The genome of the model beetle and pest Tribolium castaneum

Tribolium castaneum is a member of the most species-rich eukaryotic order, a powerful model organism for the study of generalized insect development, and an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved the ability to interact with a diverse chemical environment, as shown by large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes. Development in Tribolium is more representative of other insects than is Drosophila, a fact reflected in gene content and function. For example, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, some being expressed in the growth zone crucial for axial elongation in short-germ development. Systemic RNA interference in T. castaneum functions differently from that in Caenorhabditis elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control.

Broad-Complex acts downstream of Met in juvenile hormone signaling to coordinate primitive holometabolan metamorphosis

Metamorphosis of holometabolous insects, an elaborate change of form between larval, pupal and adult stages, offers an ideal system to study the regulation of morphogenetic processes by hormonal signals. Metamorphosis involves growth and differentiation, tissue remodeling and death, all of which are orchestrated by the morphogenesis-promoting ecdysteroids and the antagonistically acting juvenile hormone (JH), whose presence precludes the metamorphic changes. How target tissues interpret this combinatorial effect of the two hormonal cues is poorly understood, mainly because JH does not prevent larval-pupal transformation in the derived Drosophila model, and because the JH receptor is unknown. We have recently used the red flour beetle Tribolium castaneum to show that JH controls entry to metamorphosis via its putative receptor Methoprene-tolerant (Met). Here, we demonstrate that Met mediates JH effects on the expression of the ecdysteroid-response gene Broad-Complex (BR-C). Using RNAi and a classical mutant, we show that Tribolium BR-C is necessary for differentiation of pupal characters. Furthermore, heterochronic combinations of retarded and accelerated phenotypes caused by impaired BR-C function suggest that besides specifying the pupal fate, BR-C operates as a temporal coordinator of hormonally regulated morphogenetic events across epidermal tissues. Similar results were also obtained when using the lacewing Chrysopa perla (Neuroptera), a member of another holometabolous group with a primitive type of metamorphosis. The tissue coordination role of BR-C may therefore be a part of the Holometabola groundplan.

[Trauma to the triangular fibrocartilaginous complex (TFCC)]

PURPOSE OF THE STUDY

The triangular fibrocartilaginous complex (TFCC) can be injured either due to trauma or by chronic strain. Based on these findings, Palmer devised a classification system distinguishing traumatic (I) and degenerative (II) TFCC lesions. Traumatic TFCC injury may be single or involved in a combined injury of the distal radius. The aim of this study was to evaluate the results of surgical treatment in patients with traumatic TFCC injury at six-month follow-up.

MATERIAL AND METHODS

In the years 2000 to 2004, 23 patients with injury to the wrist were treated. The group comprised 16 men and 7 women at an average age of 34 years (range, 17 to 54 years). Nine patients were diagnosed with a distal radial fracture and 14 had no damage to the bony structures. Of these, seven showed clinical signs of TFCC injury and were indicated to acute arthroscopy of the wrist. The remaining seven, due to persisting complaints, were examined by arthroscopy within 3 months of injury. During the arthroscopic procedure, the Palmer type of injury was identified and arthroscopic treatment, open or closed, was carried out at the same stage. All patients were followed up for 6 months for pain relief and return to full physical activity.

RESULTS

The arthroscopic examination revealed the following TFCC lesions: 11 central ruptures (I.A), 6 ulnar tears (I.B), 4 palmar (I.C) and 2 radial (I.D) avulsions. During arthroscopy, partial resection of the disc was performed in 13 cases (I.A, I.D), and reattachment of the disc to the styloid process of the ulna was carried out in six cases (I.B). In four of these patients the intervention was done at the stage of acute lesion within 4 weeks of injury, and in two within a longer period. Four patients with type I.C injuries underwent open disc reattachment from the palmar approach. Subjective evaluation showed that 65 % of the patients had no complaints, 26 % reported pain after excessive activity and 9 % had pain associated with daily activities. Nome of the patients reported rest pain.

DISCUSSION

In our group, 91 % of the patients reported excellent and very good results at six months of follow-up. The two patients experiencing pain in daily activities (9 %) had type I.B. injury and were indicated for arthroscopy at a time longer than 6 weeks after injury.

CONCLUSIONS

TFCC lesions are wrist injuries which, if diagnosed early and treated appropriately, show good healing. If the triangular fibrocartilage complex is damaged by a central tear, disc resection gives good results. However, if the distal radioulnar ligaments are torn, their reattachment is necessary in order to prevent instability of the distal radioulnar joint. Open surgical procedures interfere with integrity of the distal radioulnar joint ligaments, which may lead to joint instability and prolonged healing.

Juvenile hormone resistance gene Methoprene-tolerant controls entry into metamorphosis in the beetle Tribolium castaneum

Besides being a spectacular developmental process, metamorphosis is key to insect success. Entry into metamorphosis is controlled by juvenile hormone (JH). In larvae, JH prevents pupal and adult morphogenesis, thus keeping the insect in its immature state. How JH signals to preclude metamorphosis is poorly understood, and a JH receptor remains unknown. One candidate for the JH receptor role is the Methoprene-tolerant (Met) Per-Arnt-Sim (PAS) domain protein [also called Resistance to JH, Rst (1)JH], whose loss confers tolerance to JH and its mimic methoprene in the fruit fly Drosophila melanogaster. However, Met deficiency does not affect the larval-pupal transition, possibly because this process does not require JH absence in Drosophila. By contrast, the red flour beetle Tribolium castaneum is sensitive to developmental regulation by JH, thus making an ideal system to examine the role of Met in the antimetamorphic JH action. Here we show that impaired function of the Met ortholog TcMet renders Tribolium resistant to the effects of ectopic JH and, in a striking contrast to Drosophila, causes early-stage beetle larvae to undergo precocious metamorphosis. This is evident as TcMet-deficient larvae pupate prematurely or develop specific heterochronic phenotypes such as pupal-like cuticular structures, appendages, and compound eyes. Our results demonstrate that TcMet functions in JH response and provide the critical evidence that the putative JH receptor Met mediates the antimetamorphic effect of JH.

[Wrist arthroscopy]

BACKGROUND

Pain in the wrist area is quite a frequent lesion. If it is not treated soon enough, it leads to development of degenerative changes which are curable with difficulty. Diagnosing is complicated because it is often difficult to diagnose them by means of radiological methods. Wrist arthroscopy is a method which enables to assess the problem and very often it also helps to solve it with an operation.

METHODS AND RESULTS

Authors evaluated 93 wrist arthroscopies performed in their departments during 2004-2005. There were 28 arthroscopies performed due to an acute lesion and 65 arthroscopies due to chronic problems. There were 59 arthroscopic curative interventions performed during the operation and 64 open interventions were indicated on the basis of an arthroscopic examination.

CONCLUSIONS

All wrist lesions where the lesion of connective tissues structures is suspected, accompanied with edema and hematoma, should be indicated for acute wrist arthroscopy, even though there is no finding on radiographs. Another group of patients indicated for the acute wrist arthroscopy are young patients with wrist fractures where there is a frequent ligament lesion associated, and patients with persisting ailments, even after radiologically confirmed healing of the fracture when intra-articular pathology can be expected. All patients with pain in the wrist area are indicated for arthroscopy, including those with not obvious cause of pain and with symptoms of arthrosis, because it is possible to evaluate further procedure of the therapy.

Crosstalk between a nuclear receptor and beta-catenin signaling decides cell fates in the C. elegans somatic gonad

beta-Catenin signaling determines the proximal-distal axis of the C. elegans gonad by promoting distal fate in asymmetrically dividing somatic gonad precursor cells (SGPs). Impaired function of the Wnt effector POP-1/TCF, its coactivator SYS-1/beta-catenin, and of upstream components including beta-catenin WRM-1 causes all SGP daughters to adopt the proximal fate. Consequently, no distal tip cells (DTCs) that would lead differentiation of gonad arms form in the affected hermaphrodites. Here, we show that deficiency of the nuclear receptor NHR-25 has the opposite effect: extra DTCs develop instead of proximal cells. NHR-25 knockdown restores DTC formation and fertility in pop-1 and sys-1 mutants, suggesting that a balance between NHR-25 and beta-catenin pathway activities is required to establish both proximal and distal fates. This balance relies on direct crossregulation between NHR-25 and the distinct beta-catenin proteins WRM-1 and SYS-1. The nuclear receptor-beta-catenin interaction may be an ancient mechanism of cell-fate decision.

Storage of bovine isolated follicles: a new alternative way to improve the recovery rate of viable embryos from ovarian follicles of slaughtered cows

The vitality of bovine oocytes stored in isolated follicles was examined. The aim of this work was to prolong the time of in vitro manipulation of oocytes before their maturation and develop a new alternative of oocyte "capacitation" to improve the quality of in vitro produced embryos. Follicles were dissected from the ovaries of slaughtered cows; subsequently, follicles were divided according to their diameter into three categories (2-3, 3-4 and 4-6 mm), and stored at 17-18 degrees C for 24 or 48 h in a modified tissue culture medium-199 (TCM-199) with reduced pH. After that time, the cumulus-oocyte complexes (COCs) were isolated, matured, fertilized, and embryos cultured in vitro for a total of 9 days. The percentage of total blastocysts, and hatched blastocysts developed from oocytes, initially kept ("capacitated") for 24h at 17-18 degrees C, within follicles of 3-6mm size categories, were significantly higher than that oocytes of the control [of control oocytes] (44.9 and 30.3% versus 36.2 and 20.4%, respectively). The oocytes of follicles stored for 48 h at 17-18 degrees C already had decreased developmental capacity. Interesting data were obtained when COCs of the 3-4 and 4-6 categories were additionally divided into two subgroups according to their presumed developmental history (originating from the supposed growing "fit" in contrast to the supposed regressing "unfit" follicles). The higher improvement in the rate of hatched blastocysts from 24h stored oocytes was observed only in the subgroup originated from "fit" COCs (15.3 versus 25.0%, and 20.0 versus 34.4%, in the 3-4 and 4-6mm categories, respectively). The transfer of 26 blastocysts (developed of follicles kept for 24h at 17-18 degrees C) to 26 recipient heifers resulted in 18 pregnancies. Storage of follicles at 17-18 degrees C in vitro resulted not only in recovery of higher numbers of blastocysts of better quality but also facilitated the safe transport of follicles for a long distance. The extended, time of follicle storage before the proper oocyte maturation allowed also the synchronization of an appropriate number of recipient animals according to the number of isolated follicles.

Nuclear receptor NHR-25 is required for cell-shape dynamics during epidermal differentiation in Caenorhabditis elegans

Epithelial cell shape changes underlie important events in animal development. During the postembryonic life of the nematode Caenorhabditis elegans, stem epidermal seam cells lose and actively renew mutual adherens junction contacts after each asymmetric division that separates them. The seam cell contacts are important for epidermal differentiation, but what regulates the cell-shape changes that restore them is unknown. Here, we show that NHR-25, a transcription factor of the nuclear receptor family, is expressed in the seam cells and is necessary for these cells to elongate and reach their neighbors after the asymmetric divisions. A failure to do so, caused by nhr-25 RNA interference, compromises the subsequent fate of seam-cell anterior daughters. Unexpectedly, the lack of cell-cell contacts does not prevent a unique seam cell to produce a neuroblast, even though a homeotic gene (mab-5) that normally prevents the neuroblast commitment is ectopically expressed in the absence of nhr-25 function. Seam cells lacking mutual contacts display reduced expression of a Fat-like cadherin marker cdh-3::gfp. Although some seam cells retain the ability to fuse at the final larval stage, the resulting syncytium shows gaps and bifurcations, translating into anomalies in cuticular ridges (alae) produced by the syncytium. nhr-25 RNAi markedly enhances branching of the alae caused by a mutant cuticular collagen gene rol-6. Silencing of nhr-25 also disturbs epidermal ultrastructure, which is probably the cause of compromised cuticle secretion and molting. Cell shape dynamics and molting thus represent distinct roles for NHR-25 in epidermal development.

Coactivator MBF1 preserves the redox-dependent AP-1 activity during oxidative stress in Drosophila

Basic leucine zipper proteins Jun and Fos form the dimeric transcription factor AP-1, essential for cell differentiation and immune and antioxidant defenses. AP-1 activity is controlled, in part, by the redox state of critical cysteine residues within the basic regions of Jun and Fos. Mutation of these cysteines contributes to oncogenic potential of Jun and Fos. How cells maintain the redox-dependent AP-1 activity at favorable levels is not known. We show that the conserved coactivator MBF1 is a positive modulator of AP-1. Via a direct interaction with the basic region of Drosophila Jun (D-Jun), MBF1 prevents an oxidative modification (S-cystenyl cystenylation) of the critical cysteine and stimulates AP-1 binding to DNA. Cytoplasmic MBF1 translocates to the nucleus together with a transfected D-Jun protein, suggesting that MBF1 protects nascent D-Jun also in Drosophila cells. mbf1-null mutants live shorter than mbf1+ controls in the presence of hydrogen peroxide (H2O2). An AP-1-dependent epithelial closure becomes sensitive to H2O2 in flies lacking MBF1. We conclude that by preserving the redox-sensitive AP-1 activity, MBF1 provides an advantage during oxidative stress.

Cell-autonomous roles of the ecdysoneless gene in Drosophila development and oogenesis

Steroid signaling underlies developmental processes in animals. Mutations that impair steroidogenesis in the fruit fly Drosophila melanogaster provide tools to dissect steroid hormone action genetically. The widely used temperature-sensitive mutation ecdysoneless(1) (ecd(1)) disrupts production of the steroid hormone ecdysone, and causes developmental and reproductive defects. These defects cannot be satisfactorily interpreted without analysis of the ecd gene. Here, we show that ecd encodes an as yet functionally undescribed protein that is conserved throughout eukaryotes. The ecd(1) conditional allele contains an amino acid substitution, whereas three non-conditional larval lethal mutations result in truncated Ecd proteins. Consistent with its role in steroid synthesis, Ecd is expressed in the ecdysone-producing larval ring gland. However, development of ecd-null early larval lethal mutants cannot be advanced by Ecd expression targeted to the ring gland or by hormone feeding. Cell-autonomous ecd function, suggested by these experiments, is evidenced by the inability of ecd(-) clones to survive within developing imaginal discs. Ecd is also expressed in the ovary, and is required in both the follicle cells and the germline for oocyte development. These defects, induced by the loss of ecd, provide the first direct evidence for a cell-autonomous function of this evolutionarily conserved protein.

Development of a new Sindbis virus transducing system and its characterization in three Culicine mosquitoes and two Lepidopteran species

Alphavirus transducing systems (ATSs) are alphavirus-based tools for expressing genes in insects. Here we describe an ATS (5'dsMRE16ic) based entirely on Sindbis MRE16 virus. GFP expression was used to characterize alimentary tract infections and dissemination in three Culicine and two Lepidopteran species. Following per os infection, 5'dsMRE16ic-EGFP efficiently infected Aedes aegypti and Culex tritaeniorhynchus, but not Culex pipiens pipiens. Ae. aegypti clearly showed accumulation of green fluorescent protein (GFP) in the posterior midgut and foregut/midgut junction within 2-3 days postinfection. Following parenteral infection of larvae, Bombyx mori had extensive GFP expression in larvae and adults, but Manduca sexta larvae were mostly resistant. 5'dsMRE16ic should be a valuable tool for gene expression in several important insect species that are otherwise difficult to manipulate genetically.

Use of Sindbis virus-mediated RNA interference to demonstrate a conserved role of Broad-Complex in insect metamorphosis

The transcription factor Broad-Complex (BR-C) is required for differentiation of adult structures as well as for the programmed death of obsolete larval organs during metamorphosis of the fruit fly Drosophila melanogaster. Whether BR-C has a similar role in other holometabolous insects could not be proven without a loss-of-function genetic test, performed in a non-drosophilid species. Here we use a recombinant Sindbis virus as a tool to silence BR-C expression in the silkmoth Bombyx mori. The virus expressing a BR-C antisense RNA fragment reduced endogenous BR-C mRNA levels in infected tissues (adult wing and leg primordia) via RNA interference (RNAi). The RNAi knock-down of BR-C resulted in the failure of animals to complete the larval-pupal transition or in later morphogenetic defects, including differentiation of adult compound eyes, legs, and wings from their larval progenitors. BR-C RNAi also perturbed the programmed cell death of larval silk glands. These developmental defects correspond to loss-of-function phenotypes of BR-C Drosophila mutants in both the morphogenetic and degenerative aspects, suggesting that the critical role of BR-C in metamorphosis is evolutionarily conserved. We also demonstrate that the Sindbis virus is a useful vehicle for silencing of developmental genes in new insect models.

Drosophila MBF1 is a co-activator for Tracheae Defective and contributes to the formation of tracheal and nervous systems

During gene activation, the effect of binding of transcription factors to cis-acting DNA sequences is transmitted to RNA polymerase by means of co-activators. Although co-activators contribute to the efficiency of transcription, their developmental roles are poorly understood. We used Drosophila to conduct molecular and genetic dissection of an evolutionarily conserved but unique co-activator, Multiprotein Bridging Factor 1 (MBF1), in a multicellular organism. Through immunoprecipitation, MBF1 was found to form a ternary complex including MBF1, TATA-binding protein (TBP) and the bZIP protein Tracheae Defective (TDF)/Apontic. We have isolated a Drosophila mutant that lacks the mbf1 gene in which no stable association between TBP and TDF is detectable, and transcription of a TDF-dependent reporter gene is reduced by 80%. Although the null mutants of mbf1 are viable, tdf becomes haploinsufficient in mbf1-deficient background, causing severe lesions in tracheae and the central nervous system, similar to those resulting from a complete loss of tdf function. These data demonstrate a crucial role of MBF1 in the development of tracheae and central nervous system.

Heat-inducible transgenic expression in the silkmoth Bombyx mori

Germline transformation with new transposon vectors now enables causal tests of gene function via ectopic protein expression or RNA interference in non-drosophilid insects. The problem remains of how to drive the transgene expression in vivo. We employed germline transformation using the piggyBac 3xP3-EGFP vector to test whether the Drosophila heat shock hsp70 promoter will be active in the live silkworm. We modified the original vector by cloning the coding sequence for Bombyx nuclear receptor Ftz-F1 between the hsp70 promoter and the terminator. Three independent transgenic lines expressing the Pax-6-driven EGFP marker in larval and adult photoreceptors were obtained with efficiencies of up to 1.7% of fertile G0 adults that gave GFP-positive progeny. Chromosomal integration of the transposon was confirmed with inverse PCR. Heat induction of the transgenic BmFtz-F1 was proven at both the mRNA and protein levels. RT-PCR data showed that the Drosophila heat shock promoter was functional in all three transgenic lines. Although basal activity was apparent at 25 degrees C, 1 h at 42 degrees C induced BmFtz-F1 mRNA at different stages of development and in diverse tissues. The relative levels of induction differed among the transgenic lines. Northern blot hybridization detected transgenic BmFtz-F1 only after heat shock and low levels of the mRNA were still present 6 h after the heat treatment. Immunostaining of epidermis using anti-BmFtz-F1 antibody showed a clear increase of nuclear signal 90 min after a heat shock.

The allatostatin gene of the cricket Gryllus bimaculatus (Ensifera, Gryllidae)

The gene encoding allatostatins (AST) of the FGLamide family from the cricket Gryllus bimaculatus is expressed in the brain. The mRNA, which contains four polyadenylation signals, encodes a hormone precursor that is split into at least 14 putative hormones. Five of them have been previously found in the cricket, six to seven others, or their close homologues, are known from other insects. Hormone AST 2 contains an internal cleavage site and may exist in a shorter version 2b. The hormones AST 3 and 4 are identical. The cDNA sequence revealed that a single point mutation and a single deletion eliminated an additional hormone between AST 12 and 13. The deduced hormone precursor is very similar to that in cockroaches, but is different from a shorter precursor in locusts, indicating that the gene evolved very fast in the latter. Regions conserved between cockroaches and crickets include parts of the acidic spacers that separate clusters of hormones, suggesting that these spacers may have additional functions.

The conserved nuclear receptor Ftz-F1 is required for embryogenesis, moulting and reproduction in Caenorhabditis elegans

BACKGROUND

Nuclear receptors are essential players in the development of all metazoans. The nematode Caenorhabditis elegans possesses more than 200 putative nuclear receptor genes, several times more than the number known in any other organism. Very few of these transcription factors are conserved with components of the steroid response pathways in vertebrates and arthropods. Ftz-F1, one of the evolutionarily oldest nuclear receptor types, is required for steroidogenesis and sexual differentiation in mice and for segmentation and metamorphosis in Drosophila.

RESULTS

We employed two complementary approaches, direct mutagenesis and RNA interference, to explore the role of nhr-25, a C. elegans ortholog of Ftz-F1. Deletion mutants show that nhr-25 is essential for embryogenesis. RNA interference reveals additional requirements throughout the postembryonic life, namely in moulting and differentiation of the gonad and vulva. All these defects are consistent with the nhr-25 expression pattern, determined by in situ hybridization and GFP reporter activity.

CONCLUSIONS

Our data link the C. elegans Ftz-F1 ortholog with a number of developmental processes. Significantly, its role in the periodical replacement of cuticle (moulting) appears to be evolutionarily shared with insects and thus supports the monophyletic origin of moulting.

Activation of a delayed-early gene encoding MHR3 by the ecdysone receptor heterodimer EcR-B1-USP-1 but not by EcR-B1-USP-2

MHR3, a homolog of the retinoid orphan receptor (ROR), is a transcription factor in the nuclear hormone receptor family that is induced by 20-hydroxyecdysone (20E) in the epidermis of the tobacco hornworm, Manduca sexta. Its 2.7-kb 5' flanking region was found to contain four putative ecdysone receptor response elements (EcREs) and a monomeric (GGGTCA) nuclear receptor binding site. Activation of this promoter fused to a chloramphenicol acetyltransferase (CAT) reporter by 2 micrograms of 20E per ml in Manduca GV1 cells was similar to that of endogenous MHR3, with detectable CAT by 3 h. When the ecdysone receptor B1 (EcR-B1) and Ultraspiracle 1 (USP-1) were expressed at high levels under the control of a constitutive promoter, CAT levels after a 3-h exposure to 20E increased two- to sixfold. In contrast, high expression of EcR-B1 and USP-2 caused little increase in CAT levels in response to 20E. Moreover, expression of USP-2 prevented activation by EcR-B1-USP-1. Deletion experiments showed that the upstream region, including the three most proximal putative EcREs, was responsible for most of the 20E activation, with the EcRE3 at -671 and the adjacent GGGTCA being most critical. The EcRE1 at -342 was necessary but not sufficient for the activational response but was the only one of the three putative EcREs to bind the EcR-B1-USP-1 complex in gel mobility shift assays and was responsible for the silencing action of EcR-B1-USP-1 in the absence of hormone. EcRE2 and EcRE3 each specifically bound other protein(s) in the cell extract, but not EcR and USP, and so are not EcREs in this cellular context. When cell extracts were used, the EcR-B1-USP-2 heterodimer showed no binding to EcRE1, and the presence of excess USP-2 prevented the binding of EcR-B1-USP-1 to this element. In contrast, in vitro-transcribed-translated USP-1 and USP-2 both formed heterodimeric complexes with EcR-B1 that bound ponasterone A with the same Kd (7 x 10(-10) M) and bound to both EcRE1 and heat shock protein 27 EcRE. Thus, factors present in the cell extract appear to modulate the differential actions of the two USP isoforms.

Regulation of the transcription factor E75 by 20-hydroxyecdysone and juvenile hormone in the epidermis of the tobacco hornworm, Manduca sexta, during larval molting and metamorphosis

The homolog of the ecdysteroid-induced transcription factor E75A in Drosophila melanogaster was cloned from the tobacco hornworm, Manduca sexta, and its developmental expression and hormonal regulation were analyzed. Both E75A and E75B mRNAs were found in the abdominal epidermis during both the larval and the pupal molts, with E75A appearing before E75B, coincident with the rise of ecdysteroid. Exposure of either fourth or fifth instar epidermis to 20E in vitro caused the rapid, transient induction of E75A RNA with a peak at 6 and 3 h, respectively, followed by maintenance at low levels until 24 h. Epidermis from fourth instar larvae with high endogenous juvenile hormone (JH) showed a 10-fold higher sensitivity to 20E (EC50 = 2 x 10(-8) M for fourth instar and 2 x 10(-7) M for fifth instar epidermis). The presence of the protein synthesis inhibitor anisomycin had no effect on the induction but prevented the decline, indicating that E75A RNA was directly induced by 20E, but its down-regulation depended on protein synthesis. Exposure of day 2 fifth instar epidermis to 20E in the presence of JH I, which prevents the 20E-induced pupal commitment, caused an increased accumulation of E75A RNA throughout the culture period although the temporal pattern was unaffected. These findings show for the first time that JH plays a role in 20E-induced early gene expression and suggest that the higher levels of E75A may be required for maintenance of larval commitment of this epidermis.

Identification and mRNA developmental profiles of two ultraspiracle isoforms in the epidermis and wings of Manduca sexta

cDNAs were isolated from Manduca sexta that encode two isoforms of an ultraspiracle (USP) homologue MsUSP-1 and MsUSP-2 with different N-terminal A/B regions. The MsUSP-1 cDNA predicts a protein with 97% and 45% amino acid identities in the DNA- and ligand-binding domains respectively to the Drosophila USP and 89% overall identity with Bombyx mori CF1 (an USP homologue). Northern blot hybridizations with probes specific to MsUSP-1 and MsUSP-2 showed transcripts of an approximately equal size (4.5 kb), but with diverse developmental profiles in Manduca epidermis during the two final larval instars and the onset of the adult moult. The MsUSP-1 mRNA was expressed during the intermoult periods, with higher levels around the time of the larval ecdyses and at the onset of wandering behaviour. In contrast, the MsUSP-2 mRNA was up-regulated at times of high ecdysteroid titre during the larval moults, when the MsUSP-1 mRNA disappeared. Together, these conversely regulated isoform mRNAs contribute to the constitutive expression profile of total MsUSP mRNA.

Developmental profiles and ecdysteroid regulation of the mRNAs for two ecdysone receptor isoforms in the epidermis and wings of the tobacco hornworm, Manduca sexta

Ecdysteroids acting through multiple isoforms of the ecdysone receptor (EcR) initiate molting and metamorphosis of insects. Two isoforms of EcR, A (this paper) and B1 (Fujiwara et al., Insect Biochem. Mol. Biol. 25, 845-856, 1995), were isolated from the tobacco hornworm, Manduca sexta, and shown to be similar to the corresponding Drosophila EcR isoforms. The developmental profiles of both EcR-A and EcR-B1 (determined by both analysis of isoform-specific mRNAs and use of monoclonal antibodies that detect either EcR-B1 or all forms), however, were different in Manduca epidermis, which produces sequentially the larval, the pupal, and the adult cuticles. EcR-B1 predominated through the larval, pupal, and early developing adult stages with an upregulation early in each molt. By contrast, EcR-A was present only at the onset of new cuticle synthesis during the larval molt, but in the pupal and adult molts was upregulated slightly later than EcR-B1 during the commitment period and was present during the predifferentiative phase. Both isoforms appeared in the larval wing discs after pupal commitment and persisted through pupal differentiation. The mRNAs for both isoforms were directly induced in larval epidermis in vitro by 20-hydroxyecdysone, but EcR-B1 mRNA accumulated more rapidly, peaking at 3 hr. In the presence of a protein synthesis inhibitor, the accumulation of EcR-B1 mRNA was slower and its subsequent decline was prevented, but the accumulation of EcR-A mRNA was unaffected. Thus, in this polymorphic epidermis both isoforms appear in every molt, with EcR-B1 present during the commitment and predifferentiative phases and then at the onset of cuticle synthesis EcR-A prevails. Additionally, EcR-A is apparently associated with the switching and predifferentiative events necessary for a new synthetic program.

Cloning of an ecdysone receptor homolog from Manduca sexta and the developmental profile of its mRNA in wings

Using the Drosophila melanogaster ecdysone receptor (DmEcR) B1 cDNA clone, we isolated three genomic clones for EcR from the tobacco hornworm, Manduca sexta. Subsequent isolation and sequencing of several cDNAs yielded a homolog of the B1 isoform with 50, 95 and 70% amino acid identities with DmEcR in the N-terminal A/B, the DNA binding and the ligand binding domains respectively. Unlike Drosophila, an intron occurs between the exons encoding the two zinc fingers of Manduca EcR (MsEcR). A 6.0 kb mRNA encoding MsEcR was found in both larval wing discs and prothoracic glands and in pupal wings. During the final larval instar, the mRNA was maximal in the wing discs at one day after wandering (W1), whereas in the prothoracic gland EcR mRNA increased rapidly to high levels on day 2 and remained high thereafter. During the onset of adult development, two peaks of EcR mRNA were observed in wings from day 3 to 5 and on day 8 after pupal ecdysis. These two peaks correlated with the time of increasing titers of ecdysone (E) and 20-hydroxyecdysone (20E), respectively. The EcR mRNA peaks always preceded the large ecdysteroid peak, suggesting that the transcription of the EcR gene is induced by a low concentration of ecdysteroid in vivo.