Schistocerca gregaria

The stereochemistry of hydroxylation at C-2 during the biosynthesis of ecdysone in the ovaries of Schistocerca gregaria was investigated by incorporation of [1 alpha,2 alpha-3H(n)]cholesterol in admixture with [4-14C]cholesterol into oöcyte 2-deoxyecdysone and ecdysone conjugates in maturing adult female S. gregaria. Extraction of the eggs followed by enzymic hydrolysis of the ecdysteroid conjugate fraction yielded free ecdysteroids, from which 2-deoxyecdysone and ecdysone were purified. The 3H/14C ratios in the 2-deoxyecdysone and ecdysone were similar, suggesting that the 2 alpha hydrogen of cholesterol was retained during hydroxylation at C-2. This was corroborated by oxidation at C-2 of the 3,22-diacetate derivative of the ecdysone, yielding the corresponding 2-oxo compound with removal of essentially all the 3H originally present at the 2 alpha position of cholesterol. The results indicate that the 2 beta hydrogen of cholesterol has been eliminated during the hydroxylation at C-2. Thus, during ecdysone biosynthesis, hydroxylation at C-2 is direct and occurs with retention of configuration.