Are lysosomes directly involved in the iron uptake by reticulocytes?

• 1.1. The mechanism by which iron is transferred from the plasma protein transferrin into erythroid precursors for incorporation in heme is not completely understood.
• 2.2. To show a direct functional role of lysosomes in the process of iron uptake we tried to isolate lysosomes from reticulocytes, which have been incubated with ¹²⁵ITf⁵⁹Fe.
• 3.3. However, with various cell fractionating techniques described for liver cells no pure lysosomes from reticulocytes could be obtained.
• 4.4. Fluorescence and electron microscopy showed that reticulocytes hardly contain well-defined lysosomes.
• 5.5. There are several indications that in reticulocytes acid vacuoles instead of lysosomes are involved in the removal of iron from endocytosed transferrin.
• 6.6. The presence of apoTf, monoferric TfFe(A), monoferric TfFe(B) in the medium after incubation of reticulocytes with diferric transferrin, together with the fact that both iron binding sites of transferrin release their iron at pH present in acid vacuoles, suggests a second mechanism of iron uptake by reticulocytes, in which acid vacuoles are not involved.

     

Are cyclooxygenase-2 and nitric oxide involved in the dyskinesia of Parkinson's disease induced by l-DOPA?

Inflammatory mechanisms are proposed to play a role in l-DOPA-induced dyskinesia. Cyclooxygenase-2 (COX2) contributes to inflammation pathways in the periphery and is constitutively expressed in the central nervous system. Considering that inhibition of nitric oxide (NO) formation attenuates l-DOPA-induced dyskinesia, this study aimed at investigating if a NO synthase (NOS) inhibitor would change COX2 brain expression in animals with l-DOPA-induced dyskinesia. To this aim, male Wistar rats received unilateral 6-hydroxydopamine microinjection into the medial forebrain bundle were treated daily with l-DOPA (21 days) combined with 7-nitroindazole or vehicle. All hemi-Parkinsonian rats receiving l-DOPA showed dyskinesia. They also presented increased neuronal COX2 immunoreactivity in the dopamine-depleted dorsal striatum that was directly correlated with dyskinesia severity. Striatal COX2 co-localized with choline-acetyltransferase, calbindin and DARPP-32 (dopamine-cAMP-regulated phosphoprotein-32), neuronal markers of GABAergic neurons. NOS inhibition prevented l-DOPA-induced dyskinesia and COX2 increased expression in the dorsal striatum. These results suggest that increased COX2 expression after l-DOPA long-term treatment in Parkinsonian-like rats could contribute to the development of dyskinesia.     

Are separable aromatase systems involved in hormonal regulation of the male brain?

In vitro study of testosterone (T) metabolism shows that formation of estradiol-17β (E₂) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E₂ required for specific components of male sexual behavior. Two sub-areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high-affinity enzyme occurs in both areas (apparent K_m < 14nM), but the V_max of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic-anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.     

Are separable aromatase systems involved in hormonal regulation of the male brain?

In vitro study of testosterone (T) metabolism shows that formation of estradiol-17 beta (E2) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E2 required for specific components of male sexual behavior. Two sub-areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high-affinity enzyme occurs in both areas (apparent Km less than 14 nM), but the Vmax of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic-anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.     

Defence strategies against a parasitoid wasp in Drosophila: fight or flight?

Hosts may defend themselves against parasitism through a wide variety of defence mechanisms, but due to finite resources, investment in one defence mechanism may trade-off with investment in another mechanism. We studied resistance strategies against the parasitoid wasp Leptopilina boulardi in two Drosophila species. We found that D. melanogaster had significantly lower physiological resistance against L. boulardi than D. simulans, and hypothesized that D. melanogaster might instead invest more heavily in other forms of defence, such as behavioural defence. We found that when given a choice between clean oviposition sites and sites infested with wasps, both D. melanogaster and D. simulans detected and avoided infested sites, which presumably limits later exposure of their offspring to infection. Unlike D. simulans, however, D. melanogaster laid significantly fewer eggs than controls in the forced presence of wasps. Our findings suggest that D. melanogaster relies more heavily on behavioural avoidance as defence against wasp parasitism than D. simulans, and that this may compensate for a lack of physiological defence.     

Does a deletion in a virus-like particle protein have pleiotropic effects on the reproductive biology of a parasitoid wasp?

Endoparasitoid insects have evolved mechanisms to counteract host immune defences. At oviposition, the endoparasitoid Venturia canescens injects virus-like particles (VLPs) together with the egg that interfere with the immune system of the host. These prevent encapsulation of the parasitoid egg. It has been shown that the gene coding for one of the VLP proteins exists in two variants (called Repeat-Plus (RP) and Repeat-Minus (RM)). Previous observations suggested that these variants induce pleiotropic effects on the reproductive biology of the female resulting, in an impeded transfer of eggs from the ovarioles to the oviducts in RM females, and in alterations in the egg laying sequence. We show that RM females from another geographical locality do not exhibit any phenotypic alteration of the reproductive biology. By showing a lack of association between VLP alleles and the reproductive phenotypic characteristics in a given strain, our results do not support the hypothesis of pleiotropic effects. Conversely, the results suggest that different genes code for the VLPs and for the reproductive biology characteristics. Different phenomena such as linkage, the action of pathogens, etc. could explain the association between characters that is observed in some strains.     

Are behavioural traits in prey sensitive to the risk imposed by predatory fish?

1. Behavioural differences among prey species may result from evolutionary adaptations that facilitate coexistence with different predators and influence vulnerability to predators. It has been hypothesised that prey species modify their behaviour in relation to the risk posed by particular predators. 2. We examined the relationship between anti‐predator behaviour and predation risk in five species of larval odonates in combination with three predatory fish species (perch, gudgeon and rudd) that differ in foraging behaviour. The odonates, Platycnemis pennipes, Coenagrion puella, Lestes sponsa, Sympetrum striolatum and Libellula depressa, differ with regard to their life cycle and habitat, including water depth, occurrence in temporary ponds and co‐existence with fish. 3. The odonate species differed in their response to fish: (i) Two species showed a flexible response. Larval C. puella reduced activity in the presence of fish, regardless of species, whereas L. depressa altered their activity only in the presence of gudgeon. (ii) Independent of fish species, all odonates except L. depressa exhibited spatial avoidance of fish. This was interpreted as a more general anti‐predator response. (iii) In some cases the odonates showed no response to predators and their behaviour was thus independent of predation risk. 4. Our results confirm that all odonates responded to the presence of at least some predatory fish, and that some odonate species discriminated between fish species. However, we found no significant correlation between behavioural modifications and predation risk, indicating that anti‐predator responses and predation risk depend on the particular predator and the species being preyed on.     

Are bulbo-spinal serotonergic systems involved in the detection of nociceptive messages? (author's transl)

Intensely noxious peripheral stimuli of the anaesthetized rat produce two changes in the activity of convergent dorsal horn units: the segmental neuronal pool is activated, while all other convergent neurones are inhibited. These Diffuse Noxious Inhibitory Controls (DNIC) are highly potent (60-80% inhibition) and suppress all convergent neuronal activity, whether spontaneous or evoked by noxious or nonnoxious stimuli. On the other hand, they have no effect on other dorsal horn cell types, including noxious-only and proprioceptive units. The "DNIC" circuits include at least one supraspinal relay since DNIC is not seen in spinal animals. Furthermore, they are greatly reduced by lesions of the Nucleus Raphé Magnus (NRM). It has been shown that this nucleus massively projects onto the spinal cord, in particular onto the dorsal horn, and that stimulation of the NRM results in convergent unit inhibition of the same degree of magnitude as with DNIC. The role of serotonergic mechanisms in DNIC can be demonstrated pharmacologically: pCPA pre-treatment (3 daily I.P. injections, 300 mg/kg) or cinanserin (4 mg/kg I.V.) both result in a potent decrease (50-80%). We have proposed that the nociceptive message from the convergent units could result in a contrast between activity of the activated segmental pool and silence of the remaining convergent units. If this hypothesis can be verified, then some raphé nuclei and brain stem serotonergic pathways may function as filters in the detection of nociceptive messages, allowing extraction of information from somatic background activity including the firing from peripheral mechanoreceptors. While superficially paradoxical in fact our hypothesis fits well with the observation of profound analgesia following NRM stimulation: indeed, this hypothetical contrast would be completely eliminated by NRM stimulation since both neuronal pools would then be inhibited.     

Host–parasitoid development and survival strategies in a non-pollinating fig wasp community

In a tritrophic system, parasitoid development and galler host survival strategies have rarely been investigated simultaneously, an approach crucial for a complete understanding of the complexity of host–parasitoid interactions. Strategies in parasitoids to maximize host exploitation and in gallers to reduce predation risk can greatly affect the structure of tritrophic communities. In this study, the developmental strategies of galler hosts and their associated parasitoids in the tritrophic fig–fig wasp system are experimentally investigated for the first time. In this highly co-evolved system, wasp development is intrinsically tied with the phenology of the wasp brood sites that are restricted to the enclosed urn-shaped fig inflorescence called the syconium which can be regarded as a microcosm. Wasp exclusion experiments to determine host specificity, gall dissections and developmental assays were conducted with non-pollinating fig wasps in Ficus racemosa. Our results provide evidence for exceptions to the widely accepted koinobiont–idiobiont parasitoid dichotomy. This is also the first time fig wasps were raised ex situ from non-feeding stages onwards, a technique that enabled us to monitor their development from their pre-pupal to adult stages and record their development time more accurately. Based on variation in development time and host specificity, the possibility of a cryptic parasitoid species is raised. The frequency of different wasp species eclosing from the microcosms of individual syconia is explained using host–parasitoid associations and interactions under the modulating effect of host plant phenology.     

Are polyphosphoinositides involved in platelet activation?

In human platelets, the amounts of triphosphoinositides (TPI) and diphosphoinositides (DPI) increase after 30 sec and level off after 120 sec of thrombin stimulation. After 180 sec of thrombin challenge, TPI and DPI increase accounts for 66 and 80%, respectively. Polyphosphoinositide changes roughly parallel the release of N-acetyl-beta-D-glucosaminidase and appear as a later event compared to aggregation and serotonin secretion. It is concluded that an increased phosphorylation of polyphosphoinositides might participate in platelets to the process of stimulus-activation coupling and might be linked to thrombin receptor occupancy. A role of DPI in platelet activation is suggested by the observation that DPI promote platelet aggregation, the mechanism of which is discussed.     

Are caveolae involved in clathrin-independent endocytosis?

In addition to endocytosing molecules via clathrin-coated pits, cells also internalize membrane and fluid by a clathrin-independent endocytic mechanism. In this article we search for the equivalent of clathrin-coated pits in clathrin-independent endocytosis, and discuss some pitfalls in the interpretation of electron micrographs. We also discuss how the early steps in clathrin-independent endocytosis might be analysed morphologically, and we argue that caveolae are not involved in clathrin-independent endocytosis.     

Are multiple predator effects directed by prey availability?

Antagonistic/synergistic interactions among predators foraging on the same prey have been assumed to play a major role in shaping community structure. Studies in systems with multiple predator species have shown that the strength of these interactions may not be predictable and is largely dependent on individual behavioural traits, species density and habitat complexity. Although the association of prey consumption and satiation of a foraging predator has long been recognized, there has been relatively little research on how prey availability affects multiple predators’ effects. In this work, we present a framework to investigate the variation in two coexisting/competing predators’ effects on prey risk as affected by the prey availability rate. Functional responses by each predator species were first studied in single-predator treatments. Then, the intra- and inter-specific competition was investigated by employing additive and substitutative experimental designs to highlight the nature of multiple effects. Intra- and interspecific interactions were found to be similar and there was risk reduction, and risk enhancement for the prey at intermediate and high levels, respectively, according to the multiplicative risk model (MRM). The results indicated that when similar predators are concerned, the outcomes of MRM may vary according to the functional response curve of these predators. Thus, studies involving a wide range of prey densities are required to explore the nature of interactions. Moreover, this kind of experimental data can contribute to unravelling complexities in theoretical approaches by earlier studies and ultimately promote understanding the effect of multiple predators on prey population regulation.     

Does cold tolerance plasticity correlate with the thermal environment and metabolic profiles of a parasitoid wasp?

Tolerance of ectotherm species to cold stress is highly plastic according to thermal conditions experienced prior to cold stress. In this study, we investigated how cold tolerance varies with developmental temperature (at 17, 25 and 30 °C) and whether developmental temperature induces different metabolic profiles. Experiments were conducted on the two populations of the parasitoid wasp, Venturia canescens, undergoing contrasting thermal regimes in their respective preferential habitat (thermally variable vs. buffered). We predicted the following: i) development at low temperatures improves the cold tolerance of parasitoid wasps, ii) the shape of the cold tolerance reaction norm differs between the two populations, and iii) these phenotypic variations are correlated with their metabolic profiles. Our results showed that habitat origin and developmental acclimation interact to determine cold tolerance and metabolic profiles of the parasitoid wasps. Cold tolerance was promoted when developmental temperatures declined and population originating from variable habitat presented a higher cold tolerance. Cold tolerance increases through the accumulation of metabolites with an assumed cryoprotective function and the depression of metabolites involved in energy metabolism. Our data provide an original example of how intraspecific cold acclimation variations correlate with metabolic response to developmental temperature.     

Enhancement of transformation rates in higher plants by low-dose irradiation: Are DNA repair systems involved in the incorporation of exogenous DNA into the plant genome?

Irradiation (X-ray; 5–15 Gy) of protoplasts treated with plasmid-DNA and PEG yielded higher transformation rates in comparison to non-irradiated protoplasts transformed by the same method. This could be demonstrated for four plant species. The irradiation doses used did not affect the total number of colonies regenerated without selection pressure, but resulted in 3–6-fold enhancement of hygromycin- or kanamycin-resistant colonies. Plant regeneration frequencies of transformed colonies derived from irradiated and non-irradiated protoplasts were similar in tobacco as well as in Petunia. Higher integration rates of foreign DNA as a consequence of an increased recombination machinery in irradiated cells may be responsible for the enhancement of the number of stably transformed colonies.     

Sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni: is it adaptive?

Many species of parasitoid wasps produce a greater proportionof sons in small than in large hosts. As described by the host-sizemodel, natural selection is becoming a standard explanationfor the evolution of this phenomenon. We examined a criticalassumption of the host-size model, that host size has a morepositive effect on female than on male reproductive success.In laboratory experiments with the parasitoid wasp Spalangiacameroni, females that developed on larger hosts contained moreeggs at emergence. However, more eggs did not translate intomore offspring, at high or low density and regardless of whethera female had to burrow to reach hosts. The size of host on whicha female developed was also unrelated to her longevity, regardlessof the presence or absence of hosts. The size of host on whicha male developed had no effect on his sperm production or abilityto inseminate females, regardless of whether insemination abilitywas measured by the amount of sperm transferred to a female,by the proportion of a male's mates that produced any daughters,or by the proportion of daughters that a male's mates produced.Thus, despite data on multiple measures of fitness under a rangeof conditions, sex ratio manipulation in response to host sizein S. cameroni does not appear to be adaptive, and another explanationis needed.     

Does synovigeny confer reproductive plasticity upon a parasitoid wasp that is faced with variability in habitat richness?

Understanding the factors that constrain the reproductive success of animals and their demographics requires detailed insight into the processes of resource acquisition and allocation in relation to habitat richness. Parasitoid wasp females are valuable models in this respect because their lifetime reproductive success is closely tied to host availability. Parasitoids that manufacture eggs throughout adult life (i.e. ‘synovigenic’ species) and characteristically acquire nutrients via feeding are predicted to be plastic in their allocation to egg manufacture. Using the synovigenic parasitoid wasp Venturia canescens, we tested whether this prediction holds when females are faced with variation in the availability of both hosts and food. Laboratory experiments were conducted to determine how environmental variation affects parasitoid reproductive success and the lifetime dynamics of egg load and of major nutrient types. Our results, surprisingly, show that female V. canescens lacks a significant degree of reproductive plasticity under our experimental conditions. In particular, allocation of resources to reproduction was high irrespective of host availability. We attribute this lack of flexibility to the low energy content of V. canescens' eggs and to features peculiar to the ecology of this species. Our findings shed new light on the physiological factors that constrain parasitoid lifetime reproductive success. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 621–632.     

Superparasitism and sex ratio adjustment in a wasp parasitoid: results at variance with Local Mate Competition?

Anaphes nitens is a solitary parasitoid of the egg capsules of the Eucalyptus snout beetle, Gonipterus scutellatus. Some traits of its natural history suggest that Local Mate Competition (LMC) could account for sex ratio adjustment in this species. We tested whether males emerged early, a prerequisite for fully local mating, and investigated the occurrence and effect of superparasitism on adult size and pre-emergence mortality, factors that might influence sex ratio adjustment. We found in field-collected egg capsules that males emerged first. To investigate the effects of superparasitism on adult size, we compared the sizes of parasitoids that emerged early and late from egg capsules collected in the field, and from egg capsules parasitized and superparasitized in the laboratory. Superparasitism reduced parasitoid size, affecting females more strongly than males, and increased pre-emergence mortality. We estimated A. nitens sex ratio and parasitism rate in the field during 2 years in five localities and during 4 years in a sixth. Following LMC we expected an increase in sex ratio (proportion of males) with increasing parasitism rate (assumed to reflect parasitoid density). We found that sex ratio decreased from 0.38 when the parasitism rate was low (0-20%) to 0.21 when parasitism was high (80-100%). In contrast with field results, a laboratory experiment showed that: (1) at a low parasitism level sex ratio was clearly female biased (0.28+/-0.04), (2) at a high parasitism level sex ratio increased (0.40+/-0.07), (3) male larval survivorship was not lower than female survivorship, and (4) low-quality hosts (i.e. superparasitized) were allocated more males. We conclude that LMC cannot explain the sex ratio adjustment observed in the field, even at low parasitism rates, and alternative explications for highly female-biased sex ratios must be found. One such alternative is female-biased dispersal.