Regulation of expression of arylphorin and female-specific protein mRNAs in the tobacco hornworm, Manduca sexta

miRNA-34 and miRNA-210 target hexamerin genes enhancing their differential expression during early brain development of honeybee (Apis mellifera) castes

During the honeybee larval stage, queens develop larger brains than workers, with morphological differentiation appearing at the fourth larval phase (L4), just after a boost in nutritional difference both prospective females experience. The molecular promoters of this caste-specific brain development are already ongoing in previous larval phases. Transcriptomic analyses revealed a set of differentially expressed genes in the L3 brains of queens and workers, which represents the early molecular response to differential feeding females receive during larval development. Three genes of this set, hex70b, hex70c and hex110, are more highly transcribed in the brain of workers than in queens. The microRNAs miR-34, miR-210 and miR-317 are in higher levels in the queens' brain at the same phase of larval development. Here, we tested the hypothesis that the brain of workers expresses higher levels of hexamerins than that of queens during key phases of larval development and that this differential hexamerin genes expression is further enhanced by the repressing activity of miR-34, miR-210 and miR-317. Our transcriptional analyses showed that hex70b, hex70c and hex110 genes are differentially expressed in the brain of L3 and L4 larval phases of honeybee queens and workers. In silico reconstructed miRNA-mRNA interaction networks were validated using luciferase assays, which showed miR-34 and miR-210 negatively regulate hex70b and hex110 genes by directly and redundantly binding their 3'UTR (untranslated region) sequences. Taken together, our results suggest that miR-34 and miR-210 act together promoting differential brain development in honeybee castes by downregulating the expression of the putative antineurogenic hexamerin genes hex70b and hex110.

Molecular characterization of Antheraea mylitta arylphorin gene and its encoded protein

Antheraea mylitta arylphorin protein was extracted from the silk gland of fifth instar larvae and purified by ammonium sulphate precipitation, ion-exchange, and gel filtration chromatography. The N-terminal sequencing of ten amino acids (NH₂-SVVHPPHHEV-COOH) showed similarity with Antheraea pernyi arylphorin. Based on N-terminal and C-terminal A. pernyi arylphorin sequences, primers were designed, and A. mylitta arylphorin cDNA was cloned by RT-PCR from silk gland mRNA. Sequencing of complete cDNA including 25 nucleotides at 5' UTR (obtained by 5' RACE) showed that it consisted of an ORF of 2115 nucleotides which could encode a protein of 704 amino acids (predominantly aromatic residues) having molecular weight 83 kDa. Homology modelling was done using A. pernyi arylphorin as a template. Cloned arylphorin cDNA was expressed in E. coli and recombinant His-tagged protein was purified by Ni-NTA affinity chromatography. Analysis of tissue-specific expression of arylphorin by real-time PCR showed maximum expression in the fat body followed by silk gland and integument. 5' flanking region (759 bp) of arylphorin gene was amplified by inverse PCR and the full length gene (5359 nucleotides) containing five exons and four introns was cloned from the A. mylitta genomic DNA and sequenced. Polyclonal antibody was raised against purified arylphorin and more native arylphorin protein (500 kDa) was purified from the fat body by antibody affinity chromatography. Study of mitogenic effect of native and chymotrypsin hydrolysate of arylphorin on different insect cell lines showed that arylphorin could be used as serum substitute for in vitro cultivation of insect cells.

A Life's Journey Through Insect Metamorphosis

This autobiographical article describes the research career of Lynn M. Riddiford from its early beginnings in a summer program for high school students at Jackson Laboratory to the present "retirement" at the Friday Harbor Laboratories. The emphasis is on her forays into many areas of insect endocrinology, supported by her graduate students and postdoctoral associates. The main theme is the hormonal regulation of metamorphosis, especially the roles of juvenile hormone (JH). The article describes the work of her laboratory first in the elucidation of the endocrinology of the tobacco hornworm, Manduca sexta, and later in the molecular aspects of the regulation of cuticular and pigment proteins and of the ecdysone-induced transcription factor cascade during molting and metamorphosis. Later studies utilized Drosophila melanogaster to answer further questions about the actions of JH.

Expression and evolution of hexamerins from the tobacco hornworm, Manduca sexta, and other Lepidoptera

Hexamerins are large hemolymph-proteins that accumulate during the late larval stages of insects. Hexamerins have emerged from hemocyanin, but have lost the ability to bind oxygen. Hexamerins are mainly considered as storage proteins for non-feeding stages, but may also have other functions, e.g. in cuticle formation, transport and immune response. The genome of the hornworm Manduca sexta harbors six hexamerin genes. Two of them code for arylphorins (Msex2.01690, Msex2.15504) and two genes correspond to a methionine-rich hexamerin (Msex2.10735) and a moderately methionine-rich hexamerin (Msex2.01694), respectively. Two other genes do not correspond to any known hexamerin and distantly resemble the arylphorins (Msex2.01691, Msex2.01693). Five of the six hexamerin genes are clustered within ∼45 kb on scaffold 00023, which shows conserved synteny in various lepidopteran genomes. The methionine-rich hexamerin gene is located at a distinct site. M. sexta and other Lepidoptera have lost the riboflavin-binding hexamerin. With the exception of Msex2.01691, which displays low mRNA levels throughout the life cycle, all hexamerins are most highly expressed during pre-wandering phase of the 5th larval instar of M. sexta, supporting their role as storage proteins. Notably, Msex2.01691 is most highly expressed in the brain, suggesting a divergent function. Phylogenetic analyses showed that hexamerin evolution basically follows insect systematics. Lepidoptera display an unparalleled diversity of hexamerins, which exceeds that of other hexapod orders. In contrast to previous analyses, the lepidopteran hexamerins were found monophyletic. Five distinct types of hexamerins have been identified in this order, which differ in terms of amino acid composition and evolutionary history: i. the arylphorins, which are rich in aromatic amino acids (∼20% phenylalanine and tyrosine), ii. the distantly related arylphorin-like hexamerins, iii. the methionine-rich hexamerins, iv. the moderately methionine rich hexamerins, and v. the riboflavin-binding hexamerins.

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

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

Factors affecting proliferation and differentiation of Lepidopteran midgut stem cells

Midgut stem cells of last instar larvae and pupae of Heliothis virescens, Lymantria dispar and several other Lepidopteran species have been cultured in vitro and have been induced to proliferate using low titers of ecdysteroids and the 77-Kda peptide fragment, alpha-arylphorin, isolated and identified from pupal fat body tissue. The insulin-related hormone, Bombyxin, also induced mitosis in cultured midgut stem cells; it appeared to be fast-acting and quickly inactivated, while alpha-arylphorin was slower to act and had a longer lasting effect in vitro, indicating different functions for these proliferation agents. Changes in Calcium ion concentration within or outside the cells discretely affected stem cell differentiation, indicating a role for second messenger participation in peptide regulation of this process. Four different peptides (MDFs 1-4) that induced midgut stem cells to differentiate to mature midgut cell types in vitro were isolated and characterized from conditioned media and hemolymph of H. virescens and L. dispar. However, platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and all-trans retinoic acid (RA) from vertebrate sources induced differentiation to non-midgut cell types as well. MDF1 was located in basal areas of columnar cells of midgut epithelium, although MDF2 was observed in all of the cytoplasm of columnar cells and in droplets of antibody positive material in the midgut lumen, suggesting a digestive function as well for this peptide. Anti-MDF-3 stained the central areas of cultured midgut columnar cells and the bases of columnar cells of midgut epithelium in vivo. Midgut secretory cells stained with anti-MDF-4; streams of MFD-4-positive material were observed extending from secretory cells facing the epithelial lumen, and as a layer on the hemolymph-facing side, suggesting an endocrine or paracrine function for this or an immunologically similar peptide.

Correlation of hemocyte counts with different developmental parameters during the last larval instar of the tobacco hornworm, Manduca sexta

We determined the changes in hemocyte titer and in the abundance of hemocyte types of the tobacco hornworm Manduca sexta during the fourth and fifth larval stadium and the beginning of the pupal stadium. As we analyzed the samples of individual insects at daily intervals, we were able to correlate phenotypical features, body weight, as well as total protein content and lysozyme activity in the hemolymph with the observations on hemocytes. In the course of the fifth larval stadium, the hemocyte titer decreased slightly and declined further after pupation. Using calculated values for total hemocyte numbers, females had about five times and males three times more hemocytes in the circulating population at the beginning of the wandering stage (in the middle of the fifth larval stadium) than immediately after the last larval--larval molt (from the fourth to the fifth larval stadium). This sexual difference was mainly due to an increase in the number of plasmatocytes, which was more prominent in females than in males. Granular cells were dominant in early fifth larval stadium while plasmatocytes were the most abundant cells in pupae. Oenocytoids and spherule cells disappeared during the wandering stage. Lysozyme activity in the hemolymph rose to a maximum during the wandering stage, with females having lysozyme values twice as high as those for males. These changes in lysozyme activity, however, did not correlate with the increase of total hemolymph protein titer which occurred already at the beginning of the wandering stage. We postulate that changes in hemocyte titers are under direct hormonal control, which has to be proven in future experiments.

Identification and expression profile of a putative basement membrane protein gene in the midgut of Helicoverpa armigera

BACKGROUND

The midgut undergoes histolysis and remodeling during the larval to adult transition in holometabolous insects, but the molecular mechanisms underlying this process are not well understood.

RESULTS

Using Suppression Subtractive Hybridization (SSH), we identified a 531 bp cDNA predicted to encode a 176 amino acid protein, which we call hmg176. Northern and western blot analysis suggested that high levels of hmg176 are expressed in the midgut during molting, but not during metamorphosis. HMG176 protein was detected by immunofluorescence within the membrane of fat bodies and the basement membrane of the midgut of both molting and feeding larvae, but not in metamorphically committed larvae. In situ hybridization revealed that hmg176 transcripts mainly localized to the columnar cells of the midgut. Interestingly, a non-steroidal ecdysone agonist, RH-2485, significantly upregulated expression of hmg176.

CONCLUSION

These observations suggest that hmg176 encodes a larval-specific protein that may participate in sustaining larval midgut during larval development, possibly in response to ecdysteroid in vivo. This study will enlighten our understanding of the molecular mechanisms of tissue histolysis during metamorphosis.

Differentially-expressed glycoproteins in Locusta migratoria hemolymph infected with Metarhizium anisopliae

Glycoproteins play important roles in insect physiology. Infection with pathogen always results in the differential expression of some glycoproteins, which may be involved in host-pathogen interactions. In this report, differentially-expressed glycoproteins from the hemolymph of locusts infected with Metarhizium anisopliae were analyzed by two-dimensional electrophoresis (2-DE) and PDQuest software. The results showed that 13 spots were differentially expressed, of which nine spots were upregulated and four were downregulated. Using MS/MS with de novo sequencing and NCBI database searches, three upregulated proteins were identified as locust transferrin, apolipoprotein precursor, and hexameric storage protein 3. These proteins have been reported to be involved in the insect innate immune response to microbial challenge. Due to the limited available genome information and protein sequences of locusts, the possible functions of the other 10 differentially-expressed spots remain unknown.

Developmental and hormonal regulation of midgut remodeling in a lepidopteran insect, Heliothis virescens

Midgut tissue undergoes remodeling during metamorphosis in insects belonging to orders Lepidoptera and Diptera. We investigated the developmental and hormonal regulation of these remodeling events in lepidopteran insect, Heliothis virescens. In H. virescens, programmed cell death (PCD) of larval midgut cells as well as proliferation and differentiation of imaginal cells began at 108 h after ecdysis to the final larval instar (AEFL) and proceeded through the pupal stages. Expression patterns of pro- cell death factors (caspase-1 and ICE) and anti-cell death factor, Inhibitor of Apoptosis (IAP) were studied in midguts during last larval and pupal stages. IAP, Caspase-1 and ICE mRNAs showed peaks at 48 h AEFL, 96 h AEFL and in newly formed pupae, respectively. Immunohistochemical analysis substantiated high caspase-3 activity in midgut at 108 h AEFL. Application of methoprene, a juvenile hormone analog (JHA) blocked PCD by maintaining high levels of IAP, downregulating the expression of caspase-1, ICE and inhibiting an increase in caspase-3 protein levels in midgut tissue. Also, the differentiation of imaginal cells was impaired by methoprene treatment. These studies demonstrate that presence of JHA during final instar larvae affects both midgut remodeling and larval-pupal metamorphosis leading to larval/pupal deformities in lepidopteran insects, a mechanism that is different from that in mosquito, Ae. aegypti where JHA uncouples midgut remodeling from metamorphosis.

Characterization and expression of the Hex 110 gene encoding a glutamine-rich hexamerin in the honey bee, Apis mellifera

An N-terminal amino acid sequence of a previously reported honey bee hexamerin, HEX 110 [Danty et al., Insect Biochem Mol Biol 28:387-397 (1998)], was used as reference to identify the predicted genomic sequence in a public GenBank database. In silico analysis revealed an ORF of 3,033 nucleotides that encompasses eight exons. The conceptual translation product is a glutamine-rich polypeptide with a predicted molecular mass of 112.2 kDa and pI of 6.43, which contains the conserved M and C hemocyanin domains. Semiquantitative and quantitative RT-PCR with specific primers allowed for an analysis of mRNA levels during worker bee development and under different physiological conditions. Concomitantly, the abundance of the respective polypeptide in the hemolymph was examined by SDS-PAGE. Hex 110 transcripts were found in high levels during the larval stages, then decreased gradually during the pupal stage, and increased again in adults. HEX 110 subunits were highly abundant in larval hemolymph, decreased at the spinning-stage, and remained at low levels in pupae and adults. In 5th instar larvae, neither starvation nor supplementation of larval food with royal jelly changed the Hex 110 transcript levels or the amounts of HEX 110 subunit in hemolymph. In adult workers, high levels of Hex 110 mRNA, but not of the respective subunit, were related to ovary activation, and also to the consumption of a pollen-rich diet.

Effect of Campoletis sonorensis ichnovirus cys-motif proteins on Heliothis virescens larval development

Polydnaviruses are obligate symbionts of some parasitic hymenopteran wasps responsible for modifying the physiology of their host lepidopteran larvae to benefit the endoparasite. Injection of Campoletis sonorensis ichnovirus (CsIV) into Heliothis virescens larvae alters larval growth, development and immunity but genes responsible for alterations of host physiology are not well described. Recent studies of polydnavirus genomes establish that these genomes encode families of related genes expressed in parasitized larvae. Here we evaluate five members of the CsIV cys-motif gene family for their ability to inhibit growth and development of lepidopteran larvae. To study the function of cys-motif proteins, recombinant proteins were produced from baculovirus expression vectors and injected or fed to H. virescens larvae in diet. rVHv1.1 was identified as the most potent protein tested causing a significant reduction in growth of H. virescens and Spodoptera exigua larvae. H. virescens larvae ingesting this protein also exhibited delayed development, reductions in pupation and increased mortality. Increased mortality was associated with chronic sub-lethal baculovirus infections. Taken together, these data indicate that the cys-motif proteins have pleiotropic effects on lepidopteran physiology affecting both development and immunity.

Molecular cloning and expression of a hexamerin cDNA from the honey bee, Apis mellifera

A cDNA encoding a hexamerin subunit of the Africanized honey bee (Apis mellifera) was isolated and completely sequenced. In the deduced translation product we identified the N-terminal sequence typical of the honey bee HEX 70b hexamerin. The genomic sequence consists of seven exons flanked by GT/AT exon/intron splicing sites, which encode a 683 amino acid polypeptide with an estimated molecular mass of 79.5 kDa, and pI value of 6.72. Semi-quantitative RT-PCR revealed high levels of Hex 70b message in larval stages, followed by an abrupt decrease during prepupal-pupal transition. This coincides with decaying titers of juvenile hormone (JH) and ecdysteroids that is the signal for the metamorphic molt. To verify whether the high Hex 70b expression is dependent on high hormone levels, we treated 5th instar larvae with JH or 20-hydroxyecdysone (20E). In treated larvae, Hex 70b expression was maintained at high levels for a prolonged period of time than in the respective controls, thus indicating a positive hormone regulation at the transcriptional level. Experiments designed to verify the influence of the diet on Hex 70b expression showed similar transcript amounts in adult workers fed on a protein-enriched diet or fed exclusively on sugar. However, sugar-fed workers responded to the lack of dietary proteins by diminishing significantly the amount of HEX 70b subunits in hemolymph. Apparently, they use HEX 70b to compensate the lack of dietary proteins.

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

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

cDNA cloning, expression, and characterization of an arylphorin-like hexameric storage protein, AgeHex2, from the mulberry longicorn beetle, Apriona germari

An arylphorin-like hexameric storage protein, AgeHex2, cDNA was cloned from the mulberry longicorn beetle, Apriona germari (Coleoptera, Cerambycidae), larval cDNA library. The complete cDNA sequence of AgeHex2 is comprised of 2,088 bp encoding 696 amino acid residues. The AgeHex2 had four potential N-glycosylation sites. The AgeHex2 contained the highly conserved two larval storage protein signature motifs. The deduced protein sequence of AgeHex2 showed high homology with A. germari hexamerin1 (51% amino acid identity), Tenebrio molitor hexamerin2 (49% amino acid identity), T. molitor early-staged encapsulation inducing protein (43% amino acid identity), and Leptinotarsa decemlineata diapause protein1 (43% amino acid identity). Phylogenetic analysis further confirmed the AgeHex2 is more closely related to coleopteran hexamerins than to the other insect storage proteins. Northern blot analysis confirmed that the AgeHex2 showed fat body-specific expression. The cDNA encoding AgeHex2 was expressed as a 75-kDa protein in the baculovirus-infected insect cells. Furthermore, N-glycosylation of the recombinant AgeHex2 was revealed by tunicamycin to the recombinant virus-infected Sf9 cells, demonstrating that the AgeHex2 is N-glycosylated. Western blot analysis using the polyclonal antiserum against recombinant AgeHex2 indicated that the AgeHex2 corresponds to a 75-kDa storage protein present in the A. germari larval hemolymph.

Stimulation of midgut stem cell proliferation by Manduca sexta alpha-arylphorin

Extracts of the green-colored perivisceral fat body of newly ecdysed Manduca sexta pupae stimulate mitosis in midgut stem cells of Heliothis virescens cultured in vitro. Using a combination of cation- and anion-exchange chromatography, we have isolated a protein from these fat body extracts that accounts for the observed stem cell proliferation. SDS-PAGE analysis of the protein results in a single band of 77 kDa. Sequences of tryptic peptides from this protein are identical to internal sequences of the storage hexamer alpha-arylphorin. The alpha-arylphorin isolated by our procedure represents a small fraction of the total arylphorin present in the fat body extract. However, it alone seems responsible for the stimulation of mitotic activity in H. virescens midgut stem cells.

Two juvenile hormone suppressible storage proteins may play different roles in Hyphantria cunea Drury

We isolated and sequenced cDNA clones corresponding to two storage proteins (HcSP-1 and HcSP-2) from fall webworm, Hyphantria cunea. The cDNAs for HcSP-1 (2,337 bp) and HcSP-2 (2,572 bp) code for 753 and 747 residue proteins with predicted molecular masses of 88.3 and 88.5 kDa, respectively. The calculated isoelectric points are pI = 8.4 (HcSP-1) and 7.6 (HcSP-2). Multiple alignment analysis of the amino acid sequence revealed that HcSP-1 is most similar to SL-1 from S. litura (73.8% identity) and other methionine-rich hexamers, whereas HcSP-2 is most similar to the SL-2 alpha subunit from S. litura (74.8% identity) and other moderately methionine-rich hexamers. The two storage proteins from H. cunea shared only 38.4% identity with one another. According to both phylogenetic analyses and the criteria of amino acid composition, HcSP-1 belongs to the subfamily of Met-rich storage proteins (6% methionine, 10% aromatic amino acid), and HcSP-2 belongs to the subfamily of moderately methionine-rich storage proteins (3.2% methionine, 12.9% aromatic amino acid). Topical application of the JH analog, methoprene, after head ligation of larvae, suppressed transcription of the SP genes, indicating hormonal effects at the transcriptional level. The HcSP-1 transcript was detected by Northern blot analysis in Malpighian tubule, testis, and ovary, in addition to fat body where it was most abundant. The HcSP-2 transcript was detected only in fat body and Malpighian tubule. The accumulation of HcSP-1 in ovary and HcSP-2 in Malpighian tubule might be related to differential functions in both organs.

cDNA sequences and mRNA levels of two hexamerin storage proteins PinSP1 and PinSP2 from the Indianmeal moth, Plodia interpunctella

In insects, storage proteins or hexamerins accumulate apparently to serve as sources of amino acids during metamorphosis and reproduction. Two storage protein-like cDNAs obtained from a cDNA library prepared from fourth instar larvae of the Indianmeal moth (Plodia interpunctella) were cloned and sequenced. The first clone, PinSP1, contained 2431 nucleotides with a 2295 nucleotide open reading frame (ORF) encoding a protein with 765 amino acid residues. The second cDNA, PinSP2, consisted of 2336 nucleotides with a 2250-nucleotide ORF encoding a protein with 750 amino acid residues. PinSP1 and PinSP2 shared 59% nucleotide sequence identity and 44% deduced amino acid sequence identity. A 17-amino acid signal peptide and a molecular mass of 90.4 kDa were predicted for the PinSP1 protein, whereas a 15-amino acid signal peptide and a mass of 88 kDa were predicted for PinSP2. Both proteins contained conserved insect larval storage protein signature sequence patterns and were 60-70% identical to other lepidopteran larval storage proteins. Expression of mRNA for both larval storage proteins was determined using the quantitative reverse transcription polymerase chain reaction method. Only very low levels were present in the second instar, but both mRNAs dramatically increased during the third instar, peaked in the fourth instar, decreased dramatically late in the same instar and pupal stages, and were undetectable during the adult stage. Males and females exhibited similar mRNA expression levels for both storage proteins during the pupal and adult stages. The results support the hypothesis that P. interpunctella, a species that does not feed after the larval stage, accumulates these two storage proteins as reserves during larval development for subsequent use in the pupal and adult stages.

Expression ofManduca sextaV-ATPase genesmvB, mvGandmvdis regulated by ecdysteroids

V-ATPases are complex proteins consisting of a peripheral, ATP-hydrolysing V1 complex and a membrane-bound H+-translocating Vo complex. The plasma membrane V-ATPase from the tobacco hornworm(Manduca sexta) midgut is made up of eight different V1and four different Vo subunits. During starvation and moulting,V-ATPase activity decreases as a result of the dissociation of the V1 complex from the Vo complex. To determine whether subunit biosynthesis is reduced during periods of enzyme inactivity, we measured the transcript levels and transcriptional activities of V-ATPase genes. Northern blots revealed the downregulation of almost all V-ATPase transcripts during starvation. During moulting, transcript levels of the three V-ATPase genes examined, mvB, mvG and mvd, also decreased,and this decrease was negatively correlated with the titre of 20-hydroxyecdysone (20-HE) and positively correlated with the titre of juvenile hormone (JH). To test the biological significance of these correlations, we injected both hormones into feeding larvae and measured transcript levels several hours later. A short-term increase and a long-term decrease in levels of mRNA were observed after 20-HE injection, whereas JH injection had no significant effect. Immunohistochemical studies of the midgut epithelium revealed that 20-HE injection led to changes in goblet cell morphology and in the subcellular distribution of the V1 complex comparable with the situation during the moult and during starvation. Reporter gene assays in Sf21 cells using mvB, mvG and mvdpromoters to initiate transcription of firefly luciferase led, after incubation of the cells with 20-HE, to results comparable with those obtained in the injection experiments. These findings suggest that putative ecdysone-responsive elements are present in all three promoters. Taken together, our results suggest that the expression of V-ATPase genes is controlled in a coordinated manner by ecdysteroids.

Female-specific expression of a hexamerin gene in larvae of an autogenous mosquito

Fourth-instar larvae of the autogenous mosquito, Aedes atropalpus, synthesize three hexamerins or hexameric storage proteins which are distinguished by different methionine and aromatic amino-acid contents. One protein, Hexamerin-1.2 (AatHex-1.2) is only found in female larvae and pupae. In order to investigate the molecular basis for this sex-specific accumulation, we have cloned and sequenced the cDNA encoding AatHex-1.2 and isolated and sequenced over 1 kb of the 5' flanking region of the AatHex-1.2 gene. The AatHex-1.2 transcript encodes a 81.6-kDa hexamerin subunit which contains 19.8% phenylalanine, tyrosine and tryptophan and 8.6% methionine residues. The single-copy AatHex-1.2 gene consists of three exons and two small introns located at its 5' end. A 2.3-kb AatHex-1.2 mRNA accumulates only in female larvae and pupae and is expressed at very low levels in adult female mosquitoes. The temporal expression profile of this transcript is typical of other mosquito hexamerin genes, with rapid disappearance of the mRNA shortly after pupation. Hence this is the first observation of exclusively female-specific gene activity during preadult development of an insect. In the 5' flanking region of the AatHex-1.2 gene, we identified putative binding sites for transcription factors, such as GATA, C/EBP and Doublesex, typically involved in fat body- and female-specific gene activity in Diptera. These findings suggest that mechanisms for sex-specific transcription in the fat body may be well conserved between flies and mosquitoes.

Hexameric storage proteins during metamorphosis and egg production in the diamondback moth, Plutella xylostella (Lepidoptera)

As in many Lepidoptera, Plutella xylostella adults do not feed on protein and females must use accumulated reserves to supply vitellogenin synthesis. Storage proteins were quantified in females and males from the late larval stage through day 4 of adult life. The level of storage protein peaked in the early pupal stage, with females having about twice as much as males. In males, the level fell through pupal development and dropped to a trace by one day after eclosion. In females, level of storage proteins fell until eclosion, and then rose dramatically within four hours after the molt to about 2/3 of the original peak level. This post-eclosion increase, which has not been reported previously in insects, suggests that adult females synthesize hexamerins to resequester amino acids. Subsequently, the level of storage proteins fell as vitellogenin appeared and eggs were laid. The ability to synthesize and sequester amino acids as storage proteins during the adult stage has wide-ranging implication for protein management in insects, particularly those that are long-lived and have flexible schedules of reproduction.

Equivalence of riboflavin-binding hexamerin and arylphorin as reserves for adult development in two saturniid moths

The riboflavin-binding hexamerin (RbH) and arylphorin (ArH) were compared as storage reservoirs for adult development in Hyalophora cecropia. The two hexamerins were metabolically labeled with [3H]leucine and [35S]methionine, isolated by column chromatography, and separately injected into pupae whose diapause had been terminated by chilling. By the time of eclosion at least 98% of both hexamerins had been cleared from the hemolymph. Every reproductive and somatic tissue tested contained trichloroacetic acid-precipitable label; consistent differences between the two hexamerins were not detected in the distribution of their label to these tissues. While incorporation of intact hexamerins was not ruled out, hydrolysis and reincorporation of the liberated amino acids were indicated by label in vitellogenin and lipophorin, and by differences in 35S/3H ratios, which ranged from over 1.0 in chorions to 0.4 in wings, as compared with 0.75 in the injected hexamerins. Injection of [35S,3H]RbH from H. cecropia into A. luna, a species in the same subfamily whose pupae lack this hexamerin, resulted in a pattern of isotope incorporation similar to that yielded by RbH in the donor species. In neither species was there indication of a developing adult tissue that distinguished between RbH and ArH as precursor reservoirs for morphogenesis. This equivalence helps explain how many species of Lepidoptera are able to complete metamorphosis and reproduce without expressing an RbH gene. Evidence is also presented that ArH stored in the fat body protein granules during pupation may be utilized differently from that remaining in pupal hemolymph.

Molecular cloning and expression of two hexamerin cDNAs from the mosquito, Aedes aegypti

Fourth-instar larvae of Aedes aegypti synthesize two types of hexamerins, Hexamerin-1 (AaHex-1) and Hexamerin-2 (AaHex-2), whose subunits are distinguished by different methionine and aromatic amino acid contents. In early female pupae only the methionine-rich AaHex-1gamma subunit accumulates to two-fold higher levels than in males. To investigate the relationship between hexamerin structure and the roles of Hex-1 and Hex-2 during mosquito development and reproduction, we have cloned and sequenced cDNAs encoding the AaHex-2alpha, -2beta and AaHex-1gamma subunits. Comparison with other insect hexamerins revealed that the Aedes Hex-1 and Hex-2 proteins belong, respectively, to the two hexamerin subfamilies previously defined for brachyceran Diptera. Probes specific for the Hex-2alpha and Hex-1gamma transcripts showed that expression of both genes follows the same developmental timetable. However, greater Hex-1gamma mRNA accumulation may contribute to the higher levels of Hex-1 gamma protein in early female pupae.

Uncoupling of sequential heteromorphic developmental programs

The regulatory basis for differences among species in the developmental rate at which successive life stages are reached ("heterochrony") is a subject of much controversy among vertebrate and invertebrate developmental biologists. The heterochrony in development of different insect species is characterized in part by the intercalcation between the embryo and adult of a (varied) number of heteromorphic larval instars. These heteromorphic larval instars exhibit changes of body form from one larval instar to the next, prior to the final metamorphic molt to the pupal form. The intractability of larval heteromorphosis to experimental dissection is due in part to the lack of suitable experimental probes that can test the nature of the coupling of each heterochronically expressed instar-specific program. The epistatic basis of expression of heteromorphic developmental programs was assessed by two-dimensional electrophoretic analysis of hemolymph proteins during the normal and experimentally manipulated feeding stages of the 3rd, 4th, and 5th (final) instar larvae, and during the prepupal stage, of Trichoplusia ni. Of the several hundred protein spots tracked, some were identified that were uniquely detected during a single stage, while others were observed during combinations of certain stages. The nature of coupling of sequential heterochronic expression of these proteins during successive instars or stages was tested by use of a parasite (Chelonus sp.) that injects regulatory material into the host embryo that later causes the subsequent precocious expression of the final instar larval program. Following the expression of a normal 3rd instar pattern, such larvae were observed to omit expression of the 4th instar program, including omission of the proteins heteromorphically specific to that instar, and instead then express an essentially normal final instar pattern. Thus, normal expression of the final instar feeding stage pattern was not invariantly coupled to prior expression of the penultimate instar-specific proteins or pattern. Also, expression of the full program of the final instar feeding stage was epistatic to teh penultimate instar program, i.e., the protein pattern unique to the penultimate larval instar was not co-expressed with the precociously expressed final instar pattern. Larvae developmentally redirected in this manner failed to fully express the final instar prepupal stage pattern of protein expression, due at least in part to failed expression of prepupal ecdysteroids, but this was shown not to arise from omission of any of the first 4 larval instars per se. The nature of the redirections in host development caused by this parasite finally provides means of probing the coupling of successive expression on heteromorphic programs during larval development.

Differential gene expression in insects: transcriptional control

Studies on transcriptional control of gene expression play a pivotal role in many areas of biology. In non-Drosophilid insects, the cuticle, chorion, immune response, silk gland, storage proteins, and vitellogenin are foci for advances in basic research on promoter elements and transcription factors. Insects offer other advantages for gene regulation studies, including the availability of applied problems. In non-Drosophilid insects, the most serious problem for transcriptional control studies is the lack of homologous in vivo expression systems. Once this deficiency is addressed, the full impact of research on transcription control will be realized throughout the field of entomology.

Developmental changes of storage proteins and biliverdin-binding proteins in the haemolymph and fat body of the common cutworm, Spodoptera litura

The concentrations of three storage proteins (SL-1,SL-2 and SL-3, hexamers of 70-80kDa subunits) and two biliverdin-binding proteins (BP-A and BP-B, dimers of 165kDa) in the haemolymph and fat body during larval and pupal development of Spodoptera litura were determined by immunodiffusion tests using polyclonal antisera. SL-1 and SL-2 (methionine-rich) first appeared in the haemolymph of one-day-old sixth (final) instar larvae, prominently increased in the haemolymph during the later feeding period and were almost totally sequestered by the fat body after gut purge. SL-3 (arylphorin) was first detected in the haemolymph during the molting period to the final larval ecdysis, increased in concentration throughout the entire feeding period of the final larval instar and was partly sequestered by the fat body several hours later than the other storage proteins. BP-A showed nearly the same pattern in the haemolymph as SL-3: BP-B increased during feeding period and decreased during molting period and attained a maximum level during the penultimate larval instar, however its concentration decreased considerably and remained low in the final larval instar. BP-A was partly and BP-B was almost totally sequestered by the fat body 8 h after sequestration of SL-1 and SL-2, rendering the fat body blue in colour. These facts suggest an additional function of biliverdin-binding proteins as amino acid storage proteins and the results show a differential uptake mechanism for these proteins by the fat body.

Regulation of serpin gene-1 in Manduca sexta

Hemolymph of Manduca sexta contains proteins from the serpin superfamily, which are inhibitors of serine proteinases. We have used probes specific for M. sexta serpin gene-1 mRNA and protein to study the expression and hormonal regulation of this gene. Serpin gene-1 is expressed at a high level in larval fat body and at a lower abundance in hemocytes, where serpin protein is localized in the granules of granular cells. Serpin gene-1 mRNA is abundant in the fat body of feeding fourth and fifth instar larvae, but disappears abruptly at molts and at the wandering stage. The concentration of serpin proteins in hemolymph during development is correlated with the abundance of serpin mRNA in fat body. Results of in vivo and in vitro experiments indicate that 20-hydroxyecdysone has a role in negative regulation of serpin gene-1.

Cloning and developmental expression of the ecdysone receptor gene from the spruce budworm, Choristoneura fumiferana

Degenerate oligonucleotides were designed on the basis of conserved amino acid sequences in the DNA and ligand-binding regions of the members of the steroid hormone receptor superfamily. Using these oligonucleotides in RNA-PCR, a cDNA fragment was isolated from the spruce budworm, Choristoneura fumiferana. Comparison of the deduced amino acid sequence of this cDNA fragment with the members of the steroid hormone receptor superfamily suggested that this PCR fragment is a region of the ecdysone receptor from C. fumiferana. Using this cDNA fragment as a probe, 10 clones were isolated from a cDNA library that was constructed using the RNA from 4- and 5-day old embryos of C. fumiferana. Two cDNA clones (1.3 and 3 kb) that overlap and show amino acid identity with Drosophila melanogaster ecdysone receptor B-1 isoform (DmEcR) were characterized and sequenced. The longest open reading frame had 539 codons and covered the complete EcR coding region. The deduced amino acid sequence of this open reading frame had all five of the regions typical for a steroid hormone nuclear receptor. The C domain or DNA binding region showed the highest identity wit EcR proteins from D. melanogaster, Chironomus tendons, Aedes aegypti, Manduca sexta, and Bombyx mori. The A/B region, D domain or hinge region, E domain, or ligand binding region also showed significant amino acid similarity with the EcR proteins from the five insects mentioned above. The C. fumiferana ecdysteroid receptor (CfEcR) cDNA probe detected a 6.0-kb mRNA that was present throughout the development of C. fumiferana. The CfEcR mRNA increases in abundance at the time of the ecdysteroid peak during the molting phase in the embryonic, larval and pupal stages but remains low during the intermolt period. In the 6th instar larvae, the 6-kb CfEcR mRNA was detected in the epidermis, fat body, and midgut and maximum expression was observed during the prepupal peak of ecdysteroids in the hemolymph. CfEcR mRNA was induced in ecdysone treated CF-203 cells as well in the epidermis and midgut of larvae that were fed the nonsteroidal ecdysteroid agonist, RH-5992. The induction occurred within an hour and reached maximum levels around 3 hr, after which it decreased to the basal level by 6 hr. In vitro transcription and translation of the CfEcR cDNA yielded a 67-Kda protein that bound to the ecdysone response element (EcRE) as a heterodimer, along with the ultraspiracle protein.

Apparent functional role for a cysteine-rich polydnavirus protein in suppression of the insect cellular immune response

Polydnaviruses suppress the cellular immune response and inhibit growth and development in their lepidopteran host, allowing survival of their endoparasitic hymenopteran host. Characterization of genes disrupting insect physiological systems is a major objective in the study of polydnaviruses. Recently, a cysteine-rich gene family encoding a motif composed of invariable cysteine residues flanking hypervariable intercysteine amino acids was described (S.D. Dib-Hajj, B.A. Webb, and M.D. Summers, Proc. Natl. Acad. Sci. USA 90:3765-3769, 1993). They noted similarities to the positive selection pressure for mutations within the vertebrate major histocompatibility complex (MHC) class II genes and speculated that this class of polydnavirus genes may target and disrupt the insect immune system. To study the functional activity of this family of predicted cysteine-rich proteins, the VHv1.1 gene product was produced from bacterial and baculovirus expression systems. Polyclonal antiserum produced from the bacterial fusion protein reacted with a 30-kDa protein from hemocytes, cell-free plasma, and fat body of parasitized larvae. Immunofluorescence analysis of hemocytes from parasitized insects detected the 30-kDa protein bound to granulocytes and plasmacytes. To assay the functional activity of the 30-kDa VHv1.1 protein, a recombinant baculovirus was constructed allowing in vivo expression of the 30-kDa polydnavirus protein from infected insects. Expression of the VHv1.1 protein from the baculovirus system reduced the encapsulation response to washed wasp eggs relative to controls. The experimental evidence demonstrates that Campoletis sonorensis polydnavirus-infected cells secrete VHv1.1 into the hemolymph, where it binds to hemocytes and is associated with the inhibition of the cellular immune response.

Structure, expression and gene sequence of a juvenile hormone esterase-related protein from metamorphosing larvae of Trichoplusia ni

A carboxylesterase with an encoded molecular size of 61 kDa and a high sequence similarity to juvenile hormone esterase (JHE) has been cloned from cDNA prepared from final instar larvae of Trichoplusia ni. The absence of a recognizable encoded signal peptide suggests that the enzyme, JHER (for JHE-related) may not be secreted, in contrast to JHE. When the amino acid sequence of JHE, JHER and other esterases were mapped onto the secondary and tertiary structure determined crystallographically for acetylcholinesterase, certain structural features for the substrate binding/catalytic site were identified as common only to JHE and JHER. However, several differences between JHE and JHER were identified in residues at the binding/catalytic site, suggesting that although the two enzymes prefer similar natural substrates, these substrates are not identical. JHER is present as a single-copy gene, transcribed during the feeding stage of the final stage of the final larval stadium, but not after metamorphic commitment to the pupal developmental programme. The gene transcribes a single-size message of 2.0 kb. The genes for JHER and JHE appear to be physically juxtaposed in the T. ni genome. The 5' flanking sequence to the JHER gene possesses some sequences in common with the JHE gene, but is also missing some regulatory elements previously identified in the JHE gene. Sequences conserved between the promoters for the two genes were identified that were different from previously reported regulatory elements of eukaryotic transcription factors.

Nucleotide sequence, structure and developmental regulation of LHP82, a juvenile hormone-suppressible hexamerin gene from the waxmoth, Galleria mellonella

We cloned and sequenced a composite cDNA corresponding to the 2.6 kb last instar-specific, juvenile hormone-suppressible Lhp82 mRNA from Galleria mellonella. The identity of the cDNA was confirmed by N-terminal amino acid sequencing of the purified Lhp82 subunit. In addition, we sequenced all coding regions and most of the intronic DNA as well as 1300 nucleotides of 5' flanking DNA from the Lhp82 gene. The eight exons of the Lhp82 gene specify a pre-protein of 706 residues, including the signal peptide of 18 amino acids. The deduced amino acid sequence of Lhp82 contains four potential N-glycosylation sites, and the calculated isoelectric point and molecular weight of secreted Lhp82 are pI = 6.43 and 79.9 kDa, respectively. Inspection of the 5' flanking and intronic regions of Lhp82 DNA revealed a 301 nucleotide cassette in intron 6 that appears to be a recently inserted repetitive element. We also performed Northern blot and nuclear run-off transcription experiments in order to determine the basis for Lhp82 gene inactivity after day 2 of the pupal stage. The results of these studies indicate that Lhp82 transcription is permanently shut off by the ecdysteroid pulse which occurs in the absence of juvenile hormone beginning 24 h post-pupation.

Transcriptional regulation of an unusual trypsin-related protein expressed during insect metamorphosis

The full-length cDNA for a trypsin-related protein expressed during larval-pupal metamorphosis was obtained. The encoded N-terminal half of the protein possessed similarity to trypsin proteases, including the correctly positioned histidine and aspartic acid members of the catalytic triad. However, the remainder of the encoded protein bore little resemblance to trypsin, and was altogether missing the canonical sequence containing the catalytic serine residue. The product of in vitro transcription/translation of the cDNA was a 28 kDa protein. Under normal conditions of a declining juvenile hormone titer, transcription of the mRNA as a proportion of total genomic transcription steadily increased for the first 3 days of the final stadium, but this increase was delayed and suppressed by maintenance of a high juvenile hormone titer. During the normal increase in transcription on day 3 of the final stadium, a sharp decline was observed in the steady-state abundance of the transcript, measured relative to abundance of the remaining mRNAs, suggesting that the stability of the message decreases after tissue commitment for a pupal molt.

Polymorphic cDNAs encode for the methionine-rich storage protein from Manduca sexta

By cDNA cloning and sequencing we have shown that Manduca sexta larvae produce three very closely related methionine-rich storage proteins, MMR1, MMR2 and MMR3. Out of 2256 nucleotides in the coding region, the cDNAs differ by at most twenty-one bases and this leads to a single amino acid difference between MMR1 and MMR2, and between MMR2 and MMR3, whereas MMR1 and MMR3 differ by two amino acids. Using both distance and parsimony methods, similarities between the M. sexta and Bombyx mori methionine-rich and arylphorin storage proteins were examined. Homologous proteins from the two species tend to be more closely related than are the two classes of storage proteins in a single species.

Juvenile hormone action to suppress gene transcription and influence message stability

Proteins normally expressed in high abundance only at larval-pupal metamorphosis in Trichoplusia ni were examined in a comparative analysis of the role and level of hormonal control of their expression. Some related proteins in the hemocyanin-superfamily (i.e., an acidic protein [AJHSP1] and two basic proteins [BJHSP1, BJHSP2]) were shown by nuclear run-on analysis to be specifically transcriptionally suppressed by juvenile hormone (JH), while transcription of another member of that family which is also metamorphosis-associated (arylphorin) was not specifically sensitive to JH. The stability of the mRNA for those members transcriptionally down-regulated by JH appeared to decrease under high JH conditions. While each protein was resorbed to some extent by the prepupal fat body, only the two basic proteins were quantitatively cleared from prepupal hemolymph. The JH-sensitive proteins studied appear to be encoded in single copy genes not immediately juxtaposed in the genome. These and previous studies now permit a more comprehensive understanding of the different combinations of mechanisms involving transcription, mRNA stability, translation, and protein clearance that operate to regulate these metamorphosis-associated proteins.

Stimulation of polydnavirus replication by 20-hydroxyecdysone

During oviposition the endoparasitic wasp Campoletis sonorensis, introduces a polydnavirus into parasitized insects where viral gene expression is required for endoparasite survival. The polydnavirus is integrated into wasp chromosomal DNA and replicates only in the ovary. Ecdysteroids regulate the developmental expression of many insect genes and may regulate polydnavirus replication. Direct verification of viral replication was performed by dot blot hybridization and by amplifying DNA sequences containing the viral integration site; this 'junction' fragment cannot be amplified from integrated virus. Thoracic ligations and in vitro ecdysteroid treatments of wasp ovaries support the hypothesis that polydnavirus DNA replication is regulated by ecdysteroid during parasite development.

Venom and viral expression products of the endoparasitic wasp Campoletis sonorensis share epitopes and related sequences

Endoparasitic wasps of lepidopteran insects must induce changes in host immunity and development to survive. Depending on the species, this may require wasp venom proteins and/or a polydnavirus. We describe an immunological and genetic relationship between the Campoletis sonorensis polydnavirus and the wasp's venom gland. Monoclonal antibodies raised against venom glands recognized epitopes conserved on several polydnavirus proteins and on multiple wasp oviduct and venom proteins. The viral envelope proteins had molecular masses of 16, 20, 45, and 50 kDa, while a complex of at least five immunoreactive venom-gland and soluble oviduct proteins ranged in size from 24 to 36 kDa. Since the conserved epitopes were present on the viral envelope, neutralization assays were performed. Monoclonal antibodies added to purified virus blocked the normal viral inhibition of host growth and development. To determine whether venom mRNA and viral genes were also related, venom-related cDNA clones were isolated from the wasp oviduct with a venom-gland cDNA probe. Venom-related viral clones were then identified and selected from a viral genomic library and from a parasitized Heliothis virescens cDNA library. Venom-related mRNAs were expressed in the venom gland, the oviduct, and the parasitized host. We propose that the immunological relationship between venom and viral proteins, and the hybridization of venom and viral genes, may reflect an evolutionary relationship in which venom gene homologs were incorporated into the viral genome, thereby allowing viral expression of venom-related genes and enhancing parasite survival.

Juvenile hormone receptors in insect larval epidermis: identification by photoaffinity labeling

Tritiated photoaffinity analogs of the natural lepidopteran juvenile hormones, JH I and II [epoxy[3H]bishomofarnesyl diazoacetate ([3H]EBDA) and epoxy[3H]homofarnesyl diazoacetate ([3H]EHDA)], and of the JH analog methoprene [[3H]methoprene diazoketone ([3H]MDK)] were synthesized and used to identify specific JH binding proteins in the larval epidermis of the tobacco hornworm (Manduca sexta). EBDA and EHDA specifically photolabeled a 29-kDa nuclear protein (pI 5.8). This protein and a second 29-kDa protein (pI 6.0) were labeled by MDK, but excess unlabeled methoprene or MDK only prevented binding to the latter. These 29-kDa proteins are also present in larval fat body but not in epidermis from either wandering stage or allatectomized larvae, which lack high-affinity JH binding sites. A 29-kDa nuclear protein with the same developmental specificity as this JH binder bound the DNA of two larval endocuticle genes. A 38-kDa cytosolic protein was also specifically photolabeled by these photoaffinity analogs. The 29-kDa nuclear protein is likely the high-affinity receptor for JH that mediates its genomic action, whereas the 38-kDa cytosolic protein may serve as an intracellular carrier for these highly lipophilic hormones and hormone analogs.

Synthesis of two storage proteins during larval development of the tobacco hornworm, Manduca sexta

Studies of synthesis and accumulation of the two storage proteins arylphorin and female-specific protein (FSP) during the final two larval instars of the tobacco hornworm showed both stage and temporal specificity. Arylphorin was present in both stages, but its synthesis ceased during the molt, during starvation, and at the wandering stage, and then resumed about 24 hr after the onset of feeding. During the larval molt about 25% of injected iodinated arylphorin was incorporated into the newly forming fifth instar cuticle. The cessation of arylphorin synthesis was mimicked by exposure of the fat body to 1 microgram/ml 20-hydroxyecdysone (20HE) in complete Grace's medium or to dilutions of Grace's medium greater than 50%. Lower concentrations of 20HE were ineffective, indicating that the cessation of synthesis in vivo was likely due to a combination of lack of excess nutrients and the hormonal milieu. The female-specific protein was not synthesized until the final larval instar, appearing first in females on Day 2 and later in males at the time of wandering, with synthesis continuing throughout the prepupal period. In vitro studies showed that this protein was synthesized as a 620-kDa protein, and then during secretion a 730-kDa immunoreactive form also appeared. Synthesis of FSP was inhibited by exposure of Day 2 fat body to 1 microgram/ml 20HE for 24 hr. Ligation followed by 20HE infusion showed that the disappearance of FSP from the hemolymph during the prepupal period was controlled by the rising ecdysteroid titer.