Neb-colloostatin, a second folliculostatin of the grey fleshfly, Neobellieria bullata

Disruption of insect immunity using analogs of the pleiotropic insect peptide hormone Neb-colloostatin: a nanotech approach for pest control II

This work continues our studies on the pleiotropic activity of the insect peptide Neb-colloostatin in insects. In vivo immunological bioassays demonstrated that hemocytotoxic analogs of Neb-colloostatin injected into Tenebrio molitor significantly reduced the number of hemocytes in the hemolymph and impaired phagocytosis, nodulation and phenoloxidase activities in the insects. Among the analogs tested, [Ala¹]-,[Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin were particularly potent in disrupting cellular immunity in larvae, pupae and adult insects. This result suggests that the most effective analogs showed increases in the bioactivity period in the hemolymph of insects when compared to Neb-colloostatin. Recently, we demonstrated that it is possible to introduce Neb-colloostatin through the cuticle of an insect into the hemolymph when the peptide is coupled with nanodiamonds. In this study, we showed that [Ala¹]-, [Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin, when complexed with nanodiamonds, may also pass through the cuticle into the hemolymph and induce long-term impairments of immunity in T. molitor at all developmental stages. Studies on the tissue selectivity and effectiveness of Neb-colloostatin analogs and efficient methods for their introduction into insects may contribute to the development of eco-friendly pest control methods based on bioactive peptidomimetics.

Impairment of the immune response after transcuticular introduction of the insect gonadoinhibitory and hemocytotoxic peptide Neb-colloostatin: A nanotech approach for pest control

This article shows that nanodiamonds can transmigrate through the insect cuticle easily, and the doses used were not hemocytotoxic and did not cause inhibition of cellular and humoral immune responses in larvae, pupae and adults of Tenebrio molitor. The examination of the nanodiamond biodistribution in insect cells demonstrated the presence of nanodiamond aggregates mainly in hemocytes, where nanoparticles were efficiently collected as a result of phagocytosis. To a lesser extent, nanodiamond aggregates were also detected in fat body cells, while they were not observed in Malpighian tubule cells. We functionalized nanodiamonds with Neb-colloostatin, an insect hemocytotoxic and gonadoinhibitory peptide, and we showed that this conjugate passed through the insect cuticle into the hemolymph, where the peptide complexed with the nanodiamonds induced apoptosis of hemocytes, significantly decreased the number of hemocytes circulating in the hemolymph and inhibited cellular and humoral immune responses in all developmental stages of insects. The results indicate that it is possible to introduce a peptide that interferes with the immunity and reproduction of insects to the interior of the insect body by means of a nanocarrier. In the future, the results of these studies may contribute to the development of new pest control agents.

Peptide hormones regulate the physiological functions of reproductive organs in Tenebrio molitor males

In insects, the majority of studies have been conducted on the hormonal regulation of female reproduction. Thus far, little is known about the regulation of male reproductive physiology, especially by peptide hormones. We report here, for the first time in insects, the effects of three peptides, Neb-colloostatin (SIVPLGLPVPIGPIVVGPR), Neb-TMOF (NPTNLH) and Lepde-NPF-I (ARGPQLRLRFa), on various aspects of reproduction in male Tenebrio molitor beetles. All three tested peptides increased the soluble protein concentration in the testes and the dry mass of the beetle's testes. They also significantly changed the protein profiles of the testes. Injection of these peptides also significantly changed the number of sperm cells in the testes. However, the observed effects were age specific. The most prominent changes were observed in 4-day-old males. Neb-colloostatin and Neb-TMOF decreased the number of sperm cells, whereas Lepde-NPF-I increased the number of spermatocytes. Moreover, in vitro experiments revealed that Neb-TMOF and Lepde-NPF-I increased the contractility of the ejaculatory duct of T. molitor males. The results obtained suggest that different reproductive processes in males might be regulated by complex mechanisms.

The natural insect peptide Neb-colloostatin induces ovarian atresia and apoptosis in the mealworm Tenebrio molitor

Background

The injection of Neb-colloostatin into T. molitor females causes gonadoinhibitory effects on ovarian development. This peptide inhibits intercellular space formation (patency) in follicular epithelium and results in slowed vitellogenesis, delayed ovulation, reduced number of eggs laid and presumably cell death in the terminal follicles. However, as does the form of cell death in the terminal follicle, the mode of action of Neb-colloostatin remains unknown.

Results

We tested Neb-colloostatin for a sterilizing effect on females of Tenebrio molitor. We report that injection of nanomolar doses of Neb-colloostatin induce ovarian follicle atresia in 4-day old females during their first gonadotropic cycle. Light microscope observations revealed morphological changes in the ovary: after Neb-colloostatin injection the terminal oocytes are significantly smaller and elicit massive follicle resorption, but the control terminal follicles possess translucent ooplasm in oocytes at different stages of vitellogenesis. A patency is visible in follicular epithelium of the control vitellogenic oocytes, whereas peptide injection inhibits intercellular space formation and, in consequence, inhibits vitellogenesis. Confocal and electron microscope examination showed that peptide injection causes changes in the morphology indicating death of follicular cells. We observed F-actin cytoskeleton disorganization, induction of caspase activity, changes in chromatin organization and autophagic vacuole formation. Moreover, the apical cytoplasm of follicular cells is filled with numerous free ribosomes, probably indicating a higher demand for protein biosynthesis, especially in preparation for autophagic vacuole formation. On the other hand, the process of polyribosomes formation is inhibited, indicating the contributing effect of this hormone.

Conclusion

Neb-colloostatin induces atresia in the mealworm ovary. Degeneration of T. molitor follicles includes changes in morphology and viability of follicular cells, and oosorption as a consequence of these changes.

The pro-apoptotic action of new analogs of the insect gonadoinhibiting peptide Neb-colloostatin: synthesis and structure-activity studies

Neb-colloostatin (SIVPLGLPVPIGPIVVGPR), an insect oostatic factor found in the ovaries of the flesh fly Neobellieria bullata, strongly induces apoptosis in insect haemocytes. To explain the role of Ser(1) and Pro(4) residues of Neb-colloostatin in the pro-apoptotic activity of this peptide, the synthesis of a series of analogs was performed, such as: [Ac-Ser(1)]- (1), [d-Ser(1)]- (2), [Thr(1)]- (3), [Asp(1)]- (4), [Glu(1)]- (5), [Gln(1)]- (6), [Ala(1)]- (7), [Val(1)]- (8), [d-Pro(4)]-(9), [Hyp(4)]- (10), [Acp(4)]- (11), [Ach(4)]- (12), [Ala(4)]- (13), [Ile(4)]- (14), and [Val(4)]-colloostatin (15). All peptides were bioassayed in vivo for the pro-apoptotic action on haemocytes of Tenebrio molitor. Additionally, the structural properties of Neb-colloostatin and its analogs were examined by the circular dichroism in water and methanol. Peptides 1, 4, 5, 7, 8, 10, 12, 14, and 15 strongly induce T. molitor haemocytes to undergo apoptosis and they show about 120-230% of the Neb-colloostatin activity at a dose of 1nM. The CD conformational studies show that the investigated peptides seem to prefer the unordered conformation.

Oostatic peptides

Oostatic peptides are organic molecules, which influence an insect reproduction due to a regulation of the eggs development. It was proved that decapeptide-H-Tyr-Asp-Pro-Ala-Pro-Pro-Pro-Pro-Pro-Pro-OH (YDPAPPPPPP)-isolated from mosquito Aedes aegypti, inhibits trypsin activity in the midgut of the mosquito. Therefore, it was named trypsin-modulating oostatic factor (Aea-TMOF). Feeding the recombinant cells with cloned and expressed TMOF on the coat protein of tobacco mosaic virus (TMV) to mosquito larvae, caused larval mortality. The TMOF was therefore designed for usage as a new biorational insecticide against mosquito. Similarly, a hexapeptide-H-Asn-Pro-Thr-Asn-Leu-His-OH (NPTNLH)-was isolated from the grey flesh fly Neobellieria bullata. This peptide and some of its analogs inhibited trypsin-like synthesis by the midgut in female flies and was therefore entitled Neb-TMOF. Interestingly, the synthetic Aea-TMOF and mainly its C-terminus shorten analogs, including those containing D-amino acids or methylene-oxy isosteric bond, quickly and strongly inhibited the hatchability and egg development in the flesh fly N. bullata.

The pro-apoptotic action of the peptide hormone, Neb-colloostatin, on insect haemocytes

The gonadoinhibitory peptide hormone, Neb-colloostatin, was first isolated from ovaries of the flesh fly Neobellieria bullata. This 19-mer peptide is thought to be a cleaved product of a collagen-like precursor molecule that is formed during remodelling of the extracellular matrix. In this study, we report that upon injection of pico- and nanomolar doses, this peptide exerts a pro-apoptotic action on haemocytes of Tenebrio molitor adults, as visualized by changes in morphology and viability. The F-actin cytoskeleton was found aggregating into distinctive patches. This may be responsible for the observed inhibition of adhesion of haemocytes and for the stimulation of filopodia formation. However, Neb-colloostatin injection did not induce the formation of authophagic vacuoles. Our results suggest that physiological concentrations of Neb-colloostatin may play an important role in controlling the quantity and activity of haemocytes in insect haemolymph. They also suggest that in periods that Neb-colloostatin is released, this peptide may cause a weakening of the insects' immune system. This is the first report that exposure to a peptide hormone causes apoptosis in insect haemocytes.

Ecdysteroids, juvenile hormone and insect neuropeptides: Recent successes and remaining major challenges

In the recent decade, tremendous progress has been realized in insect endocrinology as the result of the application of a variety of advanced methods in neuropeptidome- and receptor research. Hormones of which the existence had been shown by bioassays four decades ago, e.g. bursicon (a member of the glycoprotein hormone family) and pupariation factor (Neb-pyrokinin 2, a myotropin), could be identified, along with their respective receptors. In control of diurnal rhythms, clock genes got company from the neuropeptide Pigment Dispersing Factor (PDF), of which the receptor could also be identified. The discovery of Inka cells and their function in metamorphosis was a true hallmark. Analysis of the genomes of Caenorhabditis elegans, Drosophila melanogaster and Apis mellifera yielded about 75, 100 and 200 genes coding for putative signaling peptides, respectively, corresponding to approximately 57, 100 and 100 peptides of which the expression could already be proven by means of mass spectrometry. The comparative approach invertebrates-vertebrates recently yielded indications for the existence of counterparts in insects for prolactin, atrial natriuretic hormone and Growth Hormone Releasing Hormone (GRH). Substantial progress has been realized in identifying the Halloween genes, a membrane receptor(s) for ecdysteroids, a nuclear receptor for methylfarnesoate, and dozens of GPCRs for insect neuropeptides. The major remaining challenges concern the making match numerous orphan GPCRs with orphan peptidic ligands, and elucidating their functions. Furthermore, the endocrine control of growth, feeding-digestion, and of sexual differentiation, in particular of males, is still poorly understood. The finding that the prothoracic glands produce an autocrine factor with growth factor-like properties and secrete proteins necessitates a reevaluation of their role in development.

Insect gonadotropic peptide hormones: some recent developments

Gonadotropic peptides are a new generation of peptide hormone regulators of insect reproduction. They have been isolated from ovaries, oviducts, or brains of insects. The subject of this paper is insect peptides that exert stimulatory or inhibitory effects on ovarian development and oocyte maturation. On the basis of the literature data and the results of our investigations, the structure and biological properties of different groups of peptides are presented.

Gonadoinhibitory effects of Neb-colloostatin and Neb-TMOF on ovarian development in the mealworm, Tenebrio molitor L

The gonadostatic action of the peptides Neb-colloostatin (SIVPLGLPVPIGPIVVGPR) and Neb-TMOF (NPTNLH) from Neobellieria bullata was studied in female mealworm Tenebrio molitor. Both peptides potently inhibit ovarian development and terminal oocyte maturation of mated females during their first reproductive cycle. Injection of 4 mug of Neb-colloostatin or Neb-TMOFNeb-TMOF reduced, at day 4 of the cycle, the size of the terminal oocytes to about half or one third of the normal size in saline-injected controls. In addition, follicular patency was arrested. The injections of Neb-colloostatin and Neb-TMOF also caused a delay to the first ovulation and oviposition as well as a reduction of the number of eggs by about 50% in the first 3 days of the oviposition period. At 4 days after adult emergence, none of the peptides had caused significant changes in protein concentration or composition of the haemolymph. However, both peptides reduced total protein content in ovaries and induced qualitative changes in ovarian protein patterns. Electrophoretic analyses indicated that Neb-colloostatin and Neb-TMOF caused a loss of two proteins (150, 180 kDa) and a drastic reduction of 4 others (39, 43, 47, 130 kDa), which are the most abundant ones in ovaries of control females. On the other hand, they increased the concentration of 2 other polypeptides (65, 70 kDa), which normally occur in insignificant quantities in ovaries. Our results indicate that both peptides have a very similar mode of action despite the differences in their amino acid sequence. They seem to interfere with vitellogenin production by the fat body as well as with vitellogen uptake by the oocytes through modification of patency.

The NMDA receptor antagonist MK-801 inhibits vitellogenesis in the flesh fly Neobellieria bullata and in the desert locust Schistocerca gregaria

We found that in the flesh fly Neobellieria bullata, vitellogenesis can be inhibited in a dose-dependent way by two injections of 60 microg MK-801/g body mass. In the desert locust Schistocerca gregaria, vitellogenesis can also be fully inhibited but only by repeated injections of 200-400 microg/g body mass. In this species, the inhibition can be overruled by coapplication of juvenile hormone. Vitellogenin bands remained visible in electropherograms of hemolymph of MK-801-treated female locusts, but vitellogenin did not accumulate as might be expected when only its uptake by the oocytes, and not its synthesis by the fat body, would be affected. Whether MK-801 acts by inhibiting juvenile hormone synthesis by the corpora allata remains to be investigated.

Isolation and characterization of an angiotensin converting enzyme substrate from vitellogenic ovaries of Neobellieria bullata

Vitellogenic ovaries of the gray fleshfly Neobellieria bullata contain a variety of unidentified substances that interact, either as a substrate or as an inhibitor, with angiotensin converting enzyme (ACE). We here report the isolation and characterization of the first ACE interactive compound hereof. This 1312.7 Da peptide with the sequence NKLKPSQWISL, is substrate to both insect and human ACE. It is a novel peptide that shows high sequence similarity to a sequence at the N-terminal part of dipteran yolk polypeptides (YPs). We propose to call it N. bullata ovary-derived ACE interactive factor or Neb-ODAIF. Both insect and human ACE hydrolyze Neb-ODAIF by sequentially cleaving off two C-terminal dipeptides. K(m) values of Neb-ODAIF and Neb-ODAIF(1-9) (NKLKPSQWI) for human somatic ACE (sACE) are 17 and 81 microM, respectively. Additionally, Neb-ODAIF(1-7) (NKLKPSQ) also interacts with sACE (K(m/i)=90 microM). These affinity-constants are in range with those of the physiological ACE substrates and suggest the importance of Neb-ODAIF and its cleavage products in the elucidation of the physiological role of insect ACE. Alternatively, they can serve as lead compounds in the development of new drugs against ACE-related diseases in humans.

Characterization of four substrates emphasizes kinetic similarity between insect and human C-domain angiotensin-converting enzyme

Angiotensin converting enzyme (ACE) was already discovered in insects in 1994, but its physiological role is still enigmatic. We have addressed this problem by purifying four new ACE substrates from the ovaries of the grey fleshfly, Neobellieria bullata. Their primary structures were identified as NKLKPSQWISLSD (Neb-ODAIF-1(1-13)), NKLKPSQWI (Neb-ODAIF-1(1-9)), SLKPSNWLTPSE (Neb-ODAIF-2) and LEQIYHL. Database analysis showed significant homology with amino acid sequence stretches as present in the N-terminal part of several fly yolk proteins. An antiserum raised against Neb-ODAIF-1(1-9) immunostained one out of three yolk protein bands of SDS/PAGE-separated fly haemolymph and egg homogenate, thus confirming that these peptides originate from a yolk protein gene product. Kinetic analysis of these peptides and of the peptides Neb-ODAIF and Neb-ODAIF-1(1-7) with insect ACE and human ACE show both similar and unique properties for insect ACE as compared with human C-domain ACE.

Led-NPF-1 stimulates ovarian development in locusts

For more than a decade, immunohistochemical results on FMRFamide related peptides (FaRP's) have been reported extensively, suggesting many possible roles for these peptides associated with behavioural and physiological events as well as reproduction. This study provides a clear effect in vivo of members of this family of insect neuropeptides. The effect of two neuropeptide F-related peptides from the Colorado potato beetle, Leptinotarsa decemlineata, Led-NPF-1 and Led-NPF-2 as well as the locusts myotropins, Lom-PK-1, Lom-PK-2 and Lom-SK, was screened in an ovarian development assay in the African migratory locust and the grey fleshfly, Neobellieria bullata. Led-NPF-1 (Ala-Arg-Gly-Pro-Gln-Leu-Arg-Leu-Arg-Phe-NH2) was shown to be a potent gonadostimulin in Locusta migratoria, but not in Neobellieria bullata. A minimal dose of 0.05 microg of Led-NPF-1 per animal, every 12 h, during 5 consecutive injections into 6 day old virgin females, could accelerate egg development. Higher doses of prolonged injections were demonstrated to be even more potent in the ovarian development assay. Led-NPF-2 (Ala-Pro-Ser-Leu-Arg-Leu-Arg-Phe-NH2) was far less active. The other tested peptides scored no reproducible effect what so ever on ovarian growth, in locusts, nor in flies. The gonadotropic action of a NPF-like peptide on oocyte growth implies a complex regulation of oogenesis in the locust and adds to our knowledge of insect neuroendocrinology in general. The results also suggest that a peptide of similar sequence also resides in the locust.

"Insects do not have sex hormones": a myth?

Mammals have two genes (SRY and DMT1) for testis formation-androgenesis, an anti-testis gene, DAX1, an anti-Müllerian duct hormone, and steroid sex hormones. Drosophila uses the sex-lethal, transformer, and doublesex genes for sexual differentation and is supposed to lack sex hormones. However, the statement that insects do not have sex hormones loses much of its credibility if one considers (1) the classical endocrinological work on sexual differentiation in the firefly Lampyris and in the hevea tussock moth Orgyia; (2) the recent identification of an androgenic hormone and its role in sex determination in the isopod Armadillidium; (3) the similarity between steroidogenic factor 1 (SF-1) of mammals and fushi tarazu factor 1 (FTZ-F1) of Drosophila; and (4) the steroidogenic effect of gonadotropins secreted by the brain of female locusts and mosquitoes and of male gypsy moth. In our model, based on data from the literature, ecdysone, when present in high concentrations, might function as an androgenic sex steroid. It is also the precursor of 20-OH-ecdysone, which is the moulting hormone of insects, and in vitellogenic females of many species, the counterpart of estrogens as well. Other gender-specific hormones are likely to exist in the brain-gonad axis.

Reproduction and love: strategies of the organism's cellular defense system?

A novel view is presented which states that primordial germ cells and their descendants can be regarded as 'cancerous cells' which emit signals that activate a whole array of cellular defensive mechanisms by the somatoplasm. These cells have become unrestrained in response to the lack of typical cell adhesion properties of epithelial cells. From this point of view: (1) the encapsulation of oocytes by follicle cells, vitelline membrane and egg shell; (2) the suppression of gonadal development in larval life; (3) the production of sex steroid hormones and of vitellogenin; and (4) the expulsion of the gametes from the body fit into a general framework for a defense strategy of the somatoplasm against germ line cells. Accordingly, the origin of sexual reproduction appears to be a story of failure and intercellular hostility rather than a 'romantic' and altruistic event. Yet, it has resulted in evolutionary success for the system in which it has evolved; probably through realizing feelings of 'pleasure' associated with reproduction.

Biological activity of structural analogs and effect of oil as a carrier of trypsin modulating oostatic factor of the gray fleshfly Neobellieria bullata

The trypsin modulating oostatic factor from the gray fleshfly Neobellieria bullata (Neb-TMOF) is released from the ovary at the end of vitellogenesis and inhibits trypsin biosynthesis in the midgut. This inhibition indirectly results in an arrest of oocyte growth. Additional experiments with N. bullata were performed to characterize its trypsin modulating and oostatic properties in more detail. After suspending the peptide in wheat germ oil, the threshold dose for oostatic activity was lowered one thousand times (2.10(-5) in oil versus 2.10(-2) pmoles per fly in Ringer). By use of the Neobellieria trypsin biosynthesis assay, 17 analogs of the hexapeptide were tested for inhibitory activity. The following structural elements were demonstrated to be critical for biological activity: the alcohol function at position 3 (Thr residue); a positively charged basic group at the C terminus (His residue); and the Asn side chain at positions 1 and 4.

Hormones and the cytoskeleton of animals and plants

It is often overlooked that a cell can exert its specific functions only after it has acquired a specific morphology: function follows form. The cytoskeleton plays an important role in establishing this form, and a variety of hormones can influence it. The cytoskeletal framework has also been shown to function in a variety of cellular processes, such as cell motility (important for behavior), migration (important for the interrelationship between the endocrine and immune systems, e.g., chemotaxis), intracellular transport of particles, mitosis and meiosis, maintenance of cellular morphology, spatial distribution of cell organelles (e.g., nucleus and Golgi system), cellular responses to membrane events (e.g., endocytosis and exocytosis), intracellular communication including conductance of electrical signals, localization of mRNA, protein synthesis, and--more specifically in plants--ordered cell wall deposition, cytoplasmic streaming, and spindle function followed by phragmoplast function. All classes of hormones seem to make use of the cytoskeleton, either during their synthesis, transport, secretion, degradation, or when influencing their target cells. In this review special attention is paid to cytoskeleton-mediated effects of selected hormones related to growth, transepithelial transport, steroidogenesis, thyroid and parathyroid functioning, motility, oocyte maturation, and cell elongation in plants.

Folliculostatins, gonadotropins and a model for control of growth in the grey fleshfly, Neobellieria (sarcophaga) bullata

The sequences of two folliculostatic peptides of the fleshfly Neobellieria bullata have been determined recently. The first peptide (Neb-TMOF: H-NPTNLH-OH), originates from a 75 kDa precursor protein found in vitellogenic oocytes. The hexapeptide directly inhibits the synthesis of trypsin-like enzymes in the gut, and thus lowers the concentration of yolk polypeptides in the hemolymph. It also inhibits the biosynthesis of ecdysone in the larval ring gland. Therefore, it could also be named prothoracicostatic hormone (Neb-PTSH). The second peptide (Neb-colloostatin: H-SIV-PLGLPVPIGPIVVGPR-OH) acts on previtellogenic follicles and is a cleaved product of a collagen-like precursor molecule. Our results indicate that peptides that are cleaved from matrix proteins could act as growth-inhibiting factors. Gonadotropin releasing hormone (GnRH)-immunolike peptides were not identified, but progress is being made in the isolation and characterization of factors which stimulate cAMP production by the ovary. Using these results, a novel model of growth control in which matrix proteins play an important role as a potential source of growth regulators has been developed.