Contractile proteins in podocytes: immunocytochemical localization of actin and alpha-actinin in normal and nephrotic rat kidneys

Actin and alpha-actinin immunoreactive sites have been localized at the electron microscope level by the protein A-gold immunocytochemical technique in podocytes of normal and nephrotic rat renal tissues. In normal renal glomeruli, fibrillar networks located in the core of foot processes or bundles of micro filaments interconnecting them were found to be labelled for these two cytoskeletal proteins. On the other hand, in nephrotic renal glomeruli, concomitant with the loss of podocytic foot processes a reorganization of the podocytic cytoskeleton and a concentration of some of its elements into thick uniform bands was observed. Actin and alpha-actinin were revealed in these bands. Control experiments confirmed the specificity of the labelling obtained. Our results suggest that normal podocytes contain an actin-based contractile system that might contribute to the maintenance of the particular cell shape of these cells and that the rearrangement of the podocytic cyto-skeleton occurring in the nephrotic syndrome might account for the changes in the foot processes and contribute to the alteration in glomerular function. This work was supported by grants from the Medical Research Council of Canada     

Phosphatases; origin,characteristics and function in lakes

Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.     

Aspects of the life history of Cercopithifilaria johnstoni (Nematoda:Filarioidea)

and 1988. Aspects of the life history of Cercopithifilaria johnstoni (Nematoda:Filarioidea). International Journal for Parasitology 18: 1087–1092. Cercopithifilaria johnstoni (Nematoda:Filarioidea) occurs in the subcutaneous connective tissues of a spectrum of native murid and marsupial hosts in Eastern Australia. Life cycle studies revealed that: (i) microfilaria occur in lymphatic capillaries and extravascular connective tissue of the dermis (= ‘skin-inhabiting’), (ii) ixodid ticks, particularly Ixodes trichosuri, are intermediate hosts in nature, (iii) development from microfilariae to infective third-stage larva occurs only while the tick is off the host, that is, during ecdysis from larva to nymph or from nymph to adult. Transmission of C. johnstoni in a wild population of bush rats (Rattus fuscipes) occurred in summer and winter, and was associated with peaks in the number of larval and/or nymphal stages of ticks on rats. C. johnstoni was transmitted experimentally to bandicoots (Isoodon macrourus, Perameles nasuta), bush rats and laboratory rats (R. norvegicus), indirectly by subcutaneous inoculation of third-stage larvae and directly by tick feeding. The prepatent period was approximately 3 months and the longest duration of microfilariae in the ‘ skin’ was more than 25 months. Dermal and ocular lesions were observed in R. fuscipes. The host-parasite relationship has the potential for development as an inexpensive and practical model for human onchocerciasis.     

Phenological models of development in Pandemis heparana and Adoxophyes orana for timing the application of Insect Growth Regulators with juvenile-hormone activity

Control of leafrollers using Insect Growth Regulators with juvenile-hormone acitivity (IGR) is a major issue in research on Integrated Pest Management in apple orchards. The IGR is applied at the time of emergence of the last-larval instar of leafrollers, thus causing a disturbance of metamorphosis.Simulation models on the development of Pandemis heparana (Denn. et Schiff.) and Adoxophyes orana (F.v.R.) were developed, partly on the basis of experiments, partly on data from literature, to predict the time of emergence of the various stages, particularly of the last-larval instar and the pupa. The models use the state-variable approach, and include only temperature as a driving variable.Simulated curves of emergence of last-instar larvae, pupae and moths corresponded well with observations on field-collected larvae, reared to adult stage in an outdoor insectary. The curves of pheromone trap catches showed a delay relative to the calculated and observed curves for the eclosion of pupae.To investigate whether the time of IGR application could be related to a temperature sum, the relation between emergence curves of last-instar larvae and temperature sums was studied for several years. For this purpose simulated curves were used, because observations on emergence of last-instar covered only a few years.

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Résumé Le contrôle des Tordeuses par les régulateurs de croissance d'Insectes (IGR), à activité d'hormone juvénile, est un progrès majeur dans la recherche pour la lutte intégrée contre les ennemis des vergers de pommiers.L'IGR appliqué lors de l'apparition du dernier stade larvaire des Tordeuses, perturbe ainsi la métamorphose ultérieure. Afin de prévoir le moment d'apparition des différents stades, et plus particulièrement du dernier stade larvaire, des modèles de simulation du développement de Pandemis heparana (Denn. et Schiff.) et Adoxophyes orana (F.v.R.) ont été élaborés à partir d'expériences et en se basant sur des résultats de la littérature.Le modèle est basé sur l'examen de la variable d'état, la température étant la variable discriminante suivie.Les courbes simulées d'apparition des larves de dernier stade, des nymphes et des papillons correspondent aux observations faites sur les larves récoltées dans la nature et élevées jusqu'au stade adulte dans un insectarium en plein air.Le taux de capture dans les pièges à phéromone présente un retard par rapport aux courbes calculées et observées pour l'éclosion des nymphes. Différentes causes peuvent être attribuées à cette différence, mais l'influence d'aucune d'elles n'a été étudiée.Afin de déterminer si le moment de l'application d'IGR peut être lié à une somme de températures, les courbes d'apparition des larves de dernier stade ont été étudiées en relation avec les sommes de températures portant sur plusieurs années. Les observations concernant l'apparition des larves de dernier stade ne couvrant que 2 années, des courbes simulées ont été utilisées à cet effet. L'emploid de la relation liant le moment de l'apparition à la somme des températures permet de n'avoir à calculer que les sommes de températures pour déterminer le moment opportun de l'application des IGR.

     

Succession of phytoplankton species in indoor reservoir models varying in sediment composition and water inlet site

Using four continuous-flow indoor reservoir models, the combined effects of varying water inlet depth and sediment composition on phytoplankton species composition and its succession pattern were studied. Species which are known to bloom in eutrophicated reservoirs were dominant in the species succession in each tank. At any one time, a step-like pattern was observed in the composition of the dominant species of each tank, wherein all the species which appeared in a tank with a lower phosphorus concentration were included in the species composition of the tank with a higher phosphorus concentration in an additive relationship.     

Respiration Rate of Steinernema feltiae Infective Juveniles at Several Constant Temperatures

Respiration was measured in dauer stages of the insect-parasitic nematode Steinernema feltiae (= Neoaplectana carpocapsae) at 7, 17, and 27 C. Respiration, Q₁₀, and nematode viability were temperature dependent. Mean O₂ consumption for 5 × 10⁵ nematodes the first 24 hours was 0.27 ml at 7 C, 0.83 ml at 17 C, and 2.68 ml at 27 C. The Q₁₀ was 3.10 for 7-17 C and 3.24 for 17-27 C. Some nematodes died during 2, 14, and 21 days at 27, 17, and 7 C, respectively. The respiratory quotient was below 1 at all temperatures tested. A standard asymptotic model is expressed as oxygen consumed = 2.77 * {1 - exponent[-time * exponent(-B + C * temperature)]}; where 2.77 is the maximum response at 27 C. This model estimates nematode O₂ consumption and viability at storage temperatures between 7 and 27 C. The nematodes died when the O₂ concentration reached 0.5 ml/5 × 10⁵ nematodes. This model may be used to predict O₂ requirements of S. feltiae infective juveniles when stored as a waterless concentrate.     

Illegitimate recombination mediated by T4 DNA topoisomerase in vitro

Summary Illegitimate recombination dependent on T4 DNA topoisomerase in a cell-free system has recently been described. In that work, recombinants between two phage DNA molecules were produced by the topoisomerase alone, without an Escherichia coli extract. In this paper, it is shown that recombination between phage and circular plasmid DNA molecules can also be detected in the presence or absence of an E. coli extract but at frequencies two or three orders of magnitude lower than that observed in the phage-phage cross. The frequency is probably lower because multiple recombination is required in the case of the phage-plasmid cross.