Inhibited Egg Development Research Articles

Summer egg diapause in a matchstick grasshopper synchronizes the life cycle and buffers thermal extremes.

The phenological response is among the most important traits affecting a species' sensitivity to climate. In insects, strongly seasonal environments often select for a univoltine life cycle such that one seasonal extreme is avoided as an inactive stage. Through understanding the underlying mechanisms for univoltinism, and the consequences of its failure, we can better predict insect responses to climate change. Here we combine empirical data and simulation studies to investigate the consequences of an unusual diapause mechanism in a parthenogenetic matchstick grasshopper, Warramaba virgo, from arid southern Australia. Our field body temperature measurements indicate that this species is a thermoconformer and our laboratory studies of the thermal response of feeding rate imply strong constraints on winter activity. However, the species exhibits no obligate winter diapause, and eggs can develop in 1 month under constant temperatures approximating the mean soil temperature at the time of oviposition (summer). We show that diurnal temperature cycles exceeding a peak of 36 °C inhibit egg development in summer, and that this is sufficient to prevent autumnal hatching of eggs. Development is also strongly retarded below 24 °C. Microclimate-driven simulation studies of egg development show that these thermal responses provide robust maintenance of a univoltine life cycle, thereby resulting in survival of heat stress as an egg (due to limited developmental state) and avoidance of cold stress as a nymph and adult (due to overwintering in the soil as an egg).

F-actin rearrangement is regulated by mTORC2/Akt/Girdin in mouse fertilized eggs.

In mouse fertilized eggs, correct assembly and distribution of the actin cytoskeleton are intimately related to cleavage in early‐stage embryos. However, in mouse fertilized eggs, mechanisms and involved factors responsible for regulating the actin cytoskeleton are poorly defined. In this study, mTORC2, PKB/Akt and Girdin were found to modulate division of mouse fertilized eggs by regulating distribution of the actin cytoskeleton. RNA interference (RNAi)‐mediated depletion of mTORC2, Akt1 or Girdin disrupted F‐actin rearrangement and strongly inhibited egg development. PKB/Akt has been proven to be a downstream target of the mTORC2 signalling pathway. Girdin, a newly found actin cross‐linker, has been proven to be a downstream target of the Akt signalling pathway. Furthermore, phosphorylation of both Akt1 and girdin was affected by knockdown of mTORC2. Akt1 positively regulated development of the mouse fertilized eggs by girdin‐mediated F‐actin rearrangement. Thus it seems that girdin could be a downstream target of the Akt1‐mediated signalling pathway. Collectively, this study aimed to prove participation of mTORC2/Akt in F‐actin assembly in early‐stage cleavage of mouse fertilized eggs via the function of girdin.ObjectivesIn mouse fertilized eggs, the proper assembly and distribution of actin cytoskeleton is intimately related with the cleavage of early‐stage embryo. However, in mammals, especially in mouse fertilized eggs, the mechanisms and involved factors responsible for regulating the actin cytoskeleton are poorly defined. The aim of this study was to determine the role of mTORC2,PKB/Akt and Girdin in early development of fertilized mouse eggs, via regulating the distribution of actin cytoskeleton.Materials and methodsChanges of F‐actin after treatting with mTORC2 shRNA, Akt siRNA or Girdin siRNA were observed by Immunofluorescence staining and laser‐scanning confocal microscopy. Levels of phosphorylated Girdin at Se1417 were detected by Western immunoblotting. Percentages of cells undergoing division were determined by counting, using a dissecting microscope.ResultsRNA interference (RNAi)‐mediated depletion of mTORC2, Akt1 or Girdin disrupts F‐actin rearrangement, and remarkably inhibited the development of mouse‐fertilized eggs. PKB/Akt has been proved to be a downstream target of the mTORC2 signaling pathway. Girdin, the newly found actin‐cross linker, has been proved to be a downstream target of the Akt signaling pathway. Furthermore phosphorylation of both Akt1 and Girdin were affected by knockdown of mTORC2. Akt1 positively regulates the development of mouse‐fertilized eggs by Girdin mediated F‐actin rearrangement. Girdin could be a downstream target of the Akt1‐mediated signaling pathway.ConclusionsCollectively, this study aimed to prove the participation of mTORC2/Akt in F‐actin assembling in early‐stage cleavage of mouse fertilized eggs via the function of Girdin.

The level of embryonation influences detection of Ostertagia ostertagi eggs by semi-quantitative PCR.

BackgroundThe Internal Transcribed Spacer 2 (ITS2) is a candidate diagnostic marker of the pathogenic cattle nematode Ostertagia ostertagi. The aims of this study were: (i) to document and quantify how the development of O. ostertagi eggs affects ITS2 copies under different storage conditions, and (ii) to suggest optimal storage conditions for faecal samples in a diagnostic pipeline that involves detection and semi-quantification by real-time semi-quantitative polymerase chain reaction (qPCR).FindingsEggs of Ostertagia ostertagi were obtained from fresh faeces and stored at 4 °C or 25 °C under aerobic or anaerobic (vacuum packing) conditions. Development was monitored by microscopy for up to 336 h, and the ITS2 copies were determined by qPCR from a fixed number of parasites. Under aerobic conditions at 25 °C, embryonation and a significant increase of ITS2 copies (P < 0.0001) were observed after 12 h. At 4 °C, embryonation occurred after 168 h with a trend towards increased ITS2 copies. Anaerobic conditions inhibited egg development at both temperatures and no significant increase in ITS2 copies was noticed (P = 0.90). ITS2 copies were analysed for each parasite stage: first-stage larvae (L1) exhibited significantly higher copy numbers (20,353 ± 1,950) than unembryonated eggs (568 ± 168; P < 0.0001) with lower coefficient of variation (33 vs 266 %).ConclusionsAerobic storage of O. ostertagi eggs at 25 °C led to a significant increase in ITS2 copies after 12 h due to embryonation and subsequent hatching. In contrast, anaerobic storage (vacuum packing) at 25 °C completely inhibited egg development and any undesirable semi-quantification bias for up to 336 h. Hence, vacuum packing is an optimal storage strategy prior to molecular diagnostic analyses. Alternatively, aerobic storage at 4 °C for up to 72 h can be used. Due to high copy numbers and lower genetic variation, the L1 stage may be considered for diagnostics and further molecular research.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1657-4) contains supplementary material, which is available to authorized users.

Effect of PCBs on Egg and Larval Development of Beet Armyworm, Spodoptera exigua

Polychlorinated biphenyls (PCBs) are nondegradable pollutants that are known to affect physiology of organisms. To assess the physiological alteration of the pollutants on insects, the beet armyworm, Spodoptera exigua, was used as a model insect because of its wide-range occurrence and high biochemical detoxification against toxic chemicals. Low ppb levels of PCBs applied on newly laid eggs of S. exigua were found to inhibit egg development and later larval development. Larvae fed with PCB-contaminated artificial diet (below ppb levels) exhibited significant mortalities, though it did not affect the capacity of diet consumption or digestibility. PCBs injected into larval hemocoel of S. exigua were not excreted. In vitro assay showed that PCBs induced some fat body esterases of S. exigua. However, PCBs did not affect juvenile hormone esterase activity in larval hemolymph of S. exigua. These results suggest that the immature stages of S. exigua are highly susceptible, but responsive to PCBs by inducing some esterases.

The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers

SUMMARY1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs.2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod.3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day−1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare.4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.

Feeding the mosquito Aedes aegypti with TMOF and its analogs; effect on trypsin biosynthesis and egg development

Female Aedes aegypti that were given a blood meal by enema deposited yolk in their oocytes and synthesized trypsinlike enzymes in their midgut. When females were given an enema of Aea-TMOF (Trypsin Modulating Oostatic Factor) (NH 2-YDPAPPPPPP-COOH) and blood both egg development and trypsin biosynthesis were inhibited. Similar results were observed if TMOF was mixed with the blood meal and fed to female mosquitoes through a membrane. Renin inhibitor (NH 2-PHPFHFFVYK-COOH) or poly proline given by enema with the blood meal did not affect egg development or trypsin biosynthesis. Feeding of TMOF analogs P1 (NH 2-YDPAP-COOH) or P4 (NH 2-YDPAPPPP-COOH) inhibited trypsin biosynthesis in the midgut. Injecting or giving an enema of an amidated peptide (NH 2-WRPGPPPPPP-CONH 2) of HIV-2 X-ORF protein also inhibited egg development and trypsin biosynthesis in the mosquito gut. When [ 3H]TMOF was purified by high performance liquid chromatograophy (HPLC) and fed with the blood meal through a membrane to female mosquitoes, [ 3H]TMOF outside the gut increased linearly for the first 24 h and 28% of the hormone was found outside the gut at 72 h. These results suggest that TMOF and its active analogs traverse the gut epithelial cells into the hemolymph, bind TMOF gut receptor(s) and modulate trypsin biosynthesis.

Hormonal control of ovarian development in the tickAmblyomma hebraeumKoch (Acari: Ixodidae)

Summary Hormonal control of egg development in the ixodid tick Amblyomma hebraeum Koch was investigated as follows: ovaries from small partially fed or fully engorged females were transplanted into the haemocoel of engorged females that were undergoing vitellogenesis; the transplants responded to this milieu by completing oocyte maturation. The following treatments all failed to stimulate egg development within eight days in small partially fed ticks: (a) slow fusion of 20-hydroxyecdysone (up to 7.2 μg) over 24 h; (b) topical application or injection of up to 50 μg juvenile hormone III; (c) topical application of 10 μg of methylfarnesoate and juvenile hormone III bisepoxide; (d) a combination of 20-hydroxyecdysone and juvenile hormone III. Also, none of the latter treatments accelerated oocyte maturation in engorged females. Injections (up to 100 μg per tick) or topical application (1 mg per tick) of precocene II did not inhibit egg development in engorged females which survived this treatment. Thus, alth...

Effect of cobalt and other divalent cations on oöcyte development of the black blowfly, Phormia regina (Meigen)

Results showed that injections of the divalent cation cobalt, a calcium channel blocker, at effective haemolymph concentrations of 2.1, 3.4 or 5.0 mM, immediately prior to liver feeding, retarded or inhibited egg development by influencing vitellogenin uptake in Phormia regina. Topical application of methoprene (a juvenile hormone analogue) to cobalt-injected flies partially restored the otherwise inhibited egg development. Since vitellogenin uptake in this fly is controlled by juvenile hormone, cobalt may affect oöcyte development at least partly through its effect on juvenile hormone biosynthesis. Rates of juvenile hormone biosynthesis by the corpus allatum, in vitro, in cobalt-injected flies fell into three levels of 0.48 ± 0.01, 0.72 ± 0.12 and 0.97 ± 0.08 pmol/gland pair/h. These three levels of rates of juvenile hormone biosynthesis corresponded well with the three categories of ovary development observed in cobalt-injected flies: undeveloped, partially developed and fully developed. In comparison, the rates of juvenile hormone biosynthesis were 0.03 ± 0.00, 1.16 ± 0.08 and 1.23 ± 0.10 pmol/gland pair/h for sugar-fed, liver-fed, and liver-fed but water-injected control flies, respectively. Effects or lack of effects of several different calcium-replacement divalent cations and a dihydropyridine calcium channel blocker (i.e. nifedipine) on oöcyte development in P. regina suggested that calcium channels of the corpora allata may be involved in the regulation of juvenile hormone biosynthesis, which then affected oöcyte development.

Oostatic hormone inhibits biosynthesis of midgut proteolytic enzymes and egg development in mosquitoes

AbstractInjection of partially purified oostatic hormone (0.7 μg) into female Aedes aegypti inhibited egg development, proteolytic enzyme activity, and blood digestion in the midgut, whereas control injections of saline or insulin chain A (0.7 μg) did not affect these processes. Oostatic hormone given by enema, on the other hand, did not inhibit proteolytic enzyme activity, indicating that the hormone acts outside the midgut. A single injection of oostatic hormone (0.7 μg) caused a 1.7–1.5‐fold reduction in activity of trypsinlike enzymes during blood digestion, with a 10‐h delay in peak activity.Using [1,3‐3H]diisopropylfluorophosphate (DFP) in the presence of 8 mM tosylamide‐2‐phenylethyl chloromethyl ketone, the synthesis of trypsinlike derivatives was followed in the midgut of female A. aegypti. A 4‐fold reduction in [1,3‐3H]diisopropylphosphoryl‐trypsinlike derivatives was noted after oostatic hormone treatment. Several isozymes that are normally synthesized were absent in the presence of DFP, as assessed by polyacrylamide gel electrophoresis. Injection of oostatic hormone into decapitated and ovariectomized females that did not synthesize ecdysteroids inhibited trypsinlike enzyme synthesis and blood digestion in the midgut, indicating that oostatic hormone inhibits the midgut cells and not the ovary or the brain's endocrine system.Comparison between oostatic hormone and soybean trypsin inhibitor indicated that the former inhibited trypsin synthesis whereas the latter inhibited trypsin activity. A. aegypti oostatic hormone is not species specific and injections of the hormone into Culex quinquefasciatus, Culex nigripalpus, and Anopheles albimanus caused inhibition of egg development, blood digestion, and synthesis of trypsinlike enzymes. A direct relation between oostatic hormone synthesis and the regulation of trypsinlike activity in the midgut is proposed.

Isolation and characterization of highly purified mosquito oostatic hormone

AbstractOostatic hormone, the hormone that inhibits vitellogenesis in mosquitoes, was purified 7,000‐fold with a recovery of 70% from the ovaries of the mosquito Aedes aegypti. The purification procedure included heat treatment and chromatography on ion exchange and gel filtration columns. The hormone is a small peptidelike molecule of molecular weight 2,200 at pH 4.5, which aggregates into larger molecular species of trimer and octamer at pH 7.0 as determined by gel filtration. The hormone is positively charged at pH 7.8 and has a low Rf at pH 9.4 on disc gel electrophoresis.Injection of purified oostatic hormone (9 ng) into female mosquitoes inhibited yolk deposition and vitellogenin synthesis. Activity of the oostatic hormone in the mosquito ovary increased rapidly following blood feeding and reached a maximum after 48 h. Oostatic hormone of A. aegypti injected into autogenous Aedes taeniorhynchus inhibited egg development. Repeated injections of dilute oostatic hormone at 24 h intervals partially arrested egg development, resulting in 60% reduction in the number of eggs laid. This hormone does not block release of egg development neurosecretory hormone (EDNH) from the mosquito brain but rather appears to act on the ovary.

EFFECT OF GAMMA RADIATION ON RHIZOGLYPHUS ECHINOPUS (FUMOUZE AND ROBIN) AND ALEUROGLYPHUS OVATUS (TROUPEAU) (ACARI: ACARIDAE)

Eggs, inert deutonymphs and young, virgin adults of Rhizoglyphus echinopus (Fumouze and Robin) and Aleuroglyphus ovatus (Troupeau) were treated with 5, 10, 15, 20, 40, 60, 80, and 100 krad of gamma radiation. Fecundity, egg viability, oviposition period, survival of developmental stages, and longevity of females were compared. Doses ≥ 40 krad completely inhibited egg development. Eggs of A. ovatus were more resistant to gamma radiation than those of R. echinopus. The effect of irradiation on the inert deutonymphs was more detrimental than it was on young adults. Effect of irradiation on the life span of females of both species was stimulatory at doses of up to 60 krad and inhibitory at higher doses. The oviposition period varied inversely with the irradiation dose. Irradiation with 5 krad caused, in both mite species, at least a 50% decrease in fecundity.

Observations on the relationship betweenEylaisandHydrachna(Acari: Hydracarina) andSigaraspp. (Insecta: Hemiptera: Corixidae)

Species of Eylais and Hydrachna parasitising Sigara dorsalis and S. falleni in a reservoir in Leicestershire, England, were studied. S. dorsalis had a greater infestation of mites than S. falleni, but the latter, in one season, had more mites on the flightless than the normal flight‐muscle morph. Overwintering mite nymphochrysalids temporarily inhibited egg development in the host. This probably extended the time during which the host's spring migration could occur, and would increase the chance of dispersal for those species of mites and corixids which breed in temporary ponds and overwinter in permanent water bodies. Eylais nymphochrysalids had an aggregated distribution on S. falleni.