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At least 1,063 records · Page 59Linked to original sources
PubMed2004

Functional and comparative analysis of two distinct ecdysteroid-responsive gene expression constructs in Drosophila S2 cells.

Inducible expression systems have proven to be of major interest when analysing the function of specific genes or when expressing cytotoxic proteins. In an effort to develop inducible switches allowing for flexible fine-tuning of gene expression levels in insect cells, we have compared the induction capacities of two Drosophila minimal promoters when linked to four consecutive ecdysone response elements. These minimal promoters, either containing a TATA-box or a downstream promoter element, drove the expression of a luciferase reporter gene. Potent induction capacities were observed with the insect moulting hormone, 20-hydroxyecdysone, and with ponasterone A, a plant ecdysteroid. The developed inducible switches further expand the repertoire of molecular tools for functional expression of proteins of interest in insect cells. In addition, the combination of an ecdysone switch with promoters that possess different structural elements can provide novel insights into ecdysteroid-induced transcription in an insect cell line.

Animals↗
PubMed1996

Locust adipokinetic hormones: carrier-independent transport and differential inactivation at physiological concentrations during rest and flight.

Since concomitant release of structurally related peptide hormones with apparently similar functions seems to be a general concept in endocrinology, we have studied the dynamics of the lifetime of the three known adipokinetic hormones (AKHs) of the migratory locust, which control flight-directed mobilization of carbohydrate and lipid from fat body stores. Although the structure of the first member of the AKHs has been known for 20 years, until now, reliable data on their inactivation and removal from the hemolymph are lacking, because measurement requires AKHs with high specific radioactivity. Employing tritiated AKHs with high specific radioactivity, obtained by catalytic reduction with tritium gas of the dehydroLeu2 analogues of the AKHs synthesized by the solid-phase procedure, studies with physiological doses of as low as 1.0 pmol per locust could be conducted. The AKHs appear to be transported in the hemolymph in their free forms and not associated with a carrier protein, despite their strong hydrophobicity. Application of AKHs in their free form in in vivo and in vitro studies therefore now has been justified. We have studied the degradation of the three AKHs during rest and flight. The first cleavage step by an endopeptidase is crucial, since the resulting degradation products lack any adipokinetic activity. Half-lives for AKH-I, -II and -III were 51, 40, and 5 min, respectively, for rest conditions and 35, 37, and 3 min, respectively, during flight. The rapid and differential degradation of structurally related hormones leads to changes in the ratio in which they are released and therefore will have important consequences for concerted hormone action at the level of the target organ or organs, suggesting that each of the known AKHs may play its own biological role in the overall syndrome of insect flight.

Amino Acid Sequence↗
PubMed1995

An ecdysiostatin from flies.

A bioassay for compounds with ecdysiostatic activity ('ecdysiostatins') was developed in order to prove the existence of an ecdysiostatin in blowfly larvae. The factor eluted by HPLC like Neb-TMOF (trypsin modulating oostatic factor), a hexapeptide that inhibits ecdysone biosynthesis. The ecdysiostatic activity of Neb-TMOF is specific, related peptides were less active or inactive. TMOF inhibits ecdysone biosynthesis rather than its secretion. It increases the cAMP level of ring glands. Effectors that elevate the intracellular cAMP can mimic the inhibitory effect of the ecdysiostatin. This suggests that cAMP may control steroidogenesis in fly larvae by shutting ecdysone biosynthesis. Thus, the hexapeptide acts as a prothoracicostatic hormone (PTSH) that controls ecdysone biosynthesis.

Amino Acid Sequence↗
PubMed1995

Primary structure of a novel neuropeptide isolated from the corpora cardiaca of periodical cicadas having adipokinetic and hypertrehalosemic activities.

A new neuropeptide hormone was isolated from the corpora cardiaca of the periodical cicadas, Magicicada species. Primary structure of the peptide as determined by a combination of automated Edman degradation after enzymatic deblocking with pyroglutamate aminopeptidase and mass spectrometry is: pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp-Gly-Asn-NH2. Synthetic peptide assayed in the green stink bug Nezara viridula caused a 112% increase in hemolymph lipids at a dose of 0.625 pmol, and a 67% increase in hemolymph carbohydrates at a dose of 2.5 pmol. Based on these results we designate this peptide, a first from order Homoptera, as Magicicada species-adipokinetic hormone (Mcsp-AKH).

Amino Acid Sequence↗
PubMed2005

Activation of the lipid droplet controls the rate of lipolysis of triglycerides in the insect fat body.

The hydrolysis of triglyceride (TG) stored in the lipid droplets of the insect fat body is under hormonal regulation by the adipokinetic hormone (AKH), which triggers a rapid activation cAMP-dependent kinase cascade (protein kinase A (PKA)). The role of phosphorylation on two components of the lipolytic process, the TG-lipase and the lipid droplet, was investigated in fat body adipocytes. The activity of purified TG-lipase determined using in vivo TG-radiolabeled lipid droplets was unaffected by the phosphorylation of the lipase. However, the activity of purified lipase was 2.4-fold higher against lipid droplets isolated from hormone-stimulated fat bodies than against lipid droplets isolated from unstimulated tissue. In vivo stimulation of lipolysis promotes a rapid phosphorylation of a lipid droplet protein with an apparent mass of 42-44 kDa. This protein was identified as "Lipid Storage Droplet Protein 1" (Lsdp1). In vivo phosphorylation of this protein reached a peak approximately 10 min after the injection of AKH. Supporting a role of Lsdp1 in lipolysis, maximum TG-lipase activity was also observed with lipid droplets isolated 10 min after hormonal stimulation. The activation of lipolysis was reconstituted in vitro using purified insect PKA and TG-lipase and lipid droplets. In vitro phosphorylation of lipid droplets catalyzed by PKA enhanced the phosphorylation of Lsdp1 and the lipolytic rate of the lipase, demonstrating a prominent role PKA and protein phosphorylation on the activation of the lipid droplets. AKH-induced changes in the properties of the substrate do not promote a tight association of the lipase with the lipid droplets. It is concluded that the lipolysis in fat body adipocytes is controlled by the activation of the lipid droplet. This activation is achieved by PKA-mediated phosphorylation of the lipid droplet. Lsdp1 is the main target of PKA, suggesting that this protein is a major player in the activation of lipolysis in insects.

Adipocytes↗
PubMed1987

Microanalysis of the amino acid sequence of the eclosion hormone from the tobacco hornworm Manduca sexta.

The amino acid sequence of the eclosion hormone from the tobacco hornworm Manduca sexta has been determined, using less than 500 pmol of protein and microanalytical techniques. The protein contains 62 amino acid residues and has a molecular mass of 6813 Da. The amino-terminal sequence is similar to that of a 13-residue segment at the amino terminus of the eclosion hormone of the silkworm Bombyx mori, but the hormone is not otherwise homologous with other hormones or proteins.

Amino Acid Sequence↗
PubMed1991

The presence of peptides related to the adipokinetic hormone/red pigment-concentrating hormone family in the nematode, Panagrellus redivivus.

Immunocytochemistry using polyclonal antisera raised to fragments or derivatives of locust adipokinetic hormone (AKH) I and IIs (Schooneveld et al., 1983, 1985, 1986) selectively stained cells in the nervous system of the free-living nematode, Panagrellus redivivus. Antiserum 528 (raised to the C-terminus of AKH IIs) stained the dorsal cephalic papillary cell bodies and the anterior nerve ring. Fibres in the lateral cords were stained with antiserum 241 that recognises the C-terminus of AKH I. Substances reacting to antisera 433 (raised to the N-terminal sequence of AKH I and IIs) 528 and 241 were present in the preanal ganglion and associated ventral nerve fibres. In males, all three antisera stained fibres leading to the base of the spicules. A peptide fraction from whole P. redivivus evoked an adipokinetic response in the locust, Schistocera gregaria which was dose dependent and was abolished by treatment with endopeptidase 24:11 but not by boiling or by incubation with leucine aminopeptidase. The adipokinetic activity was reduced by over 70% on incubation of the peptide fraction with pyroglutamyl aminopeptidase. The same fraction induced hyperglycaemia when injected into the cockroach, Periplaneta americana. These results are consistent with the existence in P. redivivus of peptides that are structurally related to the arthropod adipokinetic hormone/red pigment-concentrating hormone (AKH/RPCH) family.

Amino Acid Sequence↗
PubMed2004

Continuous recording of excretory water loss from Musca domestica using a flow-through humidity meter: hormonal control of diuresis.

Water loss from adult male houseflies was continuously recorded using a flow-through humidity meter, which enabled losses to be apportioned between the sum of cuticular and respiratory transpiration, salivation and excretion. Transpiration accounted for >95% of water lost from sham-injected flies, compared with excretion (3.0%) and salivation (2.4%). In contrast, excretion accounted for 40% of water lost from flies injected with > or =3 microl of saline, whereas salivary losses were unchanged. Saline injections (1-5 microl) expanded the abdomen in the dorsal-ventral plane, and this expansion was positively correlated with the magnitude of the ensuing diuresis, suggesting the signal for diuretic hormone release originates from stretch receptors in abdominal tergal-sternal muscles. The effects of decapitation, severing the ventral nerve cord within the neck or ligaturing the neck, showed the head was needed to initiate and maintain diuresis, but was neither the source of diuretic hormone nor did it control the discharge of urine from the anus. These findings indicate the head is part of the neural-endocrine pathway between abdominal stretch receptors and sites for diuretic hormone release from the thoracic-abdominal ganglion mass. Evidence is presented for Musdo-K having a hormonal role in the control of diuresis, although other neuropeptides may also be implicated.

Animals↗
PubMed1999

Expression of the Manduca sexta allatotropin gene in cells of the central and enteric nervous systems.

Manduca sexta allatotropin (Mas-AT) was isolated and first characterized as a peptide that stimulated juvenile hormone biosynthesis in adult lepidopteran corpora allata and was subsequently shown to have cardioacceleratory activity in the pharate adult. In this study, we identified the cells in the nervous system of the insect that contain mRNA encoding Mas-AT and immunoreactivity against a polyclonal antiserum to Mas-AT. In larvae, Mas-AT mRNA and immunoreactivity was most abundant in two cells in the frontal ganglion, which project their axons down the recurrent nerve toward the gut, and in cells in the terminal abdominal ganglion. Lower levels of Mas-AT mRNA were detected in the brain and subesophageal ganglion. In the pupal and pharate adult stages, we detected Mas-AT mRNA and immunoreactivity in cells of the abdominal ganglia and in additional cells in the terminal abdominal ganglion. These additional cells in the ventral nerve cord that express Mas-AT during the pupal and pharate adult stages include cells that differentiate during metamorphosis as well as cells that exist in larvae but do not begin to express Mas-AT until these later developmental stages. Some of the cells that exhibit Mas-AT immunoreactivity lack Mas-AT mRNA, suggesting that the antisera used in this and previous studies recognizes other peptides in addition to Mas-AT. This pattern of expression suggests that Mas-AT may mediate multiple physiological functions during the life cycle of the insect, including the larval stage in which no function has yet been described for the peptide.

Animals↗
PubMed1989

Simulation of the activation of fat body glycogen phosphorylase and trehalose synthesis by peptide hormones in the American cockroach.

A model is described which simulates activation of glycogen phosphorylase and induction of trehalose synthesis in the fat body of the American cockroach, Periplaneta americana, by two hypertrehalosaemic peptides. Parameters for the model were estimated from literature data (Siegert et al., Insect Biochem. 16, 365), with the exception of the half-life of the physiologically active peptides, which was estimated from the model. The model describes satisfactorily the activation of glycogen phosphorylase and the increase of haemolymph carbohydrates, which is dependent on the activation of glycogen phosphorylase in the model. It further explains the observed differences in sensitivity for glycogen phosphorylase activation and increase in haemolymph carbohydrates by these peptides. Best fits were obtained with a physiological half-life of about 12-15 min for the peptides. This value is similar to what can be calculated from the in vivo effects of these peptides on heart beat (Gersch et al., Zool. Jb. Physiol. 86, 17), but it is considerably shorter than the published half-life of 1 h for radioactive peptide (Skinner et al., Insect Biochem. 17, 433). However, both values are compatible if part of the peptides in the haemolymph is not present in freely dissolved form, but bound to a haemolymph component. The model half-life would then represent the half-life of the free, physiologically active peptide, which was estimated from the disappearance of radioactive peptide to be about 12-15 min. This suggests, that the model half-life is realistic and physiologically more important than the half-life of radioactive peptide of 1 h.

Animals↗