Occurrence of vitellogenin in drone honeybees (Apis mellifica)

Expression and function of the vitellogenin receptor in the hypopharyngeal glands of the honey bee Apis mellifera (Hymenoptera: Apidae) workers

The vitellogenin receptor (VgR) is essential for the uptake and transport of the yolk precursor, vitellogenin (Vg). Vg is synthesized in the fat body, released in the hemolymph, and absorbed in the ovaries, via receptor-mediated endocytosis. Besides its important role in the reproductive pathway, Vg occurs in nonreproductive worker honey bee, suggesting its participation in other pathways. The objective was to verify if the VgR occurs in the hypopharyngeal glands of Apis mellifera workers and how Vg is internalized by these cells. VgR occurrence in the hypopharyngeal glands was evaluated by qPCR analyses of VgR and immunohistochemistry in workers with different tasks. The VgR gene is expressed in the hypopharyngeal glands of workers with higher transcript levels in nurse honey bees. VgR is more expressed in 11-day-old workers from queenright colonies, compared to orphan ones. Nurse workers with developed hypopharyngeal glands present higher VgR transcripts than those with poorly developed glands. The immunohistochemistry results showed the co-localization of Vg, VgR and clathrin (protein that plays a major role in the formation of coated vesicles in endocytosis) in the hypopharyngeal glands, suggesting receptor-mediated endocytosis. The results demonstrate that VgR performs the transport of Vg to the hypopharyngeal glands, supporting the Ovary Ground Plan Hypothesis and contributing to the understanding of the role of this gland in the social context of honey bees.

Queen Caging and Oxalic Acid Treatment: Combined Effect on Vitellogenin Content and Enzyme Activities in the First Post-Treatment Workers and Drones, Apis mellifera L

Varroa destructor is a mite causing serious damage to western honey bees. Managed colonies require artificial varroa control, which may be best obtained by combining mechanical and chemical methods. This study explored the possible effects of the combination of queen caging and oxalic acid treatment on the immune system (glucose oxidase, phenoloxidase, and vitellogenin) and antioxidant enzymes (superoxide dismutase, catalase, and glutathione S transferase) of first post-treatment generation drones and workers (newly emerged, nurses, and foragers). The combination of queen caging and oxalic acid treatment caused a decrease in glucose oxidase activity only in drones. This could cause issues of cuticular sclerotization, making a drone prone to bite injuries, dehydration, and pathogens. No differences in phenoloxidase activity were recorded in both post-treatment drones and workers generation. Among worker bees, the treatment determined a lower vitellogenin content in newly emerged bees while the result was higher in nurse bees. However, the treatment did not significantly affect the antioxidant enzymes activity in either drones or workers. The results obtained in this investigation suggest that the combined anti-varroa treatments had no negative effects on oxidative stress in the first post-treatment generation bees, while effects did occur on the immune system. Further investigations on the potential effects of glucose oxidase decrease in drones and vitellogenin content variation in workers are desirable.

Vitellogenin and Vitellogenin-Like Genes in the Brown Planthopper

Vitellogenin (Vg) is precursor of vitellin. Here, we identified a Vg (NlVg) and two Vg-likes (NlVg-like1 and NlVg-like2) in the brown planthopper, Nilaparvata lugens. Phylogenetic analyses showed that NlVg-like1 and NlVg-like2 are not clustered with the conventional insect Vgs associated with vitellogenesis. Temporo-spatial expression analyses showed that the NlVg and NlVg-like2 transcript levels increased significantly 24 h after emergence and were primarily expressed in female adults. However, NlVg-like1 was expressed during all stages, and in both genders. Tissue-specific analyses showed that all three genes were most highly expressed in the fat body. The injection of double-stranded RNA targeting NlVg showed that NlVg is essential not only for oocyte development but also for nymph development. The knockdown of NlVg-like1 in female adults resulted in failure to hatch or death before eggshell emergence in 18% of offspring embryos, suggesting that NlVg-like1 plays an important role during late embryogenesis. Approximately 65% of eggs laid by females that were treated with double-stranded RNA targeting NlVg-like2 failed to hatch, indicating that NlVg-like2 plays a role in nutrition absorption during oocyte, or embryonic development. Our results illustrate the structural and functional differences among the Vg and Vg-like genes and provide potential targets for RNA-interference-based insect pest management strategies.

The Year of the Honey Bee (Apis mellifera L.) with Respect to Its Physiology and Immunity: A Search for Biochemical Markers of Longevity

It has been known for many years that in temperate climates the European honey bee, Apis mellifera, exists in the form of two distinct populations within the year, short-living summer bees and long-living winter bees. However, there is only limited knowledge about the basic biochemical markers of winter and summer populations as yet. Nevertheless, the distinction between these two kinds of bees is becoming increasingly important as it can help beekeepers to estimate proportion of long-living bees in hives and therefore in part predict success of overwintering. To identify markers of winter generations, we employed the continuous long-term monitoring of a single honey bee colony for almost two years, which included measurements of physiological and immunological parameters. The results showed that the total concentration of proteins, the level of vitellogenin, and the antibacterial activity of haemolymph are the best three of all followed parameters that are related to honey bee longevity and can therefore be used as its markers.

Dynamics of expression of two vitellogenin genes in the Chagas' disease vector Triatoma infestans: Analysis throughout pre-vitellogenesis and vitellogenesis

The reproductive success of all oviparous species depends on vitellogenin (Vg) biosynthesis and its accumulation in the developing oocytes. The expression levels of two Vg genes (Vg1 and Vg2) were analyzed by qPCR and western blot in fat body and ovaries of adult females, at different times after ecdysis (pre-vitellogenic phase) and after blood feeding of females (vitellogenic phase). Vg genes were also evaluated in fat bodies of adult males as well as in female fifth instar nymphs. No trace of Vg mRNA was detected in adult males or in nymphs. Vg1 and Vg2 were expressed in the fat bodies and ovaries of adult females. The Vg genes start to be expressed slightly in both tissues of adult females during pre-vitellogenesis. After blood feeding, Vg1 and Vg2 were up regulated and significant levels of Vg transcripts as well as protein expression were observed in fat bodies sampled throughout vitellogenesis. During this period however, the distribution patterns of Vg1 and Vg2 transcripts showed two peaks around early and advanced vitellogenesis (days 4 and 12 post-feeding, respectively). In the ovaries, levels of mRNAs increased from the day 10 post-blood feeding onwards. In addition, the immunofluorescence assays showed a strong signal for vitellin in the yolk bodies of terminal follicles of vitellogenic females. The involvement of fat body and ovary in the synthesis of Vg suggests different roles of Vgs in supporting the growth of oocytes.

Vitellogenin and vitellogenin receptor gene expression is associated with male and female parenting in a subsocial insect

Complex social behaviour in Hymenoptera has been hypothesized to evolve by co-opting reproductive pathways (the ovarian ground plan hypothesis, OGPH) and gene networks (the reproductive ground plan hypothesis, RGPH). In support of these hypotheses, in eusocial Hymenoptera where there is reproductive division of labour, the yolk precursor protein vitellogenin (Vg) influences the expression of worker social behaviour. We suggest that co-opting genes involved in reproduction may occur more generally than just in the evolution of eusociality; i.e. underlie earlier stages of social evolution such as the evolution of parental care, given that reproduction and parental care rarely overlap. We therefore examined vitellogenin (vg) gene expression associated with parental care in the subsocial beetle Nicrophorus vespilloides. We found a significant reduction in the expression of vg and its receptor, vgr, in head tissue during active parental care, and confirmed that the receptor is expressed in the brains of both sexes. Ours is the first study to show that vgr is expressed in the brain of a non-eusocial insect. Given the association between behaviour and gene expression in both sexes, and the presence of vitellogenin receptors in the brain, we suggest that Vg was co-opted early in the evolution of sociality to have a regulatory function. This extends the association of Vg in parenting to subsocial species and outside of the Hymenoptera, and supports the hypothesis that the OGPH is general and that heterochrony in gene expression is important in the evolution of social behaviour and precedes subsequent evolutionary specialization of social roles.

cDNA isolation and characterization of two vitellogenin genes in the Chagas' disease vector Triatoma infestans (Hemiptera, Reduviidae)

Two vitellogenin genes (Vg1 and Vg2) were identified in the Chagas' disease vector Triatoma infestans. The putative coding sequence corresponding to Vg2 was found to be 5553bp long, encoding 1851 amino acids in a single open reading frame. The comparative analysis of the deduced amino acid sequences from Vg1 and Vg2 cDNA fragments of T. infestans revealed 58.94% of identity with 76.43% of homology. The phylogenetic tree based on the complete Vg amino acid sequences of hemimetabolous insects unambiguously supported two clusters, one consisting of Vg sequences from dictyopteran and the other containing Vg sequences of hemipteran. The Vg1 and Vg2 mRNAs were detected in fat bodies and ovaries of adult females with the highest levels of both Vg transcripts in the first tissue. Quantitative PCR showed low expression of Vg2 in head and muscle of adult females, while the Vg1 transcript was not present in these organs. Neither Vg1 nor Vg2 was expressed in fifth instar nymph fat bodies or in adult male fat bodies, heads, and muscles.

Vitellogenin underwent subfunctionalization to acquire caste and behavioral specific expression in the harvester ant Pogonomyrmex barbatus

The reproductive ground plan hypothesis (RGPH) proposes that the physiological pathways regulating reproduction were co-opted to regulate worker division of labor. Support for this hypothesis in honeybees is provided by studies demonstrating that the reproductive potential of workers, assessed by the levels of vitellogenin (Vg), is linked to task performance. Interestingly, contrary to honeybees that have a single Vg ortholog and potentially fertile nurses, the genome of the harvester ant Pogonomyrmex barbatus harbors two Vg genes (Pb_Vg1 and Pb_Vg2) and nurses produce infertile trophic eggs. P. barbatus, thus, provides a unique model to investigate whether Vg duplication in ants was followed by subfunctionalization to acquire reproductive and non-reproductive functions and whether Vg reproductive function was co-opted to regulate behavior in sterile workers. To investigate these questions, we compared the expression patterns of P. barbatus Vg genes and analyzed the phylogenetic relationships and molecular evolution of Vg genes in ants. qRT-PCRs revealed that Pb_Vg1 is more highly expressed in queens compared to workers and in nurses compared to foragers. By contrast, the level of expression of Pb_Vg2 was higher in foragers than in nurses and queens. Phylogenetic analyses show that a first duplication of the ancestral Vg gene occurred after the divergence between the poneroid and formicoid clades and subsequent duplications occurred in the lineages leading to Solenopsis invicta, Linepithema humile and Acromyrmex echinatior. The initial duplication resulted in two Vg gene subfamilies preferentially expressed in queens and nurses (subfamily A) or in foraging workers (subfamily B). Finally, molecular evolution analyses show that the subfamily A experienced positive selection, while the subfamily B showed overall relaxation of purifying selection. Our results suggest that in P. barbatus the Vg gene underwent subfunctionalization after duplication to acquire caste- and behavior- specific expression associated with reproductive and non-reproductive functions, supporting the validity of the RGPH in ants.

One of the main features of social insects is the division of labor, whereby queens monopolize reproduction while sterile workers perform all of the tasks related to colony maintenance. The workers usually do so in an age-dependent sequence: young workers tend to nurse the brood inside the nest and older workers are more likely to forage for food. Previous studies revealed that vitellogenin, a yolk protein typically involved in the regulation of reproduction in solitary insects, has been co-opted to regulate division of labor in the honeybee. In this study, we investigate such a role of vitellogenin in another group of social insects: the ants. We first use phylogenetic analyses to reveal the existence of multiple vitellogenin genes in most of the sequenced ant genomes. Then we compare the expression of the two vitellogenin genes (Pb_Vg1 and Pb_Vg2) among queens, nurses and foragers in the seed-harvester ant Pogonomyrmex barbatus. Our results suggest that, after the initial duplication in ants, the vitellogenin genes acquired caste and behavioral specific expression associated with reproductive and non-reproductive nutritionally related functions. This study also shows that ants and bees, despite having evolved sociality independently, have conserved similar mechanisms to regulate division of labor.

The gene vitellogenin affects microRNA regulation in honey bee (Apis mellifera) fat body and brain

In honey bees, Vitellogenin (Vg) is hypothesized to be a major factor affecting hormone signaling, food-related behavior, immunity, stress resistance and lifespan. Likewise microRNAs play important roles in posttranscriptional gene regulation and affect many biological processes. The action of microRNAs and Vg are known to intersect in the context of reproduction; however, the role of these associations on social behavior is unknown. The phenotypic effects of Vg knockdown are best established and studied in the forager stage of workers. Thus, we exploited the well-established RNA interference (RNAi) protocol for Vg knockdown to investigate its downstream effects on microRNA population in honey bee foragers' brain and fat body tissue. To identify microRNAs that are differentially expressed between tissues in control and knockdown foragers, we used µParaflo® microfluidic oligonucleotide microRNA microarrays. Our results show 76 and 74 microRNAs were expressed in the brain of control and knockdown foragers whereas 66 and 69 microRNAs were expressed in the fat body of control and knockdown foragers respectively. Target prediction identified potential seed matches for a differentially expressed subset of microRNAs affected by Vg knockdown. These candidate genes are involved in a broad range of biological processes including insulin signaling, juvenile hormone (JH) and ecdysteroid signaling previously shown to affect foraging behavior. Thus, here we demonstrate a causal link between the Vg knockdown forager phenotype and variation in the abundance of microRNAs in different tissues with possible consequences for regulation of foraging behavior.

A vitellogenin polyserine cleavage site: highly disordered conformation protected from proteolysis by phosphorylation

Vitellogenin (Vg) is an egg-yolk precursor protein in most oviparous species. In honeybee (Apis mellifera), the protein (AmVg) also affects social behavior and life-span plasticity. Despite its manifold functions, the AmVg molecule remains poorly understood. The subject of our structure-oriented AmVg study is its polyserine tract - a little-investigated repetitive protein segment mostly found in insects. We previously reported that AmVg is tissue specifically cleaved in the vicinity of this tract. Here, we show that, despite its potential for an open, disordered structure, AmVg is unexpectedly resistant to trypsin/chymotrypsin digestion at the tract. Our findings suggest that multiple phosphorylation plays a role in this resilience. Sequence variation is highly pronounced at the polyserine region in insect Vgs. We demonstrate that sequence differences in this region can lead to structural variation, as NMR and circular dichroism (CD) evidence assign different conformational propensities to polyserine peptides from the honeybee and the jewel wasp Nasonia vitripennis; the former is extended and disordered and the latter more compact and helical. CD analysis of the polyserine region of bumblebee Bombus ignitus and wasp Pimpla nipponica supports a random coil structure in these species. The spectroscopic results strengthen our model of the AmVg polyserine tract as a flexible domain linker shielded by phosphorylation.

Vitellogenin gene expression in autogenous Culex tarsalis

Autogeny, the ability of a mosquito to mature an initial batch of eggs without blood feeding, is an alternative reproductive strategy with important implications for vector-borne disease transmission. Regulation of the major yolk protein (vitellogenin; Vg) genes during bloodmeal-induced oogenesis is well studied, but little is known about regulation of vitellogenesis in autogenous mosquitoes. We characterized the expression of four vitellogenin genes (Vg1a, Vg1b, Vg2a and Vg2b) in an autogenous strain of the West Nile Virus vector, Culex tarsalis. All vitellogenin genes were expressed during autogenous reproduction and following a bloodmeal, although the intensity and duration of expression varied amongst genes. Quantitative PCR analysis of vitellogenin transcription during autogeny revealed a similar temporal pattern to known vitellogenin expression profiles in anautogenous Aedes aegypti. Vitellogenin transcript, primarily produced from the Vg1b gene, was also detected in the larval and pupal stages of development, but no detectable vitellogenin protein was produced during this time period.

Molecular characteristics of insect vitellogenins

Vitellogenins (Vgs) are precursors of the major egg storage protein, vitellin (Vn), in many oviparous animals. Insects Vgs are large molecules ( approximately 200-kD) synthesized in the fat body in a process that involves substantial structural modifications (e.g., glycosylation, lipidation, phosphorylation, and proteolytic cleavage, etc.) of the nascent protein prior to its secretion and transport to the ovaries. However, the extent to which Vgs are processed in the fat body varies greatly among different insect groups. We provide evidence by cloning and peptide mapping of four Vg molecules from two cockroach species (Periplaneta americana and Leucophaea maderae) that, in hemimetabolous insects, the pro-Vg is cleaved into several polypeptides (ranging from 50-to 180-kD), unlike the holometabolans where the Vg precursor is cleaved into two polypeptides (one large and one small). An exception is the Vg of Apocrita (higher Hymenoptera) where the Vg gene product remains uncleaved. The yolk proteins (YPs) of higher Diptera (such as Drosophila) form a different family of proteins and are also not cleaved. So far, Vgs have been sequenced from 25 insect species; 9 of them belong to Hemimetabola and 16 to Holometabola. Alignment of the coding sequences revealed that some features, like the GL/ICG motif, cysteine residues, and a DGXR motif upstream of the GLI/CG motif, were highly conserved near the carboxy terminal of all insect Vgs. Moreover, a consensus RXXR cleavage sequence motif exists at the N-terminus of all sequences outside the Apocrita except for Lymantria dispar where it exists at the C-terminus. Phylogenetic analysis using 31 Vg sequences from 25 insect species reflects, in general, the current phylogenies of insects, suggesting that Vgs are still phylogenetically bound, although a divergence exists among them.

Evidence for two vitellogenin-related genes in Leucophaea maderae: the protein primary structure and its processing

We previously reported a cDNA for vitellogenin (Vg) from the cockroach, Leucophaea maderae (Lm). In the present study, we identified another cDNA encoding a second Vg (Vg2) having stretches of amino acid sequences different from the first one, Vg1, reported earlier. The complete nucleotide sequence of Vg2 consisted of 5,915 bp, which encoded a primary protein of 1,911 residues including a 16-residue putative signal peptide. The regions different in both Vg precursors (Pro-Vg1 and pro-Vg2) were four in number, and two, relatively longer, existed at the carboxy terminal. The presence of two Vg-related cDNAs was confirmed by sequencing of RT-PCR products generated using primers designed based on the common sequences flanking the regions different in amino acid sequences. Both forms were transcribed since they could be amplified on mRNA from fat bodies of different individual females. Southern blot analysis of digested genomic DNA revealed the existence of two Vg-related genes in L. maderae indicating that each Vg cDNA originated from a separate gene. Also, the immunoblot analysis using antibodies generated against peptides unique to both Vg1 and Vg2 probed the same antigen in the same individual, suggesting LmVg to be a product coded by two different Vg precursors. Both Vg primary products showed 96% similarity at an amino acid level. Compared to other insect Vgs, Vg2 showed a slightly higher (1-2%) similarity than Vg1. We previously reported, based on amino-terminal sequence analysis, that L. maderae pro-Vg was cleaved into four subunit polypeptides (112-, 100-, 92-, and 55-kD), which were deposited in the egg as four respective vitellin (Vn) polypeptides. We show now based on immunoblot analysis that the 112-kD polypeptide is further cleaved, near the C-terminus, to an 87-kD polypeptide before it is secreted into the hemolymph. Both the L. maderae Vgs were compared with each other and with other insect Vgs and the processing pattern is discussed.

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.

Vitellogenin expression in queen ovaries and in larvae of both sexes of Apis mellifera

In the honeybee, Apis mellifera, vitellogenin (Vg) expression has been detected in the ovary of queens, but not in that of workers. In addition, larvae of both sexes produce Vg in significant amounts, which suggest that Vg serves for functions additional to oocyte growth and energy supply to the embryo. In vivo hormone treatment experiments suggest that the decrease of 20-hydroxyecdysone concentration occurring in previtellogenic phases allows Vg production. Southern analysis indicates that the Vg gene is present as a single copy in the honeybee genome.

The vitellogenin of the honey bee, Apis mellifera: structural analysis of the cDNA and expression studies

The cDNA of Apis mellifera vitellogenin was cloned and sequenced. It is 5440 bp long and contains an ORF of 1770 amino acids (including a putative signal peptide of 16 residues). The deduced amino acid sequence shows significant similarity with other hymenopteran vitellogenins (58% with Pimpla nipponica and 54% with Athalia rosae). The alignment with 19 insect vitellogenins shows a high number of conserved motifs; for example, close to the C-terminus there is a GL/ICG motif followed by nine cysteines, as occurs in all hymenopteran species, and, as in other insect vitellogenins, a DGXR motif is located 18 residues upstream the GL/ICG motif. Phylogenetic analysis of vitellogenin sequences available in insects gave a tree that is congruent with the currently accepted insect phylogenetic schemes. Using two fragments of the vitellogenin cDNA as probes, we analyzed by Northern blot the sex- and caste-specific patterns of vitellogenin expression in pupae and adults of A. mellifera. In queens, vitellogenin mRNA was first detected in mid-late pupal stage, whereas in workers it was first detected in late pupal stage. Vitellogenin mRNA was also observed in drones, although it was first detected not in pupae but in freshly molted adults.

Characterization of vitellogenin in the red imported fire ant, Solenopsis invicta (Hymenoptera: Apocrita: Formicidae)

Vitellin (VN) and vitellogenin (VG) profiles were analyzed in monogyne and polygyne colonies of the red imported fire ant, Solenopsis invicta. Non-denaturing and SDS-polyacrylamide gel electrophoresis (PAGE) analyses indicated that the native VN was likely 350 kDa and comprised of two subunits in the molecular size range of 170-185 kDa. SDS-PAGE of hemolymph showed that the relative mobilities and subunit patterns of VG and VN were similar. VG was present in the hemolymph of reproductive queens; alate, virgin queens; and workers, but not in males. Anti-VN, prepared from polygyne egg homogenates, reacted with egg homogenates and with hemolymph VG from reproductive, monogyne and polygyne queens and alate, virgin polygyne queens. Analysis of circulating VG and ovarian development in alate, virgin queens showed that low levels of VG appeared by five days following adult eclosion, but egg development was not observed until seven weeks. VG was evident in newly inseminated queens, and increased steadily for the first three weeks following dealation. VG levels declined slightly near eclosion of the first workers (= nanitics) and dropped sharply after nanitic emergence at five weeks following dealation. Oocyte maturation peaked at days 15-25 following dealation, but otherwise remained low but steady. These studies provide the basis for future investigations into endocrine regulations of vitellogenesis in S. invicta queens.

Cloning of cDNA for vitellogenin of the parasitoid wasp, Pimpla nipponica (Hymenoptera: Apocrita: Ichneumonidae): vitellogenin primary structure and evolutionary considerations

The cDNA for vitellogenin (Vg) of the parasitoid wasp Pimpla nipponica (Hymenoptera: Apocrita) was cloned and sequenced. The deduced amino acid sequence with 1807 residues was obtained. The N-terminal 20 amino acids chemically determined for vitellin (Vn) agreed completely with the deduced 20 amino acids that follow the 16 amino acid residues for putative signal peptide. The cDNA clone for the Vg of the turnip sawfly Athalia rosae (Hymenoptera: Symphyta), previously obtained and partially sequenced, was also completely sequenced and the amino acid sequence deduced. Amino acid sequences were compared between these two species and also with known Vg sequences from other insects. Common to all these insects is the presence of two long regions with relatively well-conserved amino acid sequences, one near the N-terminal extending 267-282 residues (including two cysteines at conserved locations), and the other starting at position 450 to 655 and extending 279-283 residues, and of a region at the C-terminal extending some 200 residues (about 250 in Aedes aegypti due to the presence of a serine-rich stretch) with 10 cysteines at conserved locations. A molecular phylogenetic tree was constructed.