Release of egg development neurosecretory hormone in Aedes aegypti and Aedes taeniorhynchus induced by an ovarian factor

Ovariectomized Aedes aegypti do not synthesize vitellogenin after a blood meal, unless an ovary from a blood-fed donor is implanted. Decapitation, however, prior to implantation inhibits vitellogenin synthesis. A female ovariectomized and decapitated 6 hr after a blood meal, synthesizes vitellogenin if an ovary from a blood-fed donor is implanted. On the other hand, females that are fed on blood and immediately decapitated can not be stimulated to synthesize vitellogenin with implanted ovaries removed from blood-fed donors. These experiments led to the hypothesis that the blood meal stimulates the ovary to secrete a corpus cardiacum stimulating factor, that in turn promotes release of egg development neurosecretory hormone stored in the corpus cardiacum.Injection of 20-hydroxy-ecdysone or ovarian extract prepared from ovaries removed from unfed females does not release egg development neurosecretory hormone. Thus corpus cardiacum stimulating factor is not 20-hydroxy-ecdysone, and ovaries removed from unfed females do not store it.The rate of inactivation of egg development neurosecretory hormone released from the corpus cardiacum after a blood meal was investigated by implanting an ovary into females that were blood fed for various intervals than decapitated and ovariectomized. Seventy per cent of implants grow when the operation is done 18 hr after feeding, and 30% when the operation is done between 18 and 24 hr after feeding, indicating that egg development neurosecretory hormone is stable for the first 18 hr after a blood meal.Aedes taeniorhynchus females ovariectomized 24 hr after adult emergence do not synthesize vitellogenin. When such a female is implanted with an ovary removed from a sugar-fed or blood-fed Aedes aegypti donor vitellogenin synthesis is initiated, and the implant grows. Decapitation prior to implantation inhibit vitellogenin synthesis and implants do not grow. These results indicate that corpus cardiacum stimulating factor is not species specific.     

Partial localization of a brain factor inhibiting egg production in the blood-feeding insect,Rhodnius prolixus

A previous study by Davey [Can J Zool 4:243–249 (1987)] showed that egg production in the blood-feeding insect Rhodnius prolixus is greatly enhanced when the corpus allatum (CA) is denervated. This result supported findings of others that the brain of Rhodnius imposes an inhibition on the CA via its connections to the CA. The present study identifies the nervus corporis cardiacum II (NCCII) as the nerve responsible for this inhibitory influence. Transecting the NCCII before feeding causes a dramatic increase in the number of eggs made. Since the NCCII is a relatively small nerve that may contain only axons of lateral and posterior neurosecretory cells in the protocerebrum, this result suggests that one or both of these cell types produce the brain factor inhibiting egg production in this insect. Arch. Insect Biochem. Physiol. 39:126–131, 1998. © 1998 Wiley-Liss, Inc.     

Ecdysteroidostatin from the house fly,Musca domestica

Ovaries from house flies maintained on sucrose secrete large amounts of ecdysteroid when they are cultured with ovarian ecdysteroidogenic hormone, OEH. However, ovarian ecdysteroid secretion is reduced by incubation with both OEH and the ovarian ecdysteroidostatin (OES). A partially purified OES fraction from a semi-preparative reverse phase HPLC C₁₈ column caused a 98% inhibition of ovarian ecdysteroid secretion in vitro at a concentration of 0.8 equivalents per μl. Ovaries can be activated to produce ecdysteroid in vivo by feeding diet containing protein to flies maintained on sucrose. Ecdysteroid secretion was inhibited when the in vivo stimulated ovaries were cultured with OES. This suggests that OES does not interfere with the OEH activation mechanism, but blocks ovarian ecdysteroid synthesis or release. Furthermore, OES inhibition is reversible and ecdysteroid secretion resumes when OES is removed. Musca OES could explain the decrease in ecdysteroid levels found in flies after mid-vitellogenesis. Both adult male and female abdomens contain OES, but OES was not transferred to females during mating. Evidence is presented that OES is not a trypsin modulating oostatic factor. Arch. Insect Biochem. Physiol. 38:166–176, 1998. © 1998 Wiley-Liss, Inc.     

Purification and partial characterization of mosquito egg development neurosecretory hormone: Evidence for gonadotropic and steroidogenic effects

Egg development neurosecretory hormone (EDNH), a hormone that stimulates vitellogenesis in mosquitoes, was purified 10,000-fold from the mosquito Aedes aegypti. The purification procedure included chromatography on hydrophobic, ion exchange, and gel filtration columns, and preparative electrophoresis to give an almost homogeneous preparation. The hormone is a polypeptide monomer of molecular weight of 18,700 ± 500 as determined from SDS electrophoresis and gel filtration chromatography. Using lowpressure chromatography throughout the purification procedure, the hormone was recovered at a high yield (39%). The amount of EDNH in a mosquito is about 0.6-1.6 ng, corresponding to 32–85 fmol. Injection of purified EDNH into female mosquitoes resulted in the conversion of [¹⁴C]cholesterol into labeled ecdysone and 20-hydroxyecdysone which were separated and identified using thin-layer chromatography and high-performance liquid chromatography separation procedures. Egg development and vitellogenin synthesis were also induced when EDNH was injected into several mosquito species, indicating that the hormone is not species-specific. This report is the first to show that a purified preparation of EDNH has both steroidogenic and a gonadotropic effects on female mosquitoes.     

Biosynthesis and distribution of ecdysone and 20-OH-ecdysone in Aedes aegypti

The distribution and biosynthesis of ecdysone and 20-hydroxyecdysone (20-OH-ecdysone) was followed in sugar- and blood-fed female Aedes aegypti. In both sugar- and early blood-fed animals most of the ecdysteroid determined by radioimmunoassay was found outside the ovary. Twenty-four to 40 h after blood feeding, however, ecdysteroid was distributed between ovary and carcass in the ratio of 1:1.5. Ecdysteroid titer reached a plateau between 18 to 40 h after the blood meal and decreased thereafter. Analysis of the ecdysteroid titer using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) revealed that both 20-OH-ecdysone and ecdysone were synthesized after the blood meal. The ratio of 20-OH-ecdysone to ecdysone remained essentially constant and fluctuated in parallel throughout egg development. Chromatography of the early ecdysteroid peak (8 h after feeding) using TLC and HPLC indicated that although it cross-reacted with ecdysteroid antibodies, it did not have the same elution times as ecdysone and 20-OH-ecdysone and is, therefore, probably a precursor of these ecdysteroids. Injections of egg development neurosecretory hormone (EDNH) preparation purified to near homogeneity, into ligated abdomens, induced ecdysteroid synthesis only if the abdomens were first treated with methoprene (12.5 pg). Methoprene at this concentration did not stimulate ecdysteroid synthesis in these abdomens. When blood-fed females were treated with [4-¹⁴C] cholesterol and analyzed using TLC and HPLC procedures, both [¹⁴C]labeled ecdysone and [¹⁴C]labeled 20-OH-ecdysone were synthesized in the ratio of 1:1.5. This report is the first to show that both ecdysone and 20-OH-ecdysone are synthesized in vivo in female A. aegypti.     

Effects of growth hormone-releasing factor, somatostatin and dopamine on growth hormone and prolactin secretion from cultured ovine pituitary cells

A synthetic form of human pancreatic growth hormone releasing factor (GRF-44-NH2) was shown to be a potent stimulator of growth hormone (GH) secretion and cellular cyclic AMP levels in cultured sheep pituitary cells. A small dose-dependent stimulation of prolactin secretion was also observed. Somatostatin (0.5 microM) completely blocked the maximal GRF (1 nM)-stimulated secretion without a significant effect on cyclic AMP levels. Dopamine (0.1 microM) inhibited the GRF-elevated GH secretion by 50% and lowered cyclic AMP levels by 30%. Dopamine (0.1 microM) inhibition of basal prolactin secretion was not affected by GRF (1 nM). The data support the hypothesis that cyclic AMP is involved in the action of GRF but suggest that somatostatin can inhibit GRF-induced secretion of GH independently of cyclic AMP.     

两种散白蚁两性生殖与孤雌生殖胚胎发育比较研究

【目的】探究散白蚁两性生殖胚胎和兼性孤雌生殖胚胎各自的发育特点。【方法】以黑胸散白蚁Reticulitermes chinensis和尖唇散白蚁R.aculabialis各自的受精卵(雌雄配对所产的卵)和未受精卵(雌雌配对所产的卵)为研究对象,采用激光共聚焦显微镜观测两种散白蚁的受精卵和未受精卵的卵裂状态,数码显微系统拍照观察卵的外部形态变化。【结果】黑胸散白蚁蚁后所产的受精卵和未受精卵在巢中均能进行卵裂,但是未受精卵在24和48 h时的卵核数无显著性差异,而受精卵卵核数在24和48 h时有显著性差异;15 d时未受精卵的体积没有发生显著变化,而受精卵的体积显著性增大;15-20 d时未受精的蚁卵死亡,而受精卵正常发育。尖唇散白蚁受精卵和未受精卵在相同的时间段内卵核数没有显著性差异,48 h时的卵核数明显比24 h时多;第10天时受精卵长度和宽度发生显著性变化,同时体积也明显增大,而未受精卵在第15天时长度和宽度才开始发生显著性变化,同时体积也开始显著增大。【结论】具有兼性孤雌生殖能力的尖唇散白蚁,受精卵和未受精卵卵裂速度相同,但受精卵外形体积变化比未受精卵早。黑胸散白蚁未受精卵能继续进行卵裂,但发育异常,不能孵化;两种白蚁卵发育过程中卵的长度和宽度同时发生变化。黑胸散白蚁孤雌卵的卵裂特性可能是白蚁两性生殖向兼性孤雌生殖进化的过渡适应阶段。     

A factor derived from chick embryo retina which inhibits DNA synthesis of retina itself

Chick embryo retinas contain a peptide factor that inhibits DNA synthesis in explants of chick embryo retina. The inhibitory factor, obtained by acid/ethanol extraction from 15-day-old chick embryo retinas, was partially purified by affinity chromatography on heparin-sepharose CL-6B and gel filtration on Sephadex G-100. The inhibitor reduced DNA synthesis with maximal effects observed in retinal explants from 7 to 8-day-old chick embryos. The inhibitory effect became apparent after 10 h of incubation and reached the maximum levels after 16 h. DNA-inhibiting activity was heat and acid-stable and was destroyed by trypsin and alkaline treatments. The inhibitory effect was observed in retinal explants incubated in a medium free froml-glutamine, and the addition of this compound to the medium reduced the inhibitory effect in a concentration-dependent manner.     

Detection and Partial Characterization of Egg Polypeptides from Heterodera glycines

The presence of two major egg polypeptides was demonstrated in the plant-parasitic nematode Heterodera glycines. The polypeptides were present in equal amounts in, and were most abundant in, eggs from yellow females. They were also present in brown females but were not detected in second-stage juveniles (J2). The two major egg polypeptides, MEP-I and MEP-II, accounted for more than 50% of the total protein in egg extracts evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. During development of females from the yellow stage to the brown stage, the levels of MEP-I and MEP-II declined at twice the rate as total protein. MEP-I and MEP-II had estimated molecular masses of 190 kD and 180 kD, respectively, similar to those reported for female-specific proteins, vitellins, from free-living nematodes.     

Binding of complement regulators factor H and C4b binding protein to group A streptococcal strains isolated from tonsillar tissue and blood

Group A streptococcus (GAS) is the most common pathogen causing bacterial pharyngitis. We isolated streptococcal strains from tonsils removed from patients with tonsillar disease (n=202) and studied their ability to bind the complement regulators factor H (FH) and C4b binding protein (C4BP) using 125 I-labeled proteins. Blood isolates of GAS (n=10) were obtained from patients with bacteraemia. Streptococci were isolated from 21% of the tonsillitis patients. The emm and T types of the GAS strains were determined. Of the 26 GAS strains studied, only six could bind FH and/or C4BP above the threshold levels. The fraction of the offered radioactive protein bound ranged between 6-12% for FH and 19-56% for C4BP. The clinical course of the tonsillar disease was not related to the binding of FH or C4BP by GAS. The binding strains were mostly of the T4M4 or T28M28 type. From the invasive strains (n=10), three bound FH (binding level: 8-11%) and two C4BP (36-39%). The binding correlated only partially to M-protein (emm) type suggesting that the binding was not exclusively due to M-protein. The results indicate that complement regulator binding by GAS is only partially related to pathogenicity and not a universal property of all group A streptococci.