Presence of Bombyxin-(4K-PTTH)-Like Molecules in Neurosecretory Granules of Brain-Corpora Cardiaca Complexes ofLocusta migratoriaDevelopmental Aspects

The effects of acute exposure to magnetic fields on morphometric characteristics of bombyxin-producing neurosecretory neurons in gypsy moth caterpillars

PURPOSE

To examine the effects of acute exposure to strong static magnetic fields and extremely low frequency magnetic fields, on neurosecretory neurons which synthesise insulin-like neurohormone.

MATERIALS AND METHODS

Immunocytochemical detection of bombyxin-like material in the protocerebral neurosecretory neurons of Lymantria dispar caterpillars was performed using a monoclonal antibody directed against a synthetic dekapeptide corresponding to the N-terminus of the bombyxin A-chain. Caterpillars were exposed to strong static magnetic fileds (235 mT) and extremely low frequency magnetic fields (2 mT) for three days after moulting into the 4th instar.

RESULTS

We report the presence of immunoreactive molecules in A2 type of medial neurosecretory neurons (nsn) in caterpillars' brain of L. dispar. The three-day exposure of caterpillars to stresogenic external magnetic fields changed the size of A2 type nsn, their nuclei and the intensity of protein band in the region of bombyxin molecular mass (4-6 kD) after exposure to extremely low frequency magnetic fields in comparison to control group and group treated by strong static magnetic fields.

CONCLUSION

These are the first data on the influence of external magnetic fields on the polyphagous phytophagous forest pest L. dispar L. (Lepidoptera: Lymantridae) indicating an intensive synthesis of insulin-like neurosecretory material.

Molecular characterization of insulin-like peptides in the yellow fever mosquito, Aedes aegypti: expression, cellular localization, and phylogeny

Insulin-like peptides are key regulators of metabolism, reproduction, and senescence in higher eukaryotic organisms. Here we present the identification, expression, and tissue localization of eight genes encoding insulin-like peptides (ILPs) in the yellow fever mosquito, Aedes aegypti. All eight ILPs share the conserved features of the insulin superfamily as prepropeptides consisting of contiguous signal, B, C, and A peptides. However, one of the ILPs has a truncated C peptide and a carboxy terminal extension, features consistent with insulin growth factors. Transcripts for five of the ILPs occurred predominantly in the heads (brains) of larval, pupal, and adult mosquitoes. Transcripts of two other genes, one of which was the putative insulin growth factor, were present in the head, thorax and abdomens of all stages. The final ILP was predominantly expressed in abdomen. Results from immunocytochemistry with two different ILP antisera showed cellular localizations in the nervous system and midgut that corroborated the existence of these expression patterns. Three of the ILP genes are so closely linked that only the 5' region of the first ILP gene likely suffices as a promoter, indicating that these genes form a eukaryotic operon. The nearly identical expression pattern of these three ILPs supported this idea. Finally, the phylogenetic relationship of ILPs from three dipteran species, Ae. aegypti, the African malaria mosquito (Anopheles gambiae), and Drosophila melanogaster is presented as a step towards understanding the structural and functional diversity of insect ILPs.

Molecular characterization of insulin-like peptide genes and their expression in the African malaria mosquito, Anopheles gambiae

Of the seven genes encoding insulin-like peptides (ILPs) in the mosquito, Anopheles gambiae, four are arrayed proximally as duplicate pairs on chromosome three. Amino acid substitutions encoded in the duplicate genes occur in the C peptide and not the B and A peptides. Except for one duplicated gene, sequence-specific transcripts for all other AgamILPs were obtained from female mosquitoes. Transcript expression of each AgamILP was determined by RT-PCR in the head, thorax, and abdomen of all life stages and both sexes of this mosquito. Two AgamILPs were ubiquitously expressed, suggesting a growth factor function, whereas the other AgamILPs were expressed primarily in heads, as confirmed by the immunostaining of ILPs in the neurosecretory cells of female brains, thus indicating a hormonal function.

Glucose stimulates the release of bombyxin, an insulin-related peptide of the silkworm Bombyx mori

The effects of starvation and feeding on the release of bombyxin, a peptide of insulin superfamily in insects, from the larval brain of the silkworm Bombyx mori were investigated. Following starvation, the bombyxin titer in the hemolymph of larvae decreased, whereas its content in the brain increased. On the other hand, refeeding of the starved larvae resulted in an increase in the hemolymph bombyxin titer and a rapid decrease in the hormone level in the brain. These results indicate that the release of bombyxin from the brain is suppressed by starvation and stimulated by feeding. The hemolymph glucose titer also changed sharply upon starvation and refeeding, and a close relationship was observed between the changes in glucose concentrations and bombyxin titers in the hemolymph. The injection of glucose into starved larvae could mimic the effect of refeeding on the release of bombyxin, suggesting that glucose serves as the signal for the "fed" state of the animal. It is likely that glucose is a common nutritional signal for inducing the release of mammalian and insect insulins.

Ecdysteroidogenic action of Bombyx prothoracicotropic hormone and bombyxin on the prothoracic glands of Rhodnius prolixus in vitro

An in-vitro assay for ecdysteroid synthesis by the prothoracic glands (PGs) of fifth instar Rhodnius prolixus has been employed to evaluate the actions of prothoracicotropic neuropeptides from the silkmoth, Bombyx mori. Crude prothoracicotropic hormone (PTTH) extracts of recently emerged adult brain complexes of Bombyx induced a dose-dependent stimulation of ecdysteroid synthesis by Rhodnius PGs, which was similar to that obtained using crude Rhodnius PTTH. In both cases, maximum stimulation was obtained with one brain equivalent. Rhodnius PGs were then challenged with incremental doses of recombinant Bombyx PTTH and synthetic bombyxin-II. Dose-response curves for the action of both peptides on Rhodnius PGs were very similar to those obtained for their action on the pupal PGs of Bombyx in vitro. Bombyx PTTH stimulated the PGs of Rhodnius at concentrations comparable to those effective on Bombyx. The curve for Bombyx PTTH showed a steep ascending region from 3 to 8ng/ml and a sharp peak. For bombyxin, concentrations 40-fold higher were required to elicit the same amount of stimulation as obtained using Bombyx PTTH. Therefore, Rhodnius PGs possess recognition sites for both Bombyx PTTH and bombyxin. This is the first study of the ecdysteroidogenic properties of the Bombyx peptides on a heterologous species. It is suggested that the function and conformation of PTTH may be conserved between distantly related insect groups.

Life cycle expression of a bombyxin-like neuropeptide in the tobacco hornworm, Manduca sexta

Immunocytochemistry was used to investigate the developmental expression of the insulin-like neuropeptide bombyxin in the tobacco hornworm, Manduca sexta. A mouse monoclonal antibody raised against a synthetic peptide corresponding to bombyxin's A-chain N-terminus was used to localize a bombyxin-like peptide to a group of cerebral medial neurosecretory cells, the M-NSC IIa(2). Immunostaining was first detected on day 0 of the second larval instar, localized in the M-NSC IIa(2) somata and in the neurohemal organ, the corpora allata (CA). By day 0 of the fourth larval instar, the peptide was present throughout the M-NSC IIa(2) somata, axons, dendritic fields and CA. Between days 7 and 9 of the fifth instar, a dramatic reduction in the dendritic fields and CA staining occurred, suggesting the peptide is released. After day 2 of the pupal period, only M-NSC IIa(2) somata immunostained, a pattern that persisted through day 2 of the adult stage. The specificity of immunostaining was demonstrated by using a synthetic bombyxin peptide to block staining. These developmental data reveal times of potential Manduca bombyxin-like peptide release which should provide insight into the peptide's function.

Insulin receptor-like tyrosine kinase in the tobacco hornworm, Manduca sexta

Phosphotyrosine-containing proteins are present in the prothoracic glands, muscle, and fat body of Manduca sexta, as determined by immunoprecipitation followed by kinase assay, and by Western blotting. One such protein (M(r) 178,000) can also be immunoprecipitated using antibodies directed against the human insulin receptor and insulin receptor substrate. The 178 kD protein appears to be expressed more strongly in prothoracic glands removed just prior to wandering (days 3-4) and prior to pupation (days 7-9), and phosphorylation of the protein is enhanced by an M. sexta brain factor. The results suggest that a tyrosine-kinase-linked molecule similar to the insulin receptor may play a regulatory role in M. sexta.

Neuropeptides and related nucleic acid sequences detected in peneid shrimps by immunohistochemistry and molecular hybridizations

The neurosecretory cells in the eyestalks of Penaeus indicus and P. vannamei were studied by immunocytochemistry using polyclonal antisera raised against purified Homarus americanus neuropeptides. Cross-reactions between two H. americanus anti-crustacean hyperglycemic hormone antisera and Penaeus neurosecretory material were observed. The specific anti-vitellogenesis inhibiting hormone antiserum only showed an immunological reaction in the nervous tract and the sinus gland of Penaeus, suggesting a progressive exposure of a characteristic epitope which was amenable to immunological detection. Molecular hybridizations were performed in P. indicus and P. vannamei with a digoxigenin tailed 23mer oligonucleotide probe deduced from two partial sequences of uncharacterized, purified P. duorarum neuropeptides. Two distinct clusters of positive cells were observed by in situ hybridization experiments in the medulla terminalis ganglionic X-organ. Classical control tests gave negative results. Northern and Southern blot analyses were performed with the same tailed probed and allowed the determination of molecular weights for the mRNA and for a DNA restriction fragment (Pst 1), 1.7 kb and 200 bp, respectively. These observations show the existence of a strong homology between the P. duorarum sequence (selected for synthesizing the probe), and some P. indicus and P. vannamei neuropeptide sequence(s). Heterologous antisera were tested in other Arthropods to complete our analyses. In the centipede Lithobius forficatus and the scorpion Euscorpius carpathicus, the anti-crustacean hyperglycemic hormone antiserum induced a strong cross-reaction. A monoclonal anti-bombyxin-1 antiserum showed an immunoreaction in the neurosecretory system of the insects Tenebrio molitor and Labidura riparia. In contrast, the anti-bombyxin-1 antiserum did not react either in Penaeus or in Lithobius, and the Homarus hyperglycemic hormone antiserum did not react in the insects that were tested. A comprehensive view of these observations is discussed in relation to a divergence in Arthropod evolution.

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust, Locusta migratoria. A comparison with neuroparsin and insulin-related peptide

Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A1 cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A2 cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.

Insulin-like immunoreactivity and molting in Rhodnius prolixus

Two prominent cells were observed when fifth stage Rhodnius female larval brains were stained with anti-insulin serum. The staining intensity of these cells varied during the instar, being lowest on Day 1 and Days 5 and 6 after feeding. Injection of anti-insulin serum into 5th stage larvae immediately after feeding and on Days 4 and 5 in females and on Days 5 and 6 in males prevented molting. Control antiserum had no effect on the molting process. Injections at other times during the instar had no effect unless serum was injected just prior to ecdysis. Control or anti-insulin serum injected at this time disrupted normal ecdysis. These results are discussed in terms of the control of the developmental program of the insect.

Isolation and structure of two novel 6-kDa dimeric peptides from the corpora cardiaca of the insect Locusta migratoria. Molecular mass determination by mass spectrometry

We have isolated two major 6-kDa peptides from extracts of corpora cardiaca of adult females of Locusta migratoria. These peptides have been characterized by peptide sequencing and liquid secondary-ion mass spectrometry. They are structurally related dimers, one (6278.5 Da) being a homodimer (A-A chains), the other (6280.5 Da) being a heterodimer (A-B chains). A 60% similarity exists between the A and B chains. Both peptides have been chemically synthesized and the synthetic compounds appeared to be identical to the native ones. Polyclonal antibodies raised against each of these peptides demonstrated that they were contained within the secretory granules of the intrinsic cells of the glandular lobes of the corpora cardiaca. The physiological significance of these two peptides is unknown but, using the synthetic peptides, we are currently probing their biological role.