Search PubMed⌕ Search

Biomedical subjects

A De Loof

Publications and source records attributed to A De Loof.

At least 127 records · Page 7Linked to original sources
PubMed1991

Synthesis and metabolism of vertebrate-type steroids by tissues of insects: a critical evaluation.

This review covers the synthesis and the metabolism of vertebrate-type steroids (progesterone, testosterone, estradiol, corticosteroids) by insect tissues and discusses the significance of the reactions for insect physiology. Biosynthesis of vertebrate-type steroids from cholesterol hitherto has been demonstrated in only two insect species, i.e. the water beetle Acilius sulcatus (Coleoptera) and the tobacco hornworm Manduca sexta (Lepidoptera). In Acilius, steroid synthesis is associated with exosecretion (chemical defense). Nothing, however, is known about a physiological role of the C21 steroid conjugate present in ovaries and eggs of Manduca. No synthesis of vertebrate-type steroids was observed in any other insect investigated to date. Most metabolic conversions of steroids by insects concerned oxidoreduction of oxygen groups (hydroxysteroid dehydrogenase activity) and (polar and apolar) conjugate formation. All important enzymatic steps involved in synthesis and catabolism, as known from studies with tissues of vertebrates, were not, or hardly observed. The conclusion is drawn that typical vertebrate-type (C21, C19 and C18) steroids probably do not act as physiologically active substances in insects.

Animals↗
PubMed1991

Lack of essential enzymes for the biosynthesis of C19 and C18 steroids in gonads of the migratory locust, Locusta migratoria.

Ovaries and testes of the African migratory locust, Locusta migratoria migratorioides, were incubated in vitro with six tritiated steroid precursors. Three developmental stages were investigated--1 day, 14 days, and 6 weeks after adult moulting. 20 alpha-Hydroxysteroid dehydrogenase (HSD), 20 beta-HSD, 17 beta-HSD, 3 beta-HSD/isomerase, C17-C20 lyase, glucuronyl-transferase, sulfotransferase, and acyltransferase were identified in both sexes. A synthesis of androgens or estrogens comparable to the vertebrate type, however, was not apparent in the locust gonads. 20 alpha-HSD, 20 beta-HSD, and 17 beta-HSD activities were high, while more important steps in steroid synthesis such as 3 beta-HSD and C17-C20 lyase were far less intense. Ovarian 17 alpha-hydroxylase activity was slight. Aromatase activity was not demonstrated. Water-soluble conjugate formation was high in the incubations of "14th-day" and "6th-week" gonads but was absent in "1st-day" ovaries and testes. Active ester formation of pregnenolone was demonstrated in "6th-week" testes. The other steroid conversions were similar in all developmental stages investigated. Major differences between testes and ovaries were not observed. The gonads of the migratory locust are concluded not to produce androgens or estrogens.

Animals↗
PubMed1991

Isolation, primary structure, and synthesis of locustapyrokinin: a myotropic peptide of Locusta migratoria.

A neuropeptide which stimulates the motility of the cockroach hindgut has been isolated from an extract of 9000 brain-corpora cardiaca-corpora allata-subesophageal ganglion complexes of Locusta migratoria. Biological activity was monitored during HPLC purification by observing the myotropic effect of column fractions on the isolated hindgut of Leucophaea maderae. The primary structure of this myotropic peptide was established as a blocked 16-residue peptide: pGlu-Asp-Ser-Gly-Asp-Gly-Trp-Pro-Gln-Gln-Pro-Phe-Val-Pro-Arg-Leu-NH2. This novel locust peptide was designated as locustapyrokinin, or Lom-PK. Lom-PK was synthesized and shown to have chromatographic and biological properties identical to those of the native material. Lom-PK has a Phe-X-Pro-Arg-Leu-NH2 carboxy terminal in common with leucopyrokinin (or Lem-PK), a blocked myotropic neuropeptide isolated from the cockroach hindgut. The constituent amino acids of this C-terminal are important for biological activity on the Leucophaea hindgut. The primary structure of this novel insect peptide is, however, substantially different from Lem-PK at the amino-terminal sequence.

Amino Acid Sequence↗
PubMed1991

Cytoskeletal F-actin patterns in whole-mounted larval and adult salivary glands of the fleshfly, Sarcophaga bullata.

The patterns of filamentous actin were analysed in different larval, pupal and adult stages in the salivary glands of the fleshfly Sarcophaga bullata. Using the rhodamine labelled phalloidin staining method in combination with detergent extraction specific actin filament distribution was detected. The salivary glands which are histolysed during the process of metamorphosis show distinct cellular morphology and actin filament patterns in larvae and adults. The large third instar larval salivary gland cells contain a well developed apicolateral microvillar zone. In third instar larvae this microvillar zone invaginates and expands in the basal part of the lateral membranes. Larval salivary gland cells also contain numerous parallel basal actin bundles. The larval glands are histolysed during metamorphosis and adult glands are formed out of the imaginal cell group. At the onset of metamorphosis these basal actin bundles form a network of crossing bundles. The filamentous actin patterns of the proximal part of adult gland cells is confined to the apicolateral microvillar membranes. The cells in the distal, tubular part of the adult salivary glands show intense staining of their folded lateral membranes.

Actin Cytoskeleton↗
PubMed1990

Locustatachykinin III and IV: two additional insect neuropeptides with homology to peptides of the vertebrate tachykinin family.

Two myotropic peptides termed locustatachykinin III and IV were isolated from 9000 brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. The primary structures of Lom-TK III and IV were established as amidated decapeptides: Ala-Pro-Gln-Ala-Gly-Phe-Tyr-Gly-Val-Arg-NH2 (Lom-TK III) and Ala-Pro-Ser-Leu-Gly-Phe-His-Gly-Val-Arg-NH2 (Lom-TK IV). The locustatachykinins were synthesized and shown to have chromatographic and biological properties identical with those of the native materials. They stimulate visceral muscle contractions of the oviduct and the foregut of Locusta migratoria and of the hindgut of Leucophaea maderae. Both peptides exhibit sequence homologies with the vertebrate tachykinins. Sequence similarity is greater with the fish and amphibian tachykinins (up to 40%) than with the mammalian tachykinins. In addition, the intestinal and oviducal myotropic activity of the locustatachykinins is analogous to that of vertebrate tachykinins. Both chemical and biological similarities of vertebrate and insect tachykinins substantiates the evidence for a long evolutionary history of the tachykinin peptide family.

Amino Acid Sequence↗
PubMed1990

Locustatachykinin I and II, two novel insect neuropeptides with homology to peptides of the vertebrate tachykinin family.

Two myotropic peptides termed locustatachykinin I (Gly-Pro-Ser-Gly-Phe-Tyr-Gly-Val-Arg-NH2) and locustatachykinin II (Ala-Pro-Leu-Ser-Gly-Phe-Tyr-Gly-Val-Arg-NH2) were isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. Both peptides exhibit sequence homologies with the vertebrate tachykinins. Sequence homology is greater with the fish and amphibian tachykinins (up to 45%) than with the mammalian tachykinins. In addition, the intestinal myotropic activity of the locustatachykinins is analogous to that of vertebrate tachykinins. The peptides discovered in this study may just be the first in a whole series of substances from arthropod species to be identified as tachykinin family peptides. Moreover, both chemical and biological similarities of vertebrate and insect tachykinins substantiate the evidence for a long evolutionary history of the tachykinin peptide family.

Amino Acid Sequence↗
PubMed1990

Immunocytochemical localization in the central nervous system of four different insect species of molecules immunoreactive against peptides present in the caudodorsal cells of Lymnaea stagnalis.

The use of polyclonal antisera directed against three peptides (ovulation hormone (CDCH), alpha, and beta caudodorsal cell peptide (alpha- and beta-CDCP) produced by the caudodorsal cells of the snail Lymnaea stagnalis resulted in positive immunoreaction in Sarcophaga bullata (Diptera), Leptinotarsa decemlineata (Coleoptera), Locusta migratoria, and Periplaneta americana (Orthoptera). In three species, colocalization was detected using the antisera against CDCH and alpha-CDCP.

Animals↗
PubMed1990

Cytoskeletal F-actin patterns in whole-mounted insect Malpighian tubules.

The distribution of actin filaments in Malpighian tubules of the fleshfly Sarcophaga bullata (Parker) was investigated before and after metamorphosis by means of the rhodamine phalloidin staining method. The numerous primary cells show a pattern of thick basal actin bundles resembling stress fibres of cultured cells, while the apical microvillar zone shows a bright and homogeneous labelling. The less abundant stellate cells contain no such basal actin bundles and their apical microvillar zone gets only faintly stained. Late larval stages display fingerlike infoldings and an increased actin filament concentration at the apical membrane of the stellate cells. During metamorphosis the Malpighian tubules dedifferentiate and eventually redifferentiate to give rise to adult tubules resembling larval ones. The different types of actin filament organisation in the primary and stellate cells of the Malpighian tubules are discussed.

Actin Cytoskeleton↗
PubMed1990

Immunocytochemical localization of human growth hormone- and prolactin-like antigenic determinants in the insects, Locusta migratoria and Sarcophaga bullata.

1. By use of the peroxidase-antiperoxidase immunocytochemical method, substances immunoreactive to antisera directed against human growth hormone (hGH) and prolactin (hPrl) were localized in the nervous system of larval and adult Locusta migratoria and of adult Sarcophaga bullata belonging to different age groups. 2. No major differences in the distribution of cerebral immunoreactive materials were observed between males and females or between juvenile and adult insects. 3. Differential immuno-labeling of alternating tissue sections demonstrated that materials resembling hGH or hPrl are present in distinct neurons in the locust, whereas neurons immunoreactive to both antisera were detected in the fleshfly (Sarcophaga).

Animals↗
PubMed1990

Comparative developmental physiology and molecular cytology of the polytrophic ovarian follicles of the blowfly Sarcophaga bullata and the fruitfly Drosophila melanogaster.

1. The ovarian follicles of Sarcophaga and Drosophila consist of one oocyte and 15 nurse cells, the whole being surrounded by follicle cells. Although oocyte and nurse cells are genetically identical sibling cells, and although they are interconnected by cytoplasmic bridges, their physiology is very different. 2. The DNA content of the oocyte nucleus (germinal vesicle) never exceeds 4C, while values of polyploidisation up to 1024C have been measured in the nurse cells, this being dependent on their position within a follicle. 3. The nurse cell nuclei very actively synthesize RNA, while the germinal vesicle is almost completely inactive in this respect. 4. It has been possible to visualise the major cytoskeletal elements in the different ovarian cell types. Cellular markers of polarity and dorsoventral asymmetry have been described. 5. Electrophysiological measurements have been performed to find out whether or not the self-electrophoresis principle may be involved in polarised transport between nurse cells and oocyte. 6. Most of the vitellogenin is synthesized by the fat body but some follicle cells also synthesize small amounts. 7. The role of 20-OH ecdysone in the induction of vitellogenin synthesis in the fat body, as well as the presence of met-enkephalin like immunoreactivity in the gonads is well established in both species. Not so clear is the exact role of juvenile hormones and the nature of brain factors controlling ovarian development. 8. Drosophila has the advantage of its well documented genetics while the larger species Sarcophaga is preferable for the study of (electro-) physiological and cell biological mechanisms.

Animals↗
PubMed1990

Homologies between the amino acid sequences of some vertebrate peptide hormones and peptides isolated from invertebrate sources.

1. The 4K-prothoracicotropic hormone (PTTH) or bombyxin and the melanization-reddish coloration hormone of the silkworm Bombyx mori resemble insulin and insulin-like growth factors. 2. The family of adipokinetic/red pigment concentrating hormones has some similarity with glucagon. 3. Members of the FMRFamide family are found in vertebrates as well as in invertebrates. 4. In Locusta, a molecule immunologically and biologically related to amphibian melanophore stimulating hormone has been partially characterized. 5. Enkephalins and enkephalin-related peptides occur in insects and other invertebrates. 6. Peptides belonging to the tachykinin family have been isolated from molluscan (Octopus) salivary glands and from insect nervous tissue (Locusta migratoria). 7. Invertebrate arginine-vasotocin homologs have been isolated from an insect (Locusta migratoria) and from a mollusc (Conus). 8. In Leucophaea, Locusta and Drosophila, peptides resembling those of the vertebrate gastrin/cholecystokinin family have been identified. 9. As the number of different neuro-/gut peptides with possible function(s) as hormone, neurotransmitter or neuromodulator is now estimated to be of the order of a few hundred, more similarities will probably show up in the near future.

Amino Acid Sequence↗
PubMed1990

Effects of Bacillus thuringiensis delta-endotoxin on the permeability of brush border membrane vesicles from tobacco hornworm (Manduca sexta) midgut.

1. The effect of two recombinant Bacillus thuringiensis delta-endotoxins on brush border membrane vesicles of Manduca sexta midgut was investigated using an in vitro assay system, based on ion-amino acid cotransport. 2. A CryIA(b)-toxin provoked an increase in the permeability of the vesicles. 3. A CryIB-toxin, not toxic to M. sexta larvae in vivo, had no effect in our assay. 4. In contrast to earlier reports, the increase in permeability was found to be neither selective for K+ nor specifically inhibited by Ca2+ or Ba2+. 5. Our data support the hypothesis that B. thuringiensis delta-endotoxins create non-specific pores.

Alanine↗
PubMed1989

Immunohistochemical localisation of the hypertrehalosaemic hormone II (Cam-HrTH-II) and related peptides in the nervous system of Carausius morosus and Sarcophaga bullata.

A polyclonal antiserum was prepared against an N-terminal modified Cam-HrTH-II (Leu-Asn-Phe-...), one of the members of the large AKH/RPCH peptide family, first isolated from Carausius morosus. The localisation of this peptide was performed by means of immunocytochemical methods in the brain and corpora cardiaca-corpora allata complex of the stick insect, Carausius morosus and the grey fleshfly, Sarcophaga bullata. The distribution patterns of molecules reactive to the Cam-HrTH-II and the Lom-AKH-I antisera in both insect species were compared. In Carausius, both antisera reacted in the same cell bodies. In Sarcophaga, some neurons were stained by both, others only by one of the two antisera. By combining two different antisera, we demonstrated that there are no Lom-AKH-I-like molecules present in Carausius and that there must occur at least three different AKH-like molecules in the brain of Sarcophaga. One is similar to Cam-HrTH-II, the second to Lom-AKH-I and the third is an AKH/RPCH-like peptide, different from Lom-AKH-I and Cam-HrTH-II.

Amino Acid Sequence↗
PubMed1989

A substance resembling somatomedin C in the American cockroach.

Material antigenically resembling somatomedin C (type I insulin-like growth factor, IGF-I) is demonstrated in the American cockroach Periplaneta americana by means of a monoclonal antibody immunoperoxidase technique. It was localized histochemically in neuronal cell somata and axonal fibers (probably interneurons) of the central nervous/neuroendocrine system and in 'endocrine-type' cells lining the midgut epithelium. The IGF-I-like substance is different from vertebrate insulin and also distinct from materials immunostained by different insulin antibodies in the brain and neurohaemal complex of this insect species. These findings are viewed in the light of recent reports on the presence and action of insulin-like chemicals in insects, and with respect to the existence of an insect brain-midgut system similar to the mammalian brain-gastroenteropancreatic system.

Animals↗
PubMed1988

Coexistence of melanin-concentrating hormone and alpha-melanocyte-stimulating hormone immunoreactivities in the central nervous system of the locust, Locusta migratoria.

The distribution of melanin concentrating hormone (MCH) in the central nervous system of the locust Locusta migratoria was studied by the indirect immunofluorescence technique, using antibodies against salmon MCH. Most MCH-immunoreactive perikarya were found in the optic lobes at both sides of the brain, dorsally with respect to the lamina ganglionaris. The same neurons also contain alpha-melanocyte-stimulating hormone (alpha-MSH)-like material. In addition, a moderate number of MCH-like neurons, which were devoid of alpha-MSH-immunoreactive substances, was observed in the pars intercerebralis. Bright immunofluorescent fibers were visualized in various regions of the central nervous system of the locust: the optic lobes, the ocelli, the proto-and deuterocerebrum, the subesophageal connectives and the corpora cardiaca. In the ventral nerve cord and the subesophageal ganglion, where alpha-MSH-like cell bodies were encountered, MCH immunoreactive perikarya were absent and immunoreactive fibers were scarce. The coexistence of MCH and alpha-MSH-immunoreactive material within the same specific neurons might indicate an evolutionary relationship of both peptides.

Animals↗
PubMed1988

Methionine-enkephalin immunoreactivity in the gonads and nervous system of two insect species: Locusta migratoria and Sarcophaga bullata.

Methionine(met)-enkephalin immunoreactivity as visualized by the peroxidase-antiperoxidase procedure, is present in spermatogonia, spermatocytes, spermatids, and young ovarian follicles of Locusta (panoistic type) and Sarcophaga (polytrophic type). Follicle cells and mature spermatozoa are always immunonegative as are locust vitellogenic follicles. In oocytes and in trophocytes, the met-enkephalin-like material first appears around the nucleus and is then dispersed throughout the cytoplasm. Later, it is present only in the periphery. In the ovary of both insects, no immunoreactivity is found with antisera against adrenocorticotrophic hormone, melanophore stimulating hormone, beta-endorphin, corticotropin releasing factor, or leucine-enkephalin. All these antisera yield a positive reaction when applied to the central nervous system as does the met-enkephalin antiserum. This study indicates that the met-enkephalin-like peptide may play a role in reproductive physiology.

Animals↗