Evolution and functional divergence of enzymes involved in sesquiterpenoid hormone biosynthesis in crustaceans and insects

Transcriptomic analysis of sexually dimorphic cypris larvae of the rhizocephalan barnacle Peltogasterella gracilis

Peltogasterella gracilis (Cirripedia: Rhizocephala), a crustacean parasite of hermit crabs, displays genotypic sex determination. Its larvae are planktonic, and female larvae settle on the host. Subsequently, the females control the host's behavior by spreading a root-like structure called "the interna" within the host's body, and form sacs containing eggs called "the externae" outside the host's body. On the other hand, male larvae settle on immature externae and become dwarf males. The cypris larvae of P. gracilis show sexual dimorphism in size and morphology. However, there is no understanding of the molecular mechanisms underlying the sexual dimorphism observed at the larval stage. Here, we conducted a transcriptome analysis and compared the expression of genes in male and female cyprids to better understand their sexual differentiation and settlement processes. A total of 2870 differentially expressed transcripts, comprising 456 female- and 2414 male-biased transcripts were identified. Among the male-biased ones, ionotropic glutamate receptor-, heat shock protein-, acetylcholine-, and homeobox-, cuticle-related transcripts were included. Additionally, 29 gene ontology terms were associated with the sex-specific traits. The present study improves our understanding of sex determination, sexual differentiation, and settlement processes of rhizocephalans.

Comparative Transcriptome Analysis of Hepatopancreas Reveals Sexual Dimorphic Response to Methyl Farnesoate Injection in Litopenaeus vannamei

Sexually dimorphic traits such as growth and body size are often found in various crustaceans. Methyl farnesoate (MF), the main active form of sesquiterpenoid hormone in crustaceans, plays vital roles in the regulation of their molting and reproduction. However, understanding on the sex differences in their hormonal regulation is limited. Here, we carried out a comprehensive investigation on sexual dimorphic responses to MF in the hepatopancreas of the most dominant aquacultural crustacean-the white-leg shrimp (Litopenaeus vannamei). Through comparative transcriptomic analysis of the main MF target tissue (hepatopancreas) from both female and male L. vannamei, two sets of sex-specific and four sets of sex-dose-specific differentially expressed transcripts (DETs) were identified after different doses of MF injection. Functional analysis of DETs showed that the male-specific DETs were mainly related to sugar and lipid metabolism, of which multiple chitinases were significantly up-regulated. In contrast, the female-specific DETs were mainly related to miRNA processing and immune responses. Further co-expression network analysis revealed 8 sex-specific response modules and 55 key regulatory transcripts, of which several key transcripts of genes related to energy metabolism and immune responses were identified, such as arginine kinase, tropomyosin, elongation of very long chain fatty acids protein 6, thioredoxin reductase, cysteine dioxygenase, lysosomal acid lipase, estradiol 17-beta-dehydrogenase 8, and sodium/potassium-transporting ATPase subunit alpha. Altogether, our study demonstrates the sex differences in the hormonal regulatory networks of L. vannamei, providing new insights into the molecular basis of MF regulatory mechanisms and sex dimorphism in prawn aquaculture.

Possible Regulation of Larval Juvenile Hormone Titers in Bombyx mori by BmFAMeT6

Juvenile hormone (JH) plays a vital role in the growth, development, and reproduction of insects and other arthropods. Previous experiments have suggested that BmFAMeT6 could affect the duration of the silk moth's larval stage. In this study, we established the BmFAMeT6 overexpression strain and BmFAMeT6 knockout strain using the GAL4/UAS binary hybrid system and CRISPR/Cas 9 system, respectively, and found that the larval stage of the overexpression strain was shorter, while the knockout strain was longer. Our results exhibited that both the JH titers and BmKr-h1 levels in the larvae of the third instar were reduced significantly by BmFAMeT6 overexpression, but were increased obviously by BmFAMeT6 knockout. In addition, injection of farnesoic acid induced changes in the JH I and JH II levels in the hemolymphs of larvae. This study is the first to directly reveal the role of BmFAMeT6 in the regulation of insect JH titers and the relationship between farnesoic acid and JH (JH I and JH II). This provides a new perspective on regulating the growth and development of insects such as Bombyx mori.

Evolution of proteins involved in the final steps of juvenile hormone synthesis

Juvenile hormone (JH), a sesquiterpenoid produced by the insect corpus allatum gland (CA), is a key regulator of insect metamorphosis, reproduction, caste differentiation, and polyphenism. The first part of JH biosynthesis occurs via the universal eukaryotic mevalonate pathway. The final steps involve epoxidation and methylation. However, the sequence of these steps might not be conserved among all insects and Crustacea. Therefore, we used available genomic and transcriptomic data and identified JH acid methyltransferase (JHAMT), analyzed their genomic duplications in selected model organisms, and reconstructed their phylogeny. We have further reconstructed phylogeny of FAMeT proteins and show that evolution of this protein group is more complicated than originally appreciated. The analysis delineates important milestones in the evolution of several JH biosynthetic enzymes in arthropods, reviews major literature data on the last steps of JH synthesis, and defines questions and some hypotheses worth pursuing experimentally.

Sesquiterpenoid pathway in the mandibular organ of Penaeus monodon: Cloning, expression, characterization of PmJHAMT and its alteration response to eyestalk ablation

Methyl farnesoate (MF), a crustacean equivalent of juvenile hormone (JH) of insects, is known to be produced from the mandibular organ (MO). This study reports transcriptome analysis of Penaeus monodon MO and identifies putative genes encoding enzymes in the sesquiterpenoid pathway. A total of 44,490,420 clean reads were obtained and utilized for subsequent analysis. De novo assembly created 31,201 transcripts and 31,167 unigenes. To archive the functional annotation, all unigenes were annotated with KOG, KEGG, and GO. Putative genes encoding enzymes and regulatory proteins involved in the sesquiterpenoid pathway were obtained from the MO transcriptome data based on the conserved domains and sequence homology. They included S-adenosylmethionine synthetase, farnesyl pyrophosphate synthase, short chain dependent dehydrogenase/reductase (SDR), NAD(P) + -dependent aldehyde dehydrogenase, S-adenosylmethionine-dependent methyltransferases or juvenile hormone acid-O-methyl transferase (JHAMT), farnesoic acid O-methyl transferase (FAMeT), juvenile hormone binding protein, cytochrome C/P-450 family 15 (CRYP15A1)/methylfarnesoate epoxidase (MFE), juvenile hormone epoxide hydrolase (JHEH), and juvenile hormone esterase (JHE). We first identified and characterized JHAMT orthologs inP. monodon(PmJHAMT). The complete cDNA sequence ofPmJHAMTconsisted of 1,221 nt encoded 271 amino acids with a conserved S-adenosyl methionine (SAM) binding domain. Phylogenetic analysis clusteredPmJHAMTinto the group JHAMT with the same clade of the crabPortunus trituberculausJHAMT. Moreover, the predicted three-dimensional structure of PmJHAMT showed remarkable similarity with the recent crystal structure ofthe Bombyx moriJHAMT homodimer. RT-PCR analysis revealed that PmJHAMT was exclusively expressed in MO and initially expressed at stage 3 postlarvae. In situ hybridization with a specific probe to PmJHAMT validated the specific expression of this gene in MO cells. Finally, we evaluated the regulation of MO by eyestalk inhibitory peptides. Diminishing MO inhibitory hormone through unilateral eyestalk ablation resulted in a significantly higher expression ofPmJHAMTin MO by quantitative PCR. This result indicated that the eyestalk inhibitory hormone inhibited MF synthesis byPmJHAMTgene suppression in the MO. This finding provides insight into the crustacean sesquiterpenoid pathway and improves our understanding of crustacean endocrinology.

Ovarian transcriptome and metabolic responses of RNAi-mediated farnesyl pyrophosphate synthase knockdown in Neocaridina denticulata sinensis

Methyl farnesoate (MF) is considered the equivalent of JH in crustaceans and plays an essential role in many crucial physiological processes. It is believed that farnesyl pyrophosphate synthase (FPPS) plays an essential role in the biosynthesis of mevalonate, which is a branch of the JH/MF pathway. The full-length cDNA of FPPS (NdFPPS) from Neocaridina denticulata sinensis was isolated and characterized, and the deduced amino acid of NdFPPS contained a polyprenyl_synt domain. In addition to its ubiquitous tissue expression, NdFPPS was significantly expressed in the ovary. In vivo gene silencing with dsRNA interference was performed to further investigate the function of NdFPPS. An ovarian transcriptomic analysis of dsNdFPPS experimental and control groups was used to compare, annotate, and classify differentially expressed genes (DEGs). A total of 9230 DEGs were identified in the experimental and control groups based on FPKM values, of which 5082 were up-regulated genes and 4148 were down-regulated genes. 761 GO terms and 102 KEGG pathways were enriched for the DEGs. Our results suggest that NdFPPS might play an important role in ovarian development, however, further functional study is needed to elucidate physiological role of NdFPPS in reproduction.

Rethinking Sesquiterpenoids: A Widespread Hormone in Animals

The sesquiterpenoid hormone juvenile hormone (JH) controls development, reproduction, and metamorphosis in insects, and has long been thought to be confined to the Insecta. While it remains true that juvenile hormone is specifically synthesized in insects, other types or forms of sesquiterpenoids have also been discovered in distantly related animals, such as the jellyfish. Here, we combine the latest literature and annotate the sesquiterpenoid biosynthetic pathway genes in different animal genomes. We hypothesize that the sesquiterpenoid hormonal system is an ancestral system established in an animal ancestor and remains widespread in many animals. Different animal lineages have adapted different enzymatic routes from a common pathway, with cnidarians producing farnesoic acid (FA); non-insect protostomes and non-vertebrate deuterostomes such as cephalochordate and echinoderm synthesizing FA and methyl farnesoate (MF); and insects producing FA, MF, and JH. Our hypothesis revolutionizes the current view on the sesquiterpenoids in the metazoans, and forms a foundation for a re-investigation of the roles of this important and yet neglected type of hormone in different animals.

Eusociality is linked to caste-specific differences in metabolism, immune system, and somatic maintenance-related processes in an ant species

The social organization of many primate, bird and rodent species and the role of individuals within that organization are associated with specific individual physiological traits. However, this association is perhaps most pronounced in eusocial insects (e.g., termites, ants). In such species, genetically close individuals show significant differences in behavior, physiology, and life expectancy. Studies addressing the metabolic changes according to the social role are still lacking. We aimed at understanding how sociality could influence essential molecular processes in a eusocial insect, the black garden ant (Lasius niger) where queens can live up to ten times longer than workers. Using mass spectrometry-based analysis, we explored the whole metabolome of queens, nest-workers and foraging workers. A former proteomics study done in the same species allowed us to compare the findings of both approaches. Confirming the former results at the proteome level, we showed that queens had fewer metabolites related to immunity. Contrary to our predictions, we did not find any metabolite linked to reproduction in queens. Among the workers, foragers had a metabolic signature reflecting a more stressful environment and a more highly stimulated immune system. We also found that nest-workers had more digestion-related metabolites. Hence, we showed that specific metabolic signatures match specific social roles. Besides, we identified metabolites differently expressed among behavioral castes and involved in nutrient sensing and longevity pathways (e.g., sirtuins, FOXO). The links between such molecular pathways and aging being found in an increasing number of taxa, our results confirm and strengthen their potential universality.

RNAi silencing of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) gene inhibits vitellogenesis in Chinese mitten crab Eriocheir sinensis

The sesquiterpenoid methyl farnesoate (MF), a de-epoxide form of insect juvenile hormone III (JH III), plays an essential role in regulating many crucial physiological processes in crustaceans including vitellogenesis and reproduction. 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is an important rate-limiting enzyme in the mevalonate pathway, which is critical for the synthesis of JH III and MF. In the present study, a full-length cDNA encoding HMGR (EsHMGR) in Eriocheir sinensis was isolated and characterised. Sequence analysis of EsHMGR revealed that it belongs to Class I HMGR family proteins with HMG-CoA-binding and NADPH-binding domains, both important for HMGR activity. In addition to its ubiquitous tissue expression, expression of EsHMGR was highly specific to the ovary, the main site of Vg synthesis. During ovarian development, EsHMGR expression in ovary displayed a stage-specific pattern, and was correlated with expression of vitellogenin (EsVg) in hepatopancreas, which suggests that EsHMGR possibly involved in vitellogenesis. To further investigate the functional role of EsHMGR in vitellogenin biosynthesis in E. sinensis, RNA interference-mediated gene silencing was carried out both in vitro and in vivo. Quantitative PCR results showed that injection of EsHMGR double-stranded RNA (dsRNA) led to a significant decrease in EsVg expression levels in ovary and hepatopancreas both in vitro and in vivo. Taken together, the results suggest that EsHMGR is involved in vitellogenin biosynthesis in female E. sinensis, which may provide a new resource for HMGR enzymes participating in reproduction in crustaceans.

A Crab Is Not a Fish: Unique Aspects of the Crustacean Endocrine System and Considerations for Endocrine Toxicology

Crustaceans-and arthropods in general-exhibit many unique aspects to their physiology. These include the requirement to moult (ecdysis) in order to grow and reproduce, the ability to change color, and multiple strategies for sexual differentiation. Accordingly, the endocrine regulation of these processes involves hormones, receptors, and enzymes that differ from those utilized by vertebrates and other non-arthropod invertebrates. As a result, environmental chemicals known to disrupt endocrine processes in vertebrates are often not endocrine disruptors in crustaceans; while, chemicals that disrupt endocrine processes in crustaceans are often not endocrine disruptors in vertebrates. In this review, we present an overview of the evolution of the endocrine system of crustaceans, highlight endocrine endpoints known to be a target of disruption by chemicals, and identify other components of endocrine signaling that may prove to be targets of disruption. This review highlights that crustaceans need to be evaluated for endocrine disruption with consideration of their unique endocrine system and not with consideration of the endocrine system of vertebrates.

Effects of methyl farnesoate on Krüppel homolog 1 (Kr-h1) during vitellogenesis in the Chinese mitten crab (Eriocheir sinensis)

Methyl farnesoate (MF), a de-epoxidized form of juvenile hormone (JH) Ⅲ in insects, may regulate developmental processes such as reproduction and ovarian maturation in crustaceans. Krüppel homolog 1 (Kr-h1) is a target response gene for the methoprene-tolerant (Met) protein that is a component of the JH signaling pathway in insects. In the present study, Es-Kr-h1 was cloned from E. sinensis and characterized to ascertain whether JH/MF signaling in insects is conserved in crustaceans. The findings with molecular structure analysis indicated Es-Kr-h1 contains seven zinc finger motifs (Zn2-Zn8) commonly conserved in other crustaceans, but the Zn1 motif was not detected to be present. The PCR results indicated that relative abundance of Es-Kr-h1 mRNA transcript in the hepatopancreas was greatest in the Stage Ⅱ, followed by the Stage Ⅳ ovarian developmental categories. The relative abundance of Es-Kr-h1 mRNA transcript in vitro was greater after MF addition to the hepatopancreas, however, not the ovarian tissues. The results from in vivo and eyestalk ablation experiments indicated the relative abundance of Es-Kr-h1 mRNA transcript was greater after MF treatment and bilateral eyestalk removal in the hepatopancreas, however, not ovarian tissues. Notably, there were effects of MF on relative abundance of Es-Kr-h1 mRNA transcript pattern. The Es-Kr-h1 protein, therefore, may be involved in MF-mediated vitellogenesis resulting from the response to Es-Met in E. sinensis, and the JH/MF signaling pathway is potentially conserved in crustaceans.

Diversity of Insect Sesquiterpenoid Regulation

Insects are arguably the most successful group of animals in the world in terms of both species numbers and diverse habitats. The sesquiterpenoids juvenile hormone, methyl farnesoate, and farnesoic acid are well known to regulate metamorphosis, reproduction, sexual dimorphism, eusociality, and defense in insects. Nevertheless, different insects have evolved with different sesquiterpenoid biosynthetic pathway as well as products. On the other hand, non-coding RNAs such as microRNAs have been implicated in regulation of many important biological processes, and have recently been explored in the regulation of sesquiterpenoid production. In this review, we summarize the latest findings on the diversity of sesquiterpenoids reported in different groups of insects, as well as the recent advancements in the understanding of regulation of sesquiterpenoid production by microRNAs.

Gammarid exposure to pyriproxyfen and/or cadmium: what effects on the methylfarnesoate signalling pathway?

Due to expected changes in climate, it is predicted that disease-carrying mosquitoes will expand their geographical range, resulting in increased use of insect growth regulators (IGRs) to face their proliferation. Among IGRs, pyriproxyfen (PXF) is widely used and has been shown to prevent larvae from developing into adults, rendering them unable to reproduce. However, because of the similarity of crustacean and insect endocrine systems, PXF could also impact aquatic crustaceans. In addition, when spreading in the environment, PXF is found in a mixture with other pollutants such as metallic trace elements, which could alter its effect. Consequently, the present work was devoted to analysing the effects of PXF on the methylfarnesoate (MF) hormonal pathway of the freshwater amphipod Gammarus pulex, as well as its combined binary effects with cadmium (Cd), by measuring MF concentration, as well as the relative transcriptional expression of the farnesoic acid O-methyltransferase (FAMeT) (enzyme limiting the MF production), the methoprene-tolerant receptor (Met), and the broad-complex (BrC) as a transcription factor. Results revealed that single exposures to PXF or Cd have mainly overexpressed FAMeT, Met, and BrC but did not significantly affect MF concentration. Conversely, the mixture exposures seemed to suppress these effects and even achieve antagonistic effects. This work confirmed that PXF single exposure could impact non-target organisms such as amphipods through changes in hormonal pathways of MF. In the same way, it highlighted that Cd could also impair the endocrine system of exposed organisms. However, antagonistic effects have been observed in exposure to mixtures, suggesting different long-term consequences on the growth of amphipods under realistic exposure conditions.

Effects of two juvenile hormone analogue insecticides, fenoxycarb and methoprene, on Neocaridina davidi

Juvenile hormone analogue (JHA) insecticides are endocrine disrupters that interfere with hormonal action in insects by mimicking their juvenile hormones (JH). As the structure and functions of methyl farnesoate in crustaceans are similar to those of JH in insects, exogenous JHA insecticides could have adverse effects on the development and reproduction of crustaceans. This study examined the toxic effects of two JHA insecticides, fenoxycarb and methoprene, on a freshwater shrimp model of cherry shrimp, Neocaridina davidi. Both insecticides had detrimental effects on cherry shrimp, but fenoxycarb was more toxic than methoprene. Chronic exposure to these insecticides reduced the shrimp's body length and molting frequency. Based on transcriptome annotations for N. davidi, we identified important gene homologues that were active in both insect JH biosynthetic and degradative pathways as well as JH and ecdysteroid signaling pathways. Chronic treatments with JHAs had significant effects on these genes in N. davidi. Our transcriptomic analysis showed that genes involved in the pathways related to cuticle development, serine protease activity, and carbohydrate, peptide and lipid metabolic processes were differentially expressed in shrimp exposed to JHAs. These results demonstrate the toxicity of fenoxycarb and methoprene to freshwater crustaceans and indicate the need to monitor the use of JHA insecticides.

The crustacean ecdysone cassette: A gatekeeper for molt and metamorphosis

Arthropods have long been utilized as models to explore molecular function, and the findings derived from them can be applied throughout metazoa, including as a basis for medical research. This has led to the adoption of many representative insect models beyond Drosophila, as each lends its own unique perspective to questions in endocrinology and genetics. However, non-insect arthropods are yet to be realised for the potential insight they may provide in such studies. The Crustacea are among the most ancient arthropods from which insects descended, comprising a huge variety of life histories and ecological roles. Of the events in a typical crustacean development, metamorphosis is perhaps the most ubiquitous, challenging and highly studied. Despite this, our knowledge of the endocrinology which underpins metamorphosis is rudimentary at best; although several key molecules have been identified and studied in depth, the link between them is quite nebulous and leans heavily on well-explored insect models, which diverged from the Pancrustacea over 450 million years ago. As omics technologies become increasingly accessible, they bring the prospect of explorative molecular research which will allow us to uncover components and pathways unique to crustaceans. This review reconciles known components of crustacean metamorphosis and reflects on our findings in insects to outline a future search space, with focus given to the ecdysone cascade. To expand our knowledge of this ubiquitous endocrine system not only aids in our understanding of crustacean metamorphosis, but also provides a deeper insight into the adaptive capacity of arthropods throughout evolution.

Delegating Sex: Differential Gene Expression in Stolonizing Syllids Uncovers the Hormonal Control of Reproduction

Stolonization in syllid annelids is a unique mode of reproduction among animals. During the breeding season, a structure resembling the adult but containing only gametes, called stolon, is formed generally at the posterior end of the animal. When stolons mature, they detach from the adult and gametes are released into the water column. The process is synchronized within each species, and it has been reported to be under environmental and endogenous control, probably via endocrine regulation. To further understand reproduction in syllids and to elucidate the molecular toolkit underlying stolonization, we generated Illumina RNA-seq data from different tissues of reproductive and nonreproductive individuals of Syllis magdalena and characterized gene expression during the stolonization process. Several genes involved in gametogenesis (ovochymase, vitellogenin, testis-specific serine/threonine-kinase), immune response (complement receptor 2), neuronal development (tyrosine-protein kinase Src42A), cell proliferation (alpha-1D adrenergic receptor), and steroid metabolism (hydroxysteroid dehydrogenase 2) were found differentially expressed in the different tissues and conditions analyzed. In addition, our findings suggest that several neurohormones, such as methyl farnesoate, dopamine, and serotonin, might trigger stolon formation, the correct maturation of gametes and the detachment of stolons when gametogenesis ends. The process seems to be under circadian control, as indicated by the expression patterns of r-opsins. Overall, our results shed light into the genes that orchestrate the onset of gamete formation and improve our understanding of how some hormones, previously reported to be involved in reproduction and metamorphosis processes in other invertebrates, seem to also regulate reproduction via stolonization.

Juvenile hormone and sesquiterpenoids in arthropods: Biosynthesis, signaling, and role of MicroRNA

Arthropod molting and reproduction are precisely controlled by the levels of sesquiterpenoids, a class of C15 hormones derived from three isoprene units. The two major functional arthropod sesquiterpenoids are juvenile hormone (JH) and methyl farnesoate (MF). In hemimetabolous insects (such as the aphids, bugs, and cockroaches) and holometabolous insects (such as beetles, bees, butterflies, and flies), dramatic decrease in the titers of JH and/or MF promote metamorphosis from larvae to adults either directly or through an intermediate pupal stage, respectively. JH is absent in crustaceans (lobster, shrimp, crab) and other arthropods (chelicerates such as ticks, mites, spiders, scorpions and myriapods such as millipede and centipedes). In some crustaceans, molting and reproduction is dependent on changing levels of MF. The regulation of sesquiterpenoid production is thus crucial in the life cycle of arthropods. Dynamic and complex mechanisms have evolved to regulate sesquiterpenoid production. Noncoding RNAs such as the microRNAs are primary regulators. This article provides an overview of microRNAs that are known to regulate sesquiterpenoid production in arthropods.

Role of Kruppel homolog 1 (Kr-h1) in methyl farnesoate-mediated vitellogenesis in the swimming crab Portunus trituberculatus

Similar to the role of juvenile hormone (JH) in insects, methyl farnesoate (MF), the unepoxidized form of JH III, regulates many developmental processes in crustaceans, such as molting and reproduction. We have previously showed that the JH receptor, Methoprene-tolerant (Met), which is also a candidate receptor for MF, might be involved in the MF-mediated vitellogenesis in the swimming crab Portunus trituberculatus. In this study, the role of Kruppel homolog 1 (Kr-h1), a transcription factor downstream Met in JH signaling, was further investigated. The deduced protein of Pt-Kr-h1 contained seven repeats of zinc finger motifs, similar to Kr-h1s from other crustacean species, but differing from the eight zinc finger motifs found in insect Kr-h1s. MF treatment in vitro induced the expression of Pt-Kr-h1 in hepatopancreas but not ovary, which is similar to the MF-responsive pattern of Pt-Met as previously reported. Moreover, the expression of Pt-Kr-h1 decreased significantly after treating with Pt-Met dsRNA, strongly indicating that the Pt-Kr-h1 might be involved in the Met-mediated MF signaling pathway. RNAi of Pt-Met and Pt-Kr-h1 both led to a decrease in vitellogenin (Vg) expression, and the reduction cannot be rescued by adding MF, suggesting the regulation of vitellogenesis by MF may act through Met and Kr-h1. These results would help to enhance the current understanding of the regulatory mechanism of MF signaling, and provide a vital resource for further research into the evolution of hormonal pathways in arthropods.

MicroRNAs regulate the sesquiterpenoid hormonal pathway in Drosophila and other arthropods

Arthropods comprise the majority of all described animal species, and understanding their evolution is a central question in biology. Their developmental processes are under the precise control of distinct hormonal regulators, including the sesquiterpenoids juvenile hormone (JH) and methyl farnesoate. The control of the synthesis and mode of action of these hormones played important roles in the evolution of arthropods and their adaptation to diverse habitats. However, the precise roles of non-coding RNAs, such as microRNAs (miRNAs), controlling arthropod hormonal pathways are unknown. Here, we investigated the miRNA regulation of the expression of the juvenile hormone acid methyltransferase gene (JHAMT), which encodes a rate-determining sesquiterpenoid biosynthetic enzyme. Loss of function of the miRNA bantam in the fly Drosophila melanogaster increased JHAMT expression, while overexpression of the bantam repressed JHAMT expression and resulted in pupal lethality. The male genital organs of the pupae were malformed, and exogenous sesquiterpenoid application partially rescued the genital deformities. The role of the bantam in the regulation of sesquiterpenoid biosynthesis was validated by transcriptomic, qPCR and hormone titre (JHB3 and JH III) analyses. In addition, we found a conserved set of miRNAs that interacted with JHAMT, and the sesquiterpenoid receptor methoprene-tolerant (Met) in different arthropod lineages, including insects (fly, mosquito and beetle), crustaceans (water flea and shrimp), myriapod (centipede) and chelicerate (horseshoe crab). This suggests that these miRNAs might have conserved roles in the post-transcriptional regulation of genes in sesquiterpenoid pathways across the Panarthropoda. Some of the identified lineage-specific miRNAs are potential targets for the development of new strategies in aquaculture and agricultural pest control.

The potential role of juvenile hormone acid methyltransferase in methyl farnesoate (MF) biosynthesis in the swimming crab, Portunus trituberculatus

Juvenile hormone (JH) and methyl farnesoate (MF) play essential roles in the development and reproduction of insects and crustaceans respectively. Juvenile hormone acid methyltransferase (JHAMT) catalyzes the methyl esterification in insect JH biosynthesis, while the corresponding step in crustacean MF biosynthesis was long thought to be catalyzed by farnesoic acid O-methyltransferase (FAMeT). However, the new discovery of JHAMT orthologs in crustaceans indicates that JHAMT may also play essential role in the MF biosynthesis in crustaceans. Here we cloned and characterized the full-length cDNA encoding JHAMT in the swimming crab Portunus trituberculatus (PtJHAMT). Sequence and structure analysis of PtJHAMT revealed that it was composed of a 6-stranded β sheet with 9 α helices, and contained a signature Sadenosyl-L-methionine (SAM) binding motif, which is the hallmark in all SAM dependent methyltransferases (SAM-MTs). Several active sites that are critical for the interaction of SAM and JH/FA substrate were also conserved in PtJHAMT. The gene expression of PtJHAMT was highly specific to the mandibular organ, which is the sole site of MF synthesis. PtJHAMT expression significantly increased in the late-vitellogenic stage and mature stage, which suggests a possible role of PtJHAMT in modulating ovarian development. The role of PtJHAMT and PtFAMeT in MF biosynthesis was further investigated by RNA interfering (RNAi). Injection of PtJHAMT and PtFAMeT dsRNA both led to a decrease in hemolymph MF titers. Injection of PtHMGR dsRNA caused the decrease in PtJHAMT expression, but had no effect on mRNA level of PtFAMeT. Together these results suggested that JHAMT and FAMeT are both involved in the MF biosynthesis in crustaceans, while the JHAMT is highly specific to FA substrate, and FAMeT may have more catalytic functions.

Methyl farnesoate synthesis is necessary for the environmental sex determination in the water flea Daphnia pulex

Sex-determination systems can be divided into two groups: genotypic sex determination (GSD) and environmental sex determination (ESD). ESD is an adaptive life-history strategy that allows control of sex in response to environmental cues in order to optimize fitness. However, the molecular basis of ESD remains largely unknown. The micro crustacean Daphnia pulex exhibits ESD in response to various external stimuli. Although methyl farnesoate (MF: putative juvenile hormone, JH, in daphnids) has been reported to induce male production in daphnids, the role of MF as a sex-determining factor remains elusive due to the lack of a suitable model system for its study. Here, we establish such a system for ESD studies in D. pulex. The WTN6 strain switches from producing females to producing males in response to the shortened day condition, while the MFP strain only produces females, irrespective of day-length. To clarify whether MF has a novel physiological role as a sex-determining factor in D. pulex, we demonstrate that a MF/JH biosynthesis inhibitor suppressed male production in WTN6 strain reared under the male-inducible condition, shortened day-length. Moreover, we show that juvenile hormone acid O-methyltransferase (JHAMT), a critical enzyme of MF/JH biosynthesis, displays MF-generating activity by catalyzing farnesoic acid. Expression of the JHAMT gene increased significantly just before the MF-sensitive period for male production in the WTN6 strain, but not in the MFP strain, when maintained under male-inducible conditions. These results suggest that MF synthesis regulated by JHAMT is necessary for male offspring production in D. pulex. Our findings provide novel insights into the genetic underpinnings of ESD and they begin to shed light on the physiological function of MF as a male-fate determiner in D. pulex.

How Did Arthropod Sesquiterpenoids and Ecdysteroids Arise? Comparison of Hormonal Pathway Genes in Noninsect Arthropod Genomes

The phylum Arthropoda contains the largest number of described living animal species, with insects and crustaceans dominating the terrestrial and aquatic environments, respectively. Their successful radiations have long been linked to their rigid exoskeleton in conjunction with their specialized endocrine systems. In order to understand how hormones can contribute to the evolution of these animals, here, we have categorized the sesquiterpenoid and ecdysteroid pathway genes in the noninsect arthropod genomes, which are known to play important roles in the regulation of molting and metamorphosis in insects. In our analyses, the majority of gene homologs involved in the biosynthetic, degradative, and signaling pathways of sesquiterpenoids and ecdysteroids can be identified, implying these two hormonal systems were present in the last common ancestor of arthropods. Moreover, we found that the “Broad-Complex” was specifically gained in the Pancrustacea, and the innovation of juvenile hormone (JH) in the insect linage correlates with the gain of the JH epoxidase (CYP15A1/C1) and the key residue changes in the binding domain of JH receptor (“Methoprene-tolerant”). Furthermore, the gain of “Phantom” differentiates chelicerates from the other arthropods in using ponasterone A rather than 20-hydroxyecdysone as molting hormone. This study establishes a comprehensive framework for interpreting the evolution of these vital hormonal pathways in these most successful animals, the arthropods, for the first time.

Identification of putative ecdysteroid and juvenile hormone pathway genes in the shrimp Neocaridina denticulata

Although the sesquiterpenoid juvenile hormone (JH) and the steroidal ecdysteroids are of vital importance to the development and reproduction of insects, our understanding of the evolution of these crucial hormonal regulators in other arthropods is limited. To better understand arthropod hormone evolution and regulation, here we describe the hormonal pathway genes (e.g. those involved in hormone biosynthesis, degradation, regulation and signal transduction) of a new decapod model, the shrimp Neocaridina denticulata. The majority of known insect sesquiterpenoid and ecdysteroid pathway genes and their regulators are contained in the N. denticulata genome. In the sesquiterpenoid pathway, these include biosynthetic pathway components: juvenile hormone acid methyltransferase (JHAMT); hormone binding protein: juvenile hormone binding protein (JHBP); and degradation pathway components: juvenile hormone esterase (JHE), juvenile hormone esterase binding protein (JHEBP) and juvenile hormone epoxide hydrolase (JHEH), with the JHBP, JHEBP and JHEH genes being discovered in a crustacean for the first time here. Ecdysteroid biosynthetic pathway genes identified include spook, phantom, disembodied, shadow and CYP18. Potential hormonal regulators and signal transducers such as allatostatins (ASTs), Methoprene-tolerant (Met), Retinoid X receptor (RXR), Ecdysone receptor (EcR), calponin-like protein Chd64, FK509-binding protein (FKBP39), Broad-complex (Br-c), and crustacean hyperglycemic hormone/molt-inhibiting hormone/gonad-inhibiting hormone (CHH/MIH/GIH) genes are all present in the shrimp N. denticulata. To our knowledge, this is the first report of these hormonal pathways and their regulatory genes together in a single decapod, providing a vital resource for further research into development, reproduction, endocrinology and evolution of crustaceans, and arthropods in general.

Cloning and expressing a highly functional and substrate specific farnesoic acid o-methyltransferase from the Asian citrus psyllid (Diaphorina citri Kuwayama)

The Asian citrus psyllid, Diaphorina citri, transmits a phloem-limited bacterium, Candidatus 'Liberibacter' asiaticus that causes citrus greening disease. Because juvenile hormone (JH) plays an important role in adult and nymphal development, we studied the final steps in JH biosynthesis in D. citri. A putative JH acid methyltransferase ortholog gene (jmtD) and its cognate cDNA were identified by searching D. citri genome database. Expression analysis shows expression in all life stages. In adults, it is expressed in the head-thorax, (containing the corpora allata), and the abdomen (containing ovaries and male accessory glands). A 3D protein model identified the catalytic groove with catalytically active amino acids and the S-adenosyl methionine (SAM)-binding loop. The cDNA was expressed in Escherichia coli cells and the purified enzyme showed high preference for farnesoic acid (FA) and homoFA (kcat of 0.752 × 10(-3) and 0.217 × 10(-3) s(-1), respectively) as compared to JH acid I (JHA I) (cis/trans/cis; 2Z, 6E, 10cis), JHA III (2E, 6E, 10cis), and JHA I (trans/cis/cis; 2E, 2Z, 10cis) (kcat of 0.081 × 10(-3), 0.013 × 10(-3), and 0.003 × 10(-3) s(-1), respectively). This suggests that this ortholog is a DcFA-o-methyl transferase gene (fmtD), not a jmtD, and that JH biosynthesis in D. citri proceeds from FA to JH III through methyl farnesoate (MF). DcFA-o-MT does not require Ca(2+), Mg(2+) or Zn(2+), however, Zn(2+) (1 mM) completely inhibits the enzyme probably by binding H115 at the active groove. This represents the first purified FA-o-MT from Hemiptera with preferred biological activity for FA and not JHA.

Identification of genes associated with reproduction in the Mud Crab (Scylla olivacea) and their differential expression following serotonin stimulation

The central nervous system (CNS) is often intimately involved in reproduction control and is therefore a target organ for transcriptomic investigations to identify reproduction-associated genes. In this study, 454 transcriptome sequencing was performed on pooled brain and ventral nerve cord of the female mud crab (Scylla olivacea) following serotonin injection (5 µg/g BW). A total of 197,468 sequence reads was obtained with an average length of 828 bp. Approximately 38.7% of 2,183 isotigs matched with significant similarity (E value < 1e⁻⁴) to sequences within the Genbank non-redundant (nr) database, with most significant matches being to crustacean and insect sequences. Approximately 32 putative neuropeptide genes were identified from nonmatching blast sequences. In addition, we identified full-length transcripts for crustacean reproductive-related genes, namely farnesoic acid o-methyltransferase (FAMeT), estrogen sulfotransferase (ESULT) and prostaglandin F synthase (PGFS). Following serotonin injection, which would normally initiate reproductive processes, we found up-regulation of FAMeT, ESULT and PGFS expression in the female CNS and ovary. Our data here provides an invaluable new resource for understanding the molecular role of the CNS on reproduction in S. olivacea.

The first myriapod genome sequence reveals conservative arthropod gene content and genome organisation in the centipede Strigamia maritima

Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.

Arthropods are the most abundant animals on earth. Among them, insects clearly dominate on land, whereas crustaceans hold the title for the most diverse invertebrates in the oceans. Much is known about the biology of these groups, not least because of genomic studies of the fruit fly Drosophila, the water flea Daphnia, and other species used in research. Here we report the first genome sequence from a species belonging to a lineage that has previously received very little attention—the myriapods. Myriapods were among the first arthropods to invade the land over 400 million years ago, and survive today as the herbivorous millipedes and venomous centipedes, one of which—Strigamia maritima—we have sequenced here. We find that the genome of this centipede retains more characteristics of the presumed arthropod ancestor than other sequenced insect genomes. The genome provides access to many aspects of myriapod biology that have not been studied before, suggesting, for example, that they have diversified receptors for smell that are quite different from those used by insects. In addition, it shows specific consequences of the largely subterranean life of this particular species, which seems to have lost the genes for all known light-sensing molecules, even though it still avoids light.

Proteogenomics of Gammarus fossarum to document the reproductive system of amphipods

Because of their ecological importance, amphipod crustacea are employed worldwide as test species in environmental risk assessment. Although proteomics allows new insights into the molecular mechanisms related to the stress response, such investigations are rare for these organisms because of the lack of comprehensive protein sequence databases. Here, we propose a proteogenomic approach for identifying specific proteins of the freshwater amphipod Gammarus fossarum, a keystone species in European freshwater ecosystems. After deep RNA sequencing, we created a comprehensive ORF database. We identified and annotated the most relevant proteins detected through a shotgun tandem mass spectrometry analysis carried out on the proteomes from three major tissues involved in the organism's reproductive function: the male and female reproductive systems, and the cephalon, where different neuroendocrine glands are present. The 1,873 mass-spectrometry-certified proteins represent the largest crustacean proteomic resource to date, with 218 proteins being lineage specific. Comparative proteomics between the male and female reproductive systems indicated key proteins with strong sexual dimorphism. Protein expression profiles during spermatogenesis at seven different stages highlighted the major gammarid proteins involved in the different facets of reproduction.

Genome-wide comparison of genes involved in the biosynthesis, metabolism, and signaling of juvenile hormone between silkworm and other insects

Juvenile hormone (JH) contributes to the regulation of larval molting and metamorphosis in insects. Herein, we comprehensively identified 55 genes involved in JH biosynthesis, metabolism and signaling in the silkworm (Bombyx mori) as well as 35 in Drosophila melanogaster, 35 in Anopheles gambiae, 36 in Apis mellifera, 47 in Tribolium castaneum, and 44 in Danaus plexippus. Comparative analysis showed that each gene involved in the early steps of the mevalonate (MVA) pathway, in the neuropeptide regulation of JH biosynthesis, or in JH signaling is a single copy in B. mori and other surveyed insects, indicating that these JH-related pathways or steps are likely conserved in all surveyed insects. However, each gene participating in the isoprenoid branch of JH biosynthesis and JH metabolism, together with the FPPS genes for catalyzing the final step of the MVA pathway of JH biosynthesis, exhibited an obvious duplication in Lepidoptera, including B. mori and D. plexippus. Microarray and real-time RT-PCR analysis revealed that different copies of several JH-related genes presented expression changes that correlated with the dynamics of JH titer during larval growth and metamorphosis. Taken together, the findings suggest that duplication-derived copy variation of JH-related genes might be evolutionarily associated with the variation of JH types between Lepidoptera and other insect orders. In conclusion, our results provide useful clues for further functional analysis of JH-related genes in B. mori and other insects.

Comparison of JH signaling in insects and crustaceans

Physiological importance of sesquiterpenoids such as the juvenile hormone (JH) has been recognized in both insects and crustaceans. Yet, little is known about when and how these two closely related arthropod groups acquired the JH signaling system. Methyl farnesoate (MF), a natural precursor of insect JH, has been identified as an innate JH of crustaceans. However, the reception and molecular signaling downstream of MF in crustaceans is much less explored than JH signaling is in insects, where the Methoprene-tolerant (Met) protein has been characterized as a JH receptor. A recent study has shown that Daphnia Met responds to MF in a way insect Met responds to JH, suggesting that JH reception is conserved between insects and crustaceans. To understand the origin and evolution of JH signaling, further studies, extended to more ancestral arthropods, are needed.

How are comparative genomics and the study of microRNAs changing our views on arthropod endocrinology and adaptations to the environment?

As the last few decades of work has shown, precise regulation of biosynthesis and release of arthropod hormones is essential to cope with environmental stresses and challenges. In crustaceans and insects, the sesquiterpenoids methyl farnesoate (MF), farnesoic acid (FA) and juvenile hormone (JH) regulate many developmental, physiological, and reproductive processes. In this review, we discuss how comparative genomics has and will impact our views on arthropod endocrinology. We will also highlight the current knowledge of regulation of genes involved in arthropod hormone biosynthesis by microRNAs, and describe the potential insights into arthropod endocrinology, evolution, and adaptation that are likely to come from the study of microRNAs.

Identification of relevant cancer related-genes in the flat oyster Ostrea edulis affected by disseminated neoplasia

Disseminated neoplasia (DN), an oyster disease resembling leukaemia, has been reported in a number of species of marine bivalve molluscs. The disease is characterised by a proliferation of abnormal circulating cells of unknown origin resulting in the invasion of tissues and organs, frequently with a fatal end of the affected individuals. To obtain a more comprehensive view of bivalve cancer processes, suppressive subtracted hybridisation (SSH) and quantitative RT-PCR (q-PCR) approaches were combined to investigate changes in the transcriptome of Ostrea edulis haemolymph cells associated to DN. Two SSH libraries were constructed and 587 expressed sequence tags (ESTs) were sequenced, obtaining 329 ESTs which showed expression changes in neoplastic process. Transcription expression analyses (q-PCR) were done for a total of 24 genes that could be relevant in neoplastic process, including genes with role in the regulation of cell cycle, apoptosis or chromosomal defects. Most of those genes had not been reported in association with cancer in non-vertebrate organisms. The over-expression and under-expression of some of those genes in DN-affected oysters was in agreement with observations in vertebrate cancer. The results herein reported contribute to cancer understanding in bivalve molluscs.

Farnesoic acid and methyl farnesoate production during lobster reproduction: possible functional correlation with retinoid X receptor expression

Farnesoic acid (FA) and methyl farnesoate (MF) are juvenile hormone-related compounds secreted by the mandibular organ (MO) of crustaceans and play an important role in stimulation of ovarian maturation. To better understand how the MO activity influences female reproduction by secretion of FA and MF, the biosynthesis and release of these two compounds were measured in vitro by the incorporation of l-[(3)H-methyl]methionine into MF and [2-(14)C]acetate into FA by the MO of Homarus americanus. The production of FA is 7.5 times that of MF, and most FA and MF synthesized remained within the gland, and was not released into the surrounding medium. Most FA and MF were synthesized in the anterior fan-fold region of the MO. The rates of biosynthesis of FA and MF were stage-related, with maximal production occurring during secondary vitellogenesis (i.e. stages 4 and 5). A potential juvenoid receptor, retinoid X receptor (RXR), HaRXR, was characterized using PCR cloning techniques. HaRXR belongs to the nuclear hormone receptor superfamily and its deduced amino acid sequence shares a high homology to other RXRs of crustaceans, insects, and vertebrates. Transcripts of HaRXR can be detected in many tissues, and significant high expression level was detected in the MO, especially in the anterior fan-fold region. Expression of HaRXR was also related to reproductive stage, and maximal level of expression was observed at stage 4, in which secondary vitellogenesis is occurring. Changes in transcript level of HaRXR and the rates of FA/MF biosynthesis in the female reproductive cycle indicate that HaRXR and FA/MF may play important roles in crustacean reproduction.

Final steps in juvenile hormone biosynthesis in the desert locust, Schistocerca gregaria

Two genes coding for enzymes previously reported to be involved in the final steps of juvenile hormone (JH) biosynthesis in different insect species, were characterised in the desert locust, Schistocerca gregaria. Juvenile hormone acid O-methyltransferase (JHAMT) was previously described to catalyse the conversion of farnesoic acid (FA) and JH acid to their methyl esters, methyl farnesoate (MF) and JH respectively. A second gene, CYP15A1 was reported to encode a cytochrome P450 enzyme responsible for the epoxidation of MF to JH. Additionally, a third gene, FAMeT (originally reported to encode a farnesoic acid methyltransferase) was included in this study. Using q-RT-PCR, all three genes (JHAMT, CYP15A1 and FAMeT) were found to be primarily expressed in the CA of the desert locust, the main biosynthetic tissue of JH. An RNA interference approach was used to verify the orthologous function of these genes in S. gregaria. Knockdown of the three genes in adult animals followed by the radiochemical assay (RCA) for JH biosynthesis and release showed that SgJHAMT and SgCYP15A1 are responsible for synthesis of MF and JH respectively. Our experiments did not show any involvement of SgFAMeT in JH biosynthesis in the desert locust. Effective and selective inhibitors of SgJHAMT and SgCYP15A1 would likely represent selective biorational locust control agents.

Putative-farnesoic acid O-methyltransferase (FAMeT) in medfly reproduction

A gene potentially involved in juvenile hormone (JH) biosynthesis was previously identified in Ceratitis capitata as the putative-farnesoic acid O-methyltransferase (FAMeT). Since JH is involved in insect reproduction, we silenced the putative-FAMeT expression by RNA interference in Ceratitis capitata to evaluate its implication in egg production. FAMeT gene expression was knocked down in females and males after eclosion and in 1- and 2-day-old females. Treated specimens were left to mate with each other or with untreated partners to evaluate the extent of each sex influencing egg production. Gene silencing was investigated by Real-Time PCR. Results unambiguously showed that FAMeT has a measurable role on the fertility of both medfly sexes.