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A De Loof

Publications and source records attributed to A De Loof.

At least 109 records · Page 6Linked to original sources
PubMed1994

Inhibition of ecdysone biosynthesis in flies by a hexapeptide isolated from vitellogenic ovaries.

The only identified insect peptides known to be involved in controlling the biosynthesis of ecdysone, the steroid moulting hormone of arthropods, are the prothoracicotropic hormones (PTTH). These neuropeptides stimulate ecdysone biosynthesis. Recently, a hexapeptide (NPTNLH) with folliculostatic and trypsin modulating activity was isolated from vitellogenic ovaries of the fleshfly Neobellieria bullata. Here we report that the hexapeptide, when tested in vitro on the isolated ring gland of flies, inhibited ecdysone biosynthesis immediately and completely (EC50 = 5 nM). The hexapeptide is the first known factor with 'prothoracicostatic activity' and may form part of the endocrine system that controls ecdysone biosynthesis in vivo.

Animals↗
PubMed1993

Isolation, identification, and synthesis of AKH-I4-10 from Locusta migratoria.

A heptapeptide was isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, 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: Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2. The chromatographic and biological properties of the synthetic peptide were the same as those of the native peptide, thus confirming structural analysis. This heptapeptide is identical to the carboxyterminal heptamer of AKH-I and therefore designated as AKH-I4-10. AKH-I4-10 has no adipokinetic activity. AKH-I4-10 is most likely a breakdown product of Lom-AKH-I, suggesting that an endopeptidase which cleaves between Asn and Phe is present in the brain complex of L. migratoria. Such an endopeptidase has recently been characterized in in synaptic membranes of the nervous system of Schistocerca gregaria.

Amino Acid Sequence↗
PubMed1993

Isolation, identification and synthesis of locustapyrokinin II from Locusta migratoria, another member of the FXPRL-amide peptide family.

1. A blocked decapeptide was isolated from brain corpora cardiaca-corpora allata suboesophageal ganglion extracts of the locust, Locusta migratoria. Biological activity was monitored during HPLC purification by observing the myotropic effect of column fractions on the isolated hindgut of Leucophaea maderae. 2. The primary structure of this myotropic peptide was established as: pGlu-Ser-Val-Pro-Thr-Phe-Thr-Pro-Arg-Leu-NH2. 3. The chromatographic and biological properties of the synthetic peptide were the same as those of the native peptide, thus confirming structural analysis. 4. This decapeptide is the sixth natural analog of a series of locust peptides with a Phe-X-Pro-Arg-Leu-NH2 carboxyterminus. This carboxyl terminal sequence is also found in other peptides identified in other insects and it is the biological active core sequence for diverse biological activities: muscle contraction, pheromone production, pigment synthesis and diapauze. 5. Like the locustamyotropins and locustapyrokinin I, locustapyrokinin II stimulates contractions of the oviduct in Locusta.

Amino Acid Sequence↗
PubMed1993

The myotropic peptides of Locusta migratoria: structures, distribution, functions and receptors.

The search for myotropic peptide molecules in the brain, corpora cardiaca, corpora allata suboesophageal ganglion complex of Locusta migratoria using a heterologous bioassay (the isolated hindgut of the cockroach, Leucophaea maderae) has been very rewarding. It has lead to the discovery of 21 novel biologically active neuropeptides. Six of the identified Locusta peptides show sequence homologies to vertebrate neuropeptides, such as gastrin/cholecystokinin and tachykinins. Some peptides, especially the ones belonging to the FXPRL amide family display pleiotropic effects. Many more myotropic peptides remain to be isolated and sequenced. Locusta migratoria has G-protein coupled receptors, which show homology to known mammalian receptors for amine and peptide neurotransmitters and/or hormones. Myotropic peptides are a diverse and widely distributed group of regulatory molecules in the animal kingdom. They are found in neuroendocrine systems of all animal groups investigated and can be recognized as important neurotransmitters and neuromodulators in the animal nervous system. Insects seem to make use of a large variety of peptides as neurotransmitters/neuromodulators in the central nervous system, in addition to the aminergic neurotransmitters. Furthermore quite a few of the myotropic peptides seem to have a function in peripheral neuromuscular synapses. The era in which insects were considered to be "lower animals" with a simple neuroendocrine system is definitely over. Neural tissues of insects contain a large number of biologically active peptides and these peptides may provide the specificity and complexity of intercellular communications in the nervous system.

Amino Acid Sequence↗
PubMed1993

Baculovirus immediate early gene promoter based expression vectors for transient and stable transformation of insect cells.

A recombinant plasmid vector was constructed in which the bacterial LacZ gene was placed under the control of a Bombyx mori baculovirus early promoter. The vector proved to be active in transfected cultured dipteran and lepidopteran cells. Co-transfection carried out with this recombinant plasmid vector and a plasmid containing the hygromycin phosphotransferase gene followed by selection with the antibiotic hygromycin B, resulted in stable transformation of cultured Drosophila melanogaster Schneider 2 cells. Southern blot analysis of the host cell's genomic DNA in combination with chromosomal in situ hybridization demonstrated that multiple copies of both plasmids were integrated in the host cell's genome.

Animals↗
PubMed1992

Distribution of locustamyotropin-like immunoreactivity in the nervous system of Locusta migratoria.

Locustamyotropin-like immunoreactivity was visualized in the nervous system of Locusta migratoria by means of the peroxidase antiperoxidase method. Highly specific antibodies to the carboxy-terminus of the locustamyotropins were obtained by elution through an affinity column to which Lom-MT II was covalently bound. Specific cells in the nervous system of Locusta migratoria contain substances immunoreactive to anti-locustamyotropin. In total, about 100 cells immunoreactive to the Lom-MT-II antiserum were detected in the head ganglia, in the abdominal neuromeres of the metathoracic ganglion, and in the five free abdominal ganglia. In the brain, immunoreactive cell groups were situated in the inner and outer edge of the tritocerebrum. Prominent axon bundles tightly surround the tractus I to the corpora cardiaca. The corpora allata were innervated by the nervus corporis allati I coming from the corpora cardiaca and by fibers in the nervus corporis allati II originating from cell bodies in the suboesophageal ganglion. Immunoreactive cell bodies in the suboesophageal and abdominal ganglia are distributed along the anterior posterior midline axis, both dorsally and ventrally. The processes of the cell bodies in the abdominal ganglia leave the ganglia and were traced in the respective median nerves into the neurohaemal organs. Since the Lom-MT-II antiserum cross-reacts with all peptides of the locustamyotropin family that have a carboxy-terminus in common, these cells may contain one or several locustamyotropins. The Lom-MT antiserum also recognizes pheromone biosynthesis activating neurohormone, as was revealed by the intensive labeling of suboesophageal cell bodies in Bombyx mori.

Amino Acid Sequence↗
PubMed1992

Locustakinin, a novel myotropic peptide from Locusta migratoria, isolation, primary structure and synthesis.

The isolated hindgut of the cockroach, Leucophaea maderae is a very efficient bioassay tool for the monitoring of certain structural types of insect myotropic peptides during HPLC purification. Using this detection system, a six residue peptide has been isolated from an extract of 9000 brain corpora cardiaca-corpora allata suboesophageal ganglion complexes of Locusta migratoria. Amino acid composition and sequence analysis combined with enzymatic digestion data established the structure of the novel peptide as Ala-Phe-Ser-Ser-Trp-Gly-amide. The chromatographic and biological properties of the synthetic peptide were the same as those of the native peptide, thus confirming structural analysis. The carboxy-terminal pentamer sequence is the active core of leucokinins II, V and VII and of achetakinin III (myotropic neuropeptides isolated from Leucophaea m. and from Acheta domesticus; Holman et al., 1990). Furthermore, the octapeptide leucokinin VII contains the novel sequence as its carboxy-terminal hexamer and Achetakinin V (AFHSWGamide) differs from it by one residue. This new peptide designated as locustakinin I (locusts) may therefore represent an evolutionary molecular link between leucokinin VII (cockroaches) and achetakinin V (crickets). Using synthetic locustakinin, physiological studies will be performed in the locust. In view of the known effects of leucokinins, locustakinin may be important in the stimulation of ion transport and inhibition of diuretic activity in Malpighian tubules. This study indicates that the AFXSWGamide sequence appears to have been well conserved and that members of this peptide family may be widely distributed among insects and posses a number of functions.

Amino Acid Sequence↗
PubMed1992

All animals develop from a blastula: consequences of an undervalued definition for thinking on development.

An early embryo becomes a blastula at the moment that its constituent cells become organised into a simple epithelium. Epithelial folding and compartmentation are essential elements of animal development. All the different cell types--epithelial and other ones--of which a differentiated organism consists differ in their plasmamembrane-cytoskeletal complex but they are assumed to have an identical genome. The hypothesis is put forward that, perhaps, the basic mechanism underlying differentiation can be defined as the generation of cells which have an identical genome but which differ in their plasmamembrane-cytoskeletal complex and which, because of these differences, can engage in differential protein synthesis-physiology.

Animal Population Groups↗
PubMed1992

Localization of Lom-AG-myotropin I-like substances in the male reproductive and nervous tissue of the locust, Locusta migratoria.

Lom-AG myotropin I (Lom-AG-MTI) was the first peptide to be isolated from the male accessory reproductive glands of the locust, Locust migratoria. It shows no sequence similarity to any of the peptides identified from vertebrate or invertebrate tissues. A polyclonal antiserum was used to localize Lom-AG-MTI-like material in the male reproductive system and nervous system of the locust. Immunoreactivity was found in two of the hyaline gland tubules. In the brain, cell bodies were detected in the photo- and deuterocerebrum as well as the frontal ganglion. Nerve fibers were stained in the neuropils of the brain and throughout the labial nerves into the recurrent nerve. Thoracic and last abdominal ganglia contained neurons which could be stained with Lom-AG-MTI antiserum. The pronounced reactivity in the central nervous system suggests a possible neuroregulatory function of the peptide.

Amino Acid Sequence↗
PubMed1992

Electrical-ionic control of gene expression.

1. Changes in turgor, in cell volume, in membrane potential, in intracellular ionic activities and, more recently, in spontaneous electrical activity have been reported to be causally linked to the expression of specific genes. 2. As a result, it has become clear that changes in membrane properties and/or in the intracellular "ionic environment" can play an important role in generating cell type specific physiological responses which indirectly--or maybe directly--affect gene expression. 3. Possible targets of the ionic "environment" are: the selective transport across biological membranes; the activity of certain (regulatory) enzymes; the conformation of some (regulatory) proteins; of chromatin; of the cytoskeleton; of the nuclear matrix; the association of the cytoskeleton with plasmamembrane proteins or RNA; the association chromatin-nuclear matrix; protein-DNA and protein-protein interactions etc. All these sites may be instrumental to "fine or coarse" tuning of gene expression. 4. The exact mechanisms by which changes in intracellular ionic environment are transduced, directly or indirectly, into alterations of the activity of trans-acting factors have not yet been fully uncovered. Changes in the degree of phosphorylation of regulatory proteins and/or of trans-acting factors may provoke fine tuning effects on cell type specific gene expression activity. 5. The intranuclear ionic environment is difficult to measure in an exact way. It can be influenced in a number of ways. The location of a gene, as determined by the position of the nucleus in the cytoplasm and by the association of chromatin to the nuclear matrix may be especially important in cells which can generate some type of intracellular gradient or in excitable cells. 6. In some somatic cell types--germinal vesicles may behave differently--the intranuclear inorganic ionic "environment" has been reported to be distinct from the cytoplasmic one. This challenges the widespread assumption that the nuclear envelope is always freely permeable to small molecules and inorganic ions. 7. It can be expected that the fast progress in the cloning of "electrically" controlled genes, in the identification of trans-acting factors, in their mode of interaction with genes and in the precise localization of genes within the nucleus may soon lead to substantial progress in this domain.

Animals↗
PubMed1992

The pivotal role of the plasma membrane-cytoskeletal complex and of epithelium formation in differentiation in animals.

1. If a few exceptions are disregarded, the several somatic cell types of a differentiated organism all have an identical genome. They all differ in their plasma membrane-cytoskeletal complex. 2. Differences in plasma membrane properties usually result in differences in ionic concentrations/activities in the cytoplasm and nucleoplasm. A basic question therefore is whether there exists a causal relationship between the ionic environment of the nucleus and differential gene expression/protein synthesis. 3. Development is switched on by a "Ca2+ explosion", often accompanied by pH changes and plasma membrane depolarisation. The penetration of the spermatozoon in the plasma membrane acts as a trigger. 4. All animal species develop from a blastula. At this stage they organise themselves as an epithelium enclosing an inner (fluid) compartment. This suggests that epithelium formation is absolutely essential in animal development. 5. As development proceeds, more and more compartments, lined by different epithelia, are formed. Differentiated organisms largely consist of folded epithelia. Some cells leave their original epithelial environment and become free floating (e.g. blood cells) or engage in other types of organisation. 6. Epithelial cells have the ability to segregate some membrane proteins, e.g. receptors, ion pumps, ion channels etc., so as to make selective transcellular transport possible. The cytoskeleton plays an important role in this segregation and in the interconnection of epithelial cells. 7. Transembryonic electric currents which have been measured by the vibrating probe technique, are due to electrogenic ion transport by epithelia. 8. Segregation of membrane proteins is not an exclusive property of epithelial cells but it is probably a property of all animal cell types, single cells inclusive; asymmetry is the rule, symmetry--if it exists at all--the exception. 9. Differences in several plasma membrane proteins (receptors, ion transporting molecules, cell adhesion molecules and signal transducing systems) are not only causally related to differential transcellular transport but also indirectly to differential protein synthesis and hence to differentiation. There are already a few well documented examples of "electrical" control of gene expression. 10. The major "strategy" which applies in differentiation seems to be to keep the genome constant but to change over and over its ionic and macromolecular environment, both acting in a complementary way. The first one may be considered as the coarse tuning mechanism of gene expression-protein synthesis, the second as the fine one. In our opinion this might be a principle universal to differentiation processes in all animal species.

Animals↗
PubMed1992

On the origin of vertebrate-type steroids present in Locusta migratoria: do they originate from the food?

1. This study investigates the origin of vertebrate-type steroids which were reported to be present in Locusta migratoria: are the steroids synthesized by the locust or are they derived from the diet, i.e. grass and rolled oats? 2. It is unlikely that the steroids are synthesized by locust tissues. In vitro incubations of eleven different tissues with labeled pregnenolone or androstenedione did not result in androgen or estrogen synthesis respectively. 3. Steroid synthesis was also not detected when tissues were incubated in the presence of the early precursors cholesterol and isopentenyl pyrophosphate. 4. It is unlikely that the steroids are derived from the diet. Feeding experiments indicate that only low amounts of steroids are capable of crossing the gut-body barrier. 5. Injection of testosterone in the hemolymph also resulted in rapid excretion, instead of storage in tissues. 6. Moreover, radioimmunological measurements indicate that vertebrate-type steroids are absent in the food of locusts. 7. Specificity studies indicate that substances other than vertebrate-type steroids are detected by radioimmunoassay in locust tissue extracts. 8. Because vertebrate-type steroids are absent in locust tissues, it can be concluded that vertebrate-type steroids do not have a physiological function in Locusta.

Androstenedione↗
PubMed1992

Isolation, primary structure and synthesis of neomyosuppressin, a myoinhibiting neuropeptide from the grey fleshfly, Neobellieria bullata.

1. An amidated decapeptide, showing strong inhibitory activity of spontaneous visceral muscle movement was isolated, from head extracts of 42 thousand fleshflies, Neobellieria bullata (Diptera, Sarcophagidae). 2. Amino acid sequencing and verification by peptide synthesis revealed the following primary structure: Thr-Asp-Val-Asp-His-Val-Phe-Leu-Arg-PheNH2. 3. The novel peptide was termed neomyosuppressin or Neb-MS. 4. During the process of consecutive high performance liquid chromatography (HPLC) purifications the biological activity of the samples was monitored using heterologous bioassay system. 5. The threshold level of synthetic Neb-MS was found to be 8.6 +/- 0.5 x 10(-11) M on the Leucophaea hindgut and 3.4 +/- 0.5 x 10(-10) M on the Locusta oviduct bioassay, respectively.

Amino Acid Sequence↗
PubMed1992

Isolation and primary structure of two sulfakinin-like peptides from the fleshfly, Neobellieria bullata.

1. Two novel insect myotropic peptides termed neosulfakinin-I (Neb-SK-I) and neosulfakinin-II (Neb-SK-II) were isolated from the heads of 42 thousand fleshflies, Neobellieria bullata (Diptera, Sarcophagidae). 2. A series of four, high-performance liquid chromatographic (HPLC), fractionations performed on columns with different characteristic features yielded two purified biologically active, hindgut motility stimulating fractions, suitable for amino acid sequence analysis. 3. The proposed sequences for the two peptides are: Phe-Asp-Asp-Tyr-Gly-His-Met-Arg-Phe-(NH2), (Neb-SK-I) and X-X-Glu-Glu-Gln-Phe-Asp-Asp-Tyr-Gly-His-Met-Arg-Phe-(NH2), (Neb-SK-II). 4. These sulfakinins exhibit very high homology to putative drosulfakinin sequences which, however, have not yet been isolated, but were deduced from a cloned Drosophila gene encoding these peptides. 5. Here we provide the first evidence for the expression of such peptides present in Dipterans. 6. Insect sulfakinins show structural identities with the hormonally-active portion of vertebrate gastrin II-, cholecystokinin- and caerulin-related peptides and they share common carboxy terminal sequences with invertebrate/vertebrate peptides of the FMRFamide peptide family.

Amino Acid Sequence↗
PubMed1992

Transport of the cationic fluorochrome rhodamine 123 in an insect's Malpighian tubule: indications of a reabsorptive function of the secondary cell type.

The pathway of rhodamine 123 was examined after injection into Sarcophaga flies and after in vitro labeling of the Malpighian tubules. After in vitro labeling the primary cells only retained this potential-sensitive dye for a short period while all secondary cells accumulated the dye from the tubule lumen. In vivo the secondary cells also accumulated rhodamine 123 from the lumen, but the primary cells in the distal parts of all four tubules retained the dye for prolonged periods. This was most pronounced in the distal part of the anterior Malpighian tubules, where rhodamine 123 was eventually precipitated on the luminal concretions. Rhodamine 123 initially accumulated in the secondary cell mitochondria and eventually in intensely fluorescing vesicles, probably lysosomes. No evidence for endocytotic processes from the lumen was found using Lucifer Yellow CH, fluorescent dextrans and fluorescent albumin. Prior incubation with the ionophores valinomycin, nigericin, CCCP (all 1 micrograms/ml), dinitrophenol (1 mM) and NaN3 (10(-2) M) inhibited the selective accumulation of rhodamine 123 to a large extent while monensin (1-5 micrograms/ml) showed little inhibitory effect. Furthermore, only cationic and no anionic or neutral dyes were accumulated by the secondary cells. In the fleshfly Calliphora and the fruitfly Drosophila, the dye rhodamine 123 also selectively accumulated in the secondary cells, as well in vitro as in vivo.

2,4-Dinitrophenol↗
PubMed1991

Isolation, identification and synthesis of locustamyoinhibiting peptide (LOM-MIP), a novel biologically active neuropeptide from Locusta migratoria.

A novel peptide termed locustamyoinhibiting peptide (LOM-MIP) was isolated from brain-corpora cardiaca-corpora allata-suboesophageal ganglion extracts of the locust, Locusta migratoria. The primary structure of this nonapeptide has been determined Ala-Trp-Gln-Asp-Leu-Asn-Ala-Gly-Trp-NH2. LOM-MIP suppresses the spontaneous contractions of the hindgut and oviduct of Locusta migratoria and of the hindgut of Leucophaea maderae. This novel peptide is, however, structurally different from leucomyosuppressin, a hindgut suppressing peptide isolated from Leucophaea maderae heads. LOM-MIP has a Gly-TrpNH2 carboxy-terminal in common with APGWamide, a penis retractor muscle inhibiting peptide isolated from the snail, Lymnea stagnalis. In addition, it shows carboxy-terminal sequence similarities with locust AKH II which ends in AGWamide. No sequence similarities were found with other vertebrate or invertebrate peptides. Synthetic LOM-MIP showed biological as well as chemical characteristics indistinguishable from those of native LOM-MIP.

Amino Acid Sequence↗