A single gene integrates sex and hormone regulators into sexual attractiveness

Juvenile hormone signaling is indispensable for late embryogenesis in ametabolous and hemimetabolous insects

BACKGROUND

Juvenile hormone (JH) is an insect-exclusive hormone involved in regulating diverse aspects of insect physiology, and the evolution of its diverse function is widely interesting. Studying embryogenesis in basal wingless insects is important to understand the functional evolution of JH; however, experimental studies in this regard are scarce. In this study, we conducted CRISPR/Cas9-mediated knockout (KO) of genes involved in JH biosynthesis and signaling cascades in the ametabolous firebrat, Thermobia domestica. Additionally, we investigated whether the primitive action of JH is conserved in the hemimetabolous cricket, Gryllus bimaculatus.

RESULTS

We observed that KO of JHAMT, CYP15A1, Met, and Kr-h1 resulted in embryonic lethality in T. domestica. Deprivation of JH or JH signaling arrested the progression of extraembryonic fluid resorption after dorsal closure and hatching, which is consistent with the gene expression pattern showing high Kr-h1 expression in the late embryos of T. domestica. The embryos deficient in JH signaling displayed wrinkled and weak legs. Comparative transcriptome analysis revealed that JH signaling promotes embryonic leg maturation through inducing energy supply and muscle activity, as validated by transmission electron microscopy (TEM). In addition, JH signaling exhibited similar embryonic effects in G. bimaculatus.

CONCLUSIONS

This study reveals the indispensable role of JH signaling in facilitating the maturation of terminal tissues during late embryogenesis, as demonstrated by the regulation of leg development, in ametabolous and hemimetabolous insects. These findings further indicate that the embryonic functions of JH evolved earlier than its anti-metamorphic functions during postembryonic development.

Ben-JNK signaling is required for host mortality during Periplaneta fuliginosa densovirus infection

BACKGROUND

Cockroaches are widely acknowledged as significant vectors of pathogenic microorganisms. The Periplaneta fuliginosa densovirus (PfDNV) infects the smoky-brown cockroach P. fuliginosa and causes host mortality, which identifies the PfDNV as a species-specific and environmentally friendly biopesticide. However, although the biochemical characterization of PfDNV has been extensively studied, the immune response against PfDNV remains largely unclear.

RESULTS

Here, we investigated the replication of PfDNV and its associated pathological phenotype in the foregut and hindgut. Consequently, we dissected and performed transcriptome sequencing on the foregut, midgut, and hindgut separately. We revealed the up-regulation of immune response signaling pathway c-Jun N-terminal kinase (JNK) and apoptosis in response to viral infection. Furthermore, knockdown of the JNK upstream gene Ben resulted in a decrease in virus titer and delayed host mortality.

CONCLUSION

Taken together, our findings provide evidence that the Ben-JNK signaling plays a crucial role in PfDNV infection, leading to excessive apoptosis in intestinal tissues and ultimately resulting in the death of the host. Our results indicated that the host response to PfDNV fosters viral infection, thereby increasing host lethality. This underscores the potential of PfDNV as a viable, environmentally friendly biopesticide. © 2024 Society of Chemical Industry.

Dibutyl phthalate released by solitary female locusts mediates sexual communication at low density

Sex pheromones play a crucial role in mate location and reproductive success. Insects face challenges in finding mates in low-density environments. The population dynamics of locusts vary greatly, ranging from solitary individuals to high-density swarms, leading to multiple-trait divergence between solitary and gregarious phases. However, differences in sexual communication between solitary and gregarious locusts have not been sufficiently explored. Herein, we found that solitary locusts but not gregarious ones heavily rely on a single compound, dibutyl phthalate (DBP), for sexual communication. DBP is abundantly released by solitary female locusts and elicits strong attraction of male solitary and gregarious locusts. Solitary adult males display much higher electrophysiological responses to DBP than adult females. Additionally, LmigOr13 was identified as the DBP-specific odorant receptor expressed in neurons housed in basiconic sensilla. Male LmigOr13-/- mutants generated by CRISPR/Cas9 have low electrophysiological responses and behavioral attraction to DBP in both laboratory and field cage experiments. Notably, the attractiveness of DBP to male locusts becomes more evident at lower population densities imposed by controlling the cage size. This finding sheds light on the utilization of a sex pheromone to promote reproductive success in extremely low-density conditions and provides important insights into alternative approaches for population monitoring of locusts.

Two sex pheromone receptors for sexual communication in the American cockroach

Volatile sex pheromones are vital for sexual communication between males and females. Females of the American cockroach, Periplaneta americana, produce and emit two sex pheromone components, periplanone-A (PA) and periplanone-B (PB). Although PB is the major sex attractant and can attract males, how it interacts with PA in regulating sexual behaviors is still unknown. In this study, we found that in male cockroaches, PA counteracted PB attraction. We identified two odorant receptors (ORs), OR53 and OR100, as PB/PA and PA receptors, respectively. OR53 and OR100 were predominantly expressed in the antennae of sexually mature males, and their expression levels were regulated by the sex differentiation pathway and nutrition-responsive signals. Cellular localization of OR53 and OR100 in male antennae further revealed that two types of sensilla coordinate a complex two-pheromone-two-receptor pathway in regulating cockroach sexual behaviors. These findings indicate distinct functions of the two sex pheromone components, identify their receptors and possible regulatory mechanisms underlying the male-specific and age-dependent sexual behaviors, and can guide novel strategies for pest management.

RNAi of yellow-y, required for normal cuticle pigmentation, impairs courtship behavior and oviposition in the German cockroach (Blattella germanica)

The insect cuticle plays a key role in maintaining the insect's physiological function and behavior. Herein, the yellow-y protein is required to produce black melanin, and is expressed in a pattern that correlates with the distribution of this pigment. However, yellow-y can also have other functions, for instance, in insect behavior, but not much is known. In this study, we have studied the yellow-y gene in one important model and pest species, namely the German cockroach (Blattella germanica), which is to our knowledge the first time reported. In essence, we identified the yellow-y gene (BgY-y) and characterized its function by using RNA interference (RNAi). Silencing of BgY-y gene led to different developmental abnormalities (body weight and wings) in both genders. Specifically, there was an abundant decrease in melanin, turning the body color in pale yellow and the cuticle softer and more transparent. Interestingly, we also observed that the knockdown of BgY-y impaired the male cockroaches to display a weaker response to female-emitted contact sex pheromones, and also that the oviposition ability was weakened in the RNAi females. This study comprehensively analyzed the biological functions of the yellow-y gene in German cockroaches from the perspectives of development, body color, courtship behavior and oviposition, and as a consequence, this may opens new avenues to explore it as a novel pest control gene.

Hexamerin and allergen are required for female reproduction in the American cockroach, Periplaneta americana

Reproduction is of great importance for the continuation of the species. In insects, the fat body is the major tissue for nutrient storage and involved in vitellogenesis, which is essential for female reproduction. Here, 2 proteins, hexamerin and allergen, were separated from the fat bodies of adult female American cockroaches (Periplaneta americana) and identified as storage proteins, encoding for 733 amino acids with molecular weight of 87.88 kDa and 686 amino acids with molecular weight of 82.18 kDa, respectively. The encoding genes of these 2 storage proteins are mainly expressed in the fat body. RNA interference-mediated knockdown of Hexamerin and Allergen in the early stage of the first reproductive cycle in females suppressed vitellogenesis and ovarian maturation, indicating that these storage proteins are involved in controlling reproduction. Importantly, the expression of Hexamerin and Allergen was repressed by knockdown of the juvenile hormone (JH) receptor gene Met and the primary response gene Kr-h1, and was induced by methoprene, a JH analog, in both in vivo and in vitro experiments. Altogether, we have determined that hexamerin and allergen are identified as storage proteins and play an important role in promoting female reproduction in the American cockroach. The expression of their encoding genes is induced by JH signaling. Our data reveal a novel mechanism by which hexamerin and allergen are necessary for JH-stimulated female reproduction.

Molecule characterization of chemosensory and metabolism-related genes in the proboscis of Athetis lepigone

Introduction: The moth species Athetis lepigone (Möschler) (Lepidoptera: Noctuidae), which has recently been identified as a pest of summer maize (Zea mays L.) in China, has demonstrated a rapid proliferation with in the Huang-Huai-Hai Plain region since its initial discovery in Hebei Province in 2005. It has become a prevalent pest of corn crops, and its ability to adapt quickly to its surroundings is currently being investigated. One of the key characteristics of its siphoning mouthparts is not only the feeding apparatus itself but also the chemosensory organs that enable the detection of chemical signals from the surrounding environment. However, there is a lack of comprehensive research on the genes responsible for chemosensory and metabolic mechanisms in the proboscises of male and female A. lepigone adults. Methods: In this study, we utilized transcriptome analysis to identify a total of fifty chemosensory genes from six distinct families, including 19 odorant-binding proteins (OBPs), 22 chemosensory proteins (CSPs), one co-receptor (Orco), six odorant receptors (ORs), four ionotropic receptors (IRs), and two sensory neuron membrane proteins (SNMPs) in the proboscis. Notably, seven OBPs, two CSPs, and one OR were discovered for the first time. Additionally, fourteen genes related to metabolism, including cytochrome P450 (CYPs) and carboxylesterases (CXEs), were also identified. Furthermore, a qualitative analysis was conducted on the relative transcript levels of eight related genes. The expression of 21 annotated chemosensory and metabolic genes was compared between A. lepigone adults and larvae using qRT-PCR, revealing tissue specificity. The majority of genes exhibited predominant expression in the antennae and proboscis during the adult stage, while showing slight expression in the combination of sixth-instar larval head oral appendages (maxilla, labium, and antenna) and pheromone gland-ovipositors of female adults. Results/discussion: Our study points to a new pest control strategies that these newly discovered genes have the potential to serve as targets for enhancing future pest control, including mating disruption and the use of food attractants. And it would be advantageous to ascertain the distribution of chemosensory gene expression and gain insights into the functionalities of these genes, thereby establishing a novel theoretical framework for the advancement of eco-friendly pesticides and efficient pest management strategies in the future.

Female semiochemicals stimulate male courtship but dampen female sexual receptivity

Chemical communication plays a vital role in mate attraction and discrimination among many insect species. Here, we document a unique example of semiochemical parsimony, where four chemicals act as both aphrodisiacs and anti-aphrodisiacs in different contexts in Bactrocera dorsalis. Specifically, we identified four female-specific semiochemicals, ethyl laurate, ethyl myristate, ethyl cis-9-hexadecenoate, and ethyl palmitate, which serve as aphrodisiacs to attract male flies and arouse male courtship. Interestingly, these semiochemicals, when sexually transferred to males during mating, can function as anti-aphrodisiacs, inhibiting the receptivity of subsequent female mates. We further showed that the expression of elongase11, a key enzyme involved in the biosynthesis of these semiochemicals, is under the control of doublesex, facilitating the exclusive biosynthesis of these four semiochemicals in females and guaranteeing effective chemical communication. The dual roles of these semiochemicals not only ensure the attractiveness of mature females but also provide a simple yet reliable mechanism for female mate discrimination. These findings provide insights into chemical communication in B. dorsalis and add elements for the design of pest control programs.

Nutrition- and hormone-controlled developmental plasticity in Blattodea

Blattodea, which includes cockroaches and termites, possesses high developmental plasticity that is mainly controlled by nutritional conditions and insect hormones. Insulin/insulin-like growth factor signaling (IIS), target of rapamycin complex 1 (TORC1), and adenosine monophosphate-activated protein complex are the three primary nutrition-responsive signals. Juvenile hormone (JH) and 20-hydroxyecdysone (20E) constitute the two most vital insect hormones that might interact with each other through the Met, Kr-h1, E93 (MEKRE93) pathway. Nutritional and hormonal signals interconnect to create a complex regulatory network. Here we summarize recent progress in our understanding of how nutritional and hormonal signals coordinately control the developmental plasticity of metamorphosis, reproduction, and appendage regeneration in cockroaches as well as caste differentiation in termites. We also highlight several perspectives that should be further emphasized in the studies of developmental plasticity in Blattodea. This review provides a general landscape in the field of nutrition- and hormone-controlled developmental plasticity in insects.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte Nuclear Factor 4

Sexual attraction and perception are crucial for mating and reproductive success. In Drosophila melanogaster, the male-specific isoform of Fruitless (Fru), FruM, is a known master neuro-regulator of innate courtship behavior to control the perception of sex pheromones in sensory neurons. Here, we show that the non-sex-specific Fru isoform (FruCOM) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of FruCOM in oenocytes resulted in adults with reduced levels of cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 (Hnf4) as a key target of FruCOM in directing fatty acid conversion to hydrocarbons. Fru or Hnf4 depletion in oenocytes disrupts lipid homeostasis, resulting in a sex-dimorphic CHC profile that differs from doublesex- and transformer-dependent CHC dimorphism. Thus, Fru couples pheromone perception and production in separate organs to regulate chemosensory communications and ensure efficient mating behavior.

Integrating lipid metabolism, pheromone production and perception by Fruitless and Hepatocyte nuclear factor 4

Sexual attraction and perception, governed by separate genetic circuits in different organs, are crucial for mating and reproductive success, yet the mechanisms of how these two aspects are integrated remain unclear. In Drosophila , the male-specific isoform of Fruitless (Fru), Fru M , is known as a master neuro-regulator of innate courtship behavior to control perception of sex pheromones in sensory neurons. Here we show that the non-sex specific Fru isoform (Fru COM ) is necessary for pheromone biosynthesis in hepatocyte-like oenocytes for sexual attraction. Loss of Fru COM in oenocytes resulted in adults with reduced levels of the cuticular hydrocarbons (CHCs), including sex pheromones, and show altered sexual attraction and reduced cuticular hydrophobicity. We further identify Hepatocyte nuclear factor 4 ( Hnf4 ) as a key target of Fru COM in directing fatty acid conversion to hydrocarbons in adult oenocytes. fru - and Hnf4 -depletion disrupts lipid homeostasis, resulting in a novel sex-dimorphic CHC profile, which differs from doublesex - and transformer -dependent sexual dimorphism of the CHC profile. Thus, Fru couples pheromone perception and production in separate organs for precise coordination of chemosensory communication that ensures efficient mating behavior.

Teaser

Fruitless and lipid metabolism regulator HNF4 integrate pheromone biosynthesis and perception to ensure robust courtship behavior.

Exposure to artificial light at night mediates the locomotion activity and oviposition capacity of Dastarcus helophoroides (Fairmaire)

Light entrains the endogenous circadian clocks of organisms to synchronize their behavioral and physiological rhythms with the natural photoperiod. The presence of artificial light at night disrupts these photoperiodic cues and is currently considered to be a major threat to key fitness-related behaviors, including sleep disruption and physiological stress. Research on the ecological influence of forest pest and their natural enemies is lacking. The wood-boring insects significantly damage forest and urban forest ecosystem functions. The parasitic beetles, Dastarcus helophoroides is an important natural enemy of wood-boring insects, especially those in the Cerambycidae family. However, the effect of artificial light at night on the locomotor rhythms and oviposition capacity of D. helophoroides has received little attention. To address this gap, diel changes in the locomotor activity and number of eggs laid by female D. helophoroides was analyzed under different light-dark (LD) cycles and temperatures. The results showed that the 24-h rhythmic of locomotor activity in these beetles was elevated in darkness and reduced under illumination, indicating that they are nocturnal insects. This activity has two major peaks, the evening (1-8 h after lights off) and morning (3.5-12.5 h after lights off) components, reflecting that light mediate regular changes in locomotor activity. Moreover, the circadian rhythms and active percentage were influenced by the illumination duration and temperature, especially constant light and 40°C. Females laid more eggs under the 16 L: 8 D cycles at 30°C than under the other combinations of photoperiod (including constant light and darkness) and temperature. Finally, the potential influence of exposure to four ecologically relevant intensities of artificial light at night (0, 1, 10 or 100 lx) on oviposition capacity was studied. The results showed that lifetime exposure to bright artificial light (1-100 lx) at night decreased the number of eggs laid relative to those laid with no lighting at night. These results demonstrate that chronic exposure to bright artificial light at night may influence the locomotor activity and oviposition capacity of this parasitic beetle.

Egfr signaling promotes juvenile hormone biosynthesis in the German cockroach

BACKGROUND

In insects, an interplay between the activities of distinct hormones, such as juvenile hormone (JH) and 20-hydroxyecdysone (20E), regulates the progression through numerous life history hallmarks. As a crucial endocrine factor, JH is mainly synthesized in the corpora allata (CA) to regulate multiple physiological and developmental processes, including molting, metamorphosis, and reproduction. During the last century, significant progress has been achieved in elucidating the JH signal transduction pathway, while less progress has been made in dissecting the regulatory mechanism of JH biosynthesis. Previous work has shown that receptor tyrosine kinase (RTK) signaling regulates hormone biosynthesis in both insects and mammals. Here, we performed a systematic RNA interference (RNAi) screening to identify RTKs involved in regulating JH biosynthesis in the CA of adult Blattella germanica females.

RESULTS

We found that the epidermal growth factor receptor (Egfr) is required for promoting JH biosynthesis in the CA of adult females. The Egf ligands Vein and Spitz activate Egfr, followed by Ras/Raf/ERK signaling, and finally activation of the downstream transcription factor Pointed (Pnt). Importantly, Pnt induces the transcriptional expression of two key enzyme-encoding genes in the JH biosynthesis pathway: juvenile hormone acid methyltransferase (JHAMT) and methyl farnesoate epoxidase (CYP15A1). Dual-luciferase reporter assay shows that Pnt is able to activate a promoter region of Jhamt. In addition, electrophoretic mobility shift assay confirms that Pnt directly binds to the - 941~ - 886 nt region of the Jhamt promoter.

CONCLUSIONS

This study reveals the detailed molecular mechanism of Egfr signaling in promoting JH biosynthesis in the German cockroach, shedding light on the intricate regulation of JH biosynthesis during insect development.