Physical characteristics of the cerebral big prothoracicotropic hormone from Manduca sexta

The efficiency of calcitonin transport across the C-cell-blood barrier in rat thyroid

This paper studies calcitonin (CT) transport across the C-cell-blood (CCB) barrier in normal rats. The efficiency of this transport is expressed as endogenous calcitonin bioavailability (F(CT)), i.e., that portion of CT molecules extruded by the thyroid C-cell basal pole that enters the circulating blood. Because currently F(CT) cannot be estimated directly, a novel methodology was used for its estimation. The essence of this methodology is to assess the CT level before and after the CCB barrier, to study these input-output CT relationships mathematically, and to find the F(CT) range allowed by the relationships. In this context, the subplasmalemmal granule numerical density in the C-cell basal pole (X) and the CT concentration in the right ventricular blood (Y) were found to be highly correlated: r(xy) = 0.922, P < 0.001; the covariance coefficient rho(xy) = 0.9980, P < 0.0001. Clearly, the overall variance of these input-output relationships in the covariance model (square root Var(xy) = 6.32) is explained, specifically, by CT retention (R(CT)) variability at the CCB transport stages. The greater the R(CT) mean value in the studied rats, the greater is the impact of R(CT) variability on Var(xy). The estimated variance caused by R(CT) (Var(CCBR)) makes it possible to determine R(CT) and F(CT) (F(CT) = 100% - R(CT)). Thus we estimated Var(CCBR) as Var(CCBR) < Var(xy) - CV(RIA)(2), where CV(RIA)(2) is CT assay variance: square root Var(CCBR) = 6.00% (P > or = 0.95). We then estimated F(CT) as the value range that does not contradict the Var(CCBR) obtained: 62% < F(CT) < 100% (P > or = 0.95).

Identification of a steroidogenic neurohormone in female mosquitoes

In the female mosquito, Aedes aegypti, neurohormones are released from the brain in response to a blood meal and stimulate the ovaries to secrete ecdysteroid hormones, which modulate yolk protein synthesis in the fat body. Neuropeptides with this bioactivity were isolated from head extracts, and partial sequences from these peptides when aligned gave a 31-residue sequence at the amino terminus. Oligonucleotide primers for this sequence were used to amplify with the polymerase chain reaction a genomic DNA product that hybridized to a clone from a head cDNA library. The cDNA encodes a 149-residue preprohormone that is processed into an 86-residue peptide, as indicated by the mass value obtained from the native peptide, with the expected amino-terminal sequence. After modification, the cDNA for the putative neurohormone was expressed in a bacterial system, and the purified peptide had high specific activity in bioassays, thus confirming that it is a steroidogenic gonadotropin, the first to be identified for invertebrates.

Purification and characterization of the prothoracicotropic hormone of Drosophila melanogaster

The prothoracicotropic hormone (PTTH) of Drosophila melanogaster is a modulator of ecdysteroid (molting hormone) synthesis and was isolated and characterized from extracts of whole larvae (approximately 4 x 10(5) larvae). The purification protocol included delipidation, salt-extraction, heat treatment, conventional column chromatography, and HPLC, and yielded about 50 microg of pure hormone. Biological activity was followed using a ring gland in vitro assay in which ecdysteroidogenesis by control ring glands as measured by radioimmunoassay was compared with ring gland incubations containing active fractions. The molecular weight of the purified PTTH was 45 kDa and N-terminal amino acid sequence analysis indicated that those analyzed sequences displayed no significant homology with known peptides or peptide hormones, including PTTH from the silkmoth, Bombyx mori. Western blot analysis indicated that the native form of Drosophila PTTH was a single 66-kDa polypeptide with N-linked carbohydrate chains and intrachain disulfide bonds. The purified 45-kDa peptide is the deglycosylated form, a result of glycosidase activity present during preparation of the PTTH extract. The deglycosylated form shows heterogeneity, presumably as a result of varying degrees of deglycosylation at the N terminus.

Comparison of ecdysteroid production in Drosophila and Manduca: pharmacology and cross-species neural reactivity

In both Manduca sexta and Drosophila melanogaster, metamorphic events are driven by ecdysteroids whose production in prothoracic gland (PGs) is stimulated periodically by neural factors. Differences in the life cycle of moths and flies have made it difficult to compare the regulation of ecdysteroid biosynthesis in these two species. As in Manduca, at least two neural factors in the larval Drosophila BVG complex were separable by molecular weight, and they stimulated increased ecdysteroid biosynthesis from the ring gland, a composite organ that includes PG cells. Drosophila neural extracts accelerated ecdysteroid biosynthesis in Manduca PGs and, conversely, partially purified Manduca PTTH preparations elevated ecdysteroid biosynthesis in Drosophila ring glands, suggesting that the two species may share structurally similar prothoracicotropic factors. Drosophila ring glands required the presence of calcium ions to respond to neural extracts, but the phosphodiesterase inhibitor MIX and cAMP analogues exerted little, if any, positive effect on production. Mean ecdysteroid production rates of BVG-ring gland complexes taken from Drosophila larvae during various phases of the wandering period were often submaximal and highly variable, suggesting that they fluctuate widely prior to pupariation. Based on available data in Drosophila and the Manduca model for the control of ecdysteroid biosynthesis, a developmental scheme for neuroendocrine control in Drosophila is proposed.