Secretory competence in a gateway endocrine cell conferred by the nuclear receptor βFTZ-F1 enables stage-specific ecdysone responses throughout development in Drosophila

Effect of RNAi mediated silencing of DIB, JHE, and CAM on the diapause termination of Calliptamus italicus (Orthoptera: Acrididae) eggs

BACKGROUND

Calliptamus italicus L. is a major pest in Xinjiang grassland. The diapause overwintering strategy is one of the important reasons for the large population of this pest. This study investigated the function of the genes associated with the release of diapause (DIB, JHE and CAM) in Calliptamus italicus by RNA interference (RNAi) technology to aid in its biological control.

RESULTS

The expression levels of DIB and its downstream-associated genes (EcR and FTZ-F1) in the eggs injected with dsDIB for 12 h decreased by 96.6%, 55.8% and 81.8%, respectively. Diapause began to terminate on day 3, and development was almost complete on day 6. However, the head was significantly smaller. The expression levels of JHE and its downstream-associated genes (JHEH and VgR) at 48 h after dsJHE treatment decreased by 76.5%, 85.6% and 85.9%, respectively. The termination of diapause occured on day 3 of incubation. The development was basically complete on day 6, but the yolk had been incompletely absorbed. The expression of CAM and its downstream-associated genes (CAMK4 and MYL) at 24 h after dsCAM treatment decreased by 42.4%, 95.3% and 82.7%, respectively. Diapause termination was completed on day 4 for incubation, and development was abnormal on day 6. The absorption of yolk was incomplete.

CONCLUSION

DIB, JHE and CAM can delay the diapause termination of Calliptamus italicus eggs to different degrees and can be developed as potential target genes for its biological control. © 2024 Society of Chemical Industry.

The cuticular protein gene ApCP7 and ApCP62 are essential for reproduction in Acyrthosiphon pisum, affecting ecdysis and survival

Cuticular proteins, in conjunction with chitin, compose the insect exoskeleton, and play a key role in the growth, development, and molting of insects. However, the specific functions of most cuticular protein genes in the growth, development, and reproductive processes of the pea aphid (Acyrthosiphon pisum) remain unclear. In this study, we have identified six cuticular protein genes in the pea aphid, namely ApCP7, ApCP10, ApCP19, ApCP19.8-like, ApCP35 and ApCP62. We found that the expression levels of six genes were highly expressed during the adult stage, and except for ApCP10, which is highly expressed in the pea aphid cuticle, other genes were highly expressed in the ovaries. Subsequently, we observed that the survival rate and fecundity of pea aphid were significantly lower than those of the control group after silencing ApCP7 and ApCP62 through RNA interference. Furthermore, when ApCP7 transcript levels were reduced, aphid encountered difficulties in molting, were smaller in body size, and exhibited a darker body color. These results indicate that ApCP7 and ApCP62 are involved in the development and reproduction of pea aphid, and could be used as RNAi targets for controlling pea aphid.

Molecular characterization of the cytochrome P450 enzyme CYP18A1 in Henosepilachna vigintioctopunctata

In insects, the expression of 20E response genes that initiate metamorphosis is triggered by a pulse of 20-hydroxyecdysone (20E). The 20E pulse is generated through two processes: synthesis, which increases its level, and inactivation, which decreases its titer. CYP18A1 functions as an ecdysteroid 26-hydroxylase and plays a role in 20E removal in several representative insects. However, applying 20E degradation activity of CYP18A1 to other insects remains a significant challenge. In this study, we discovered high levels of Hvcyp18a1 during the larval and late pupal stages, particularly in the larval epidermis and fat body of Henosepilachna vigintioctopunctata, a damaging Coleopteran pest of potatoes. RNA interference (RNAi) targeting Hvcyp18a1 disrupted the pupation. Approximately 75% of the Hvcyp18a1 RNAi larvae experienced developmental arrest and remained as stunted prepupae. Subsequently, they gradually turned black and eventually died. Among the Hvcyp18a1-depleted animals that successfully pupated, around half became malformed pupae with swollen elytra and hindwings. The emerged adults from these deformed pupae appeared misshapen, with shriveled elytra and hindwings, and were wrapped in the pupal exuviae. Furthermore, RNAi of Hvcyp18a1 increased the expression of a 20E receptor gene (HvEcR) and four 20E response transcripts (HvE75, HvHR3, HvBrC, and HvαFTZ-F1), while decreased the transcription of HvβFTZ-F1. Our findings confirm the vital role of CYP18A1 in the pupation, potentially involved in the degradation of 20E in H. vigintioctopunctata.

Nuclear Receptor FTZ-F1 Controls Locust Molt by Regulating the Molting Process of Locusta migratoria

Fushi-tarazu factor 1 (FTZ-F1) is a class of transcription factors belonging to the nuclear receptor superfamily and an important molting regulator in insects; however, its detailed function in the molting process of Locusta migratoria is still unclear. This study identified two FTZ-F1 transcripts (LmFTZ-F1-X1 and LmFTZ-F1-X2) in L. migratoria. The classical domains of FTZ-F1 were present in their protein sequences and distinguished based on their variable N-terminal domains. Reverse-transcription quantitative polymerase chain reaction analysis revealed that LmFTZ-F1-X1 and LmFTZ-F1-X2 were highly expressed in the integument. RNA interference (RNAi) was used to explore the function of LmFTZ-F1s in the molting of the third-instar nymph. Separate LmFTZ-F1-X1 or LmFTZ-F1-X2 silencing did not affect the normal development of third-instar nymphs; however, the simultaneous RNAi of LmFTZ-F1-X1 and LmFTZ-F1-X2 caused the nymphs to be trapped in the third instar stage and finally die. Furthermore, the hematoxylin-eosin and chitin staining of the cuticle showed that the new cuticles were thickened after silencing the LmFTZ-F1s compared to the controls. RNA-seq analysis showed that genes encoding four cuticle proteins, two chitin synthesis enzymes, and cytochrome P450 303a1 were differentially expressed between dsGFP- and dsLmFTZ-F1s-injected groups. Taken together, LmFTZ-F1-X1 and LmFTZ-F1-X2 are involved in the ecdysis of locusts, possibly by regulating the expression of genes involved in cuticle formation, chitin synthesis, and other key molting processes.

Dual function of the transcription factor Ftz-f1 on oviposition in the cockroach Blattella germanica

The transcription factor Ftz-f1 has multiple functions in insect development in a spatial-temporal line. One of these roles is in the insect ovaries, specifically in the regulation of steroidogenic enzymes production. We studied the function of F in Blattella germanica oogenesis, as it shows two moments of high expression in ovaries: before the imaginal moult, and just before ovulation in the adult. Injecting dsftz-f1 into adult females, either just after the imaginal moult or just prior to choriogenesis, prevented oviposition, with differences between the two approaches. In 3-day-old adult females treated with dsftz-f1 just after the emergence, the expression of ftz-f1 was not modified, but the steroidogenic genes increased their expression. ftz-f1 transcript levels in the ovaries of 5-day-old dsftz-f1-treated females were significantly depleted, and the expression levels of the same steroidogenic genes began to decrease. These results suggest that Ftz-f1 regulates the expression of steroidogenic genes in B. germanica, with phm possibly being a key target. Ftz-f1 has a different temporal function in the cytoskeleton of follicular cells of the basal ovarian follicles. Early in the gonadotrophic cycle, Ftz-f1 promotes the expression of genes related to the cytoskeleton and muscle proteins, while at the end of the cycle it maintains the expression levels of these genes, thus ensuring correct ovulation.

The Intricate Role of Ecdysis Triggering Hormone Signaling in Insect Development and Reproductive Regulation

Insect growth is interrupted by molts, during which the insect develops a new exoskeleton. The exoskeleton confers protection and undergoes shedding between each developmental stage through an evolutionarily conserved and ordered sequence of behaviors, collectively referred to as ecdysis. Ecdysis is triggered by Ecdysis triggering hormone (ETH) synthesized and secreted from peripheral Inka cells on the tracheal surface and plays a vital role in the orchestration of ecdysis in insects and possibly in other arthropod species. ETH synthesized by Inka cells then binds to ETH receptor (ETHR) present on the peptidergic neurons in the central nervous system (CNS) to facilitate synthesis of various other neuropeptides involved in ecdysis. The mechanism of ETH function on ecdysis has been well investigated in holometabolous insects such as moths Manduca sexta and Bombyx mori, fruit fly Drosophila melanogaster, the yellow fever mosquito Aedes aegypti and beetle Tribolium castaneum etc. In contrast, very little information is available about the role of ETH in sequential and gradual growth and developmental changes associated with ecdysis in hemimetabolous insects. Recent studies have identified ETH precursors and characterized functional and biochemical features of ETH and ETHR in a hemimetabolous insect, desert locust, Schistocerca gregaria. Recently, the role of ETH in Juvenile hormone (JH) mediated courtship short-term memory (STM) retention and long-term courtship memory regulation and retention have also been investigated in adult male Drosophila. Our review provides a novel synthesis of ETH signaling cascades and responses in various insects triggering diverse functions in adults and juvenile insects including their development and reproductive regulation and might allow researchers to develop sustainable pest management strategies by identifying novel compounds and targets.

Parental exposure to polystyrene nanoplastics and di(2-ethylhexyl) phthalate induces transgenerational growth and reproductive impairments through bioaccumulation in Daphnia magna

The ubiquitous presence of polystyrene nanoplastics (PSNPs) and di(2-ethylhexyl) phthalate (DEHP) in the aquatic environment may cause unpredictable negative effects on aquatic organisms and even continue to the offspring. This study assessed the transgenerational impacts of parental exposure to PSNPs and DEHP over four generations (F0-F3) of Daphnia magna. A total of 480 D. magna larvae (F0, 24 h old) were divided into four groups with six replicates (each of them contains 20 D. magna) and exposed with dechlorinated tap water (control), 1 mg/L PSNPs, 1 μg/L DEHP, and 1 mg/L PSNPs + 1 μg/L DEHP (PSNPs-DEHP) until spawning begins. Subsequent to exposure, all the surviving F1 offspring were transferred to new water and continued to be cultured until the end of F3 generation births in all groups. The results showed that the PSNPs accumulated in F0 generation and were inherited into F1 and F2 generations, and disappeared in F3 generation in PSNPs and PSNPs-DEHP groups. However, the accumulation of DEHP lasted from F0 generation to F3 generation, despite a significant decline in F2 and F3 generations in DEHP and PSNPs-DEHP groups. The accumulation of PSNPs and DEHP caused overproduction of reactive oxygen species in F0-F2 generations and fat deposition in F0-F3 generations. Additionally, single and in combination parental exposure to PSNPs and DEHP induced regulation of growth-related genes (cyp18a1, cut, sod and cht3) and reproduction-related genes (hr3, ftz-f1, vtg and ecr) in F0-F3 generations. Survival rates were decreased in F0-F1 generations and recovered in F2 generation in all treatment groups. Furthermore, the spawning time was prolonged and the average number of offspring was increased in F1-F2 generaions as a defense mechanism against population mortality. This study fosters a greater comprehension of the transgenerational and reproductive effects and associated molecular mechanisms in D. magna.

Endocrine modulation of primary chemosensory neurons regulates Drosophila courtship behavior

The decision to engage in courtship depends on external cues from potential mates and internal cues related to maturation, health, and experience. Hormones allow for coordinated conveyance of such information to peripheral tissues. Here, we show Ecdysis-Triggering Hormone (ETH) is critical for courtship inhibition after completion of copulation in Drosophila melanogaster. ETH deficiency relieves post-copulation courtship inhibition (PCCI) and increases male-male courtship. ETH appears to modulate perception and attractiveness of potential mates by direct action on primary chemosensory neurons. Knockdown of ETH receptor (ETHR) expression in GR32A-expressing neurons leads to reduced ligand sensitivity and elevated male-male courtship. We find OR67D also is critical for normal levels of PCCI after mating. ETHR knockdown in OR67D-expressing neurons or GR32A-expressing neurons relieves PCCI. Finally, ETHR silencing in the corpus allatum (CA), the sole source of juvenile hormone, also relieves PCCI; treatment with the juvenile hormone analog methoprene partially restores normal post-mating behavior. We find that ETH, a stress-sensitive reproductive hormone, appears to coordinate multiple sensory modalities to guide Drosophila male courtship behaviors, especially after mating.

The decision of when to reproduce is paramount for organismal survival. In models like mice and flies, we have a comprehensive understanding of neuronal substrates for perception of mates and courtship drive, but how these substrates adapt to malleable internal and external environments remains unclear. Here, we show that post-mating refractoriness depends upon a peptide hormone, Ecdysis-Triggering Hormone (ETH). We show repression of courtship toward recently-mated females depends upon pheromone cues and that ETH deficiency impairs perception of female matedness. ETH signaling appears to promote the activity and function of pheromone-sensing primary olfactory and gustatory sensory neurons. Additionally, ETH sets internal levels of Juvenile Hormone, a hormone known to inhibit courtship drive in flies. Elimination of ETH or its receptor in primary sensory neurons or the glandular source of Juvenile Hormone reduces male post-copulation courtship inhibition (PCCI), causing continued courtship toward female counterparts after successful mating. Our data suggest ETH and its targets are critical for post-mating refractoriness in males.

Interorgan communication through peripherally derived peptide hormones in Drosophila

In multicellular organisms, endocrine factors such as hormones and cytokines regulate development and homoeostasis through communication between different organs. For understanding such interorgan communications through endocrine factors, the fruit fly Drosophila melanogaster serves as an excellent model system due to conservation of essential endocrine systems between flies and mammals and availability of powerful genetic tools. In Drosophila and other insects, functions of neuropeptides or peptide hormones from the central nervous system have been extensively studied. However, a series of recent studies conducted in Drosophila revealed that peptide hormones derived from peripheral tissues also play critical roles in regulating multiple biological processes, including growth, metabolism, reproduction, and behaviour. Here, we summarise recent advances in understanding target organs/tissues and functions of peripherally derived peptide hormones in Drosophila and describe how these hormones contribute to various biological events through interorgan communications.

RNAi suppression of the nuclear receptor FTZ-F1 impaired ecdysis, pupation, and reproduction in the 28-spotted potato ladybeetle, Henosepilachna vigintioctopunctata

Fushi-tarazu factor 1 (FTZF1) is an ecdysone-inducible transcription factor that plays a vital role during the metamorphosis in insects. In this study, we functionally characterized HvFTZ-F1 in H. vigintioctopunctata, a dreadful solanaceous crop pest, by using a dietary RNA interference technique. The HvFTZ-F1 expression levels were elevated in the 1st and 2nd-instars before molting and declined immediately after ecdysis. The HvFTZ-F1 silencing led to high mortality in the 1st instars, while the expression of the osmosis-regulative gene, HvAQPAn.G, was significantly increased in the 1st instars. HvFTZ-F1 silencing downregulated the Halloween and 20E-related genes, decreased the ecdysteroids titer, suppressed the expression of pigmentation-related genes, and reduced the catecholamines titer. In the 4th instars, HvFTZ-F1 silencing caused 100% mortality by arresting the development at the prepupal stage and preventing new abdominal cuticle formation. In the female adults, HvFTZ-F1 silencing caused an evident decrease in fecundity, prolonged the pre-oviposition period, reduced the number of eggs and hatching rate, severely atrophied the ovaries. Moreover, the 20E-related genes and the dopamine synthesis genes were suppressed in the dsHvFTZ-F1-treated females. Overall, our results revealed that HvFTZ-F1 regulates ecdysis, pupation, and reproduction in H. vigintioctopunctata, thereby could be a promising molecular target for the development of RNAi-based biopesticides to control H. vigintioctopunctata.

Dissecting the Isoform-Specific Roles of FTZ-F1 in the Larval–Larval and Larval–Pupal Ecdyses in Henosepilachna vigintioctopunctata

Simple Summary

Fushi Tarazu Factor-1 (FTZ-F1) plays a crucial regulatory role in molting in insects. It is hypothesized that, by alternative transcription start and splicing, the FTZ-F1 gene generates two isomers (α- and βFTZ-F1) that exert isoform-specific roles in non-Drosophilid insects. In the present paper, we first unveiled that the same post-transcriptional processing in FTZ-F1 occurred in coleopterans, lepidopterans, dipterans and hymenopterans. We then found that αFTZ-F1 and βFTZ-F1 were actively transcribed throughout the development, from embryo to adult, in Henosepilachna vigintioctopunctata. Moreover, by RNA interference, we confirmed that both FTZ-F1 isoforms act as regulators in larval–larval molting and βFTZ-F1 is involved in the regulation of the larval–pupal transition.

Abstract

Fushi Tarazu Factor 1 (FTZ-F1), a member of the nuclear receptor superfamily, is the downstream factor of 20-hydroxyecdysone signaling. In Drosophila melanogaster, alternative transcription start and splicing in the FTZ-F1 gene generate αFTZ-F1 and βFTZ-F1 isoforms, which are vital for pair-rule segmentation in early embryogenesis and post-embryonic development, respectively. However, whether the same mRNA isoforms are present and exert the conservative roles remains to be clarified in other insects. In the present paper, we first mined the genomic data of representative insect species and unveiled that the same post-transcriptional processing in FTZ-F1 occurred in coleopterans, lepidopterans, dipterans and hymenopterans. Our expression data in Henosepilachna vigintioctopunctata, a serious polyphagous defoliator damaging a wide range of crops in Solanaceae and Cucurbitaceae, showed that both αFTZ-F1 and βFTZ-F1 were actively transcribed throughout the development, from embryo to adult. The RNA interference-aided knockdown of both isoforms completely arrested larval ecdysis from the third to the fourth instar, in contrast to the depletion of either isoform. In contrast, silencing βFTZ-F1, rather than αFTZ-F1, severely impaired the larval–pupal transformation. We accordingly propose that both FTZ-F1 isoforms are essential but mutually interchangeable for larval–larval molting, while βFTZ-F1 is necessary for the larval–pupal transition and sufficient to exert the role of both FTZ-F1s during larval–pupal metamorphosis in H. vigintioctopunctata.

Effects of flanking sequences and cellular context on subcellular behavior and pathology of mutant HTT

Huntington's disease (HD) is caused by an expansion of a poly glutamine (polyQ) stretch in the huntingtin protein (HTT) that is necessary to cause pathology and formation of HTT aggregates. Here we ask whether expanded polyQ is sufficient to cause pathology and aggregate formation. By addressing the sufficiency question, one can identify cellular processes and structural parameters that influence HD pathology and HTT subcellular behavior (i.e. aggregation state and subcellular location). Using Drosophila, we compare the effects of expressing mutant full-length human HTT (fl-mHTT) to the effects of mutant human HTTexon1 and to two commonly used synthetic fragments, HTT171 and shortstop (HTT118). Expanded polyQ alone is not sufficient to cause inclusion formation since full-length HTT and HTTex1 with expanded polyQ are both toxic although full-length HTT remains diffuse while HTTex1 forms inclusions. Further, inclusions are not sufficient to cause pathology since HTT171-120Q forms inclusions but is benign and co-expression of HTT171-120Q with non-aggregating pathogenic fl-mHTT recruits fl-mHTT to aggregates and rescues its pathogenicity. Additionally, the influence of sequences outside the expanded polyQ domain is revealed by finding that small modifications to the HTT118 or HTT171 fragments can dramatically alter their subcellular behavior and pathogenicity. Finally, mutant HTT subcellular behavior is strongly modified by different cell and tissue environments (e.g. fl-mHTT appears as diffuse nuclear in one tissue and diffuse cytoplasmic in another but toxic in both). These observations underscore the importance of cellular and structural context for the interpretation and comparison of experiments using different fragments and tissues to report the effects of expanded polyQ.

Ecdysis triggering hormone is essential for larva-pupa-adult transformation in Leptinotarsa decemlineata

In Drosophila melanogaster, ecdysis triggering hormone (ETH) is the key factor triggering ecdysis behaviour and promoting trachea clearance. However, whether ETH plays the dual roles in non-dipteran insects is unknown. In this survey, we found that Ldeth mRNA levels were positively correlated with circulating 20-hydroxyecdysone (20E) titers in Leptinotarsa decemlineata. Ingestion of an ecdysteroid agonist halofenozide or 20E stimulated the transcription of Ldeth, whereas RNA interference (RNAi) of ecdysteroidogenesis (LdPTTH or LdSHD) or 20E signalling (LdEcR, LdUSP or LdFTZ-F1) genes inhibited the expression, indicating ETH acts downstream of 20E. RNAi of Ldeth at the final instar stage impaired pupation. More than 80% of the Ldeth-depleted beetles remained as prepupae, completely wrapped in the old larval cuticles. These prepupae became withered, dried and darkened gradually, and finally died in soil. The remaining Ldeth hypomorphs pupated and emerged as abnormal adults, bearing smaller and wrinkle elytrum and hindwing. Moreover, the tracheae in the Ldeth hypomorphs were full of liquid. We accordingly proposed that the failure of trachea clearance disenabled air-swallowing after pupa-adult ecdysis and impacted wing expansion. Our results suggest that ETH plays the dual roles, initiation of ecdysis and motivation of trachea clearance, in a coleopteran.

The FTZ-F1 gene encodes two functionally distinct nuclear receptor isoforms in the ectoparasitic copepod salmon louse (Lepeophtheirus salmonis)

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic crustacean that annually inflicts substantial losses to the aquaculture industry in the northern hemisphere and poses a threat to the wild populations of salmonids. The salmon louse life cycle consists of eight developmental stages each separated by a molt. Fushi Tarazu Factor-1 (FTZ-F1) is an ecdysteroid-regulated gene that encodes a member of the NR5A family of nuclear receptors that is shown to play a crucial regulatory role in molting in insects and nematodes. Characterization of an FTZ-F1 orthologue in the salmon louse gave two isoforms named αFTZ-F1 and βFTZ-F1, which are identical except for the presence of a unique N-terminal domain (A/B domain). A comparison suggest conservation of the FTZ-F1 gene structure among ecdysozoans, with the exception of nematodes, to produce isoforms with unique N-terminal domains through alternative transcription start and splicing. The two isoforms of the salmon louse FTZ-F1 were expressed in different amounts in the same tissues and showed a distinct cyclical expression pattern through the molting cycle with βFTZ-F1 being the highest expressed isoform. While RNA interference knockdown of βFTZ-F1 in nauplius larvae and in pre-adult males lead to molting arrest, knockdown of βFTZ-F1 in pre-adult II female lice caused disruption of oocyte maturation at the vitellogenic stage. No apparent phenotype could be observed in αFTZ-F1 knockdown larvae, or in their development to adults, and no genes were found to be differentially expressed in the nauplii larvae following αFTZ-F1 knockdown. βFTZ-F1 knockdown in nauplii larvae caused both down and upregulation of genes associated with proteolysis and chitin binding and affected a large number of genes which are in normal salmon louse development expressed in a cyclical pattern. This is the first description of FTZ-F1 gene function in copepod crustaceans and provides a foundation to expand the understanding of the molecular mechanisms of molting in the salmon louse and other copepods.

Regulation of Drosophila Long-Term Courtship Memory by Ecdysis Triggering Hormone

Endocrine state is an important determinant of learning and memory in animals. In Drosophila, rejection of male courtship overtures by mated females leads to an aversive response manifested as courtship memory. Here we report that ecdysis triggering hormone (ETH) is an obligatory enabler of long-term courtship memory (LTM). ETH deficiency suppresses LTM, whereas augmented ETH release reduces the minimum training period required for LTM induction. ETH receptor knockdown either in the mushroom body (MB) γ lobe or in octopaminergic dorsal-anterior-lateral (DAL) neurons impairs memory performance, indicating its direct action in these brain areas. Consistent with these findings, brain exposure to ETH mobilizes calcium in MB γ lobe neuropils and DAL neurons. ETH receptor (ETHR) knockdown in the corpus allatum (CA) to create juvenile hormone (JH) deficiency also suppresses LTM, as does knockdown of the JH receptor Met in the MB γ lobe, indicating a convergence of ETH and JH signaling in this region of the brain. Our findings identify endocrine-enabled neural circuit components in the brain that are critical for persistent behavioral changes resulting from aversive social experience.

Dissecting the roles of FTZ-F1 in larval molting and pupation, and the sublethal effects of methoxyfenozide on Helicoverpa armigera

BACKGROUND

In holometabolous insects, the major developmental transitions - larval molting and pupation - are triggered by a pulse of 20-hydroxyecdysone (20E) and coordinated by juvenile hormone. Methoxyfenozide (MF), an ecdysteroid agonist, represents a new class of insect growth regulators and is effective against lepidopteran pests. Fushi-tarazu factor 1 (FTZ-F1) is an ecdysone-inducible transcription factor. To date, the effect of MF on 20E-response genes remains unclear, and we speculate the involvement of FTZ-F1 in MF's growth regulating effect.

RESULTS

MF at LC₂₅ and LC₁₀ caused severe ecdysis failure in Helicoverpa armigera, extended their larval duration, lowered their pupal weight, and reduced the respiratory, pupation and emergence rates. Furthermore, sublethal doses of MF inhibited ecdysteroidogenesis and lowered the intrinsic 20E titer, but showed an inductive effect on 20E-response genes including HaFTZ-F1. HaFTZ-F1, predominantly expressed in larval epidermis, was markedly upregulated before or right after larval ecdysis, and maintained a high level in prepupal stage. Knockdown of HaFTZ-F1 in 4th-instar larvae severely impaired larval ecdysis, whereas its knockdown in final-instar larvae caused abnormal pupation. Moreover, knocking down HaFTZ-F1 downregulated three critical ecdysteroidogenesis genes, lowered 20E titer, and suppressed the expression of 20E receptors and 20E-response genes. The introduction of 20E into HaFTZ-F1-RNAi larvae partly relieved the negative effects on the 20E-induced signaling cascade.

CONCLUSION

Our findings reveal the adverse effects of sublethal doses of MF on the development of H. armigera and elucidate the resulting perturbations on the 20E-induced signaling cascade; we propose that HaFTZ-F1 regulates ecdysis and pupation by mediating 20E titer and its signaling pathway. © 2020 Society of Chemical Industry.

MnFtz-f1 Is Required for Molting and Ovulation of the Oriental River Prawn Macrobrachium nipponense

Molting and ovulation are the basic processes responsible for the growth and reproduction of Macrobrachium nipponense; however, the molecular mechanisms of molting and ovulation in M. nipponense are poorly understood. The present study aimed to use MnFtz-f1 as the starting point to study the molting and ovulation phenomena in M. nipponense at the molecular level. The full-length MnFtz-f1 cDNA sequence was 2,198 base pairs (bp) in length with an open reading frame of 1,899 bp encoding 632 amino acids. Quantitative real-time PCR analysis showed that MnFtz-f1 was highly expressed in the ovary at the cleavage stage and on the fifth day after hatching. In vivo administration of 20-hydroxyecdysone (20E) showed that 20E effectively inhibited the expression of the MnFtz-f1 gene, and the silencing of the MnFtz-f1 gene reduced the content of 20E in the ovary. In situ hybridization (ISH) analysis revealed the localization of MnFtz-f1 in the ovary. Silencing of MnFtz-f1 by RNA interference (RNAi) resulted in significant inhibition of the expression of the vitellogenin (Vg), Spook, and Phantom genes, thus confirming that MnFtz-f1 had a mutual regulatory relationship with Vg, Spook, and Phantom. After RNAi, the molting frequency and ovulation number of M. nipponense decreased significantly, which demonstrated that MnFtz-f1 played a pivotal role in the process of molting and ovulation.

Two Splice Isoforms of Leptinotarsa Ecdysis Triggering Hormone Receptor Have Distinct Roles in Larva-Pupa Transition

Insect ecdysis triggering hormone (ETH) receptors (ETHRs) are rhodopsin-like G protein-coupled receptors. Upon binding its ligand ETH, ETHR initiates a precisely programed ecdysis behavior series and physiological events. In Drosophila melanogaster, the ethr gene produces two functionally distinct splicing isoforms, ethra and ethrb. ETH/ETHRA activates eclosion hormone (EH), kinin, crustacean cardioactive peptide (CCAP), and bursicon (burs and pburs) neurons, among others, in a rigid order, to elicit the behavioral sequences and physiological actions for ecdysis at all developmental stages, whereas ETH/ETHRB is required at both pupal and adult ecdysis. However, the role of ETHRB in regulation of molting has not been clarified in any non-drosophila insects. In the present paper, we found that 20-hydroxyecdysone (20E) signaling triggers the expression of both ethra and ethrb in a Coleopteran insect pest, the Colorado potato beetle Leptinotarsa decemlineata. RNA interference (RNAi) was performed using double-stranded RNAs (dsRNAs) targeting the common (dsethr) or isoform-specific (dsethra, dsethrb) regions of ethr. RNAi of dsethr, dsethra, or dsethrb by the final-instar larvae arrested larva development. The arrest was not rescued by feeding 20E. All the ethra depleted larvae stopped development at prepupae stage; the body cavity was expanded by a large amount of liquid. Comparably, more than 80% of the ethrb RNAi larvae developmentally halted at the prepupae stage. The remaining Ldethrb hypomorphs became pupae, with blackened wings and highly-expressed burs, pburs and four melanin biosynthesis genes. Therefore, ETHRA and ETHRB play isoform-specific roles in regulation of ecdysis during larva-pupa transition in L. decemlineata.

The Evolution of Insect Metamorphosis

The evolution of insect metamorphosis is one of the most important sagas in animal history, transforming small, obscure soil arthropods into a dominant terrestrial group that has profoundly shaped the evolution of terrestrial life. The evolution of flight initiated the trajectory towards metamorphosis, favoring enhanced differences between juvenile and adult stages. The initial step modified postembryonic development, resulting in the nymph-adult differences characteristic of hemimetabolous species. The second step was to complete metamorphosis, holometaboly, and occurred by profoundly altering embryogenesis to produce a larval stage, the nymph becoming the pupa to accommodate the deferred development needed to make the adult. These changing life history patterns were intimately linked to two hormonal systems, the ecdysteroids and the juvenile hormones (JH), which function in both embryonic and postembryonic domains and control the stage-specifying genes Krüppel homolog 1 (Kr-h1), broad and E93. The ecdysteroids induce and direct molting through the ecdysone receptor (EcR), a nuclear hormone receptor with numerous targets including a conserved transcription factor network, the 'Ashburner cascade', which translates features of the ecdysteroid peak into the different phases of the molt. With the evolution of metamorphosis, ecdysteroids acquired a metamorphic function that exploited the repressor capacity of the unliganded EcR, making it a hormone-controlled gateway for the tissue development preceding metamorphosis. JH directs ecdysteroid action, controlling Kr-h1 expression which in turn regulates the other stage-specifying genes. JH appears in basal insect groups as their embryos shift from growth and patterning to differentiation. As a major portion of embryogenesis was deferred to postembryonic life with the evolution of holometaboly, JH also acquired a potent role in regulating postembryonic growth and development. Details of its involvement in broad expression and E93 suppression have been modified as life cycles became more complex and likely underlie some of the changes seen in the shift from incomplete to complete metamorphosis.

The mechanism of sublethal chlorantraniliprole exposure causing silkworm pupation metamorphosis defects

BACKGROUND

Chlorantraniliprole (CAP) is widely used in agriculture and forestry to prevent and control pests. The effects of environmental CAP residue on non-target insect metamorphosis have not been reported. Our research aimed to investigate the sublethal effect of CAP on larva-pupa transformation in silkworm, and explore the mechanism of sublethal CAP exposure-mediated pupation metamorphosis defects.

RESULT

Sublethal CAP exposure affected the growth and development of silkworm larvae and caused defects in pupation metamorphosis. After CAP exposure, formation the of prepupa procuticle, ecdysial membrane and new epidermis was inhibited. Also, the level of 20-hydroxyecdysone (20E) and mRNA levels of the 20E signaling pathway-related genes EcR, USP, E74, E75 and Ftz-f1 were significantly reduced. Moreover, genes involved in chitin synthesis, such as ChsA, CDA1 and CDA2, were downregulated. Injection of 20E led to the upregulation of chitin synthesis-related genes and increased formation of new epidermis in CAP-treated silkworm. However, injection of 20E failed to prevent downregulation of Ftz-f1 and the defects in pupation metamorphosis.

CONCLUSION

Our results suggested that 20E is a target hormone of CAP exposure-mediated epidermis formation phenotype. Ftz-f1 was silenced by CAP and might be a direct target gene of sublethal CAP exposure. Our study provided new evidence of the effects of sublethal CAP exposure on insect development and metamorphosis. © 2020 Society of Chemical Industry.

Nuclear receptor Ftz-f1 promotes follicle maturation and ovulation partly via bHLH/PAS transcription factor Sim

The NR5A-family nuclear receptors are highly conserved and function within the somatic follicle cells of the ovary to regulate folliculogenesis and ovulation in mammals; however, their roles in Drosophila ovaries are largely unknown. Here, we discover that Ftz-f1, one of the NR5A nuclear receptors in Drosophila, is transiently induced in follicle cells in late stages of oogenesis via ecdysteroid signaling. Genetic disruption of Ftz-f1 expression prevents follicle cell differentiation into the final maturation stage, which leads to anovulation. In addition, we demonstrate that the bHLH/PAS transcription factor Single-minded (Sim) acts as a direct target of Ftz-f1 to promote follicle cell differentiation/maturation and that Ftz-f1’s role in regulating Sim expression and follicle cell differentiation can be replaced by its mouse homolog steroidogenic factor 1 (mSF-1). Our work provides new insight into the regulation of follicle maturation in Drosophila and the conserved role of NR5A nuclear receptors in regulating folliculogenesis and ovulation.

When animals reproduce, females release eggs from their ovaries which then get fertilized by sperm from males. Each egg needs to properly mature within a collection of cells known as follicle cells before it can be let go. As the egg matures, so do the follicle cells surrounding it, until both are primed and ready to discharge the egg from the ovary. Mammals rely on a protein called SF-1 to mature their follicle cells, but it is unclear how this process works.

Most animals – from humans to fruit flies – release their eggs in a very similar way, using many of the same proteins and genes. For example, the gene for SF-1 in mammals is similar to a gene in fruit flies which codes for another protein called Ftz-f1. Since it is more straightforward to study ovaries in fruit flies than in humans and other mammals, investigating this protein could shed light on how follicle cells mature. However, it remained unclear whether Ftz-f1 plays a similar role to its mammalian counterpart.

Here, Knapp et al. show that Ftz-f1 is present in the follicle cells of fruit flies and is required for them to properly mature. Ftz-f1 controlled this process by regulating the activity of another protein called Sim. Further experiments found that the gene that codes for the SF-1 protein in mice was able to compensate for the loss of Ftz-f1 and drive follicle cells to mature.

Studying how ovaries release eggs is an essential part of understanding female fertility. This work highlights the similarities between these processes in mammals and fruit flies and may help us understand how ovaries work in humans and other mammals. In the future, the findings of Knapp et al. may lead to new therapies for infertility in females and other disorders that affect ovaries.

The role of nuclear receptor E75 in regulating the molt cycle of Daphnia magna and consequences of its disruption

Biological rhythms regulate innumerable physiological processes, yet little is known of factors that regulate many of these rhythms. Disruption in the timing of these rhythms can have devastating impacts on population sustainability. We hypothesized that the timing of the molt infradian rhythm in the crustacean Daphnia magna is regulated by the joint action of the protein E75 and nitric oxide. Further, we hypothesized that disruption of the function of E75 would adversely impact several physiological processes related to growth and reproduction. Analysis of mRNA levels of several genes, involved in regulating the molt cycle in insects, revealed the sequential accumulation of E75, its dimer partner HR3, FTZ-F1, and CYP18a1 during the molt cycle. Exposure to the nitric oxide donor sodium nitroprusside early in the molt cycle had no effect on E75 or HR3 mRNA levels, but delayed the peak accumulation of FTZ-F1 and CYP18a1 mRNA. The subsequent exuviation was also delayed consistent with the delay in peak accumulation of FTZ-F1 and CYP18a1. These results supported our assertion that nitric oxide binds E75 rendering it incapable of binding HR3. Excess HR3 protein then enhanced the accumulation of the downstream products FTZ-F1 and CYP18a1. Similarly, suppression of E75 mRNA levels, using siRNA, had no effect on mRNA levels of HR3 but elevated mRNA levels of FTZ-F1. Consistent with these molecular responses, the suppression of E75 using siRNA increased the duration of the molt cycle and reduced the number of offspring produced. We conclude that the molt cycle of daphnids is regulated in a manner similar to insects and disruption of E75 results in a lengthening of the molt cycle and a reduction the release of viable offspring.

Transcription factor FTZ-F1 and cis-acting elements mediate expression of CYP6BG1 conferring resistance to chlorantraniliprole in Plutella xylostella

BACKGROUND

Cytochrome P450-mediated detoxification plays an important role in the development of insecticide resistance. Previous studies have demonstrated that overexpression of CYP6BG1 was responsible for permethrin resistance in Plutella xylostella, and our experiments also showed that upregulation of this gene is associated with chlorantraniliprole resistance in P. xylostella. However, the transcriptional regulation involved in the expression of CYP6BG1 remains unknown. To further investigate the regulation of CYP6BG1 expression, the promoters of this gene were cloned and analyzed from one susceptible and four different resistant populations of P. xylostella.

RESULTS

First, the promoter region of P. xylostella CYP6BG1 was compared in five populations, and three types of 5'-flanking region were found. Second, the region between -562 and +49 of CYP6BG1 in a field population (TH) of P. xylostella showed the highest promoter activity and could be induced by chlorantraniliprole. Third, the transcriptional factor FTZ-F1, which is an orphan nuclear receptor and binds to the fushi tarazu (ftz) gene, was predicted by the online software Alggen and Jaspar. It was proved to regulate the expression of CYP6BG1 by RNAi. The expression levels of FTZ-F1 and CYP6BG1 could be induced by chlorantraniliprole and were significantly higher in the resistant populations.

CONCLUSIONS

These data give a better understanding of the transcriptional regulation of an important insecticide detoxification enzyme gene, and therefore will help in understanding the molecular mechanisms of insecticide resistance in P. xylostella. © 2018 Society of Chemical Industry.

Genome-Wide Screening and Functional Analysis Reveal That the Specific microRNA nlu-miR-173 Regulates Molting by Targeting Ftz-F1 in Nilaparvata lugens

Background: Molting is a crucial physiological behavior during arthropod growth. In the past few years, molting as well as chitin biosynthesis triggered by molting, is subject to regulation by miRNAs. However, how many miRNAs are involved in insect molting at the genome-wide level remains unknown. Results: We deeply sequenced four samples obtained from nymphs at the 2nd-3rd and 4th-5th instars, and then identified 61 miRNAs conserved in the Arthropoda and 326 putative novel miRNAs in the brown planthopper Nilaparvata lugens, a fearful pest of rice. A total of 36 mature miRNAs with significant different expression levels at the genome scale during molting, including 19 conserved and 17 putative novel miRNAs were identified. After comparing the expression profiles, we found that most of the targets of 36 miRNAs showing significantly differential expression were involved in energy and hormone pathways. One of the 17 putative novel miRNAs, nlu-miR-173 was chosen for functional study. nlu-miR-173 acts in 20-hydroxyecdysone signaling through its direct target, N. lugens Ftz-F1(NlFtz-F1), a transcription factor. Furthermore, we found that the transcription of nlu-miR-173 was promoted by Broad-Complex (BR-C), suggesting that its involvement in the 20-hydroxyecdysone pathway contributes to proper molting function. Conclusion: We provided a comprehensive resource of miRNAs associated with insect molting and identified a novel miRNA as a potential target for pest control.

Leptinotarsa hormone receptor 4 (HR4) tunes ecdysteroidogenesis and mediates 20-hydroxyecdysone signaling during larval-pupal metamorphosis

Hormone receptor 4 (HR4) is involved in the regulation of 20-hydroxyecdysone (20E) biosynthesis and the mediation of 20E signaling during larval-pupal transition in a holometabolan Drosophila melanogaster, whereas it acts as a repressor in 20E-responsive transcriptional cascade in a hemimetabolan, Blattella germanica. Here we characterized two HR4 splicing variants, LdHR4X1 and LdHR4X2, in a coleopteran Leptinotarsa decemlineata. LdHR4X1 was highly expressed in the prothoracic gland and epidermis while LdHR4X2 was abundantly transcribed in the nervous system. In vivo results showed that both prothoracicotropic hormone and 20E pathways transcriptionally regulated LdHR4, in an isoform-dependent pattern. RNA interference of LdHR4 at the final (fourth) larval instar, in contrast to the second- and third-instar periods, enhanced the expression of two ecdysteroidogenesis genes, increased 20E titer, upregulated transcription of five 20E-response genes, and reduced the mRNA level of Fushi tarazu-factor 1 (FTZ-F1). As a result, the fourth-instar LdHR4 RNAi larvae exhibited accelerated development and reduced body weight. Moreover, knockdown of LdHR4 at the fourth instar resulted in larval lethality and impaired pupation. Feeding of pyriproxyfen (a mimic of juvenile hormone) or silencing of a juvenile hormone degrading enzyme gene restored the normal course of ecdysteroidogenesis, duration of larval development, and body weight in fourth-instar LdHR4 RNAi larvae. The treatment partially suppressed the larval mortality but not the failure to pupate. The dual role of HR4 during larval-pupal metamorphosis appears to be evolutionarily conserved among holometabolans.

Stress-induced reproductive arrest in Drosophila occurs through ETH deficiency-mediated suppression of oogenesis and ovulation

BACKGROUND

Environmental stressors induce changes in endocrine state, leading to energy re-allocation from reproduction to survival. Female Drosophila melanogaster respond to thermal and nutrient stressors by arresting egg production through elevation of the steroid hormone ecdysone. However, the mechanisms through which this reproductive arrest occurs are not well understood.

RESULTS

Here we report that stress-induced elevation of ecdysone is accompanied by decreased levels of ecdysis triggering hormone (ETH). Depressed levels of circulating ETH lead to attenuated activity of its targets, including juvenile hormone-producing corpus allatum and, as we describe here for the first time, octopaminergic neurons of the oviduct. Elevation of steroid thereby results in arrested oogenesis, reduced octopaminergic input to the reproductive tract, and consequent suppression of ovulation. ETH mitigates heat or nutritional stress-induced attenuation of fecundity, which suggests that its deficiency is critical to reproductive adaptability.

CONCLUSIONS

Our findings indicate that, as a dual regulator of octopamine and juvenile hormone release, ETH provides a link between stress-induced elevation of ecdysone levels and consequent reduction in fecundity.

Ecdysis Triggering Hormone Signaling (ETH/ETHR-A) Is Required for the Larva-Larva Ecdysis in Bactrocera dorsalis (Diptera: Tephritidae)

Insects must undergo ecdysis for successful development and growth, and the ecdysis triggering hormone (ETH), released by the Inka cells, is a master hormone in this process. In this study, we determined the sequence of the ETH precursor and receptors in an agriculturally important pest insect, the oriental fruit fly Bactrocera dorsalis (Hendel). We identified two functionally distinct splice receptor isoforms: BdETH-R-A and BdETH-R-B, and when expressed in Chinese hamster ovary (CHO-WTA11) cells, they exhibited a high sensitivity to the two mature peptides BdETH1 and BdETH2. The BdETH transcript was detected in the tracheal tissue of the larvae. Inka cells were identified with immunohistochemical antibody staining against Drosophila melanogaster ETH1, and in situ hybridization with specific DNA probes. Selective RNA silencing of BdETH or BdETH-R-A, but not of BdETH-R-B, caused developmental failure at ecdysis. The dsRNA-treated larvae displayed tracheal defects and could not shed the old cuticle followed by death. Our results demonstrated that BdETH, via activation of BdETH-R-A but not ETH-R-B, plays an essential role in regulating the process of larva-larva ecdysis in B. dorsalis.

Endocrine network essential for reproductive success in Drosophila melanogaster

Ecdysis-triggering hormone (ETH) was originally discovered and characterized as a molt termination signal in insects through its regulation of the ecdysis sequence. Here we report that ETH persists in adult Drosophila melanogaster, where it functions as an obligatory allatotropin to promote juvenile hormone (JH) production and reproduction. ETH signaling deficits lead to sharply reduced JH levels and consequent reductions of ovary size, egg production, and yolk deposition in mature oocytes. Expression of ETH and ETH receptor genes is in turn dependent on ecdysone (20E). Furthermore, 20E receptor knockdown specifically in Inka cells reduces fecundity. Our findings indicate that the canonical developmental roles of 20E, ETH, and JH during juvenile stages are repurposed to function as an endocrine network essential for reproductive success.

Ecdysone Receptor Agonism Leading to Lethal Molting Disruption in Arthropods: Review and Adverse Outcome Pathway Development

Molting is critical for growth, development, reproduction, and survival in arthropods. Complex neuroendocrine pathways are involved in the regulation of molting and may potentially become targets of environmental endocrine disrupting chemicals (EDCs). Based on several known ED mechanisms, a wide range of pesticides has been developed to combat unwanted organisms in food production activities such as agriculture and aquaculture. Meanwhile, these chemicals may also pose hazards to nontarget species by causing molting defects, and thus potentially affecting the health of the ecosystems. The present review summarizes the available knowledge on molting-related endocrine regulation and chemically mediated disruption in arthropods (with special focus on insects and crustaceans), to identify research gaps and develop a mechanistic model for assessing environmental hazards of these compounds. Based on the review, multiple targets of EDCs in the molting processes were identified and the link between mode of action (MoA) and adverse effects characterized to inform future studies. An adverse outcome pathway (AOP) describing ecdysone receptor agonism leading to incomplete ecdysis associated mortality was developed according to the OECD guideline and subjected to weight of evidence considerations by evolved Bradford Hill Criteria. This review proposes the first invertebrate ED AOP and may serve as a knowledge foundation for future environmental studies and AOP development.

Large-scale identification of differentially expressed genes during pupa development reveals solute carrier gene is essential for pupal pigmentation in Chilo suppressalis

Insects undergo metamorphosis, involving an abrupt change in body structure through cell growth and differentiation. Rice stem stripped borer (SSB), Chilo suppressalis, is one of the most destructive rice pests. However, little is known about the regulation mechanism of metamorphosis development in this notorious insect pest. Here, we studied the expression of 22,197 SSB genes at seven time points during pupa development with a customized microarray, identifying 622 differentially expressed genes (DEG) during pupa development. Gene ontology (GO) analysis of these DEGs indicated that the genes related to substance metabolism were highly expressed in the early pupa, which participate in the physiological processes of larval tissue disintegration at these stages. In comparison, highly expressed genes in the late pupal stages were mainly associated with substance biosynthesis, consistent with adult organ formation at these stages. There were 27 solute carrier (SLC) genes that were highly expressed during pupa development. We knocked down SLC22A3 at the prepupal stage, demonstrating that silencing SLC22A3 induced a deficiency in pupa stiffness and pigmentation. The RNAi-treated individuals had white and soft pupa, suggesting that this gene has an essential role in pupal development.

Ligand-Bound GeneSwitch Causes Developmental Aberrations in Drosophila that Are Alleviated by the Alternative Oxidase

Culture of Drosophila expressing the steroid-dependent GeneSwitch transcriptional activator under the control of the ubiquitous α-tubulin promoter was found to produce extensive pupal lethality, as well as a range of dysmorphic adult phenotypes, in the presence of high concentrations of the inducing drug RU486. Prominent among these was cleft thorax, seen previously in flies bearing mutant alleles of the nuclear receptor Ultraspiracle and many other mutants, as well as notched wings, leg malformations, and bristle abnormalities. Neither the α-tubulin-GeneSwitch driver nor the inducing drug on their own produced any of these effects. A second GeneSwitch driver, under the control of the daughterless promoter, which gave much lower and more tissue-restricted transgene expression, exhibited only mild bristle abnormalities in the presence of high levels of RU486. Coexpression of the alternative oxidase (AOX) from Ciona intestinalis produced a substantial shift in the developmental outcome toward a wild-type phenotype, which was dependent on the AOX expression level. Neither an enzymatically inactivated variant of AOX, nor GFP, or the alternative NADH dehydrogenase Ndi1 from yeast gave any such rescue. Users of the GeneSwitch system should be aware of the potential confounding effects of its application in developmental studies.

A biological timer in the fat body comprising Blimp-1, βFtz-f1 and Shade regulates pupation timing in Drosophila melanogaster

During the development of multicellular organisms, many events occur with precise timing. In Drosophila melanogaster, pupation occurs about 12 h after puparium formation and its timing is believed to be determined by the release of a steroid hormone, ecdysone (E), from the prothoracic gland. Here, we demonstrate that the ecdysone-20-monooxygenase Shade determines pupation timing by converting E to 20-hydroxyecdysone (20E) in the fat body, which is the organ that senses nutritional status. The timing of shade expression is determined by its transcriptional activator βFtz-f1. The βftz-f1 gene is activated after a decline in the expression of its transcriptional repressor Blimp-1, which is temporally expressed around puparium formation in response to a high titer of 20E. The expression level and stability of Blimp-1 is critical for the precise timing of pupation. Thus, we propose that Blimp-1 molecules function like sand in an hourglass in this precise developmental timer system. Furthermore, our data suggest that a biological advantage results from both the use of a transcriptional repressor for time determination and the association of developmental timing with nutritional status of the organism.

Involvement of FTZ-F1 in the regulation of pupation in Leptinotarsa decemlineata (Say)

During the final instar larvae of holometabolous insects, a pulse of 20-hydroxyecdysone (20E) and a drop in juvenile hormone (JH) trigger larval-pupal metamorphosis. In this study, two LdFTZ-F1 cDNAs (LdFTZ-F1-1 and LdFTZ-F1-2) were cloned in Leptinotarsa decemlineata. Both LdFTZ-F1-1 and LdFTZ-F1-2 were highly expressed just before or right after each molt, similar to the expression pattern of an ecdysteroidogenesis gene LdSHD. Ingestion of an ecdysteroid agonist halofenozide (Hal) enhanced LdFTZ-F1-1 and LdFTZ-F1-2 expression in the final larval instar. Conversely, a decrease in 20E by feeding a double-stranded RNA (dsRNA) against LdSHD repressed the expression. Moreover, Hal rescued the expression levels in LdSHD-silenced larvae. Thus, 20E peaks seem to induce the transcription of LdFTZ-F1s. Furthermore, ingesting dsLdFTZ-F1 from a common fragment of LdFTZ-F1-1 and LdFTZ-F1-2 successfully knocked down both LdFTZ-F1s, and impaired pupation. Finally, knocking down LdFTZ-F1s significantly repressed the transcription of three ecdysteroidogenesis genes, lowered 20E titer, and reduced the expression of two 20E receptor genes. Silencing LdFTZ-F1s also induced the expression of a JH biosynthesis gene, increased JH titer, but decreased the mRNA level of a JH early-inducible gene. Thus, LdFTZ-F1s are involved in the regulation of pupation by modulating 20E and JH titers and mediating their signaling pathways.

Function of the nuclear receptor FTZ-F1 during the pupal stage in Drosophila melanogaster

The nuclear receptor βFTZ-F1 is expressed in most cells in a temporally specific manner, and its expression is induced immediately after decline in ecdysteroid levels. This factor plays important roles during embryogenesis, larval ecdysis, and early metamorphic stages. However, little is known about the expression pattern, regulation and function of this receptor during the pupal stage. We analyzed the expression pattern and regulation of ftz-f1 during the pupal period, as well as the phenotypes of RNAi knockdown or mutant animals, to elucidate its function during this stage. Western blotting revealed that βFTZ-F1 is expressed at a high level during the late pupal stage, and this expression is dependent on decreasing ecdysteroid levels. By immunohistological analysis of the late pupal stage, FTZ-F1 was detected in the nuclei of most cells, but cytoplasmic localization was observed only in the oogonia and follicle cells of the ovary. Both the ftz-f1 genetic mutant and temporally specific ftz-f1 knockdown using RNAi during the pupal stage showed defects in eclosion and in the eye, the antennal segment, the wing and the leg, including bristle color and sclerosis. These results suggest that βFTZ-F1 is expressed in most cells at the late pupal stage, under the control of ecdysteroids and plays important roles during pupal development.