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[Regeneration of limbs and sensory organs in Ixodid ticks (Acari, Ixodeidea, Ixodidae and Argasidae)].

We present a review of our own and literature data on reparative regeneration in ixodid ticks (chelicerate arthropods). Ticks have a high potential for reparative regeneration and a close relationship between regeneration and development determined by similar hormonal regulatory mechanisms. These mechanisms depend on ecdysteroid hormones, which participate in the initiation of both processes, and juvenile hormones, which direct these processes either to the maintenance of larval features or to the development of nymphal and adult features. We present a detailed analysis of the regeneration of Haller's sensory organs in ixodid ticks and propose an hypothesis about the role of juvenile hormones in the modification of morphogenetic processes in this group. Furthermore, we present data on the effects of insect juvenile hormone analogs (methoprene and fenoxycarb) on the regeneration of Haller's organ, which support this hypothesis. Studies on reparative regeneration in arthropods provide a broader view of the problem of repair morphogenesis in animals.

Acari↗
PubMed1988

Ecdysteroid mediated fat body acid phosphatase activity during larval development of rice moth, Corcyra cephalonica (Lepidoptera).

20-hydroxyecdysone (20-HE) stimulates acid phosphatase activity in the fat body of ligated late-last instar larvae. This effect is time dependent and the specific activity of enzyme increases significantly in hormone treated insects. 20-HE also stimulates general protein synthesis. Cycloheximide treatment either in conjunction with 20-HE or after hormone treatment blocks the increase in enzyme activity as well as increase in protein content. However, actinomycin D treatment does not alter the enzyme activity while it blocks the increase in total RNA as well as increase in protein content.

Acid Phosphatase↗
PubMed2004

Increased juvenile hormone levels after long-duration flight in the grasshopper, Melanoplus sanguinipes.

Although, in many insects, migration imposes a cost in terms of timing or amount of reproduction, in the migratory grasshopper Melanoplus sanguinipes performance of long-duration flight to voluntary cessation or exhaustion accelerates the onset of first reproduction and enhances reproductive success over the entire lifetime of the insect. Since juvenile hormone (JH) is involved in the control of reproduction in most species, we examined JH titer after long flight using a chiral selective radioimmunoassay. JH levels increased on days 5 and 8 in animals flown to exhaustion on day 4 but not in 1-h or non-flier controls. No difference was seen in the diel pattern of JH titer, but hemolymph samples were taken between 5 and 7 h after lights on. Treatment of grasshoppers with JH-III mimicked the effect of long-duration flight in the induction of early reproduction. The increased JH titer induced by performance of long-duration flight is thus at least one component of flight-enhanced reproduction. To test the possibility that post-flight JH titer increases are caused by adipokinetic hormone (AKH) released during long flights, a series of injections of physiological doses of Lom-AKH I were given to unflown animals to simulate AKH release during long flight. This treatment had no effect on JH titers. Thus, although AKH is released during flight and controls lipid mobilization, it is not the factor responsible for increased JH titers after long-duration flight.

Analysis of Variance↗
PubMed2003

Regulation of prothoracic gland ecdysteroidogenic activity leading to pupal metamorphosis.

The prothoracic glands of early last (fifth) instar larvae of the silkworm are inactive with regard to ecdysteroidogenesis and unresponsive to prothoracicotropic hormone (PTTH) [J. Insect Physiol. 31 (1985) 455]. In an attempt to elucidate the hormonal mechanisms that cause the inactivity, we compared the effects of PTTH, dibutyryl cyclic AMP (dbcAMP), a cAMP phosphodiesterase inhibitor (IBMX), juvenile hormone analogue (JHA) and 20-hydroxyecdysone (20E) on secretory activity of the third, fourth and fifth instar glands. Among the factors examined, feedback inhibition by 20E was indicated to be the most likely factor. Inhibition was moderate in the third and early fourth instars while 20E strongly inhibited the glands of middle fourth instar larvae. The inhibitory effect of 20E was reduced by removal of the brain and corpora allata. Once the glands were suppressed by 20E to the degree of exhibiting neither secretory activity nor responsiveness to PTTH, dbcAMP or IBMX did not elicit ecdysone secretion at all. Thus the feedback inhibition may shut down ecdysteroidogenesis although it is obscure whether it affects the intracellular transductory cascade from the PTTH receptor through cAMP. Taken together, this evidence suggests that inactivity of the gland in the early fifth instar is brought about by feedback inhibition of the glands by 20E occurring in the late fourth instar, and that this inactivity is maintained by the juvenile hormone found in the early fifth instar.

1-Methyl-3-isobutylxanthine↗
PubMed1992

An affinity-amplified immunoassay for juvenile hormone esterase.

A method is described for increasing the specificity of an immunoassay for catalytically active enzymes and is specifically illustrated with a sensitive assay for an important regulatory enzyme from insects. Trifluoromethyl ketone haptens, potent inhibitors of insect juvenile hormone esterase, were bound to proteins such as hemocyanin (keyhole limpet) and conalbumin (chicken embryo). Haptens containing a thiol group were conjugated using heterobifunctional coupling reagents, and haptens with a carboxylic acid moiety were conjugated by the mixed anhydride method. The trifluoromethyl ketone-protein conjugates, shown to retain their inhibitory activity against juvenile hormone esterase, were used as coating antigens in several solid-phase enzyme-linked immunosorbent assay formats along with specific antibodies raised in rabbits against purified juvenile hormone esterase. The previously unreported format, termed affinity-amplified immunoassay (AAIA), was successfully used for quantitative monitoring of low levels of the esterase in dilute hemolymph and egg homogenates from various lepidopteran insect species, as well as for detection of the native and mutant forms of the enzyme obtained in a recombinant baculovirus expression system. The AAIA format was more sensitive for the target esterase and detected only the catalytically active form of the enzyme.

Animals↗
PubMed1985

N-terminal amino acid sequence of an insect neurohormone, melanization and reddish coloration hormone (MRCH): heterogeneity and sequence homology with human insulin-like growth factor II.

An insect neurohormone, melanization and reddish coloration hormone (MRCH), is responsible for cuticular melanization and epidermal red pigmentation in the armyworm. The three molecular forms of MRCH were isolated from adult heads of the silkworm, Bombyx mori, and their N-terminal amino acid sequences revealed a sequence homology with the C-terminal region of human insulin-like growth factor-II as well as N-terminal heterogeneity of MRCHs.

Amino Acid Sequence↗
PubMed1995

Prothoracicotropic hormone elicits a rapid, developmentally specific synthesis of beta tubulin in an insect endocrine gland.

The production of ecdysteroid (molting) hormones by the insect prothoracic gland is controlled primarily by a brain neuropeptide hormone, prothoracicotropic hormone (PTTH). PTTH stimulates also the specific synthesis of three proteins in the prothoracic glands of the tobacco hornworm Manduca sexta (Rybczynski and Gilbert, 1994). Here, one of these proteins, p50 is identified as a beta tubulin. The ability of PTTH to stimulate beta tubulin synthesis increased dramatically late on Day 3 of the 10-day fifth larval instar. At this time and later, beta tubulin synthesis in response to PTTH in vitro could be detected in some prothoracic glands 5-10 min after the onset of stimulation, and newly synthesized beta tubulin entered the microtubule pool within 12 min. Levels of beta tubulin in the glands of fifth instar larvae, measured by immunoblot, changed in a tissue-specific manner that paralleled or presaged circulating ecdysteroid levels. The accumulation of beta tubulin in PTTH-stimulated prothoracic glands resulted from increased transcription and translation and not from a decreased protein turnover rate. Pulse-chase experiments indicate that the newly synthesized beta tubulin had a very short half-life in vitro (approximately 0.5 hr). Studies with cycloheximide and actinomycin D indicated that beta tubulin synthesis and ecdysteroid synthesis are coregulated and that beta tubulin synthesis is regulated in a unique manner relative to most other prothoracic gland proteins. We conclude that beta tubulin levels may play an important role in ecdysteroidogenesis, perhaps by influencing the dynamics of microtubule-dependent secretion or interorganelle movement of ecdysteroid precursors.

Animals↗
PubMed1999

Functional binding of a vertebrate hormone, L-3,5,3'-triiodothyronine (T3), on insect follicle cell membranes.

A vertebrate hormone, L-3,5,3'-triiodothyronine (T3), induces volume reduction in the follicle cells of Locusta migratoria and Rhodnius prolixus. The effect of T3 on locust follicle cells is inhibited by ouabain and by antibodies raised against a membrane binding protein for juvenile hormone (JH). [125I]-T3 binds to membrane preparations of vitellogenic follicles in a specific and saturable fashion, with a KD in the low nanomolar range. T3 and JH III exhibited equivalent abilities to compete for the T3 binding site. These findings strongly suggest that T3 and JH act via the same receptor in follicle cells.

Animals↗
PubMed1985

Properties of an in vitro bioassay for hypertrehalosemic hormone of Blaberus discoidalis cockroaches.

The ability of the fat body to respond to the hypertrehalosemic action of corpora cardiaca-allata (CC + CA) extracts was measured in vitro with tissue from adult, male Blaberus discoidalis cockroaches. Only trehalose increased in the hemolymph when gland extracts were injected in vivo; likewise, only trehalose levels responded when fat bodies were exposed to gland extracts in vitro. Although fat bodies from 0-day-old animals gave the least response to gland extracts, all animals 5 or more days old showed elevated responses. A linear dose-response occurred between 0.02 and 0.08 CC + CA pair. Fat bodies did not show an in vitro, hypertrehalosemic response to insulin, glucagon, proctolin, dopamine, epinephrine, norepinephrine, serotonin, octopamine, or tyramine. A strong hypertrehalosemic response was found to both synthetic adipokinetic hormone and red-pigment concentrating hormone; however, reversed-phase, thin-layer chromatography of CC + CA extracts and adipokinetic hormone indicated that the hypertrehalosemic effect and the adipokinetic hormone were separate. This in vitro system comprises a relatively rapid, simple, and accurate bioassay for the hypertrehalosemic neurohormone of insects.

Adipose Tissue↗
PubMed1987

Diuretic action and immunological cross-reactivity of corticotropin and locust diuretic hormone.

A functional similarity and immunological cross-reactivity between adrenocorticotrophic hormone (ACTH) and a locust diuretic hormone (DH) is reported. The functional similarity is expressed in that ACTH mimics DH by stimulating fluid secretion and cyclic AMP (cAMP) secretion in locust Malpighian tubules. Desacetyl-alpha-melanocyte-stimulating hormone is active to a lesser degree but no other POMC-derived peptide tested was found to follow suit. Immunological cross-reactivity is shown by a positive response of HPLC-purified DH with a specific ACTH radioimmunoassay as well as a significant reduction in DH activity (fluid secretion) after incubations with ACTH antiserum. However, ACTH and DH are different peptides since they do not share common separation characteristics on HPLC and ACTH does not induce a high excess secretion of cAMP by the tubule cell as does DH.

Adrenocorticotropic Hormone↗
PubMed2004

Highly flexible ligand binding pocket of ecdysone receptor: a single amino acid change leads to discrimination between two groups of nonsteroidal ecdysone agonists.

The insect steroid hormone 20-hydroxyecdysone works through a ligand-activated nuclear receptor, the ecdysone receptor (EcR), which plays critical roles in insect development and reproduction. The EcR has been exploited to develop insecticides to control pests and gene switches for gene regulation. Recently reported crystal structures of the EcR protein show different but partially overlapping binding cavities for ecdysteroid (ECD) and diacylhydrazine (DAH) ligands, providing an explanation for the differential activity of DAH ligands in insects. 1-Aroyl-4-(arylamino)-1,2,3,4-tetrahydroquinoline (THQ) ligands were recently discovered as ecdysone agonists. Mutagenesis of the EcR (from Choristoneura fumiferana, CfEcR) ligand binding domain followed by screening in a reporter assay led to the identification of CfEcR mutants, which responded well to THQ ligands but poorly to both ECD and DAH ligands. These mutants were further improved by introducing a second mutation, A110P, which was previously reported to cause ECD insensitivity. Testing of these V128F/A110P and V128Y/A110P mutants in a C57BL/6 mouse model coactivator interaction assay and in insect cells showed that this mutant EcR is activated by THQ ligands but not by ECD or DAH ligands. The CfEcR and its V128F/A110P mutant were used to demonstrate simultaneous regulation of two reporter genes using THQ and DAH ligands.

3T3 Cells↗
PubMed1977

Effects of a juvenile hormone mimic on male and female gametogenesis of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae).

1. Effects of ingestion and topical application of 1.30 ppm methoprene, an insect juvenile hormone (JH) mimic, include gametogenesis disorders in both male and female mud-crab Rhithropanopeus harrisii. 2. Progressive inhibition of vitellogenesis and stimulation of spermatogenesis take place after a short exposure time (12-15 days), whereas a longer period (between 30 to 45 days) promotes inhibition of both spermatogenesis and vitellogenesis. Such modifications demonstrate the chemosterilizing action of methoprene on crustaceans. 3. Stoppage of vitellogenesis is characterized by a blockage of oocytes at terminal previtellogenesis and proliferation of the follicle cells involved in vitellogenic oocyte lysis. Spermatogenic degeneration begins with the amalgam of spermatocyte clusters in meiotic prophase and pycnosis of gonia. 4. Analogies between these results and those obtained from experiments involving androgenic gland implantations or the consequences of their hyperfunctioning are discussed.

Animals↗
PubMed1995

Insect nuclear receptors: a developmental and comparative perspective.

The appearance of puffs on the polytene chromosomes of insect salivary glands incubated with 20-hydroxyecdysone provided the first demonstration that steroids act directly at the gene transcriptional level to bring about subsequent cellular changes (Becker, 1959; Clever and Karlson, 1960). Despite that auspicious beginning, learning about the molecular mechanisms that underlie the hormonal regulation of insect development was impeded for many years by the difficulty associated with isolating and identifying rare regulatory factors from limited tissue sources. The advent of recombinant DNA methodology and powerful techniques such as the polymerase chain reaction (PCR) along with the recognition that many important endocrine factors are structurally conserved across a wide range of species has, however, all but eliminated the technical obstacles once facing the insect endocrinologist trying to isolate and study these regulatory molecules. This review will discuss recent progress and recall some earlier experiments concerning the molecular basis of hormonal action in insects focusing primarily on the members of the nuclear hormone receptor superfamily in Drosophila melanogaster. Two members of this family comprise the functional ecdysteroid receptor and at least a dozen other "orphans" have been identified in Drosophila for which no cognate ligand has yet been found. Many of these orphans are regulated by ecdysteroids. A discussion of juvenile hormone binding proteins that are not family members has been included because of their potential impact on nuclear receptor function. As receptor homologues have been identified in other insects, several general ideas concerning insect hormonal regulation have begun to emerge and these will be examined from a comparative point of view.

Amino Acid Sequence↗