A cysteine protease that processes insect vitellin. Purification and partial characterization of the enzyme and the proenzyme

A De Novo Transcriptomics Approach Reveals Genes Involved in Thrips Tabaci Resistance to Spinosad

The onion thrip, Thrips tabaci (Thysanoptera: Thripidae) is a major polyphagous pest that attacks a wide range of economically important crops, especially Allium species. The thrip's damage can result in yield loss of up to 60% in onions (Allium cepa). In the past few decades, thrip resistance to insecticides with various modes of actions have been documented. These include resistance to spinosad, a major active compound used against thrips, which was reported from Israel. Little is known about the molecular mechanisms underlying spinosad resistance in T. tabaci. We attempted to characterize the mechanisms involved in resistance to spinosad using quantitative transcriptomics. Susceptible (LC50 = 0.6 ppm) and resistant (LC50 = 23,258 ppm) thrip populations were collected from Israel. An additional resistant population (LC50 = 117 ppm) was selected in the laboratory from the susceptible population. De novo transcriptome analysis on the resistant and susceptible population was conducted to identify differently expressed genes (DGEs) that might be involved in the resistance against spinosad. In this analysis, 25,552 unigenes were sequenced, assembled, and functionally annotated, and more than 1500 DGEs were identified. The expression levels of candidate genes, which included cytochrome P450 and vittelogenin, were validated using quantitative RT-PCR. The cytochrome P450 expression gradually increased with the increase of the resistance. Higher expression levels of vitellogenin in the resistant populations were correlated with higher fecundity, suggesting a positive effect of the resistance on resistant populations. This research provides a novel genetic resource for onion thrips and a comprehensive molecular examination of resistant populations to spinosad. Those resources are important for future studies concerning thrips and resistance in insect pests regarding agriculture.

The mRNA expression and enzymatic activity of three enzymes during embryonic development of the hard tick Haemaphysalis longicornis

Background

Three main enzymes including cathepsin B, cathepsin D and acid phosphatase are involved in vitellin degradation, which is a major biochemical event of the embryonic development and can provide nutrients and metabolites for tick embryos. In the present study, the mRNA expression profiles and enzymatic activity of cathepsin B, cathepsin D and acid phosphatase were investigated during embryonic development in the tick Haemaphysalis longicornis.

Results

The results revealed that all three enzymes were expressed throughout embryonic development. Both cathepsin B and acid phosphatase transcripts were accumulated during the first four days. Cathepsin B reached its highest expression on day 5, whereas the peak expression of acid phosphatase and cathepsin D occurred on day 11. The highest activity of cathepsin B was observed on the first day of egg development, whereas cathepsin D reached its highest activity on day 13. Acid phosphatase activity increased gradually during the first five days and then remained stable until the end of egg development.

Conclusions

Three enzymes were expressed and activated in eggs, and also presented different dynamic changes with the development of embryos. The profiles of both mRNA expression and enzymatic activity of these enzymes indicate that they are controlled orderly and play multiple roles during embryonic development in ticks.

Two cathepsins B are responsible for the yolk protein hydrolysis in Culex quinquefasciatus

Despite the established role of Culex quinquefasciatus as a vector of various neurotropic viruses, such as the Rift Valley and West Nile viruses, as well as lymphatic filariasis, little is known regarding the organism’s reproductive physiology. As in other oviparous animals, vitellogenin, the most important source of nutrients for the embryo development, is digested by intracellular proteases. Using mass spectrometry, we have identified two cathepsin B homologues partially purified by self-proteolysis of Cx. quinquefasciatus total egg extract. The transcriptional profile of these two cathepsin B homologues was determined by quantitative RT-PCR, and the enzymatic activity associated with the peptidase was determined in ovaries after female engorgement. According to the VectorBase (vectorbase.org) annotation, both cathepsin B homologues shared approximately 66% identity in their amino acid sequences. The two cathepsin B genes are expressed simultaneously in the fat body of the vitellogenic females, and enzymatic activity was detected within the ovaries, suggesting an extra-ovarian origin. Similar to the transcriptional profile of vitellogenin, cathepsin B transcripts were shown to accumulate post-blood meal and reached their highest expression at 36 h PBM. However, while vitellogenin expression decreased drastically at 48 h PBM, the expression of the cathepsins increased until 84 h PBM, at which time the females of our colony were ready for oviposition. The similarity between their transcriptional profiles strongly suggests a role for the cathepsin B homologues in vitellin degradation.

Microscopic and molecular characterization of ovarian follicle atresia in Rhodnius prolixus Stahl under immune challenge

In this work we characterized the degenerative process of ovarian follicles of the bug Rhodnius prolixus challenged with the non-entomopathogenic fungus Aspergillus niger. An injection of A. niger conidia directly into the hemocoel of adult R. prolixus females at the onset of vitellogenesis caused no effect on host lifespan but elicited a net reduction in egg batch size. Direct inspection of ovaries from the mycosed insects revealed that fungal challenge led to atresia of the vitellogenic follicles. Light microscopy and DAPI staining showed follicle shrinkage, ooplasm alteration and disorganization of the monolayer of follicle cells in the atretic follicles. Transmission electron microscopy of thin sections of follicle epithelium also showed nuclei with condensed chromatin, electron dense mitochondria and large autophagic vacuoles. Occurrence of apoptosis of follicle cells in these follicles was visualized by TUNEL labeling. Resorption of the yolk involved an increase in protease activities (aspartyl and cysteinyl proteases) which were associated with precocious acidification of yolk granules and degradation of yolk protein content. The role of follicle atresia in nonspecific host-pathogen associations and the origin of protease activity that led to yolk resorption are discussed.

Longterm persistence of proteolytic activities in frass of Blattella germanica increases its allergenic potential

Chromogenic microplate assays in 96 wells were used to determine the stability of enzyme activity in frass of Blattella germanica (Blattodea: Blattellidae). Frass samples were exposed to controlled conditions [temperature 15-35 °C and/or 53-100% relative humidity (RH)] and to household conditions (apartment). Exposure times were 0 (control), 90, 183 and 276 days. Starch digestion and cellulolytic activities decreased during exposure. Non-specific proteolytic activities were affected by changes in selective proteolytic activities. Activities towards AAPpNA and SA(3) pNA strongly increased at 100% RH, indicating the possible influence of microorganisms growing on frass. Activities towards BApNA and ArgpNA decreased with increasing decomposition time, whereas activity towards ZRRpNA was not influenced by exposure time. The largest decrease in activities towards ArgpNA and BApNA occurred at temperatures of 15 °C, 30 °C and 35 °C and at 100% RH. Activities towards BApNA and ZRRpNA were very stable under different temperature and RH conditions; this was confirmed by findings showing that these activities were stable in the experimental apartment. In comparison with the control, activities towards ZRRpNA and BApNA after 276 days decreased by 1% and 19%, respectively. The longterm persistence of proteolytic activities in cockroach frass increases their allergenic hazard potential.

Functional analysis of the cathepsin-like cysteine protease genes in adult Brugia malayi using RNA interference

Background

Cathepsin-like enzymes have been identified as potential targets for drug or vaccine development in many parasites, as their functions appear to be essential in a variety of important biological processes within the host, such as molting, cuticle remodeling, embryogenesis, feeding and immune evasion. Functional analysis of Caenorhabditis elegans cathepsin L (Ce-cpl-1) and cathepsin Z (Ce-cpz-1) has established that both genes are required for early embryogenesis, with Ce-cpl-1 having a role in regulating in part the processing of yolk proteins. Ce-cpz-1 also has an important role during molting.

Methods and Findings

RNA interference assays have allowed us to verify whether the functions of the orthologous filarial genes in Brugia malayi adult female worms are similar. Treatment of B. malayi adult female worms with Bm-cpl-1, Bm-cpl-5, which belong to group Ia of the filarial cpl gene family, or Bm-cpz-1 dsRNA resulted in decreased numbers of secreted microfilariae in vitro. In addition, analysis of the intrauterine progeny of the Bm-cpl-5 or Bm-cpl Pro dsRNA- and siRNA-treated worms revealed a clear disruption in the process of embryogenesis resulting in structural abnormalities in embryos and a varied differential development of embryonic stages.

Conclusions

Our studies suggest that these filarial cathepsin-like cysteine proteases are likely to be functional orthologs of the C. elegans genes. This functional conservation may thus allow for a more thorough investigation of their distinct functions and their development as potential drug targets.

Filarial nematodes are an important group of human pathogens, causing lymphatic filariasis and onchocerciasis, and infecting around 150 million people throughout the tropics with more than 1.5 billion at risk of infection. Control of filariasis currently relies on mass drug administration (MDA) programs using drugs which principally target the microfilarial life-cycle stage. These control programs are facing major challenges, including the absence of a drug with macrofilaricidal or permanent sterilizing activity, and the possibility of the development of drug-resistance against the drugs available. Cysteine proteases are essential enzymes which play important roles in a wide range of cellular processes, and the cathepsin-like cysteine proteases have been identified as potential targets for drug or vaccine development in many parasites. Here we have studied the function of several of the cathepsin-like enzymes in the filarial nematode, B. malayi, and demonstrate that these cysteine proteases are involved in the development of embryos, show similar functions to their counterparts in C. elegans, and therefore, provide an important target for future drug development targeted to eliminate filariasis.

Interplay between acid phosphatase and cysteine proteases in mediating vitellin degradation during early embryogenesis of Periplaneta americana

In this work, we characterized the activities of two classes of proteases and AcP during early embryogenesis of Periplaneta americana. AcP activity was first detected at day 6 and reached a maximum level at day 10 of development. Using phosphoamino acids, phosphatase activity was shown to be directed only against phosphotyrosine at day 6 while at day 10 it was also active against phosphoserine. In parallel, two classes of proteases were detected and located within yolk granules: a clan CA-cysteine protease, which was inhibited by E-64, insensitive to CA 074 and activated by acidic pH at day 3; and a neutral serine protease, which was inhibited by aprotinin at day 6. Assays of vitellin (Vt) degradation evidenced that incubations at neutral pH induced slight proteolysis, while the incubations at acidic pH did not result in Vt degradation. However, pre-incubations of Vt with AcP increased the levels of Vt acidic proteolysis and this could be inhibited by the addition of phosphatase inhibitors. On the other hand, the same pre-incubations showed no effects on the profile of degradation at neutral pH. We propose that AcP and cysteine protease cooperate to assure Vt breakdown during early embryogenesis of P. americana.

A cysteine endopeptidase from tick (Rhipicephalus (Boophilus) microplus) larvae with vitellin digestion activity

The hard tick Rhipicephalus (Boophilus) microplus is a blood-sucking ectoparasite. R. microplus free-living stage comprises egg development, hatching, and subsequent larval development until encountering a host. In order to complete the embryological development, this tick relies on yolk reserve substances, mainly vitellin (Vt), which is still present in the larval stage. The present study demonstrates presence and digestion of Vt in unfed R. microplus larvae. An increasing proteolytic activity is observed in larval development, as well as a decrease in total protein and in Vt content. Partial purification and characterization of a R. microplus larval cysteine endopeptidase (RmLCE) with Vt-degrading activity is also described. RmLCE has optimal activity at 37 degrees C at pH 5.0, being unstable at pH > or =7.5. This enzyme is active upon fluorogenic peptide substrates and is able to degrade Vt, its putative natural substrate. These results indicate that RmLCE has a role in supporting the nutritional needs of unfed R. microplus larva through Vt proteolysis, allowing survival until the first blood meal.

Vitellin of Pteromalus puparum (Hymenoptera: Pteromalidae), a pupal endoparasitoid of Pieris rapae (Lepidoptera: Pieridae): Biochemical characterization, temporal patterns of production and degradation

Vitellin (Vt) and vitellogenin (Vg) profiles were analyzed in Pteromalus puparum, a pupal endoparasitoid of Pieris rapae. Non-denaturing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses indicated that both native Vt and Vg were likely 370 kDa in size, consisting of two subunits of approximate 206 and 165 kDa. An indirect double antibody enzyme-linked immunosorbent assay (ELISA) for monitoring hemolymph Vg and ovarian Vt levels was developed using a monoclonal antibody and a polyclonal antibody made specially against P. puparum Vt. The synthesis and uptake of Vg in this wasp was initiated immediately after adult eclosion. The hemolymph Vg and ovarian Vt reached their highest level of 0.58 and 4.51 microg per female 24 and 48 h after adult eclosion, respectively. Both Vg synthesis and uptake were in parallel with ovarian development. The Vt levels in the developing embryos decreased progressively except 12h after parasitism. Meanwhile, nine new polypeptides with sizes ranging from 59.2 to 151 kDa, possibly resulting from the limited proteolysis of Vt originally accumulated in newly laid eggs, were detected de-novo during embryonic development using Western blotting with the monoclonal antibody against Vt. These studies provide the basis for future investigation into endocrinal regulations of vitellogenesis and understanding the reproductive strategy in this wasp.

The Caenorhabditis elegans CPI-2a cystatin-like inhibitor has an essential regulatory role during oogenesis and fertilization

In the present study, we characterized a sterile cpi-2a(ok1256) deletion mutant in Caenorhabditis elegans and showed that CPI-2a has an essential regulatory role during oogenesis and fertilization. We have also shown that the CPI2a inhibitor and both Ce-CPL-1 and Ce-CPZ-1 enzymes are present in the myoepithelial sheath surrounding germ cells, oocytes, and embryos as well as in the yolk granules within normal oocytes. Staining of mutant worms with anti-yolk protein antibodies has indicted that the proteins are not present in the mature oocytes. Moreover, green fluorescent protein expression was absence or reduced in cpi-2a/yp170:gfp mutant oocytes, although it was expressed in one of the successfully developed embryos. Based on these results, we hypothesize that the sterility in cpi-2a(ok1256) mutant worms is potentially caused by two possible mechanisms: 1) defects in the uptake and/or processing of yolk proteins by the growing oocytes and 2) indirect induction of defects in cell-cell signaling that is critical for promoting germ line development, oocyte maturation, ovulation, and fertilization. A defect in any of these processes would have detrimental effects on the development of normal embryos and consequently normal production of progenies as we observed in cpi-2a mutant worms. This is the first study that demonstrates the expression of cysteine proteases and their endogenous inhibitor in the gonadal sheath cells surrounding germ cells and oocytes, which indirectly have established their potential involvement in proteolytic processing of molecules within the gonadal sheath cells, such as components of the extracellular matrix or the cytoskeletal proteins, which are essential for proper cell-cell signaling activities of the gonadal sheath cells during normal maturation and ovulation processes.

Bmcystatin, a cysteine proteinase inhibitor characterized from the tick Boophilus microplus

The bovine tick Rhipicephalus (Boophilus) microplus is a blood-sucking animal, which is responsible for Babesia spp and Anaplasma marginale transmission for cattle. From a B. microplus fat body cDNA library, 465 selected clones were sequenced randomly and resulted in 60 Contigs. An open reading frame (ORF) contains 98 amino acids named Bmcystatin, due to 70% amino acid identity to a classical type 1 cystatin from Ixodes scapularis tick (GenBank Accession No. ). The Bmcystatin amino acid sequence analysis showed two cysteine residues, theoretical pI of 5.92 and M(r) of 11 kDa. Bmcystatin gene was cloned in pET 26b vector and the protein expressed using bacteria Escherichia coli BL21 SI. Recombinant Bmcystatin (rBmcystatin) purified by affinity chromatography on Ni-NTA-agarose column and ionic exchange chromatography on HiTrap Q column presented molecular mass of 11 kDa, by SDS-PAGE and the N-terminal amino acid sequenced revealed unprocessed N-terminal containing part of pelB signal sequence. Purified rBmcystatin showed to be a C1 cysteine peptidase inhibitor with K(i) value of 0.1 and 0.6 nM for human cathepsin L and VTDCE (vitellin degrading cysteine endopeptidase), respectively. The rBmcystatin expression analyzed by semi-quantitative RT-PCR confirmed the amplification of a specific DNA sequence (294 bp) in the fat body and ovary cDNA preparation. On the other hand, a protein band was detected in the fat body, ovary, and the salivary gland extracts using anti-Bmcystatin antibody by Western blot. The present results suggest a possible role of Bmcystatin in the ovary, even though the gene was cloned from the fat body, which could be another site of this protein synthesis.

Cathepsin D-mediated yolk protein degradation is blocked by acid phosphatase inhibitors

Vitellin (VT) is a lipoglycophosphoprotein stored inside the eggs of every oviparous organism during oogenesis. In the blood-sucking bug Rhodnius prolixus, VT is deposited inside growing oocytes together with two acid hydrolases: acid phosphatase (AP) and cathepsin D (CD). Egg fertilization triggers AP activity and VT proteolysis in vivo [Insect Biochem. Mol. Biol. 2002 (32) 847]. Here, we show that CD is the main protease targeting VT proteolysis during egg development. CD activity in total egg homogenates is blocked by the classical aspartyl protease inhibitor, pepstatin A. Surprisingly, AP inhibitors such as NaF, Na+/K+ tartrate, and inorganic phosphate also block VT proteolysis, whereas this effect is not observed when tyrosine phosphatase inhibitors such as vanadate and phenylarsine oxide or an inhibitor of alkaline phosphatases such as levamisole are used in a VT proteolysis assay. NaF concentrations that block isolated AP activity do not affect the activity of partially purified CD. Therefore, a specific repressor of VT proteolysis must be dephosphorylated by AP in vivo. In conclusion, these results demonstrate for the first time that acid hydrolases act cooperatively to promote yolk degradation during egg development in arthropods.

Cathepsin L protease (CPL-1) is essential for yolk processing during embryogenesis in Caenorhabditis elegans

Cysteine proteases are involved in the degradation of intracellular and extracellular proteins, although their precise roles in vivo are not well understood. Here we characterise a genetic mutant of the Caenorhabditis elegans cathepsin L protease gene cpl-1. CPL-1 is provided maternally and is essential for C. elegans embryogenesis. Immunofluorescence and electron microscopy data show that yolk endocytosis and initial yolk platelet formation occur normally in cpl-1 mutant oocytes and embryos. However, at around the 8-12 cell stage of embryogenesis, yolk platelets begin to aggregate and these enlarged yolk platelets fill the cytoplasm of cpl-1 mutant embryos. Coincident with this aggregation is loss of fluorescence from a yolk green fluorescent protein (YP170::GFP). This suggests that loss of CPL-1 activity leads to aberrant processing and/or conformational changes in yolk proteins, resulting in abnormal platelet fusion. This study has relevance to the abnormal fusion and aggregation of lysosomes in cathepsin L-deficient mice and to other lysosomal disorders.

Venomous protease of aphid soldier for colony defense

In social aphids, morphological, behavioral, and physiological differences between soldiers and normal insects are attributed to differences in gene expression between them, because they are clonal offspring parthenogenetically produced by the same mothers. By using cDNA subtraction, we identified a soldier-specific cysteine protease of the family cathepsin B in a social aphid, Tuberaphis styraci, with a second-instar soldier caste. The cathepsin B gene was specifically expressed in soldiers and first-instar nymphs destined to be soldiers. The cathepsin B protein was preferentially produced in soldiers and showed a protease activity typical of cathepsin B. The cathepsin B mRNA and protein were localized in the midgut of soldiers. For colony defense, soldiers attack enemies with their stylet, which causes paralysis and death of the victims. Notably, after soldiers attacked moth larvae, the cathepsin B protein was detected from the paralyzed larvae. Injection of purified recombinant cathepsin B protein certainly killed the recipient moth larvae. From these results, we concluded that the cathepsin B protein is a major component of the aphid venom produced by soldiers of T. styraci. Soldier-specific expression of the cathepsin B gene was found in other social aphids of the genus Tuberaphis. The soldier-specific cathepsin B gene showed an accelerated molecular evolution probably caused by the action of positive selection, which had been also known from venomous proteins of other animals.

Proteolytic activity of Boophilus microplus Yolk pro-Cathepsin D (BYC) is coincident with cortical acidification during embryogenesis

In a previous report (Parasitology 116 (1998) 525) we isolated and characterized Boophilus Yolk pro-Cathepsin (BYC), an aspartic proteinase precursor from the eggs of the hard tick. The present study was designed to characterize the function of BYC in the consumption of vitellin (VT), the major yolk protein, during embryogenesis. Both purified BYC and total egg homogenate proteolytic activity showed a similar pH dependence profile with an acidic optimum. Purified BYC presented higher activity against VT as a substrate when compared to other proteins. The VT degradation pattern observed in vitro also showed a similar profile to that observed in vivo. Co-localization of BYC and acidic cortical yolk granules was performed by immunocytochemistry and confocal microscopy. Proton-pumping activity of yolk granules in vitro was higher in eggs collected 4 day after oviposition than in newly laid eggs. Taken together, our data suggest that BYC plays a major role in the degradation of VT and that its activity is controlled by acidification of yolk platelets localized at the cortical cytoplasm of the developing Boophilus microplus egg.

Vitellin cleavage products are proteolytically degraded by ubiquitination in stick insect embryos

Vitellin polypeptides are proteolytically processed in ovarian follicles and embryos of the stick insect Carausius morosus. Data show that vitellin polypeptide A(3) of 54kDa is processed to yield polypeptide A(3)(*) of about 48kDa upon completion of ovarian development, whereas vitellin polypeptide A(2) of 90kDa yields polypeptide E(9) during embryonic development. As vitellin polypeptides are processed, polypeptides A(3)(*) and E(9) are transferred from the yolk granules to the cytosolic space of the vitellophages and start to express a ubiquitin reactivity. At the confocal microscope, anti-ubiquitin antibodies label specifically numerous small yolk granules and the cytosolic space of vitellophages. During embryonic development, ubiquitin carrying granules undergo acidification in much the same way as larger yolk granules. However, only these latter organelles are capable of converting a latent cysteine pro-protease into an active yolk protease upon acidification of their luminal space. These data are interpreted as indicating that ubiquitin-like polypeptides are restricted to small granules throughout ovarian and embryonic development, and that vitellin cleavage products are ubiquitinated following acidification of large yolk granules and transfer to the cytosolic space of the vitellophages.

In vivo activation of pro-form Bombyx cysteine protease (BCP) in silkmoth eggs: localization of yolk proteins and BCP, and acidification of yolk granules

The present study was designed to investigate the process of acidification of yolk granules during embryogenesis. In oocytes of mature Bombyx mori silkmoth, yolk proteins and a cysteine protease (pro-form BCP) were found in yolk granules. BCP was localized in small sized yolk granules (SYG, 3-6 microm in diameter) and yolk proteins in large sized granules (LYG, 6-11 microm in diameter), which might result in a spatial separation of protease and its substrates to avoid unnecessary hydrolysis. The granules were isolated on Percoll density gradient centrifugation. Although separation of LYG and SYG was incomplete, the granules sedimented in different fractions when using unfertilized egg extract, in which LYG was recovered from heavier fractions and BCP from lighter fractions. Acid phosphatase, as well as other lysosomal marker enzymes tested, was recovered from LYG-containing fractions. When extracts were prepared from developing eggs (day 3), some BCP-containing granules co-sedimented with LYG. The inactive pro-form BCP was activated in vivo, in parallel with yolk protein degradation, and as demonstrated previously in vitro under acidic conditions (). These results suggest that acidification occurs in yolk granules during embryogenesis. This was also confirmed using acridine orange fluorescent dye. In early development, most yolk granules were neutral, but became acidic during embryonic development. SYG were progressively recovered in heavier density fractions, displaying acidic interior. In this fraction, BCP-containing granules seem to be associated with larger granules (6-11 microm in size). In addition, SYG (BCP containing granules) were likely to be acidified earlier than LYG. Our results suggest that acidification initiates yolk degradation through activation of pro-form BCP.

Molecular cloning and characterization of the cathepsin B-like proteinase from the cotton boll worm, Helicoverpa armigera

An enzyme purified from the ovaries of Helicoverpa armigera, as an active form with molecular mass of 30 kDa on SDS-PAGE, was identified as a cysteine proteinase because it could be inhibited by E-64, a specific inhibitor of cysteine proteinase, and required reducing conditions for activity. This enzyme was further identified as a cathepsin B-like cysteine proteinase by partial amino acid sequencing. A cDNA encoding this proteinase was cloned from H. armigera, using degenerate primers and RACE techniques. Results of Northern blots indicated that the mRNA encoding the proteinase was transcribed in the ovaries, the fat bodies of female and male adults, pupae and in the larvae. No mRNA was detected from the larval epidermis or from the midgut. Hence, transcription of the cathepsin B-like cysteine proteinase from H. armigera was tissue-specific, but not gender- or developmental stage-specific. However, proteolytic activities were only detected from ovaries, and adult female and male fat bodies. No activity was observed from pupal and larval fat bodies, from the larval epidermis or from the midgut. Only one form of mRNA of approximately 1100 bases was detected, and in situ hybridization showed that the transcripts were distributed in the adult female fat bodies, follicular cells and the oocytes. Since the proteinase expressed in ovaries was able to degrade vitellin in vitro, it may be involved in the degradation of vitellin during embryonic development.

Binding and storage of heme by vitellin from the cattle tick, Boophilus microplus

We have previously shown (, Curr. Biol. 9, 703-706) that the cattle tick Boophilus microplus does not synthesize heme, relying solely on the recovery of the heme from the diet to make all its hemeproteins. Here we present evidence that Vitellin (VN(1)), the main tick yolk protein, is a reservoir of heme for embryo development. VN was isolated from eggs at different days throughout embryogenesis. Immediately after oviposition, Boophilus VN contains approximately one mol of heme/mol of protein. During embryo development about one third of egg VN is degraded. The remaining VN molecules bind part of the heme released. These results suggest that VN functions as a heme reservoir, binding any free heme that exceeds the amount needed for development. In vitro measurement of the binding of heme to VN showed that each VN molecule binds up to 31 heme molecules. The association of heme with VN strongly inhibits heme-induced lipid peroxidation, suggesting that binding of heme is an important antioxidant mechanism to protect embryo cells from oxidative damage. This mechanism allows this hematophagous arthropod to safely store heme obtained from a blood meal inside their eggs for future use. Taken together our data suggest that, besides its known roles, VN also plays additional functions as a heme deposit and an antioxidant protective molecule.

Oocyte fertilization triggers acid phosphatase activity during Rhodnius prolixus embryogenesis

Acid phosphatase activity, previously identified in Rhodnius prolixus oocytes, was studied during egg development. Fertilized eggs exhibited a five fold increase of total acid phosphatase activity during the first days of development. In contrast non-fertilized oviposited eggs showed no activation of this enzyme. An optimum pH of 4.0 for pNPP hydrolysis in a saturable linear reaction and a strong inhibition by lysosomal acid phosphatase inhibitors such as NaF (10 mM) and Na(+)/K(+) tartrate (0.5 mM) are the major biochemical properties of this enzyme. Fractionation of egg homogenates through gel filtration chromatography revealed a single peak of activity with a molecular mass of 94 kDa. The role of this enzyme in VT dephosphorylation was next evaluated. Western blots probed with anti-phosphoserine polyclonal antibody demonstrated that VT phosphoaminoacid content decreases during egg development. In vivo dephosphorylation during egg development was confirmed by following the removal of (32)P from (32)P-VT in metabolically labeled eggs. Vitellin was the only phosphorylated molecule able to inhibit pNPPase activity of partially purified acid phosphatase. These data indicate that acid phosphatase activation follows oocyte fertilization and this enzyme seems to be involved in VT dephosphorylation.

Vitellin polypeptide pathways in late insect yolk sacs

A panel of monoclonal antibodies was raised against late yolk sacs of the stick insect Carausius morosus and tested by immunoblotting to establish the extent vitellin polypeptides are processed proteolytically during embryonic development. Cryosections of late yolk sacs were also examined by confocal laser microscopy to determine how vitellin cleavage products become spatially distributed amongst yolk granules during the same developmental period. Distinct labelling patterns were obtained on yolk granules depending on: (1) the nature of the proteolytic processing; (2) the origin of vitellin cleavage products; and ultimately (3) their molecular sizes. Monoclonal antibodies raised against vitellin cleavage products resulting from proteolytic processing appeared to label: (1) the entire volume of many yolk granules; (2) their limiting membrane; or (3) a number of small vesicles interposed between larger yolk granules. On the other hand, monoclonal antibodies against vitellin cleavage products that remain invariant throughout development appeared to label either the serosa membrane or the cytosolic space comprised between adjacent yolk granules. Data are interpreted as indicating that vitellin cleavage products may leak out from the yolk granules, gain access to the cytosolic space of the vitellophages and eventually percolate through the serosa membrane enclosing the yolk sac.

Functional mechanics of the plant defensive Griffonia simplicifolia lectin II: resistance to proteolysis is independent of glycoconjugate binding in the insect gut

Griffonia simplicifolia lectin II (GSII) is a plant defensive protein that significantly delays development of the cowpea bruchid Callosobruchus maculatus (F.). Previous structure/function analysis by site-directed mutagenesis indicated that carbohydrate binding and resistance to insect gut proteolysis are required for the anti-insect activity of this lectin. However, whether there is a causal link between carbohydrate binding and resistance to insect metabolism remains unknown. Two proteases principally responsible for digestive proteolysis in third and fourth instar larvae of C. maculatus were purified by activated thiol sepharose chromatography and resolved as cathepsin L-like proteases, based on N-terminal amino acid sequence analysis. Digestion of bacterially expressed recombinant GSII (rGSII) and its mutant protein variants with the purified gut proteases indicates that carbohydrate binding, presumably to a target ligand in insect gut, and proteolytic resistance are independent properties of rGSII, and that both facilitate its efficacy as a plant defensive molecule.

Preoviposition activation of cathepsin-like proteinases in degenerating ovarian follicles of the mosquito Culex pipiens pallens

Within developing ovaries of many insects, some developing follicles or oocytes usually degenerate (follicular atresia or oosorption), while the others may continue to grow to maturity, thus maintaining the balance between the number of eggs and reproductive circumstances such as available nutrients. To help clarify the phenomenon of follicular atresia during ovarian development, we examined cysteine proteinases stored in mosquito Culex pipiens pallens ovaries. First, analysis using synthesized substrates showed that cathepsin B- and L-like proteinases gradually accumulated in the developing ovaries after a blood meal, which required more than 10 min of preincubation under acidic conditions to reach their maximum activities. However, homogenates of degenerating follicles 3 days after feeding showed proteolytic activities without acid treatment, suggesting that the proteinases had already been activated, while the extract of normally developing follicles collected from the same ovaries required more than 10 min of acid preincubation to reach the optimum activities, suggesting that the enzymes remained as inactive forms. Chemical and immunohistochemical analyses showed that more proteinases are located in the cytoplasm, rather than being associated with yolk granules. Ovarian proteinases, which are believed to become activated at the onset of embryogenesis, should also be activated during oogenesis, presumably to enhance oosorption.

Is the unique negatively charged polypeptide of crayfish yolk HDL a component of crustacean vitellin?

The yolk protein of Cherax quadricarinatus contains six major high-density lipoprotein (HDL) subunits with the approximate molecular masses of 177, 155, 106, 95, 86, and 75 kDa, of which only the 106-kDa polypeptide is negatively charged. On the basis of their molecular weights, time of appearance and disappearance, their floating density and susceptibility to enzyme degradation (by a serine proteinase), these six HDL polypeptides were classified into two subgroups. One group comprises the higher-molecular-weight compounds above 106 kDa, and the other includes the lower-molecular-weight compounds up to 95 kDa. Other than being different from the lower-molecular-weight polypeptides, the negatively charged 106-kDa polypeptide was significantly different from members of its higher-molecular-weight group belonging to a different, less abundant, yolk protein as shown by HPLC separation. Immunological studies and peptide mapping in which the 106-kDa polypeptide did not show similarity to any of the other HDL components confirmed these differences. Moreover, the amino acid composition of the 106-kDa polypeptide was different from that of known vitellin from other crustacean species. This unique negatively charged polypeptide presents an enigma as it is known to be a secondary vitellogenic-related HDL polypeptide, immunolocalized in yolk globules; however, it is different to all the other HDL polypeptides, thus presenting the question whether it is indeed a component of "classical" crustacean vitellin.

Yolk utilization in stick insects entails the release of vitellin polypeptides into the perivitelline fluid

This study investigates the developmental fate of vitellin (Vt) polypeptides generated by limited proteolysis in an insect embryo. To this end, a number of polyclonal (pAb) and monoclonal antibodies (mAb) were raised against the yolk sac and the perivitelline fluid of late embryos of the stick insect Carausius morosus. Two dimensional immuno gel electrophoresis and Western blotting demonstrate that polypeptides resulting from Vt processing are present both in the yolk sac and the perivitelline fluid. At the confocal microscope, different labelling patterns were detected in the ooplasm depending on the stage of development attained by the embryo. At early developmental stages, label is associated with large unsegmented portions of the fluid ooplasm. During embryonic development, the fluid ooplasm is gradually transformed into yolk granules by intervention of vitellophages. Prior to dorsal closure, the yolk sac is separated from the perivitelline fluid by interposition of serosa cells (the so called serosa membrane). Several mAbs raised against the perivitelline fluid react specifically with this membrane suggesting that the release of Vt polypeptides from the yolk sac occurs by intracellular transit through the serosa cells. By immunocytochemistry, gold label appears associated with the cell surface and a number of vacuoles of the serosa membrane. These data are interpreted as suggesting that Vt polypeptides resulting from limited proteolysis in stick insect embryos are not exhaustively degraded within the yolk sac, but are instead transferred transcytotically to the perivitelline fluid through the serosa membrane.

Cloning and functional expression of a Boophilus microplus cathepsin L-like enzyme

A cysteine proteinase gene homologous to cathepsins L genes was isolated from a B. microplus cDNA library. The precursor protein deduced from the nucleotide sequence contains 332 amino acid residues consisting of a signal sequence (pre-region), a pro-region and a mature proteinase. The DNA fragment coding for the proenzyme was cloned and expressed using the E. coli expression vector pMAL-p. The recombinant protein (MBP+PROCP) once activated is able to hydrolyze synthetic substrates as well as protein substrates like hemoglobin, vitellin and gelatin. Its optimal enzymatic activity on both fluorogenic and protein substrates was found to occur at an acidic pH. Expression of the proteinase gene was tested by RT-PCR with tick larvae RNA. Detection of amplified sequences indicates that the gene is expressed at this stage of the tick life cycle and the molecule is therefore potentially a target for chemotherapy or an immunogen in a vaccine.

Proteome analysis of Oncorhynchus species during embryogenesis

To understand the molecular mechanisms underlying normal and abnormal development of two salmonids, masu salmon (Oncorhynchus masou) and rainbow trout (O. mykiss), we used two-dimensional (2-D) electrophoresis to construct a series of 2-D maps during the embryonic period. We identified all visible protein spots on the 2-D map by assigning numbers for masu salmon and rainbow trout, and we determined N-terminal sequences of proteins for one hundred of the spots, that appear at very high concentrations in the whole embryos of masu salmon and rainbow trout. We also characterized embryonic stages according to the periods of appearance of spots. Most of the N-terminal sequences were identical or at least highly similar to partial sequences reported for vitellogenin (Vtg) of O. mykiss. A potential proteolytic processing of Vtg for rainbow trout is discussed in relation to the time of appearance and relative position of Vtg fragments within the complete protein sequence.

Molecular cloning of cDNAs encoding a range of digestive enzymes from a phytophagous beetle, Phaedon cochleariae

To gain better knowledge of the variety of digestive enzymes in phytophagous coleopteran pests, a sequencing screen of 76 random cDNAs from a gut library from Phaedon cochleariae larvae was performed. The screen yielded 21 cDNAs encoding amino-acid sequences homologous to known digestive enzymes, most of them were cell wall-hydrolysing enzymes. The deduced protein sequences of 7 cDNAs encoding putative alpha-amylase, cysteine proteinase, trypsin, chymotrypsin, cellulase, pectinase and xylanase display all the structural features that characterize these enzymes in other eukaryotic organisms. Except the alpha-amylase and chymotrypsin cDNAs, the other cDNAs probably derive from multigene families. The distribution of the corresponding enzymatic activities at various developmental stages of P. cochleariae was examined. alpha-amylase activity is present in guts of larvae and adults, proteinases are abundant in guts of larvae and adults, but scarce in eggs and larval carcasses, xylanases are present in the guts of larvae and adults, as well as in carcasses of larvae, whereas cellulase and pectinase activities are distributed in larval and adult guts, larval carcasses, and eggs. Only a minor fraction of the cellulases is secreted by microorganisms, suggesting that P. cochleariae synthesizes most of its own cell-wall hydrolysing enzymes. The physiological role of the enzymes is discussed, as well as the significance of these results for pest management strategies involving transgenic plants expressing enzyme inhibitors.

Mosquito cathepsin B-like protease involved in embryonic degradation of vitellin is produced as a latent extraovarian precursor

Here we report identification of a novel member of the thiol protease superfamily in the yellow fever mosquito, Aedes aegypti. It is synthesized and secreted as a latent proenzyme in a sex-, stage-, and tissue-specific manner by the fat body, an insect metabolic tissue, of female mosquitoes during vitellogenesis in response to blood feeding. The secreted, hemolymph form of the enzyme is a large molecule, likely a hexamer, consisting of 44-kDa subunits. The deduced amino acid sequence of this 44-kDa precursor shares high similarity with cathepsin B but not with other mammalian cathepsins. We have named this mosquito enzyme vitellogenic cathepsin B (VCB). VCB decreases to 42 kDa after internalization by oocytes. In mature yolk bodies, VCB is located in the matrix surrounding the crystalline yolk protein, vitellin. At the onset of embryogenesis, VCB is further processed to 33 kDa. The embryo extract containing the 33-kDa VCB is active toward benzoyloxycarbonyl-Arg-Arg-para-nitroanilide, a cathepsin B-specific substrate, and degrades vitellogenin, the vitellin precursor. Both of these enzymatic activities are prevented by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64), a thiol protease inhibitor. Furthermore, addition of the anti-VCB antibody to the embryonic extract prevented cleavage of vitellogenin, strongly indicating that the activated VCB is involved in embryonic degradation of vitellin.

Vitellin processing and protein synthesis during cricket embryogenesis

At the start of insect embryogenesis most of the protein mass of the egg cytoplasm exists as vitellin (Vt) obtained endocytically during vitellogenesis. Of the new embryo polypeptides (EP) appearing in the egg during embryogenesis, many are synthesized de novo, while, in some species, others derive from developmentally programmed partial proteolysis of Vt. Earlier we showed that by the end of vitellogenesis the two native Vts in Acheta domesticus exist in opposing gradients along the longitudinal axis of the egg. Here we hypothesize that this ooplasmic Vt distribution presents a milieu for Vt processing out of which region-specific regulatory molecules could arise. The metabolic origin and stage-specific patterns of seven predominant EPs (EP 1-7) identified by SDS-PAGE were examined and the results correlated with developmental morphology during the 14 days of embryogenesis. Based on antibody reactivity, peptide mapping and in vitro radiolabeling, we determined that EPs 1-3, 6 and 7 are Vt-derived, while EPs 4 and 5 are produced de novo by the embryo. The five Vt-derived EPs appear during the first 24 h of embryogenesis when migrating cleavage nuclei and associated cytoplasm form the cellular blastoderm, and levels of EPs 4 and 5 increase during days 4-6 of embryogenesis when katatrepsis and yolk mass contraction occur. Positive periodic acid-Schiff staining indicated that EPs 1-3 and their Vt-precursor polypeptides are glycoproteins. This work shows that developmental stage-specific Vt processing occurs during A. domesticus embryogenesis and points next to investigation of the functional significance of Vt cleavage products during development.

Mono- and polyclonal antibodies as probes to study vitellin processing in embryos of the stick insect Carausius morosus

During embryonic development, insect vitellins (Vt) are degraded by limited proteolysis to yield a number of lower-molecular weight polypeptides. The aim of the present study was to identify these polypeptides in the embryo and to verify how they relate to Vt polypeptides deposited in the oocyte during vitellogenesis. To this end a panel of poly- and monoclonal antibodies (Pab, Mab) was raised against Vt polypeptides and employed by immunoelectrophoresis and immunoblotting on embryos belonging to different developmental stages. Through this approach three major staining patterns were observed. First, Mab 4 reacts with both polypeptides B1 and E20, suggesting that polypeptide B1 is gradually trimmed to yield polypeptide E20 in late embryos. Second, Mab 12 is specific for polypeptide A3 which is retained unchanged throughout embryogenesis. Third, Pab anti-A2 and Mab 13 show that polypeptide A2 is processed to yield polypeptide E9 through limited proteolysis. In conclusion, the staining patterns reported in this study show that Vt polypeptides in developing embryos of the stick insect Carausius morosus undergo at least two major processing events concerning polypeptides B1 and A2.

Localization of the proenzyme form of the vitellin-processing protease in Blattella germanica by affinity-purified antibodies

During Blattella germanica embryo development, the nutritive yolk protein vitellin is processed by a cysteine protease, which is activated proteolytically from a proprotease during acidification of yolk granules. A murine polyclonal antiserum was generated with the purified proprotease as the immunogen. The antiserum was made monospecific to proprotease by subtractive affinity chromatography using proprotease-free yolk proteins as ligand. The purified antibodies were employed to investigate the temporal and spatial expression of the proprotease during vitellogenesis and embryo development. Anti-proprotease-reactive peptides appeared in extracts of fat bodies and ovarian follicles of post-mating females, but not in fat bodies of males or the fat bodies or follicles of unmated females, suggesting that the proprotease is synthesized extraovarially. Use of the antibodies was extended to monitor the kinetics of proprotease disappearance during early embryo development.