A brief illustrated guide to the ultrastructure of Plasmodium falciparum asexual blood stages

Interpretation of the new information arising from the Plasmodium falciparum Genome Project requires a good working knowledge of the ultrastructure of the parasite; however many aspects of the morphology of this species remain obscure. Lawrence Bannister, John Hopkins and colleagues here give an illustrated overview of the three-dimensional (3-D) organization of the merozoite, ring, trophozoite and schizont stages of the parasite, based on available data that include 3-D reconstruc-tion from serial electron microscope sections. The review describes the chief organelles present in these stages, emphasizing the continuity of structure in addition to specialized, stage-specific features developed during the asexual erythrocytic cycle.     

Glucagon response to exercise is critical for accelerated hepatic glutamine metabolism and nitrogen disposal

The aim of this study was to determine the role of glucagon in hepatic glutamine (Gln) metabolism during exercise. Sampling (artery, portal vein, and hepatic vein) and infusion (vena cava) catheters and flow probes (portal vein, hepatic artery) were implanted in anesthetized dogs. At least 16 days after surgery, an experiment, consisting of a 120-min equilibration period, a 30-min basal sampling period, and a 150-min exercise period, was performed in these animals. [5-(15)N]Gln was infused throughout experiments to measure gut and liver Gln kinetics and the incorporation of Gln amide nitrogen into urea. Somatostatin was infused throughout the study. Glucagon was infused at a basal rate until the beginning of exercise, when the rate was either 1) gradually increased to simulate the glucagon response to exercise (n = 5) or 2) unchanged to maintain basal glucagon (n = 5). Insulin was infused during the equilibration and basal periods at rates designed to achieve stable euglycemia. The insulin infusion was reduced in both protocols to simulate the exercise-induced insulin decrement. These studies show that the exercise-induced increase in glucagon is 1) essential for the increase in hepatic Gln uptake and fractional extraction, 2) required for the full increment in ureagenesis, 3) required for the specific transfer of the Gln amide nitrogen to urea, and 4) unrelated to the increase in gut fractional Gln extraction. These data show, by use of the physiological perturbation of exercise, that glucagon is a physiological regulator of hepatic Gln metabolism in vivo.     

Seasonal adiposity and androstenedione production as a possible mechanism for asynchronous reproductive activity between males and females of vespertilionid bat, Scotophilus heathi

Relationship between changes in the body weight and circulating androstenedione concentration was examined in order to find out their involvement in asynchronous gametic cycle of male and female S. heathi. Body weight of both male and female bats increased from September due to accumulation of white adipose tissue and reached to a peak in November. The body weight declined gradually due to consumption of adipose tissue during December and January reaching basal level in February. A significant correlation between body weight and serum androstenedione concentration was observed. Correlated with maximum body weight, peak androstenedione level was found during November in both male and female bats. Peak androstenedione level during November may be responsible for stimulating spermatogenesis in the male, but may suppress follicular growth and ovulation in the female, thus resulting in asynchronous gametic cycle of male and female S. heathi.     

Effect of uracil on rifamycin SV production by Amycolatopsis mediterranei MV35R

The effect of different organic nitrogen compounds on the production of rifamycin SV by Amycolatopsis mediterranei MV35R and their optimum concentrations have been described. Results obtained indicate that rifamycin SV production increased from 4020 mg l-1 to 4575 mg l-1 when organic nitrogen compound uracil was added at 0.2% (w/v) concentration to the fermentation medium by A. mediterranei MV35R. The rifamycin SV yield was enhanced by 505 mg l-1 using uracil (2 g l-1) when compared with barbital.     

Variability of morphological traits in Drosophila bipectinata complex

Phenotypic or morphological differences among different populations and sexual dimorphism in certain metric traits were analysed in D. bipectinata complex. It was noticed that different populations of D. bipectinata species group harbour large amount of variation for these characters. In all the populations, morphometric characters such as lengths of femur, tibia and wing length, wing width, number of sternopleural bristles and bristles on epandrium varied significantly among populations. The study indicates that the morphological variations are due to the interplay of genetic and environmental endowments. Further, females had significantly larger values, for lengths of femur, tibia and wing length, wing width and sternopleural bristles.     

Seasonal changes in circulating testosterone and androstenedione concentration and their correlation with the anomalous reproductive pattern in the male indian sheath-tailed bat, Taphozous longimanus

The relationship between reproductive organs, circulating testosterone, and androstenedione concentration in the male sheath-tailed bat, Taphozous longimanus, was studied. The masses of testis, accessory sex gland (prostate, ampullary), and epididymides showed three peaks, one each in October, January, and April. Monthly changes in testosterone also peaked during October, January, and April and closely coincided with the peak spermatogenesis. Serum androstenedione concentration peaked during November and January. Testosterone showed a strong correlation with masses of testis and accessory sex glands, while androstenedione showed strong correlation with the body mass. Different threshold levels of testosterone may be required to trigger spermatogenesis, secretory activity of accessory sex glands and mating in Taphozous longimanus and may be responsible for reproductive asynchrony in this species. Higher circulating concentrations of testosterone and androstenedione throughout the year in this species, as compared with other mammalian species, may be responsible for prolonged retention of sperm in the epididymides.     

Control of intramolecular interactions between the pleckstrin homology and Dbl homology domains of Vav and Sos1 regulates Rac binding

Vav and Sos1 are Dbl family guanine nucleotide exchange factors, which activate Rho family GTPases in response to phosphatidylinositol 3-kinase products. A pleckstrin homology domain adjacent to the catalytic Dbl homology domain via an unknown mechanism mediates the effects of phosphoinositides on guanine nucleotide exchange activity. Here we tested the possibility that phosphatidylinositol 3-kinase substrates and products control an interaction between the pleckstrin homology domain and the Dbl homology domain, thereby explaining the inhibitory effects of phosphatidylinositol 3-kinase substrates and stimulatory effects of the products. Binding studies using isolated fragments of Vav and Sos indicate phosphatidylinositol 3-kinase substrate promotes the binding of the pleckstrin homology domain to the Dbl homology domain and blocks Rac binding to the DH domain, whereas phosphatidylinositol 3-kinase products disrupt the Dbl homology/pleckstrin homology interactions and permit Rac binding. Additionally, Lck phosphorylation of Vav, a known activating event, reduces the affinities between the Vav Dbl homology and pleckstrin homology domains and permits Rac binding. We also show Vav activation in cells, as monitored by phosphorylation of Vav, Vav association with phosphatidylinositol 3,4,5-trisphosphate, and Vav guanine nucleotide exchange activity, is blocked by the phosphatidylinositol 3-kinase inhibitor wortmannin. These results suggest the molecular mechanisms for activation of Vav and Sos1 require disruption of inhibitory intramolecular interactions involving the pleckstrin homology and Dbl homology domains.     

Preparation of recombinant bovine, porcine, and porcine W4R/R5K leptins and comparison of their activity and immunoreactivity with ovine, chicken, and human leptins

Recombinant ovine Ala-leptin (GenBank Accession No. U84247, of ovine leptin), previously prepared in our laboratory in prokaryotic expression plasmid pMON3401, was mutated using a mutagenesis kit to prepare plasmids encoding for bovine (GenBank Accession No. U50365) and porcine (GenBank Accession No. U59894) leptins and for porcine leptin analogue W4R/R5K. Escherichia coli cells transformed with these plasmids overexpressed large amounts of these proteins upon induction with nalidixic acid. The expressed proteins, found in inclusion bodies, were refolded and purified to homogeneity using subsequently anion- and cation-exchange chromatography. All three purified proteins showed a single band of the expected molecular mass of 16 kDa in SDS-PAGE in the presence of reducing agent and were composed of 90-100% monomers. Proper refolding was evidenced by comparing their CD spectra to those of previously prepared chicken and ovine leptins and to commercially available human leptin. The amino acid content of the purified proteins closely resembled the predicted composition. The biological activity of bovine leptin, porcine leptin, and porcine leptin analogue W4R/R5K was evidenced by their ability to stimulate proliferation of leptin-sensitive BAF/3 cells transfected with a long form of human leptin receptor. All three proteins, as well as ovine and chicken leptins, but not human leptin, exhibited a very high degree of cross-immunoreactivity against antiserum raised against ovine leptin in rabbits. In contrast, none or very low cross-immunoreactivity was observed against antiserum raised against ovine leptin in goats.     

Historical vehicle and positive control micronucleus data in mice and rats

The rodent bone marrow micronucleus (MN) assay has been widely used as part of an in vivo genotoxicity test battery in product safety evaluation. In this assay, the historical vehicle and positive control data form an important component in the assay performance and data interpretation. Also, in light of minimizing animal use in research and still obtain required data from a study, the routine use of positive control in every MN assay has been questioned by the scientific community, especially in laboratories which have demonstrated assay reproducibility and conduct studies under Good Laboratory Practice regulations. In this paper, mouse and rat vehicle and positive control MN data, collected manually, are described as a reference for a period of 12 years (1987-1998) in our laboratory. The vehicles generally included a variety of aqueous solutions and suspensions and cyclophosphamide dosed intraperitoneally at 20mg/kg (rats) or 40 mg/kg (mice) served as positive control, in all studies. Based on combined sex data (430 animals), for CD(1) mice, the vehicle control MN polychromatic erythrocyte (PCE) range was 0.9-3.1 with a mean of 1.75 per 1000 PCE and the positive control range (220 animals) was 8.8-42.1 with a mean of 23.1 MNPCE per 1000 PCE. Similarly, for Wistar rats, the vehicle control range (360 animals) was 1.3-5.3 with a mean of 2.6 MNPCE per 1000 PCE and the positive control range (240 animals) was 10.4-33.8 MNPCE per 1000 PCE. Vehicle control ranges reported here are comparable to the literature database and the positive control response was > or = 4-fold over vehicle control, in all studies. These data demonstrate the reproducibility of positive control response in MN assay in our laboratory and support the MN Assay Expert Panel's view that the use of positive control may not be necessary in every study.