Control Of Vitellogenin Synthesis Research Articles

RNA interference of insulin-related peptide and neuroparsins affects vitellogenesis in the desert locust Schistocerca gregaria

The ‘classic’ insect hormones, juvenile hormone and 20-hydroxyecdysone, can stimulate vitellogenesis and/or ovarian development in adult females of several insect species. Accumulating evidence also indicates a crucial role in female reproductive physiology for peptide hormones, such as insulin-related peptides (IRPs) and neuroparsins (NPs). Especially in dipteran species, IRP signaling has been shown to regulate female reproductive events. The first NP was originally identified from the migratory locust ( Locusta migratoria) as an antigonadotropic factor that delayed vitellogenesis. Moreover, NP family members display sequence similarities with the N-terminal domain of vertebrate insulin-like growth factor binding proteins (IGFBPs). In the current study, RNA interference (RNAi) was employed to investigate the possible involvement of IRP and NPs in the control of the female desert locust ( Schistocerca gregaria) reproductive system. The cDNAs encoding an IRP ( Scg-IRP) and four NPs ( Scg-NPs) had previously been cloned from S. gregaria. An RNAi-mediated knock-down of either Scg-NP or Scg-IRP transcript levels was induced in adult female desert locusts and the subsequent effects were analyzed. Knock-down of the Scg-NPs or Scg-IRP affected vitellogenin transcript levels and oocyte growth in a positive and negative way, respectively. The current findings are indicative for a role of Scg-NPs and Scg-IRP in the control of vitellogenin synthesis. A plausible hypothesis is that Scg-IRP may act as a sensor of the nutritional and metabolic status that determines whether vitellogenesis can occur. That the same processes were affected in opposite ways in both RNAi experiments offers an extra argument for antagonizing roles of Scg-NPs and Scg-IRP.

Response of cultured Aedes aegypti fat bodies to 20-hydroxyecdysone

Fat bodies from non-blood-fed Aedes aegypti, stimulated in vitro by 10 −4 M and 10 −6 M of 20-hydroxyecdysone, were found to synthesize and release vitellogenin into the culture medium. Vitellogenin-specific monoclonal antibodies were utilized in an enzyme-linked immunosorbent assay procedure for quantification of vitellogenin in small aliquots of medium taken periodically from the culture. A minimal exposure of 5 h to 20-hydroxyecdysone was shown to be needed before the fat bodies would respond. Time-course of vitellogenin production in vitro was found to be identical to that observed in vivo. Vitellogenin-titre profiles were also investigated in cultured fat bodies from blood-fed A. aegypti. In all cases, response patterns were not affected by the presence or absence of 20-hydroxyecdysone after the fat bodies had been stimulated by blood meal to produce vitellogenin. We suggest here that initiation and control of vitellogenin synthesis is a programmed response to 20-hydroxyecdysone.

INTRODUCTION: TEN YEARS OF ECDYSONE WORKSHOPS: RETROSPECT AND PERSPECTIVES

Publisher Summary This chapter provides an overview of ecdysone workshops. The methods for the separation and analysis of ecdysteroids have undergone spectacular improvements, largely because of the introduction of high-performance liquid chromatography (HPLC) and the use of combined gas chromatography–mass spectrometry (GC–MS) of 1 H-NMR and 13 C-NMR. Ecdysone and/or 20-hydroxyecdysone are inactivated primarily by the esterification or epimerization of the C-3 hydroxyl group or, to a lesser extent, by the esterification of the C-2 hydroxyl group on the A nucleus. A relatively wide-spread inactivation pathway is the hydroxylation of the C-26 methyl group followed by oxidation to an ecdysonoic acid. In higher insect orders, like the dipterans, ovarian ecdysteroids play a role in the control of vitellogenin synthesis, whereas in other orders, they play a role in the early events of embryogenesis. Vitellogenic ovaries synthesize ecdysteroids at a given stage of their development; in some species, this synthesis occurs only towards the end of vitellogenin uptake; in others, it occurs at almost the same time as concomitantly the onset of vitellogenin synthesis.

Control of vitellogenin synthesis by ecdysteroids in Sarcophaga bullata

Control of vitellogenin synthesis by ecdysteroids in Sarcophaga bullata

Similarities in vitellogenin and control of vitellogenin synthesis within the genera Sarcophaga, calliphora, phormia and lucilia (diptera)

1. 1. The major yolk polypeptides from the different species are identified by SDS-gradient gel electrophoresis. 2. 2. Vitellogenins of the 4 species have similarities in both minimum number and size of their polypeptides. They also react with antibodies raised against vitellin of Sarcophaga. 3. 3. In males of all species ecdysterone but not the JH analog methoprene induces the yolk polypeptides. 4. 4. In non-protein fed females only ecdysterone is able to replace the triggering effect of the protein meal on vitellogenin synthesis. 5. 5. The inability to stimulate vitellogenin synthesis in vivo by a JH analog is discussed.

Control of vitellogenin synthesis in the Monarch butterfly by juvenile hormone

Yolk formation in the Monarch butterfly, as in many other insects, entails juvenile hormone-induced synthesis in the fat body, transport in the hemolymph, and uptake into the oocytes of specific sex-limited protein, the vitellogenin. In the Monarch, vitellogenin first appears in the hemolymph 1 day after emergence of the adult butterfly and then rises rapidly in concentration for at least 3 days. The synthesis of vitellogenin in adult females was shown by the incorporation of [ 3H]leucine. Active labeling was observed at the same time as the presence of vitellogenin in the hemolymph was first detectable, and the radioactivity in vitellogenin expressed as a percentage of radioactivity in total blood proteins reached 50–60% 3 days after adult emergence. The appearance of vitellogenin was prevented by ligature of freshly emerged butterflies at the neck and restored by injection of juvenile hormone. A low yet significant stimulation of vitellogenin synthesis could be detected as early as 10 hr after administration of the hormone into neck-ligated butterflies, and after 30 to 50 hr about 40% of the total blood protein label was found in the specific protein. With C 18-juvenile hormone (JH-I), 0.1 μg per animal was effective in inducing a low level of vitellogenin synthesis, and between 0.01 and 1 μg, a linear relationship between synthesis and log dose was observed. The synthetic analog ZR-512 was also active. In a preliminary experiment, actinomycin D effectively blocked the induction of vitellogenin synthesis.