Effects of juvenile hormone on 20-hydroxyecdysone-inducible EcR, HR3, E75 gene expression in imaginal wing cells of Plodia interpunctella lepidoptera

Transcriptome-based analysis reveals a crucial role of the 20E/HR3 pathway in the diapause of Pieris rapae

Pieris rapae is among the most damaging pests globally, and diapause makes it highly resistant to environmental stresses, playing a crucial role in the survival and reproduction of P. rapae while exacerbating the challenges of pest management and control. However, the mechanisms of its diapause regulation remain poorly understood. This research used RNA sequencing to profile the transcriptomes of three diapause phases (induction and preparation, initiation, maintenance) and synchronous nondiapause phases in P. rapae. During each comparison phase, 759, 1045, and 4721 genes were found to be differentially expressed. Among these, seven clock genes and seven pivotal hormone synthesis and metabolism genes were identified as having differential expression patterns in diapause type and nondiapause type. The weighted gene co-expression network analysis (WGCNA) revealed the red and blue modules as pivotal for diapause initiation, while the grey module was identified to be crucial to diapause maintenance. Meanwhile, the hub genes HDAC11, METLL16D, Dyw-like, GST, and so on, were identified within these hub modules. Moreover, an ecdysone downstream nuclear receptor gene, HR3, was found to be a shared transcription factor across all three phases. RNA interference of HR3 resulted in delayed pupal development, indicating its involvement in regulating pupal dipause in P. rapae. The further hormone assays revealed that the 20-hydroxyecdysone (20E) titer in diapause type pupae was lower than that in nondiapause type pupae, which exhibited a similar trend to HR3. When 20E was injected into diapause pupae, the HR3 expression levels were improved, and the pupal diapause were broken. These results indicate that the 20E/HR3 pathway is a critical pathway for the diapause regulation of P. rapae, and perturbing this pathway by ecdysone treatment or RNAi would result in the disruption of diapause. These findings provide initial insights into the molecular mechanisms of P. rapae diapause and suggest the potential use of ecdysone analogs and HR3 RNAi pesticides, which specifically target to diapause, as a means of pest control in P. rapae.

Role of nuclear receptors NlHR3 and NlFTZ-F1 in regulating molting and reproduction in Nilaparvata lugens (stål)

The nuclear receptors HR3 and FTZ-F1 are highly conserved and function to regulate molting and reproduction in both hemimetabolous and holometabolous insects. However, their roles in Nilaparvata lugens are largely unknown. In the present study, we discover that NlHR3 and NlFTZ-F1 are activated in the nymph stages by ecdysone signaling. Transcription disruption of NlHR3 and NlFTZ-F1 expression prevents nymph ecdysis and metamorphosis, which leads to abnormal appearance, malformed ovaries, and lethal phenotypes. In addition, we demonstrate that NlHR3 and NlFTZ-F1 regulate molting and reproduction by interacting with the intrinsic 20E and JH signaling pathways. Our work offers a deep insight into the action mechanisms of HR3 and FTZ-F1 in insects. Moreover, NlHR3 and NlFTZ-F1 could properly be exploited as potential target genes for developing RNAi-based pesticides to control N. lugens.

Sob gene is critical to wing development in Bombyx mori and Tribolium castaneum

The development of insect appendages requires the expression of multiple genes in a strict spatial and temporal order. The odd-skipped family genes are vital transcriptional factors involved in embryonic development. The development and morphogenesis of the insect wing requires multiple transcription factors to regulate the expression of wing patterning genes at the transcriptional level. However, the function of odd-related genes in insect wing morphogenesis and development during postembryonic stages is unclear. We focused on the roles of the sister of odd and bowl (sob) gene, a member of odd-skipped family genes, during the wing morphopoiesis in Bombyx mori using the clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 system and in Tribolium castaneum by RNA interference. The results showed that the wings were significantly smaller and degenerated, and wing veins were indistinct in the sob gene loss-of-function group in both B. mori and T. castaneum. Quantitative real-time polymerase chain reaction revealed that the Tcsob gene regulated the expression of wing development genes, such as the cht 7 and the vg gene. The findings suggest the importance of sob gene in insect wing morphology formation during postembryonic stages.

Multiple factors correlating with wing malformations in the population of Parnassius apollo (Lepidoptera: Papilionidae) restituted from a low number of individuals: A mini review

The Apollo butterfly, Parnassius apollo (Linnaeus), was common in Europe over 100 years ago, but currently it is considered as near threatened. Different conservation programs have promoted the persistence of this species; however, it is still endangered. An example of such programs was the action devoted to reestablish the Apollo butterfly population in Pieniny National Park (Poland) from only 20-30 individuals which had survived till the last decade of the 20th century. This reintroduction has been successful; however, unexpected developmental problems appeared. Butterflies with deformed or reduced wings became frequent in the population living in the natural habitat, and particularly among those reared under seminatural conditions (in the same environment, but fenced by a net). Until recently, reasons for these malformations remained unknown. However, reports published during last months indicated that there are genetic, biochemical, and microbiological factors contributing to this phenomenon. In the malformed individuals, lesions in the wingless gene and dysfunctions of laccase 1 and 2 were found to be significantly more frequent than in normal insects. A large fraction of butterflies with deformed or reduced wings was devoid of the prokaryotic symbiont Wolbachia, which was present in most normal individuals. Moreover, Yersinia pseudotuberculosis (Pfeiffer) Smith and Thal, and Serratia sp., bacteria pathogenic to insects, were detected in the biological material from both normal and malformed butterflies from this population. These findings are summarized and discussed in this review, in the light of conservation of insects and restitution of their populations from a low number of individuals.

Larval diapause termination in the bamboo borer, Omphisa fuscidentalis

In insects, juvenile hormone (JH) and 20-hydroxyecdysone (20E) regulate larval growth and molting. However, little is known about how this cooperative control is terminating larval diapause especially in the bamboo borer, Omphisa fuscidentalis. In both in vivo and in vitro experiments, we here measured the expression levels of genes which were affected by juvenile hormone analogue (JHA: S-methoprene) and 20-hydroxyecdysone (20E) in diapausing O. fuscidentalis larvae. Corresponding mRNA expression changes in the subesophageal ganglion (SG) and prothoracic gland (PG) were evaluated using qRT-PCR. The data showed similar response patterns of JH receptor gene (OfMet), diapause hormone gene (OfDH-PBAN), ecdysone receptor genes (OfEcR-A and OfEcR-B1) and ecdysone inducible genes (OfBr-C, OfE75A, OfE75B, OfE75C and OfHR3). JHA induced the expressions of OfMet and OfDH-PBAN in both SG and PG, whereas ecdysone receptor genes and ecdysone inducible genes were induced by JHA only in PG. For 20E treatment group, expressions of ecdysone receptor genes and ecdysone inducible genes in both SG and PG were increased by 20E injection. In addition, the in vitro experiments showed that OfMet and OfDH-PBAN were up-regulated by JHA alone, but ecdysone receptor genes and ecdysone inducible genes were up-regulated by JHA and 20E. However, OfMet and OfDH-PBAN in the SG was expressed faster than OfMet and OfDH-PBAN in the PG and the expression of ecdysone receptor genes and ecdysone inducible genes induced by JHA was much later than observed for 20E. These results indicate that JHA might stimulate the PG indirectly via factors (OfMet and OfDH-PBAN) in the SG, which might be a regulatory mechanism for larval diapause termination in O. fuscidentalis.

RNA Interference of the Ecdysone Receptor Genes EcR and USP in Grain Aphid (Sitobion avenae F.) Affects Its Survival and Fecundity upon Feeding on Wheat Plants

RNA interference (RNAi) has been widely used in functional genomics of insects and received intensive attention in the development of RNAi-based plants for insect control. Ecdysone receptor (EcR) and ultraspiracle protein (USP) play important roles in molting, metamorphosis, and reproduction of insects. EcR and USP orthologs and their function in grain aphid (Sitobion avenae F.) have not been documented yet. Here, RT-PCR, qRT-PCR, dsRNA feeding assay and aphid bioassay were employed to isolate EcR and USP orthologs in grain aphid, investigate their expression patterns, and evaluate the effect of RNAi on aphid survival and fecundity, and its persistence. The results indicated that SaEcR and SaUSP exhibited similar expression profiles at different developmental stages. Oral administration of dsRNAs of SaEcR and dsSaUSP significantly decreased the survival of aphids due to the down-regulation of these two genes, respectively. The silencing effect was persistent and transgenerational, as demonstrated by the reduced survival and fecundity due to knock-down of SaEcR and SaUSP in both the surviving aphids and their offspring, even after switching to aphid-susceptible wheat plants. Taken together, our results demonstrate that SaEcR and SaUSP are essential genes in aphid growth and development, and could be used as RNAi targets for wheat aphid control.

Identification of two juvenile hormone inducible transcription factors from the silkworm, Bombyx mori

Juvenile hormone (JH) regulates many physiological processes in insects. However, the signal cascades in which JH is active have not yet been fully elucidated, particularly in comparison to another major hormone ecdysteroid. Here we identified two JH inducible transcription factors as candidate components of JH signaling pathways in the silkworm, Bombyx mori. DNA microarray analysis showed that expression of two transcription factor genes, E75 and Enhancer of split mβ (E(spl)mβ), was induced by juvenile hormone I (JH I) in NIAS-Bm-aff3 cells. Real time RT-PCR analysis confirmed that expression of four E75 isoforms (E75A, E75B, E75C and E75D) and E(spl)mβ was 3-8 times greater after JH I addition. Addition of the protein synthesis inhibitor cycloheximide did not suppress JH-induced expression of the genes, indicating that they were directly induced by JH. JH-induced expression of E75 and E(spl)mβ was also observed in four other B. mori cell lines and in larval hemocytes of final instar larvae. Notably, E75A expression was induced very strongly in larval hemocytes by topical application of the JH analog fenoxycarb; the level of induced expression was comparable to that produced by feeding larvae with 20-hydroxyecdysone. These results suggest that E75 and E(spl)mβ are general and direct target genes of JH and that the transcription factors encoded by these genes play important roles in JH signaling.

Functions of nuclear receptor HR3 during larval-pupal molting in Leptinotarsa decemlineata (Say) revealed by in vivo RNA interference

Our previous results revealed that RNA interference-aided knockdown of Leptinotarsa decemlineata FTZ-F1 (LdFTZ-F1) reduced 20E titer, and impaired pupation. In this study, we characterized a putative LdHR3 gene, an early-late 20E-response gene upstream of LdFTZ-F1. Within the first, second and third larval instars, three expression peaks of LdHR3 occurred just before the molt. In the fourth (final) larval instar 80 h after ecdysis and prepupal stage 3 days after burying into soil, two LdHR3 peaks occurred. The LdHR3 expression peaks coincide with the peaks of circulating 20E level. In vitro midgut culture and in vivo bioassay revealed that 20E and an ecdysteroid agonist halofenozide (Hal) enhanced LdHR3 expression in the final larval instars. Conversely, a decrease in 20E by feeding a double-stranded RNA (dsRNA) against an ecdysteroidogenesis gene Ldshd repressed the expression. Moreover, Hal rescued the transcript levels in the Ldshd-silenced larvae. Thus, 20E peaks activate the expression of LdHR3. Furthermore, ingesting dsRNA against LdHR3 successfully knocked down the target gene, and impaired pupation. Finally, knockdown of LdHR3 upregulated the transcription of three ecdysteroidogenesis genes (Ldphm, Lddib and Ldshd), increased 20E titer, and activated the expression of two 20E-response genes (LdEcR and LdFTZ-F1). Thus, LdHR3 functions in regulation of pupation in the Colorado potato beetle.

Endocrine regulation of predator-induced phenotypic plasticity

Elucidating the developmental and genetic control of phenotypic plasticity remains a central agenda in evolutionary ecology. Here, we investigate the physiological regulation of phenotypic plasticity induced by another organism, specifically predator-induced phenotypic plasticity in the model ecological and evolutionary organism Daphnia pulex. Our research centres on using molecular tools to test among alternative mechanisms of developmental control tied to hormone titres, receptors and their timing in the life cycle. First, we synthesize detail about predator-induced defenses and the physiological regulation of arthropod somatic growth and morphology, leading to a clear prediction that morphological defences are regulated by juvenile hormone and life-history plasticity by ecdysone and juvenile hormone. We then show how a small network of genes can differentiate phenotype expression between the two primary developmental control pathways in arthropods: juvenoid and ecdysteroid hormone signalling. Then, by applying an experimental gradient of predation risk, we show dose-dependent gene expression linking predator-induced plasticity to the juvenoid hormone pathway. Our data support three conclusions: (1) the juvenoid signalling pathway regulates predator-induced phenotypic plasticity; (2) the hormone titre (ligand), rather than receptor, regulates predator-induced developmental plasticity; (3) evolution has favoured the harnessing of a major, highly conserved endocrine pathway in arthropod development to regulate the response to cues about changing environments (risk) from another organism (predator).

Visualization of ecdysteroid activity using a reporter gene in the crustacean, Daphnia

Ecdysone is a hormone known to play a pivotal role in crustaceans and insects. In order to evaluate the ecdysone activities in the environment and within the organism, we have developed a biomonitoring Daphnia strain by introducing a reporter gene. In this study, the ecdysone response element was inserted in the upstream region of a reporter gene, and the DNA construct was injected into Daphnia eggs. The expression of the reporter gene was detected during the early embryonic development stage. In addition, when the eggs expressing the reporter gene were exposed to ecdysone, there was enhanced expression of the reporter gene at detectable levels, while the presence of an antagonist led to its downregulation. These results suggested that this system could be potentially developed for monitoring ecdysone activities in media.

Steroid hormone signaling is involved in the age-dependent behavioral response to sex pheromone in the adult male moth Agrotis ipsilon

In most animals, including insects, male reproduction depends on the detection and processing of female-produced sex pheromones. In the male moth, Agrotis ipsilon, both behavioral response and neuronal sensitivity in the primary olfactory center, the antennal lobe (AL), to female sex pheromone are age- and hormone-dependent. In many animal species, steroids are known to act at the brain level to modulate the responsiveness to sexually relevant chemical cues. We aimed to address the hypothesis that the steroidal system and in particular 20-hydroxyecdysone (20E), the main insect steroid hormone, might also be involved in this olfactory plasticity. Therefore, we first cloned the nuclear ecdysteroid receptor EcR (AipsEcR) and its partner Ultraspiracle (AipsUSP) of A. ipsilon, the expression of which increased concomitantly with age in ALs. Injection of 20E into young sexually immature males led to an increase in both responsiveness to sex pheromone and amount of AipsEcR and AipsUSP in their ALs. Conversely, the behavioral response decreased in older, sexually mature males after injection of cucurbitacin B (CurB), an antagonist of the 20E/EcR/USP complex. Also, the amount of AipsEcR and AipsUSP significantly declined after treatment with CurB. These results suggest that 20E is involved in the expression of sexual behavior via the EcR/USP signaling pathway, probably acting on central pheromone processing in A. ipsilon.

RNAi knockdown of dRNaseZ, the Drosophila homolog of ELAC2, impairs growth of mitotic and endoreplicating tissues

The Drosophila RNase Z(L) (dRNaseZ) gene encodes a member of the ELAC1/ELAC2 protein family with homologs in every living organism. All RNase Z proteins tested so far were found to possess endoribonuclease activity, which is responsible for the removal of a 3' trailer from a primary tRNA transcript. Given that tRNA 3'-end processing has been delineated using in vitro, bacterial and cell culture models, its relevance to RNase Z functions in vivo has yet to be established. In this study, we employed heritable RNA interference (RNAi) in combination with the GAL4/UAS system to spatiotemporally knockdown the dRNaseZ gene and study its biological role in cells of a developing fruit fly. We found that dRNaseZ is an essential gene, as ubiquitous knockdown caused growth arrest and early larval lethality. Molecular analysis confirmed that dRNaseZ is necessary for 3'-end processing of nuclear and mitochondrial tRNAs: knockdown larvae displayed significant accumulation of both types of processing intermediates with extensions at the 3' end. This is the first in vivo demonstration of RNase Z(L) dependent tRNA processing in the context of a metazoan model organism. Using tissue-specific GAL4 drivers, we also showed that in mitotically growing imaginal discs dRNaseZ is required for cell proliferation and/or viability, but not for the maintenance of their differentiated progeny. In endoreplicating salivary glands, dRNaseZ controls organ size by supporting cell growth but not DNA replication. Although the mechanisms remain unclear, our results support the notion that RNase Z(L) is involved in biological pathways regulating cell growth and proliferation.

Arthropod nuclear receptors and their role in molting

The molting process in arthropods is regulated by steroid hormones acting via nuclear receptor proteins. The most common molting hormone is the ecdysteroid, 20-hydroxyecdysone. The receptors of 20-hydroxyecdysone have also been identified in many arthropod species, and the amino acid sequences determined. The functional molting hormone receptors consist of two members of the nuclear receptor superfamily, namely the ecdysone receptor and the ultraspiracle, although the ecdysone receptor may be functional, in some instances, without the ultraspiracle. Generally, the ecdysone receptor/ultraspiracle heterodimer binds to a number of ecdysone response elements, sequence motifs that reside in the promoter of various ecdysteroid-responsive genes. In the ensuing transcriptional induction, the ecdysone receptor/ultraspiracle complex binds to 20-hydroxyecdysone or to a cognate ligand that, in turn, leads to the release of a corepressor and the recruitment of coactivators. 3D structures of the ligand-binding domains of the ecdysone receptor and the ultraspiracle have been solved for a few insect species. Ecdysone agonists bind to ecdysone receptors specifically, and ligand-ecdysone receptor binding is enhanced in the presence of the ultraspiracle in insects. The basic mode of ecdysteroid receptor action is highly conserved, but substantial functional differences exist among the receptors of individual species. Even though the transcriptional effects are apparently similar for ecdysteroids and nonsteroidal compounds such as diacylhydrazines, the binding shapes are different between them. The compounds having the strongest binding affinity to receptors ordinarily have strong molting hormone activity. The ability of the ecdysone receptor/ultraspiracle complex to manifest the effects of small lipophilic agonists has led to their use as gene switches for medical and agricultural applications.

Juvenile hormone regulation of Drosophila Epac--a guanine nucleotide exchange factor

Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to characterize the effects of juvenile hormone (JH) on Epac (Exchange Protein directly Activated by Cyclic AMP; NM_001103732), a guanine nucleotide exchange factor for Rap1 in Drosophila S2 cells. JH treatment led to a rapid, dose-dependent increase in Epac relative expression ratio (RER) when compared to treatment with methyl linoleate (MLA) that lacks biological activity. The minimal level of hormone needed to elicit a response was 100 ng/ml. Time-course studies indicated a significant rise in the RER 1h after treatment. S2 cells were challenged with 20-hydroxyecdysone and a series of compounds similar in structure to JH to determine the specificity of the response. Methoprene and JH III displayed the greatest increases in RER. Late third instar (96 h) Drosophila were exposed to diet containing methoprene (500 ng/g diet); significantly higher RERs for Epac were observed 12h after exposure. JH had no effect on Epac RERs in the human cell line HEK-293.

The 20-hydroxyecdysone-induced signalling pathway in G2/M arrest of Plodia interpunctella imaginal wing cells

The mechanisms involved in the control of cellular proliferation by the steroid hormone 20-hydroxyecdysone (20E) in insects are not known. We dissected the 20E signalling pathway responsible for G2/M arrest of imaginal cells from the IAL-PID2 cells of the Indian meal moth Plodia interpunctella. We first used a 5'-3' RACE-based strategy to clone a 4479bp cDNA encoding a putative P. interpunctella HR3 transcription factor named PiHR3. The deduced amino acid sequence of PiHR3 was highly similar to those of HR3 proteins from other lepidopterans, e.g. Manduca sexta and Bombyx mori. Using double-stranded RNA-mediated interference (dsRNAi), we then succeeded in blocking the ability of 20E to induce the expression of PiEcR-B1, PiUSP-2 and PiHR3 genes that encode the P. interpunctella ecdysone receptor B1-isoform, Ultraspiracle-2 isoform, the insect homologue of the vertebrate retinoid X receptor, and the HR3 transcription factor. We showed that inhibiting the 20E induction of PiEcR-B1, PiUSP-2 and PiHR3 mRNAs prevented the decreased expression of B cyclin and consequently the G2/M arrest of IAL-PID2 cells. Using this functional approach, we revealed the participation of EcR, USP and HR3 in a 20E signalling pathway that controls the proliferation of imaginal cells by regulating the expression of B cyclin.

Juvenile hormone analogs do not affect directly the activity of the ecdysteroid receptor complex in insect culture cell lines

During insect development, ecdysteroids and juvenile hormones (JHs) interact to regulate larval growth, metamorphosis and reproduction but the molecular mechanisms by which both hormones influence each other's activity remain unknown. Because of their ease of use and straightforward genetic manipulation, insect cell lines often have been used to clarify the actions and interactions of hormones at the molecular level. Here we report on the use of two insect culture cell lines, Drosophila melanogaster S2 and Bombyx mori Bm5 cells, to investigate two molecular processes in which ecdysteroids and JH have been shown to interact: (1) direct modulation of the activity of the ecdysteroid receptor transcription complex and (2) interference at the level of induction of the primary gene E75. Our data do not support JH analogs (JHAs) acting through the above processes: 'antagonism' of ecdysteroid receptor activity by JHAs correlated with cytotoxicity and induction of E75 expression by JHAs was not demonstrated. However, we confirm previous studies in which it was observed that methoprene can partially reverse the growth inhibition by 20E in S2 cells (but not Bm5 cells). Therefore, the molecular mechanism by which both hormones influence each other's activity to regulate cell growth in S2 cells remains unknown.

EcR-A expression in the brain and ovary of the honeybee (Apis mellifera L.)

We previously demonstrated that six genes involved in ecdysteroid signaling are expressed preferentially in Kenyon-cell subtypes in the mushroom bodies of the honeybee (Apis mellifera L.). To further examine the possible involvement of ecdysteroid signaling in honeybee brain function, we isolated a cDNA for the A isoform of the ecdysone receptor gene homolog AmEcR-A and analyzed its expression in the brain. In situ hybridization revealed that AmEcR-A is expressed selectively in the small-type Kenyon cells of the mushroom bodies in the worker and queen brain, like AmE74 and AmHR38, suggesting a possible association of these gene products. Analysis of AmEcR-A expression in queen and worker abdomens demonstrated that AmEcR-A is strongly expressed in nurse cells of the queen ovary, suggesting that ecdysteroid and ecdysteroid signaling have roles in oogenesis. Our present results further support the possible involvement of ecdysteroid signaling in brain function, as well as in regulating queen reproductive physiology in the adult honeybee.

Ecdysteroid-responsive genes, RXR and E75, in the tropical land crab, Gecarcinus lateralis: differential tissue expression of multiple RXR isoforms generated at three alternative splicing sites in the hinge and ligand-binding domains

In order to study the potential role of the steroid molting hormone (20-hydroxyecdysone) in regulating molt-induced claw muscle atrophy, full-length cDNAs encoding retinoid-X receptor (Gl-RXR) and E75 early ecdysone inducible gene (Gl-E75) were obtained from land crab (Gecarcinus lateralis) skeletal muscle mRNA using RT-PCR and 3' and 5' RACE. Gl-E75A (3528bp), which encoded a protein of 828 amino acids, had highest sequence identity to Me-E75A from a shrimp (Metapenaeus ensis). It was expressed in skeletal muscle and gonads. The deduced amino acid sequence of Gl-RXR was highly similar to that of the fiddler crab RXR (Up-RXR) and insect ultraspiracle (USP). Nine variant sequences occurred in Gl-RXR mRNAs at three alternative splicing sites, one in the "T box" in the linker D domain and two in the ligand-binding domain (LBD). The three T-box variants, termed T(+8), T(+7), and T(+12), contained insertions of 8, 7, or 12 amino acids, respectively. Four variants were generated at the first site in the LBD. Two of the LBD site 1 variants differed in the presence (+33) or absence (-33) of a 33-amino acid sequence; the other two were LBD truncations with or without the 33 amino acid sequence (+33DeltaE/F and -33DeltaE/F, respectively). Two variants differing in the presence (+35) or absence (-35) of a 35-amino acid sequence were generated at the second site in the LBD. The Gl-RXRa isoform (1516 bp) with the longest open reading frame (+12/+33/+35) encoded a protein of 436 amino acids. Thoracic muscle expressed only isoforms with the T(+12) sequence. In contrast, claw muscle expressed isoforms with T(+7) or T(+12) and fewer isoforms with T(+8). Ovary and testis expressed a greater number of RXR isoforms than skeletal muscle. All tissues expressed full-length and truncated RXR isoforms. These data suggest that differences in response of claw and thoracic muscles to elevated ecdysteroid are due in part to differences in the expression of RXR isoforms.

Comparative effects of a non-steroidal ecdysone agonist RH-5992 and 20-hydroxyecdysone in a lepidopteran cell line (IAL-PID2)

The non-steroidal ecdysone agonist, RH-5992, exhibits ecdysteroid activities in vivo as well as in vitro more effectively than 20-hydroxyecdysone (20E). Using the IAL-PID2 cells derived from imaginal wing discs of last larval instar of Plodia interpunctella, we investigated the action of RH-5992 in the control of cell growth. Its effects on the proliferative activity of IAL-PID2 cells, the induction level in G2/M arrest and on the expression rate of Plodia B cyclin (PcycB), ecdysone B1-isoform (PIEcR-B1) and Ultraspiracle-2 isoform (PIUSP-2) were examined. From these cellular and molecular assays, our results brought evidence that RH-5992, like 20E, induced an inhibition on cell proliferation by blocking IAL-PID2 cells in G2/M phase. Moreover, this G2/M arrest was preceded by a decrease in the expression level of PcycB and a high induction of PIEcR-B1, PIUSP-2 mRNAs. Dose-response experiments revealed that RH-5992 was even more potent than 20E. On these parameters, we therefore suggest that the differential observed in the expression level of USP and EcR by RH-5992 and 20E could contribute to the difference observed for the biological potency of these two compounds.

Cell cycle profiles of EcR, USP, HR3 and B cyclin mRNAs associated to 20E-induced G2 arrest of Plodia interpunctella imaginal wing cells

Using the IAL-PID2 cell line established from pupally committed imaginal wing discs of Plodia interpunctella, we have investigated the dynamics of cellular and molecular events involved in the G2/M arrest. We have first cloned a cDNA sequence named PIUSP-2 that likely encodes a homologue of the Ultraspiracle-2 isoform of Manduca sexta. When the IAL-PID2 cells were exposed to a 8 h 20E treatment applied at different times of the cell cycle, an optimal period of sensitivity of cells to 20E, in inducing G2 arrest, was determined at the S/G2 transition. Using cDNA probes specifically designed from Plodia B cyclin (PcycB), ecdysone receptor B1-isoform (PIEcR-B1) and HR3 transcription factor (PHR3), we provide evidence that the 20E-induced G2 arrest was correlated to a high induction of PHR3, PIEcR-B1, PIUSP-2 mRNAs at the S/G2 transition and a decrease in PcycB mRNA level at the end of G2 phase.