A novel gene in the takeout gene family is regulated by hormones and nutrients in Manduca larval epidermis

CRISPR/Cas9-mediated knockout of a male accessory glands-specific gene takeout1 decreases the fecundity of Zeugodacus cucurbitae female

BACKGROUND

The melon fly, Zeugodacus cucurbitae (Coquillett), is an invasive Tephritidae pest with robust fertility. The male accessory glands (MAGs) form a vital organ that ensures insect reproductive efficiency. Most of the secreted proteins by MAGs exhibit a male bias expression. Takeout, one of these proteins, is abundantly present in the MAGs of many insects.

RESULTS

In this study, we identified 32 takeout genes in Z. cucurbitae. The phylogenetic analysis and multiple sequence alignment results showed that Zctakeout1 is the most related homolog to the MAGs-specific takeout in Tephritidae. The real-time quantitative PCR results showed that Zctakeout1 was exclusively expressed in the male adult stage, and its expression level gradually increased with the increase in age and then remained stable at the sexually matured stage. The distribution among tissues demonstrated the specific expression of Zctakeout1 in the MAGs, and fluorescence immunohistochemical results confirmed the presence of Zctakeout1 in close proximity to binuclear cells of the mesoderm epidermal MAGs. In continuation, CRISPR/Cas9-mediated genome editing was employed, resulting in successfully generating a homozygous strain with an +8 bp insertion. The mating experiments with the Zctakeout1-/- males resulted in significant reductions in both the mating rate and egg production of females.

CONCLUSION

These findings prove that the MAGs-specific Zctakeout1 is essential in regulating fecundity in female Z. cucurbitae fruit flies. Our data suggests its utilization in future essential insect-specific gene-directed sterility insect technique (SIT) by the genetic manipulation to keep these important Tephritidae populations under control. © 2024 Society of Chemical Industry.

Identification and analysis of JHBP/TO family genes and their roles in the reproductive fitness cost of resistance in Frankliniella occidentalis (Pergande)

The juvenile hormone binding protein (JHBP) and takeout (TO) genes, mediated by the juvenile hormone (JH), play a crucial role in regulating the reproductive physiology of insects. Our previous study revealed that spinosad-resistant Frankliniella occidentalis (NIL-R) exhibited reduced fecundity and significant changes in JHBP/TO family gene expression. We hypothesized that these genes were involved in regulating the fitness costs associated with resistance. In this study, 45 JHBP/TO genes were identified in F. occidentalis, among which FoTO2 and FoTO10 were duplicates. Additionally, eight genes exhibited significant down-regulation in the NIL-R population. Two genes (FoTO6 and FoTO24) that exhibited the most significant differential expression between the spinosad-susceptible (Ivf03) and NIL-R populations were selected to investigate their roles in resistance fitness using RNA interference (RNAi). Following interference with FoTO6, FoTO24, and their combination, the expression levels of vitellogenin (Vg) were downregulated by 3%-30%, 13%-28%, and 14%-32% from the 2nd day to the 5th day, respectively; Krüppel-homolog 1 (Kr-h1) expression was down-regulated by 3%-65%, 11%-34%, and 11%-39% from the 2nd day to the 5th day, respectively; ovariole length was shortened by approximately 18%, 21%, and 24%, respectively; and the average number of eggs decreased from 407 to 260, 148, and 106, respectively. Additionally, a JH supplementation experiment on the NIL-R population revealed that the expression levels of both FoTO6, FoTO24, Vg and Kr-h1 were significantly upregulated compared with those observed in the Ivf03 population, resulting in increased fecundity. These results suggest that FoTO6 and FoTO24 are involved in JH-mediated regulation of the reproductive fitness cost of resistance to spinosad. Further, FoTO6 and FoTO24 can be considered potential target genes for applying RNAi technology in the scientific management of F. occidentalis.

Local age-dependent neuromodulation in Rhodnius prolixus antennae

Kissing bugs do not respond to host cues when recently molted and only exhibit robust host-seeking several days after ecdysis. Behavioral plasticity has peripheral correlates in antennal gene expression changes through the week after ecdysis. The mechanisms regulating these peripheral changes are still unknown, but neuropeptide, G-protein coupled receptor, nuclear receptor, and takeout genes likely modulate peripheral sensory physiology. We evaluated their expression in antennal transcriptomes along the first week postecdysis of Rhodnius prolixus 5th instar larvae. Besides, we performed clustering and co-expression analyses to reveal relationships between neuromodulatory (NM) and sensory genes. Significant changes in transcript abundance were detected for 50 NM genes. We identified 73 sensory-related and NM genes that were assigned to nine clusters. According to their expression patterns, clusters were classified into four groups: two including genes up or downregulated immediately after ecdysis; and two with genes with expression altered at day 2. Several NM genes together with sensory genes belong to the first group, suggesting functional interactions. Co-expression network analysis revealed a set of genes that seem to connect with sensory system maturation. Significant expression changes in NM components were described in the antennae of R. prolixus after ecdysis, suggesting that a local NM system acts on antennal physiology. These changes may modify the sensitivity of kissing bugs to host cues during this maturation interval.

The pharyngeal taste organ of a blood-feeding insect functions in food recognition

BACKGROUND

Obligate blood-feeding insects obtain the nutrients and water necessary to ensure survival from the vertebrate blood. The internal taste sensilla, situated in the pharynx, evaluate the suitability of the ingested food. Here, through multiple approaches, we characterized the pharyngeal organ (PO) of the hematophagous kissing bug Rhodnius prolixus to determine its role in food assessment. The PO, located antero-dorsally in the pharynx, comprises eight taste sensilla that become bathed with the incoming blood.

RESULTS

We showed that these taste sensilla house gustatory receptor neurons projecting their axons through the labral nerves to reach the subesophageal zone in the brain. We found that these neurons are electrically activated by relevant appetitive and aversive gustatory stimuli such as NaCl, ATP, and caffeine. Using RNA-Seq, we examined the expression of sensory-related gene families in the PO. We identified gustatory receptors, ionotropic receptors, transient receptor potential channels, pickpocket channels, opsins, takeouts, neuropeptide precursors, neuropeptide receptors, and biogenic amine receptors. RNA interference assays demonstrated that the salt-related pickpocket channel Rproppk014276 is required during feeding of an appetitive solution of NaCl and ATP.

CONCLUSIONS

We provide evidence of the role of the pharyngeal organ in food evaluation. This work shows a comprehensive characterization of a pharyngeal taste organ in a hematophagous insect.

Caste-specific expressions and diverse roles of takeout genes in the termite Reticulitermes speratus

Acquisition of novel functions caused by gene duplication may be important for termite social evolution. To clarify this possibility, additional evidence is needed. An important example is takeout, encoding juvenile hormone binding protein. We identified 25 takeouts in the termite Reticulitermes speratus genome. RNA-seq revealed that many genes were highly expressed in specific castes. Two novel paralogs (RsTO1, RsTO2) were tandemly aligned in the same scaffold. Real-time qPCR indicated that RsTO1 and RsTO2 were highly expressed in queens and soldiers, respectively. Moreover, the highest RsTO1 expression was observed in alates during queen formation. These patterns were different from vitellogenins, encoding egg-yolk precursors, which were highly expressed in queens than alates. In situ hybridization showed that RsTO1 mRNA was localized in the alate-frontal gland, indicating that RsTO1 binds with secretions probably used for the defence during swarming flight. In contrast, increased RsTO2 expression was observed approximately 1 week after soldier differentiation. Expression patterns of geranylgeranyl diphosphate synthase, whose product functions in the terpenoid synthesis, were similar to RsTO2 expression. In situ hybridization indicated RsTO2-specific mRNA signals in the soldier-frontal gland. RsTO2 may interact with terpenoids, with a soldier-specific defensive function. It may provide additional evidence for functionalization after gene duplication in termites.

The antennal transcriptome of Triatoma infestans reveals substantial expression changes triggered by a blood meal

BACKGROUND

Triatoma infestans is the main vector of Chagas disease in the Americas, currently transmitting it in Argentina, Paraguay, and Bolivia. Many T. infestans populations present insecticide resistance, reducing the efficiency of control campaigns. Alternative vector control methods are needed, and molecular targets mediating fundamental physiological processes can be a promising option to manipulate kissing bug behavior. Therefore, it is necessary to characterize the main sensory targets, as well as to determine whether they are modulated by physiological factors. In order to identify gene candidates potentially mediating host cue detection, the antennal transcripts of T. infestans fifth instar larvae were sequenced and assembled. Besides, we evaluated whether a blood meal had an effect on transcriptional profiles, as responsiveness to host-emitted sensory cues depends on bug starvation.

RESULTS

The sensory-related gene families of T. infestans were annotated (127 odorant receptors, 38 ionotropic receptors, 11 gustatory receptors, 41 odorant binding proteins, and 25 chemosensory proteins, among others) and compared to those of several other hemipterans, including four triatomine species. Several triatomine-specific lineages representing sensory adaptations developed through the evolution of these blood-feeding heteropterans were identified. As well, we report here various conserved sensory gene orthogroups shared by heteropterans. The absence of the thermosensor pyrexia, of pickpocket receptor subfamilies IV and VII, together with clearly expanded takeout repertoires, are revealed features of the molecular bases of heteropteran antennal physiology. Finally, out of 2,122 genes whose antennal expression was significantly altered by the ingestion of a blood meal, a set of 41 T. infestans sensory-related genes (9 up-regulated; 32 down-regulated) was detected.

CONCLUSIONS

We propose that the set of genes presenting nutritionally-triggered modulation on their expression represent candidates to mediate triatomine host-seeking behavior. Besides, the triatomine-specific gene lineages found represent molecular adaptations to their risky natural history that involves stealing blood from an enormously diverse set of vertebrates. Heteropteran gene orthogroups identified may represent unknown features of the sensory specificities of this largest group of hemipteroids. Our work is the first molecular characterization of the peripheral modulation of sensory processes in a non-dipteran vector of human disease.

Dynamic neurogenomic responses to social interactions and dominance outcomes in female paper wasps

Social interactions have large effects on individual physiology and fitness. In the immediate sense, social stimuli are often highly salient and engaging. Over longer time scales, competitive interactions often lead to distinct social ranks and differences in physiology and behavior. Understanding how initial responses lead to longer-term effects of social interactions requires examining the changes in responses over time. Here we examined the effects of social interactions on transcriptomic signatures at two times, at the end of a 45-minute interaction and 4 hours later, in female Polistes fuscatus paper wasp foundresses. Female P. fuscatus have variable facial patterns that are used for visual individual recognition, so we separately examined the transcriptional dynamics in the optic lobe and the non-visual brain. Results demonstrate much stronger transcriptional responses to social interactions in the non-visual brain compared to the optic lobe. Differentially regulated genes in response to social interactions are enriched for memory-related transcripts. Comparisons between winners and losers of the encounters revealed similar overall transcriptional profiles at the end of an interaction, which significantly diverged over the course of 4 hours, with losers showing changes in expression levels of genes associated with aggression and reproduction in paper wasps. On nests, subordinate foundresses are less aggressive, do more foraging and lay fewer eggs compared to dominant foundresses and we find losers shift expression of many genes in the non-visual brain, including vitellogenin, related to aggression, worker behavior, and reproduction within hours of losing an encounter. These results highlight the early neurogenomic changes that likely contribute to behavioral and physiological effects of social status changes in a social insect.

The Draft Genome of Yellow Stem Borer, an Agriculturally Important Pest, Provides Molecular Insights into Its Biology, Development and Specificity Towards Rice for Infestation

Simple Summary

Yellow stem borer (YSB), is the most destructive and widely occurring pest that attacks rice throughout the growing season. Rice (Oryza sativa L.) is a major staple cereal worldwide, providing essential caloric requirements for more than half of the world’s population. Annual losses to rice borers are approximately 5–10%, but losses in individual fields may reach up to 50–60%. The use of traditional pest management strategies in controlling YSB is somewhat challenging due to its unique internal feeding habit. Genome sequence information of economically important crop pests is important for designing or developing pest-resistant rice varieties. In an approach to achieve this, we present our first-ever study on the draft genome sequence of YSB. The information provided from our current study might be useful in developing genome-based approaches for the management of pest species.

Abstract

Yellow stem borer (YSB), Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), a major monophagous insect pest of rice, causes significant yield losses. The rice–YSB interaction is very dynamic, making it difficult for management. The development of resistant lines has been unsuccessful as there are no effective resistant sources in the germplasm. Genome information is necessary for a better understanding of interaction with rice in terms of its recognition, response, and infestation mechanism. The draft genome of YSB is predicted to have 46,057 genes with an estimated size of 308 Mb, being correlated with the flow cytometry analysis. The existence of complex metabolic mechanisms and genes related to specific behavior was identified, being conditioned by a higher level of regulation. We deciphered the possible visual, olfactory, and gustatory mechanisms responsible for its evolution as a monophagous pest. Comparative genomic analysis revealed that YSB is unique in the way it has evolved. The obvious presence of high-immunity-related genes, well-developed RNAi machinery, and diverse effectors provides a means for developing genomic tools for its management. The identified 21,696 SSR markers can be utilized for diversity analysis of populations across the rice-growing regions. We present the first draft genome of YSB. The information emanated paves a way for biologists to design novel pest management strategies as well as for the industry to design new classes of safer and specific insecticide molecules.

Characterization of Rhopalosiphum padi takeout-like genes and their role in insecticide susceptibility

Due to the extensive use of chemical insecticides, the field populations of Rhopalosiphum padi, a serious wheat pest worldwide, have developed resistance to insecticides. Therefore, deep understanding of the mechanisms of the aphid's physiological response to insecticides would be of importance for the management of insecticide resistance in pests. Takeout belongs to a protein superfamily found exclusively in insects. Previous research showed that the takeout gene had various functions in insect physiology and behavior. However, few studies have explored the functions of takeout in insect insecticide susceptibility. The susceptibility of R. padi to imidacloprid and beta-cypermethrin was tested. Thirteen takeout-like genes were identified based on the genome database of R. padi. The number of exons was variable in these takeout-like genes, and nine highly conserved amino acids (two Cysteine, two Proline, four Glycine and one Aspartic acid) were identified. Expression levels of takeout-like-2, takeout-like-3, takeout-like-5, takeout-like-8, takeout-like-10 and takeout-like-11 were significantly increased after imidacloprid treatment; seven genes (takeout-like-1, takeout-like-2, takeout-like-5, takeout-like-6, takeout-like-7, takeout-like-8 and takeout-like-11) tended to be upregulated after beta-cypermethrin treatment. RNA interference results showed that the mortalities of R. padi injected with dsTOL-2, dsTOL-5, dsTOL-8, dsTOL-10 and dsTOL-11 were significantly increased after exposure to imidacloprid in comparison with control (injection of dsGFP). Under two sublethal concentrations of beta-cypermethrin, the silencing of takeout-like-2, takeout-like-5 and takeout-like-11 significantly increased the mortalities of R. padi. These results provide evidence for the involvement of takeout-like genes in insecticide susceptibility of R. padi, which improves our understanding the determinant of insecticide susceptibility.

Juvenile hormone suppresses aggregation behavior through influencing antennal gene expression in locusts

Animals often exhibit dramatically behavioral plasticity depending on their internal physiological state, yet little is known about the underlying molecular mechanisms. The migratory locust, Locusta migratoria, provides an excellent model for addressing these questions because of their famous phase polyphenism involving remarkably behavioral plasticity between gregarious and solitarious phases. Here, we report that a major insect hormone, juvenile hormone, is involved in the regulation of this behavioral plasticity related to phase change by influencing the expression levels of olfactory-related genes in the migratory locust. We found that the treatment of juvenile hormone analog, methoprene, can significantly shift the olfactory responses of gregarious nymphs from attraction to repulsion to the volatiles released by gregarious nymphs. In contrast, the repulsion behavior of solitarious nymphs significantly decreased when they were treated with precocene or injected with double-stranded RNA of JHAMT, a juvenile hormone acid O-methyltransferase. Further, JH receptor Met or JH-response gene Kr-h1 knockdown phenocopied the JH-deprivation effects on olfactory behavior. RNA-seq analysis identified 122 differentially expressed genes in antennae after methoprene application on gregarious nymphs. Interestingly, several olfactory-related genes were especially enriched, including takeout (TO) and chemosensory protein (CSP) which have key roles in behavioral phase change of locusts. Furthermore, methoprene application and Met or Kr-h1 knockdown resulted in simultaneous changes of both TO1 and CSP3 expression to reverse pattern, which mediated the transition between repulsion and attraction responses to gregarious volatiles. Our results suggest the regulatory roles of a pleiotropic hormone in locust behavioral plasticity through modulating gene expression in the peripheral olfactory system.

A behavioral change from shy solitarious individuals to highly social gregarious individuals is critical to the formation of disastrous swarms of locusts. However, the underlying molecular mechanism of behavioral plasticity regulated by hormones is still largely unknown. Here, we investigated the effect of juvenile hormone (JH) on the behavioral transition in fourth-instar gregarious and solitarious locusts. We found that JH induced the behavioral shift of the gregarious locust from attraction to repulsion to the volatiles of gregarious locusts. The solitarious locust significantly decreased repulsion behavior after deprivation of JH by precocene or knockdown of JHAMT, a key enzyme to synthesize JH. JH application on gregarious locusts caused significant expression alteration of genes, especially the olfactory genes TO and CSP in the antennae. We further demonstrated that the JH signaling pathway suppressed aggregation behavior in gregarious locusts by increasing TO1 expression and decreasing CSP3 expression at the same time. Our results suggested that internal physiological factors can directly modulate periphery olfactory system to produce behavioral plasticity.

Dissecting the Role of Juvenile Hormone Binding Protein in Response to Hormone and Starvation in the Cotton Bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Juvenile hormone (JH) regulates many physiological processes in insect development, diapause, and reproduction. Juvenile hormone binding protein (JHBP), the carrier partner protein of JH, is essential for the balance of JH titer to regulate the metamorphosis and development of insect. In this study, two JHBP genes were identified from Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), namely HaJHBP1 and HaJHBP2. The tissue and temporal expression pattern revealed that both HaJHBP1 and HaJHBP2 were dominantly expressed in larval fat body, and their high transcription stages were detected in fourth and fifth instars. The ingestion of methoprene, a JH analogue, significantly induced the expression of HaJHBP1 and HaJHBP2. However, both HaJHBP1 and HaJHBP2 mRNA levels were significantly downregulated after treated with a JH antagonist, precocene. When subject to starvation, larvae showed a marked suppressive effect in the expression of HaJHBP1 and HaJHBP2. These results indicate that JHBP plays a part in the JH-regulated metabolism, growth, or development in reaction to different nutritional conditions.

High functional conservation of takeout family members in a courtship model system

takeout (to) is one of the male-specific genes expressed in the fat body that regulate male courtship behavior, and has been shown to act as a secreted protein in conjunction with courtship circuits. There are 23 takeout family members in Drosophila melanogaster, and homologues of this family are distributed across insect species. Sequence conservation among family members is low. Here we test the functional conservation of takeout family members by examining whether they can rescue the takeout courtship defect. We find that despite their sequence divergence takeout members from Aedes aegypti and Epiphas postvittana, as well as family members from D. melanogaster can substitute for takeout in courtship, demonstrating their functional conservation. Making use of the known E. postvittana Takeout structure, we used homology modeling and amphipathic helix analysis and found high overall structural conservation, including high conservation of the structure and amphipathic lining of an internal cavity that has been shown to accommodate hydrophobic ligands. Together these data suggest a high degree of structural conservation that likely underlies functional conservation in courtship. In addition, we have identified a role for a conserved exposed protein motif important for the protein’s role in courtship.

Environmental and hormonal control of body color polyphenism in late-instar desert locust nymphs: Role of the yellow protein

Locusts show body color polyphenism that is considered to be an adaptation to various biotic and abiotic environmental changes. In Schistocerca gregaria, wild-type late-instar nymphs growing under crowded conditions (gregarious form) develop yellow and black body coloration, whereas they assume various body colors under isolated conditions (solitarious form). Black and green body colorations are induced by the neuropeptide corazonin (Crz) and juvenile hormone (JH), respectively. To characterize the molecular mechanisms controlling body color polyphenism, we investigated factors influencing body coloration in S. gregaria. We report here that yellow body coloration in the last nymphal instar is caused by the yellow protein of the takeout family (YPT) in this locust. YPT transcription was enhanced under high-temperature conditions during which the nymphs turned bright yellow and had little black patterning. RNAi-mediated YPT knockdown suppressed the appearance of yellow individuals and yellow staining in the exuviae. In albino nymphs, injection of JH induced yellow and green coloration and enhanced the YPT expression levels in both yellow and green individuals. YPT knockdown also suppressed yellow staining in the exuviae but did not prevent the appearance of yellow individuals. Therefore, another factor or pigment may contribute to the observed yellow body color. Injection of Crz into wild-type nymphs caused darkening and suppressed yellowing and YPT expression at high temperatures. Thus, Crz signaling could inhibit yellowing by suppressing YPT expression. Rearing cup substrate color significantly influenced YPT expression in albino nymphs both under isolated and crowded conditions. In contrast, substrate color affected YPT expression in wild-type nymphs only under isolated conditions. From these results, we conclude that YPT is an important factor in the control of body color polyphenism in S. gregaria, and its expression is influenced by temperature, JH, Crz, and substrate color of the growing environment.

Characterization of Spodoptera litura (Lepidoptera: Noctuidae) Takeout Genes and Their Differential Responses to Insecticides and Sex Pheromone

Spodoptera litura (S. litura) is one of the most serious agricultural insect pests worldwide. Takeout (TO) is involved in a variety of physiological and biochemical pathways and performs various biological functions. We characterized 18 S. litura TO genes and investigated their differential responses to insecticides and sex pheromones. All predicted TO proteins have two Cysteines that are unique to the N-terminal of the TO family proteins and contain four highly conserved Prolines, two Glycines, and one Tyrosine. The expression levels of seven TO genes in the male antennae were higher than those in the female antennae, although the expression levels of 10 TO genes in the female were higher than those in the male. We investigated the effects of the sex pheromone and three insecticides, that is, chlorpyrifos (Ch), emamectin benzoate (EB), and fipronil (Fi), on the expression levels of the TO genes in the antennae. The results showed that the insecticides and sex pheromone affect the expression levels of the TO genes. One day after the treatment, the expression levels of SlTO15 and SlTO4 were significantly induced by the Ch/EB treatment. Two days after the S. litura moths were treated with Fi, the expression of SlTO4 was significantly induced (28.35-fold). The expression of SlTO10 changed significantly after the Ch and EB treatment, although the expression of SlTO12 and SlTO15 was inhibited by the three insecticides after two days of treatment. Our results lay a foundation for studying the role of TO genes in the interaction between insecticides and sex pheromone.

Distinct Roles of Met and Interacting Proteins on the Expressions of takeout Family Genes in Brown Planthopper

The takeout family genes encode relatively small proteins that are related to olfaction and are regulated by juvenile hormone (JH). The takeout genes modulate various physiological processes, such as behavioral plasticity in the migratory locust Locusta migraloria and feeding and courtship behaviors in Drosophila. Therefore, to understand the regulatory mechanism of these physiological processes, it is important to study the expressions of the takeout genes that are regulated by JH signaling. We used quantitative real-time PCR (qRTPCR) to study the role of JH signaling in the regulation of the takeout family genes in the brown planthopper Nilaparvata lugens (N. lugens) through the application of Juvenile hormone III (JHIII) and the down-regulation of key genes in the JH signaling pathway. The topical application of JHIII induced the expressions of most of the takeout family genes, and their expressions decreased 2 and 3 days after the JHIII application. Down-regulating the brown planthopper JH receptor NlMethoprene-tolerant (NlMet) and its interacting partners, NlTaiman (NlTai) and Nlß-Ftz-F1 (Nlß-Ftz), through RNAi, exhibited distinct effects on the expressions of the takeout family genes. The down-regulation of NlMet and NlKrüppel-homolog 1 (NlKr-h1) increased the expressions of the takeout family genes, while the down-regulation of the Met interacting partners NlTai and Nlß-Ftz decreased the expressions of most of the takeout family genes. This work advanced our understanding of the molecular function and the regulatory mechanism of JH signaling.

Combining RNA-seq and proteomic profiling to identify seminal fluid proteins in the migratory grasshopper Melanoplus sanguinipes (F)

BACKGROUND

Seminal fluid proteins control many aspects of fertilization and in turn, they play a key role in post-mating sexual selection and possibly reproductive isolation. Because effective proteome profiling relies on the availability of high-quality DNA reference databases, our knowledge of these proteins is still largely limited to model organisms with ample genetic resources. New advances in sequencing technology allow for the rapid characterization of transcriptomes at low cost. By combining high throughput RNA-seq and shotgun proteomic profiling, we have characterized the seminal fluid proteins secreted by the primary male accessory gland of the migratory grasshopper (Melanoplus sanguinipes), one of the main agricultural pests in central North America.

RESULTS

Using RNA sequencing, we characterized the transcripts of ~ 8,100 genes expressed in the long hyaline tubules (LHT) of the accessory glands. Proteomic profiling identified 353 proteins expressed in the long hyaline tubules (LHT). Of special interest are seminal fluid proteins (SFPs), such as EJAC-SP, ACE and prostaglandin synthetases, which are known to regulate female oviposition in insects.

CONCLUSIONS

Our study provides new insights into the proteomic components of male ejaculate in Orthopterans, and highlights several important patterns. First, the presence of proteins that lack predicted classical secretory tags in accessory gland proteomes is common in male accessory glands. Second, the products of a few highly expressed genes dominate the accessory gland secretions. Third, accessory gland transcriptomes are enriched for novel transcripts. Fourth, there is conservation of SFPs' functional classes across distantly related taxonomic groups with very different life histories, mating systems and sperm transferring mechanisms. The identified SFPs may serve as targets of future efforts to develop species- specific genetic control strategies.

A complex of genes involved in adaptation of Leptinotarsa decemlineata larvae to induced potato defense

The Colorado potato beetle (Leptinotarsa decemlineata) is the most important pest of potato in many areas of the world. One of the main reasons for its success lies in the ability of its larvae to counteract plant defense compounds. Larvae adapt to protease inhibitors (PIs) produced in potato leaves through substitution of inhibitor-sensitive digestive cysteine proteases with inhibitor-insensitive cysteine proteases. To get a broader insight into the basis of larval adaptation to plant defenses, we created a "suppression subtractive hybridisation" library using cDNA from the gut of L. decemlineata larvae fed methyl jasmonate-induced or uninduced potato leaves. Four hundred clones, randomly selected from the library, were screened for their relevance to adaptation with DNA microarray hybridizations. Selected enzyme systems of beetle digestion were further inspected for changes in gene expression using quantitative PCR and enzyme activity measurements. We identified two new groups of digestive cysteine proteases, intestains D and intestains E. Intestains D represent a group of structurally distinct digestive cysteine proteases, of which the tested members are strongly upregulated in response to induced plant defenses. Moreover, we found that other digestive enzymes also participate in adaptation, namely, cellulases, serine proteases, and an endopolygalacturonase. In addition, juvenile hormone binding protein-like (JHBP-like) genes were upregulated. All studied genes were expressed specifically in larval guts. In contrast to earlier studies that reported experiments based on PI-enriched artificial diets, our results increase understanding of insect adaptation under natural conditions.

Structural mechanism of JH delivery in hemolymph by JHBP of silkworm, Bombyx mori

Juvenile hormone (JH) plays crucial roles in many aspects of the insect life. All the JH actions are initiated by transport of JH in the hemolymph as a complex with JH-binding protein (JHBP) to target tissues. Here, we report structural mechanism of JH delivery by JHBP based upon the crystal and solution structures of apo and JH-bound JHBP. In solution, apo-JHBP exists in equilibrium of multiple conformations with different orientations of the gate helix for the hormone-binding pocket ranging from closed to open forms. JH-binding to the gate-open form results in the fully closed JHBP-JH complex structure where the bound JH is completely buried inside the protein. JH-bound JHBP opens the gate helix to release the bound hormone likely by sensing the less polar environment at the membrane surface of target cells. This is the first report that provides structural insight into JH signaling.

Developmental expression of mRNAs for epidermal and fat body proteins and hormonally regulated transcription factors in the tobacco hornworm, Manduca sexta

This paper provides a compilation of diagrammatic representations of the expression profiles of epidermal and fat body mRNAs during the last two larval instars and metamorphosis of the tobacco hornworm, Manduca sexta. Included are those encoding insecticyanin, three larval cuticular proteins, dopa decarboxylase, moling, and the juvenile hormone-binding protein JP29 produced by the dorsal abdominal epidermis, and arylphorin and the methionine-rich storage proteins made by the fat body. The mRNA profiles of the ecdysteroid-regulated cascade of transcription factors in the epidermis during the larval molt and the onset of metamorphosis and in the pupal wing during the onset of adult development are also shown. These profiles are accompanied by a brief summary of the current knowledge about the regulation of these mRNAs by ecdysteroids and juvenile hormone based on experimental manipulations, both in vivo and in vitro.

Catalogue of epidermal genes: genes expressed in the epidermis during larval molt of the silkworm Bombyx mori

BACKGROUND

The insect cuticle is composed of various proteins and formed during the molt under hormonal regulation, although its precise composition and formation mechanism are largely unknown. The exhaustive catalogue of genes expressed in epidermis at the molt constitutes a massive amount of information from which to draw a complete picture of the molt and cuticle formation in insects. Therefore, we have catalogued a library of full-length cDNAs (designated epM) from epidermal cells during the last larval molt of Bombyx mori.

RESULTS

Of the 10,368 sequences in the library, we isolated 6,653 usable expressed sequence tags (ESTs), which were categorized into 1,451 nonredundant gene clusters. Seventy-one clusters were considered to be isoforms or premature forms of other clusters. Therefore, we have identified 1,380 putative genes. Of the 6,653 expressed sequences, 48% were derived from 92 cuticular protein genes (RR-1, 24; RR-2, 17; glycine-rich, 29; other classes, 22). A comparison of epM with another epidermal EST data set, epV3 (feeding stage: fifth instar, day 3), showed marked differences in cuticular protein gene. Various types of cuticular proteins are expressed in epM but virtually only RR-1 proteins were expressed in epV3. Cuticular protein genes expressed specifically in epidermis, with several types of expression patterns during the molt, suggest different types of responses to the ecdysteroid pulse. Compared with other Bombyx EST libraries, 13 genes were preferentially included in epM data set. We isolated 290 genes for proteins other than cuticular proteins, whose amino acid sequences retain putative signal peptides, suggesting that they play some role in cuticle formation or in other molting events. Several gene groups were also included in this data set: hormone metabolism, P450, modifier of cuticular protein structure, small-ligand-binding protein, transcription factor, and pigmentation genes.

CONCLUSION

We have identified 1,380 genes in epM data set and 13 preferentially expressed genes in epidermis at the molt. The comparison of the epM and other EST libraries clarified the totally different gene expression patterns in epidermis between the molting and feeding stages and many novel tissue- and stage-specifically expressed epidermal genes. These data should further our understanding of cuticle formation and the insect molt.

Regulation of feeding behaviour and locomotor activity by takeout in Drosophila

The hormonal regulation of feeding behaviour is well known in vertebrates, whereas it remains poorly understood in insects. Here, we report that the takeout gene is an essential component of nutritional homeostasis in Drosophila. takeout encodes a putative juvenile hormone (JH) binding protein and has been described as a link between circadian rhythm and feeding behaviour. However, the physiological role of takeout and its putative link to JH remain unknown. In this study, we show that takeout (to(1)) flies failed to adapt their food intake according to food availability and that most defects could be genetically rescued. When food is abundant, to(1) are hyperphagic, yielding to hypertrophy of the fat body. When food reappears after a starvation period, to(1) flies do not increase their food intake as much as wild-type flies. This defect in food intake regulation is partly based on the action of Takeout on taste neurons, because the sensitivity of to(1) gustatory neurons to sugars does not increase after starvation, as in wild-type neurons. This lack of regulation is also evident at the locomotor activity, which normally increases during starvation, a behaviour related to food foraging. In addition, to(1) flies lack sexual dimorphism of locomotor activity, which has previously been linked to the JH circulating level. Moreover, application of the JH analog methoprene rescues the phenotype. These results suggest that takeout plays a central role as a feeding regulator and may act by modulating the circulating JH level.

Genes encoding putative Takeout/juvenile hormone binding proteins in the honeybee (Apis mellifera) and modulation by age and juvenile hormone of the takeout-like gene GB19811

We identified and characterized eight genes encoding putative Takeout/juvenile hormone binding proteins (To/JHBP) in the honeybee genome. Phylogenetic analyses revealed nine distinct lineages within this gene family, including those containing Takeout (To) and JHBP for which there are no honeybee homologs. Their diversity and ubiquitous expression suggest that To/JHBP proteins are involved in diverse and important processes in insects. We further characterized the expression of one of these genes, GB19811 that is ubiquitously expressed. GB19811 transcript levels in the abdomen increased, and decreased in the head with worker age. There was no influence of colony environment or brood care behavior on GB19811 expression in young bees. Young bees treated with juvenile hormone (JH) showed a decrease in head GB19811 mRNA levels. This finding is consistent with the premise that JH, for which titers typically increase with age, is involved in age-related modulation of GB19811 expression. In contrast to Drosophila Takeout, the expression of GB19811 did not vary with diurnal or circadian rhythms. Taken together, these findings suggest that GB19811 is not an ortholog of Takeout, and is involved in JH-mediated regulation of adult honeybee worker development.

The neural and genetic substrates of sexual behavior in Drosophila

fruitless (fru), originally identified with its mutant conferring male homosexuality, is a neural sex determination gene in Drosophila that produces sexually dimorphic sets of transcripts. In the nervous system, Fru is translated only in males. Fru proteins likely regulate the transcription of a set of downstream genes. The expression of Fru proteins is sufficient to induce male sexual behavior in females. A group of fru-expressing neurons called "mAL" neurons in the brain shows conspicuous sexual dimorphism. mAL is composed of 5 neurons in females and 30 neurons in males. It includes neurons with bilateral projections in males and contralateral projections in females. Terminal arborization patterns are also sexually dimorphic. These three characteristics are feminized in fru mutant males. The inactivation of cell death genes results in the production of additional mAL neurons that are of the male type in the female brain. This suggests that male-specific Fru inhibits mAL neuron death, leading to the formation of a male-specific neural circuit that underlies male sexual behavior. Fru orchestrates a spectrum of downstream genes as a master control gene to establish the maleness of the brain.

A novel Takeout-like protein expressed in the taste and olfactory organs of the blowfly, Phormia regina

In insects, the functional molecules responsible for the taste system are still obscure. The gene for a 28.5 kDa protein purified from taste sensilla of the blowfly Phormia regina belongs to a gene family that includes takeout of Drosophila melanogaster. Molecular phylogenetic analysis revealed that the Phormia Takeout-like protein is most similar to the protein encoded by a member of the Drosophila takeout gene family, CG14661, whose expression and function have not been identified yet. Western blot analyses revealed that Phormia Takeout-like protein was exclusively expressed in antennae and labellum of the adult blowfly in both sexes. Immunohistochemical experiments demonstrated that Takeout-like protein was localized around the lamella structure of the auxiliary cells and in the sensillar lymph of the labellar taste sensillum. In antennae, Takeout-like protein was distributed at the base of the olfactory sensilla as well. No significant differences in Takeout-like protein expression were found between the sexes. Our results suggest that Phormia Takeout-like protein is involved in some early events concerned with chemoreception in both the taste and olfactory systems.

Cloning and expression analysis of takeout/JHBP family genes of silkworm, Bombyx mori

A Bombyx EST cDNA database was searched using the Drosophila takeout gene and nine cDNAs were obtained. The homology search suggested that these genes are widespread in insects and organize a large gene family, and that they have hydrophobic ligands. A phylogenetic tree indicated that the genes are first divided into two large groups, juvenile hormone binding protein and other protein genes, and the latter group diversified within a short time at an early stage. The expression study of five Bombyx genes indicated that they are expressed in various tissues and are regulated by development and feeding conditions. The Bombyx genes might have roles related to the regulation of metabolism, growth or development related to nutritional conditions.

Early events in adult eye development of the moth, Manduca sexta

The eye imaginal disc of Manduca sexta is created early in the final larval instar from the adult eye primordium, which is composed of fully differentiated cells of the larval head capsule epidermis. Concomitant with the down-regulation of the larval epidermal program, expression of broad, a marker of pupal commitment, is activated in the primordium. The cells then detach from the cuticle, fold inward, and begin to proliferate at high levels to produce the inverted, eye imaginal disc. These and other events that begin on the first day of the final larval instar appear to mark the initiation of metamorphosis. Little is known about the endocrine control of the initiation of metamorphosis in any insect. The hemolymph titer of juvenile hormone (JH) declines to low levels during this period and the presence of JH is sufficient to repress development in cultured eye primordia. However, maintenance of JH at high levels in vivo by treatment with long-lasting JH mimics has no apparent effect on early steps in eye imaginal disc development. We discuss our findings in the context of the endocrine control of metamorphosis. The initiation of metamorphosis in Manduca, and perhaps a wide range of insect species, appears to involve the overcoming of JH repression by an unidentified, nutrient-dependent, hormonal factor.

Large-scale gene discovery in the pea aphid Acyrthosiphon pisum (Hemiptera)

Aphids are the leading pests in agricultural crops. A large-scale sequencing of 40,904 ESTs from the pea aphid Acyrthosiphon pisum was carried out to define a catalog of 12,082 unique transcripts. A strong AT bias was found, indicating a compositional shift between Drosophila melanogaster and A. pisum. An in silico profiling analysis characterized 135 transcripts specific to pea-aphid tissues (relating to bacteriocytes and parthenogenetic embryos). This project is the first to address the genetics of the Hemiptera and of a hemimetabolous insect.

The role of nutrition in creation of the eye imaginal disc and initiation of metamorphosis in Manduca sexta

With the exception of the wing imaginal discs, the imaginal discs of Manduca sexta are not formed until early in the final larval instar. An early step in the development of these late-forming imaginal discs from the imaginal primordia appears to be an irreversible commitment to form pupal cuticle at the next molt. Similar to pupal commitment in other tissues at later stages, activation of broad expression is correlated with pupal commitment in the adult eye primordia. Feeding is required during the final larval instar for activation of broad expression in the eye primordia, and dietary sugar is the specific nutritional cue required. Dietary protein is also necessary during this time to initiate the proliferative program and growth of the eye imaginal disc. Although the hemolymph titer of juvenile hormone normally decreases to low levels early in the final larval instar, eye disc development begins even if the juvenile hormone titer is artificially maintained at high levels. Instead, creation of the late-forming imaginal discs in Manduca appears to be controlled by unidentified endocrine factors whose activation is regulated by the nutritional state of the animal.

Antennal expressed genes of the yellow fever mosquito (Aedes aegypti L.); characterization of odorant-binding protein 10 and takeout

A small cDNA library was constructed from antennae of 100 adult male Aedes aegypti yellow fever mosquitoes. Sequencing of 80 clones identified 49 unique gene products, including a member of the Odorant Binding Protein family (Aaeg-OBP10), a homologue of Takeout (Aaeg-TO), and transposable elements of the LINE, SINE and MITE classes. Aaeg-OBP10 encodes a 140 amino acid protein including a predicted 25 amino acid signal peptide. Aaeg-OBP10 expression was adult male enriched, increased with adult age, and greatest in antennae and wings but also present in maxillary palps, proboscis and leg. Aaeg-OBP10 is a likely orthologue of Agam-OBP10 of the malaria mosquito Anopheles gambiae and shares significant similarity with members of the OBP56 gene cluster of Drosophila melanogaster. These OBP genes may represent a unified class of OBPs with unique roles in chemodetection; the expression pattern of Aaeg-OBP10 suggests it may play a role in adult male chemosensory behavior. Aaeg-TO encodes a 248 amino acid protein including a predicted 22 amino acid signal peptide. Aaeg-TO is homologous with the circadian/feeding regulated D. melanogaster Takeout protein (Dmel-TO) and a subclass of Juvenile Hormone Binding Proteins (JHBP) characterized by Moling from Manduca sexta; both Dmel-TO and Moling are sensitive to feeding, suggesting Aaeg-TO might regulate the antennal response to food, host or pheromonal odors in a JH sensitive manner. Aaeg-TO was used to identify 25 D. melanogaster and 13 A. gambiae homologues by Blast analysis suggesting these may comprise a relatively large class of protein involved in the hormonal regulation of behavior.

Critical period for pupal commitment in the yellow fever mosquito, Aedes aegypti

Changes in ecdysteroid levels that lead to commitment of pupal and adult development were studied in the yellow fever mosquito, Aedes aegypti. Application of juvenile hormone at the time of pupal commitment usually results in delay or blockage of pupal and adult development. With methoprene, a juvenile hormone mimic, the JH sensitive period was found to be within 19 h after ecdysis to the fourth instar, at which time methoprene treatment caused a delay in pupation. Consistent with this observation, there was a small peak of ecdysteroid levels between 14 and 28 h after ecdysis to the fourth instar. Therefore, the commitment to pupal development occurs most likely between 14 and 19 h after ecdysis to the fourth instar. Levels of transcription of the ecdysone receptor gene show a small peak between 12 and 24 h, and a larger peak between 46 and 66 h after ecdysis to the fourth instar.