Distinct apoptotic phenotypes induced by radiation and ceramide in both p53-wild-type and p53-mutated lymphoblastoid cells

The tumour suppressor gene p53 and the intracellular signalling molecule ceramide have both been shown to play crucial roles in the induction of apoptosis by ionising radiation. In this study we examined whether p53 and ceramide are involved in independent signal pathways, inducing different types of apoptosis. TK6 (p53^wt/wt) and WTK1 (p53^mut/mut) lymphoblastoid cells were treated with ionising radiation or N-acetyl-d-sphingosine (C₂-ceramide). Flow cytometry and fluorescence microscopy studies were performed to characterise the time kinetics and morphological features of induced apoptosis. Ceramide- and radiation-induced apoptotic cells display characteristic differences in morphology and DNA staining and ceramide-induced apoptosis is expressed much faster than radiation-induced apoptosis. Radiation-induced apoptosis is p53-dependent and ceramide-induced apoptosis is p53-independent. The p53 pathway and the ceramide pathway are two independent signal pathways leading to distinct types of apoptosis. Since p53 is very often dysfunctional in tumour cells, modifying the ceramide pathway is a promising strategy to increase tumour sensitivity to radiation and other anticancer agents. Received: 19 April 2001 / Accepted: 15 October 2001     

Identification of alanine dehydrogenase and its role in mixed secretion of ammonium and alanine by pea bacteroids

N2-fixation by Rhizobium-legume symbionts is of major ecological and agricultural importance, responsible for producing a substantial fraction of the biosphere's nitrogen. On the basis of 15N-labelling studies, it had been generally accepted that ammonium is the sole secretion product of N2-fixation by the bacteroid and that the plant is responsible for assimilating it into amino acids. However, this paradigm has been challenged in a recent 15N-labelling study showing that soybean bacteroids only secrete alanine. Hitherto, nitrogen secretion has only been assessed from in vitro 15N-labelling studies of isolated bacteroids. We show that both ammonium and alanine are secreted by pea bacteroids. The in vitro partitioning between them will depend on whether the system is open or closed, as well as the ammonium concentration and bacteroid density. To overcome these limitations we identified and mutated the gene for alanine dehydrogenase (aldA) and demonstrate that AldA is the primary route for alanine synthesis in isolated bacteroids. Bacteroids of the aldA mutant fix nitrogen but only secrete ammonium at a significant rate, resulting in lower total nitrogen secretion. Peas inoculated with the aldA mutant are green and healthy, demonstrating that ammonium secretion by bacteroids can provide sufficient nitrogen for plant growth. However, plants inoculated with the mutant are reduced in biomass compared with those inoculated with the wild type. The labelling and plant growth studies suggest that alanine synthesis and secretion contributes to the efficiency of N2-fixation and therefore biomass accumulation.     

Regulation of Tiam1 nucleotide exchange activity by pleckstrin domain binding ligands

Rho family GTPases play roles in cytoskeletal organization and cellular transformation. Tiam1 is a member of the Dbl family of guanine nucleotide exchange factors that activate Rho family GTPases. These exchange factors have in common a catalytic Dbl homology and adjacent pleckstrin homology domain. Previous structural studies suggest that the pleckstrin domain, a putative phosphoinositide-binding site, may serve a regulatory function. We identified ascorbyl stearate as a compound that binds to the pleckstrin domain of p120 Ras GTPase-activating protein. Furthermore, ascorbyl stearate appears to be a general pleckstrin domain ligand, perhaps by mimicking an endogenous amphiphilic ligand. Tiam1 nucleotide exchange activity was greatly stimulated by ascorbyl stearate. Certain phosphoinositides also stimulated Tiam1 activity but were less potent than ascorbyl stearate. Tiam1 contains an additional N-terminal pleckstrin domain, but only the C-terminal pleckstrin domain was required for activation. Our results suggest that the pleckstrin domains of Dbl-type proteins may not only be involved in subcellular localization but may also directly regulate the nucleotide exchange activity of an associated Dbl homology domain. In addition, this paper introduces ascorbyl stearate as a pleckstrin domain ligand that can modulate the activity of certain pleckstrin domain-containing proteins.     

HIV Malaria Co-Infection Is Associated with Atypical Memory B Cell Expansion and a Reduced Antibody Response to a Broad Array of Plasmodium falciparum Antigens in Rwandan Adults

HIV infected individuals in malaria endemic areas experience more frequent and severe malaria episodes compared to non HIV infected. This clinical observation has been linked to a deficiency in antibody responses to Plasmodium falciparum antigens; however, prior studies have only focused on the antibody response to <0.5% of P. falciparum proteins. To obtain a broader and less-biased view of the effect of HIV on antibody responses to malaria we compared antibody profiles of HIV positive (HIV+) and negative (HIV-) Rwandan adults with symptomatic malaria using a microarray containing 824 P. falciparum proteins. We also investigated the cellular basis of the antibody response in the two groups by analyzing B and T cell subsets by flow cytometry. Although HIV malaria co-infected individuals generated antibodies to a large number of P. falciparum antigens, including potential vaccine candidates, the breadth and magnitude of their response was reduced compared to HIV- individuals. HIV malaria co-infection was also associated with a higher percentage of atypical memory B cells (MBC) (CD19+CD10-CD21-CD27-) compared to malaria infection alone. Among HIV+ individuals the CD4⁺ T cell count and HIV viral load only partially explained variability in the breadth of P. falciparum-specific antibody responses. Taken together, these data indicate that HIV malaria co-infection is associated with an expansion of atypical MBCs and a diminished antibody response to a diverse array of P. falciparum antigens, thus offering mechanistic insight into the higher risk of malaria in HIV+ individuals.     

The biomechanics of leaping in gibbons

Gibbons are skilled brachiators but they are also highly capable leapers, crossing distances in excess of 10 m in the wild. Despite this impressive performance capability, no detailed biomechanical studies of leaping in gibbons have been undertaken to date. We measured ground reaction forces and derived kinematic parameters from high-speed videos during gibbon leaps in a captive zoo environment. We identified four distinct leap types defined by the number of feet used during take-off and the orientation of the trunk, orthograde single-footed, orthograde two-footed, orthograde squat, and pronograde single-footed leaps. The center of mass trajectories of three of the four leap types were broadly similar, with the pronograde single-footed leaps exhibiting less vertical displacement of the center of mass than the other three types. Mechanical energy at take-off was similar in all four leap types. The ratio of kinetic energy to mechanical energy was highest in pronograde single-footed leaps and similar in the other three leap types. The highest mechanical work and power were generated during orthograde squat leaps. Take-off angle decreased with take-off velocity and the hind limbs showed a proximal to distal extension sequence during take-off. In the forelimbs, the shoulder joints were always flexed at take-off, while the kinematics of the distal joints (elbow and wrist joints) were variable between leaps. It is possible that gibbons may utilize more metabolically expensive orthograde squat leaps when a safe landing is uncertain, while more rapid (less expensive) pronograde single-footed leaps might be used during bouts of rapid locomotion when a safe landing is more certain.     

Cyrtocrinids (Echinodermata,Crinoidea) from Upper Jurassic Štramberk‐type limestones in southern Poland

Abstract: A systematic account of highly diverse cyrtocrinid faunules from Upper Jurassic strata of ?tramberk type (Oxfordian–Tithonian) in southern Poland (Polish Carpathians) is presented. Fourteen taxa (Phyllocrinus malbosianus, Ph. stellaris, Ph. sp., Psalidocrinus armatus, Sclerocrinus compressus, S. polonicus sp. nov., Hemicrinus aff. kabanovi, Ancepsicrinus parvus gen. et sp. nov., Tetracrinus baumilleri sp. nov., Eugeniacrinites alexandrowiczi, E. cf. moravicus, E. sp., Eudesicrinus gluchowskii sp. nov. and Hemibrachiocrinus tithonicus sp. nov. are described and illustrated. Representatives of the genus Eudesicrinus, previously recorded only from the Lower Jurassic, are here shown to extend into the uppermost Jurassic. Other cyrtocrinids considered are common in Jurassic/Cretaceous strata across Europe. In the present faunules, isocrinid (Isocrinida), comatulid (Comatulida) and roveacrinid (Roveacrinida sensu Rasmussen, inclusive of Saccocoma) crinoids are associated.     

Ontogenetic changes in Mammalian feeding: insights from electromyographic data

All infant mammals make a transition from suckling milk to eating solid foods. Yet, the neuromuscular implications of the transition from a liquid-only diet to solid foods are unknown even though the transport and swallowing of liquids is different from that of solids. We used legacy electromyography (EMG) data to test hypotheses concerning the changes in motor pattern and neuromuscular control that occur during the transition from an all-liquid diet to consumption of solid food in a porcine model. EMG signals were recorded from five oropharyngeal muscles in pigs at three developmental stages (infants, juveniles, and adults) feeding on milk, on food of an intermediate consistency (porridge), and on dry chow (juveniles and adults only). We measured cycle frequency and its variation in "transport cycles" and "swallow cycles". In the swallow cycles, a measure of variation of the EMG signal was also calculated. Variation in cycle frequency for transport and swallow cycles was lowest in adults, as predicted, suggesting that maturation of feeding mechanisms occurs as animals reach adulthood. Infants had lower variation in transport cycle frequency than did juveniles drinking milk, which may be due to the greater efficiency of the infant's tight oral seal against the teat during suckling, compared to a juvenile drinking from a bowl where a tight seal is not possible. Within juveniles, variation in both transport and swallow cycle frequencies was directly related to food consistency, with the highest variation occurring when drinking milk and the lowest when feeding on solid food. There was no difference in the variation of the EMG activity between intact infants and juveniles swallowing milk, although when the latter swallow porridge the EMG signals were less variable than for milk. These results suggest that consistency of food is a highly significant determinant of the variation in motor pattern, particularly in newly weaned animals.     

Development and maturation in the nereidid polychaetes Platynereis dumerilii and Nereis succinea exposed to xenoestrogens

Few studies link biochemical, cellular and whole animal effects of toxic compounds with growth and reproductive output on invertebrate model organisms. Thus, we explore the effects of xenoestrogens on nereid worms. Larvae of Platynereis dumerilii exposed to estradiol (E(2)) ethynylestradiol (EE(2)) and nonyplhenol (NP) observing the effects on growth, primordial germ cell (PGC) proliferation and maturation. In addition, a single exposure study was performed with a 50 days latency period on adult worms of Nereis succinea. Since reduced glutathione (GSH) is required in detoxification of NP and is the precursor of the spawning pheromone nereithione (CSSG) in N. succinea, we analysed how the estrogenic chemical NP affects GSH concentrations. PGC were not affected by exposure to E(2) and EE(2) from 24hpf to 6 days. Chronic exposure of P. dumerilii with NP over the full life cycle did not influence segment proliferation. Mature females that developed, even at high concentrations, were able to spawn and successful fertilization occurred. However, at high NP levels no P. dumerilii males matured. A significant decline of GSH can be seen in N. succinea males upon treatment with NP, but not in females, indicating that females stabilize GSH levels even in stress situations. This study shows some results that link the foundation to causally integrate toxic exposure to xenoestrogens with development, growth and reproductive outputs in nereidid polychaetes.     

How dogs lap: ingestion and intraoral transport in Canis familiaris

It has recently been suggested that the mechanism for lifting liquid from a bowl into the oral cavity during lapping is fundamentally different in cats and dogs: cats use adhesion of liquid to the tongue tip while dogs 'scoop' with their backwardly curled tongue. High-speed light videos and X-ray videos show that on the contrary, both cats and dogs use the mechanism of adhesion. Liquid is transported through the oral cavity to the oesophagus, against gravity, on the surface of the tongue as it is drawn upwards, then a tight contact between the tongue surface and palatal rugae traps liquid and prevents its falling out as the tongue is protruded. At least three cycles are needed for intraoral transport of liquid in the dog.