Distribution and accumulation of storage protein-1 in ovary of Hyphantria cunea Drury

Potential costs of bacterial infection on storage protein gene expression and reproduction in queenless Apis mellifera worker bees on distinct dietary regimes

Insects are able to combat infection by initiating an efficient immune response that involves synthesizing antimicrobial peptides and a range of other defense molecules. These responses may be costly to the organism, resulting in it exploiting endogenous resources to maintain homeostasis or support defense to the detriment of other physiological needs. We used queenless worker bees on distinct dietary regimes that may alter hemolymph protein storage and ovary activation to investigate the physiological costs of infection with Serratia marcescens. The expression of the genes encoding the storage proteins vitellogenin and hexamerin 70a, the vitellogenin receptor, and vasa (which has a putative role in reproduction), was impaired in the infected bees. This impairment was mainly evident in the bees fed beebread, which caused significantly higher expression of these genes than did royal jelly or syrup, and this was confirmed at the vitellogenin and hexamerin 70a protein levels. Beebread was also the only diet that promoted ovary activation in the queenless bees, but this activation was significantly impaired by the infection. The expression of the genes encoding the storage proteins apolipophorins-I and -III and the lipophorin receptor was not altered by infection regardless the diet provided to the bees. Similarly, the storage of apolipophorin-I in the hemolymph was only slightly impaired by the infection, independently of the supplied diet. Taken together these results indicate that, infection demands a physiological cost from the transcription of specific protein storage-related genes and from the reproductive capacity.

Ecdysteroid-mediated expression of hexamerin (arylphorin) in the rice moth, Corcyra cephalonica

The insect development is intricately controlled by morphogenetic hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E) through the regulation of gene/protein expression. The role of hexamerins in the metamorphosis of insects and reproduction and their control by 20E at the gene level has been widely reported in insects. In the present study we for the first time report the role of ecdysteroids in the regulation of hexamerin synthesis in a lepidopteran insect Corcyra cephalonica. The hormonal studies were carried out using the normal and the thorax-ligated insects with both 20E and its non-steroidal agonist RH-5992. The in vitro as well as in vivo studies showed a stimulatory effect of 20E and its agonist on the hexamerin synthesis including arylphorin (Hex 2), whereas hormone blockade with azadirachtin caused a time dependent reduction in synthesis. The northern analysis using Hex 2b cDNA as probe too confirmed the above result. This was followed by the cloning of the Hex 2b gene. The full length of the genomic clone was found to be 3.5kb long and has four exons interspersed by three introns. The genome walking analysis revealed the presence of a steroid hormone binding sequence "Ecdysone response element" (EcRE) in the 5' untranscribed region (UTR) of the gene. The data presented in this paper clearly suggest that hexamerin synthesis in C. cephalonica is transcriptionally regulated by 20E.

Identification of 86 kDa protein as methionine rich hexamerin in the rice moth, Corcyra cephalonica

We cloned the complete cDNA of methionine rich hexamerin from rice moth, Corcyra cephalonica using RACE strategy. The amplicon size was 2.5 kb with an ORF of 2.31 kb. The cDNA clone showed high percentage of methionine (4.8%), which is consistent with the previously reported sequences in other insects. The Southern and Northern analysis carried out showed that methionine rich hexamerin in rice moth is a single copy gene. Multiple alignment analysis of amino acid sequence revealed that the cDNA clone is most similar to Plodia interpunctella hexamerin storage protein (74% identity). The calculated isoelectric point is 9.2. The deduced amino acid sequence corresponded to 86 kDa subunit of hexamerin protein in rice moth. The 86 kDa protein (methionine rich subunit) was purified and polyclonal antibodies were raised against the subunit to check the specificity of the purified subunit. The developmental profile of 86 kDa subunit during the larval stages both in the fat body and haemolymph show that it is present at a higher concentration during the LLI (late-last instar) larval stage compared to the previous stages. The present work carried out shows that the methionine rich hexamerin cloned is the 86 kDa subunit of hexamerin which was identified previously by our group in rice moth, C. cephalonica.

Life history plasticity after attaining a dietary threshold for reproduction is associated with protein storage in flesh flies

Body condition affects the timing and magnitude of life history transitions. Therefore, identifying proximate mechanisms involved in assessing condition is critical to understanding how these mechanisms affect the expression of life history plasticity. Nutrient storage is an important body condition parameter, likely playing roles in both attaining minimum body-condition thresholds for life history transitions and expression of life history traits.We manipulated protein availability for females of the flesh fly Sarcophaga crassipalpis to determine whether reproductive timing and output would remain plastic or become fixed. Liver was provided for 0, 2, 4, or 6 days of adult pre-reproductive development. Significantly, liver was removed after the feeding threshold had been attained and females had committed to producing a clutch.We also identified the major storage proteins and monitored their abundances, because protein stores may serve as an index of body condition and therefore may play an important role in life history transitions and plasticity.Flesh flies showed clear post-threshold plasticity in reproductive timing. Females fed protein for 2 days took ~30% longer to provision their clutch than those fed for 4 or 6 days. Observations of oogenesis showed the 2-day group expressed a different developmental program including slower egg provisioning.Protein availability also affected reproductive output. Females fed protein for 2 days produced ~20% fewer eggs than females fed 4 or 6 days. Six-day treated females provisioned larger eggs than 4-day treated females, followed by 2-day treated females with the smallest eggs.Two storage proteins were identified, LSP-1 and LSP-2. LSP-2 accumulation differed across feeding treatments. The 2- and 4-day treatment groups accumulated LSP-2 stores but depleted them during provisioning of the first clutch, whereas the 6-day group accumulated the greatest quantity of LSP-2 and had substantial LSP-2 stores remaining at the end of the clutch. This pattern of accumulation and depletion suggests that LSP-2 could play roles in both provisioning the current clutch and future clutches, making it a good candidate molecule for affecting reproductive timing and allotment. LSP-1 was not associated with post-threshold plasticity; it was carried over from larval feeding into adulthood and depleted uniformly across all feeding groups.

Expression and localization of storage protein 1 (SP1) in differentiated fat body tissues of red hairy caterpillar, Amsacta albistriga Walker

The accumulation and utilization of storage proteins are prominent events linked to the metamorphosis of holometabolous insects. The female-specific storage protein 1 (SP1) is the major storage protein found in the hemolymph and fat body of female larvae of the groundnut pest, Amsacta albistriga. Here we show SP1 expression and localization in differentiated fat body tissues using biochemical and immunohistochemistry scrutiny. Comparison of A. albistriga SP1 with that of other species with respect to amino acid composition and N-terminal sequences show that SP1 is a methonine-rich protein and its identity was confirmed by means of immunoblot analysis. Northern blot studies revealed that the SP1 gene demonstrates stage- and tissue-specific expression in the peripheral fat body cells during the mid-larval period of fifth instar of A. albistriga. During the larval pupal transformation, SP1 are sequestered mainly by the perivisceral fat body tissues, until they serve the purpose of supplying amino acids for the production of egg yolk proteins. Further, electron microscopic studies using immunogold tracer techniques confirmed the localization of crystalline SP1 reserves, stored in the perivisceral fat body tissues. Hence, the peripheral fat body is responsible for biosynthesis of storage proteins, whereas the perivisceral fat body is a specialized storage organ.

Expression of two methionine-rich storage protein genes of Plutella xylostella (L.) in response to development, juvenile hormone-analog and pyrethroid

We cloned and characterized cDNA of two storage protein (SP) genes, PxSP1 and PxSP2, from the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae) and investigated their expression. PxSP1 and PxSP2 each encoded a putative protein of 91 kDa. Nucleotide and deduced amino acid identities between the two genes were 79% and 82%, respectively. Amino acid composition (methionine>4%), sequence homology with other insect storage proteins and the phylogenetic analysis suggested that the genes belong to the subfamily of moderately methionine-rich SP genes. The genes were predominantly expressed in the last instar female larvae and the mRNA levels were suppressed by treatment with a juvenile hormone-analog. Treatment of female larvae with sublethal dose of a pyrethroid caused a significant increase in mRNA levels of both genes. Induction of PxSP1 and PxSP2 genes as a result of pyrethroid application may have implications with respect to reproduction as methionine-rich proteins are known as a key element for egg production.

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.

Larval nutrition affects lipid storage and growth, but not protein or carbohydrate storage in newly eclosed adults of the grasshopper Schistocerca americana

Nitrogen availability from dietary protein can have profound effects on the physiology and evolutionary ecology of insect herbivores. While many studies consider the effects of nutrition on consumption and gross body composition of protein and other important nutrients, few consider partitioning to storage for future use. I used chemically defined artificial diets to quantitatively manipulate the amount of dietary carbohydrates and proteins available to growing larvae of the grasshopper Schistocerca americana to determine how larval nutrient availability affects growth and all three classes of stored nutrients (proteins, lipids, and carbohydrates) carried over from larval feeding into adulthood. Larvae on poor diets increased consumption, but could not compensate for diet quality, eclosing small and containing no significant nutrient stores at adulthood. Individuals fed intermediate to high nutrient content diets as larvae were significantly larger and contained a significantly greater proportion of lipid stores at adult eclosion, but not protein or carbohydrate stores than individuals fed low nutrient content diets. This suggests that larvally derived lipid stores may be more important to adult fitness than carbohydrate or protein stores. This result is contrary to previous studies performed on the role of larval nutrition and allocation to protein stores, and this difference is likely due to variation in the relative availability of protein in adult diets across species.

Immune activation of apolipophorin-III and its distribution in hemocyte from Hyphantria cunea

Apolipophorin-III (apoLp-III) is a hemolymph protein whose function is to facilitate lipid transport in an aqueous medium. Recently, apoLp-III in Galleria mellonella larvae was shown to play an unexpected role in insect immune activation. We identified the cDNA sequence of Hyphantria cunea apoLp-III by oligonucleotide-primed amplification, and 5'- and 3'-RACE PCR. Since H. cunea has an unusually low level of apoLp-III in the hemolymph, a recombinant apoLp-III was overexpressed using a baculovirus expression system to investigate its biological activity. Recombinant apoLp-III and/or Escherichia coli were injected into the hemocoel of last instar larvae, and the expression of antimicrobial peptide from fat body was determined by Northern blot. Injection of apoLp-III as well as E. coli induced slight up-regulation of its transcription rate in fat body, whereas the expression of antimicrobial peptide was dramatically induced by the injection of apoLp-III and E. coli. H. cunea hemocytes had apoLp-III in the granules and expressed its transcript, albeit at a much lower level than in the fat body. Upon bacterial injection, a subpopulation of hemocytes showed degranulation and degradation. Local discharge of apoLp-III from hemocytes caused by the injection of E. coli might be related to the immune response through an unknown mechanism.

Storage protein content as a functional marker for colony-founding strategies: a comparative study within the harvester ant genus Pogonomyrmex

Claustral colony founding, in which new queens rear their first clutch of workers solely from internal reserves, is common in the higher ant subfamilies and is believed to represent a major innovation in ant life histories. The ability to store large amounts of amino acids contained in storage proteins is an essential physiological trait for claustral colony founding by ant queens. To determine whether there is an association between storage protein content and colony-founding strategy, we identified and quantified two major storage proteins in queens of five harvester ant species in the genus Pogonomyrmex that differ in colony-founding strategy. Queens of the fully claustral nonforaging species Pogonomyrmex rugosus and Pogonomyrmex maricopa contained the greatest amount of these proteins. Facultatively foraging semiclaustral Pogonomyrmex occidentalis queens contained an intermediate amount. Obligately foraging semiclaustral Pogonomyrmex californicus queens from two different populations contained significantly less storage protein than the other independent-founding species. Queens of the dependent-founding social parasite Pogonomyrmex anergismus also contained little storage protein. Our results suggest that storage protein content has evolved in concert with colony-founding strategies in the genus Pogonomyrme and provides a good functional marker for colony-founding strategy.

Presence of a single abundant storage hexamerin in both larvae and adults of the grasshopper, Schistocerca americana

We identified a single hexameric storage protein in the grasshopper, Schistocerca americana, and monitored its abundance through the last larval instar and up until reproductive competence in adults of both sexes. This storage hexamerin, termed Schistocerca americana Persistent Storage Protein (saPSP) was the most abundant soluble protein in both larvae and adults. In both sexes, saPSP abundance started out low at the onset of the last larval instar and accumulated during feeding, peaking just prior to molting. Adults of both sexes contained significant amounts of saPSP after eclosion. In adult males, saPSP content dropped continuously after eclosion and was lowest once individuals reached reproductive maturity. In contrast, adult females depleted saPSP reserves during the first days of adulthood, but subsequently accumulated significant saPSP stores. In adult females, saPSP stores peaked just prior to the completion of egg provisioning. Given the overall patterns of abundance, saPSP has functions in both larvae and adults. In addition, the observed pattern of storage hexamerin accumulation differs from patterns of accumulation in the other known grasshoppers, Locusta migratoria and Romalea microptera, suggesting that significant functional diversity has evolved in storage hexamerins among the grasshoppers.

Response of storage protein levels to variation in dietary protein levels

Storage proteins have been found to play a major role in insect metamorphosis and egg production and are accumulated during the actively feeding larval stage. Yet few studies have focused on how nutrition affects storage protein levels. Three storage proteins were identified in male and female Heliothis virescens pupae, one arylphorin and two putative high-methionine hexamers. Storage proteins were quantified in early pupae and in pharate adults. Storage protein levels peaked in 48-h pupae and were more abundant in females across all stages. Both male and female pharate adults retained a portion of total storage protein levels and females retained greater levels overall. In females, post-eclosion protein reserves will likely be used toward egg manufacturing, while the role of protein reserves in males remains speculative. In our previous study of H. virescens larvae, we found that protein-derived growth in females progressively increased as dietary protein levels increased. Our present data show that levels of storage protein also increased progressively along with dietary protein levels. This suggests that females allocated protein, in excess of adult tissue formation needs, toward storage protein. Our study is the first to demonstrate how responsive storage protein levels can be in face of varying levels of dietary protein.

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.

Local expression and distribution of a storage protein in the ovary of Hyphantria cunea

Storage protein-1 (HcSP-1) is a major storage protein found in the hemolymph and fat body of Hyphantria cunea. HcSP-1 has a high methionine (6.0%) and low aromatic amino acid content (8.5%) (Cheon et al., 1998). In this study, the accumulation and expression of HcSP-1 in ovary was investigated using biochemical and immunocytochemical methods. HcSP-1 was detected in the ovaries in 6-day-old pupae and accumulated toward the end of pupal life, when HcSP-1 transcripts were detectable by Northern blot analysis and RT-PCR. In situ hybridization showed that the HcSP-1 mRNA was located in the nurse cells and follicular epithelial cells, but not in the oocyte. Though most of the HcSP-1 that is incorporated in the yolk bodies of the oocyte is probably sequestered from the surrounding hemolymph, HcSP-1 is an important yolk protein contributing to early yolk body formation before the development of patency by the follicular epithelium.