Natural selection on the erythrocyte surface

Surface glycoproteins are principal receptors used by pathogens to invade target cells. It has been suggested that mammalian erythrocyte surface glycoproteins function as decoy receptors attracting pathogens to the anucleated erythrocyte and away from their target tissues. Glycophorin A (GYPA) is solely expressed on the erythrocyte surface where it is the most abundant sialoglycoprotein, although its function is unknown. The pathogen decoy hypothesis may be relevant here, as GYPA has been shown in vitro to bind numerous viruses and bacteria, which do not infect erythrocytes. However, it is also a receptor for erythrocyte invasion by the malarial parasite Plasmodium falciparum. Analyses of gypa sequence variation among six higher primates and within a human population show that there is a large excess of replacement (nonsynonymous) substitutions along each primate lineage (particularly on exons 2-4 encoding the extracellular glycosylated domain of GYPA) and a significant excess of polymorphisms in exon 2 (encoding the terminal portion of the extracellular domain) within humans. These two signatures suggest that there has been exceptionally strong positive selection on this receptor driving GYPA divergence during primate evolution and balancing selection maintaining allelic variation within human populations. The pathogen decoy hypothesis alone is adequate to explain both these signatures of between-species and within-species diversifying selection. This has implications for understanding the functions of erythrocyte surface components and their roles in health and disease.     

The parasitome of the phytonematode Heterodera glycines

Parasitism genes expressed in the esophageal gland cells of phytonematodes encode secretions that control the complex process of plant parasitism. In the soybean cyst nematode, Heterodera glycines, the parasitome, i.e., the secreted products of parasitism genes, facilitate nematode migration in soybean roots and mediate the modification of root cells into elaborate feeding cells required to support the growth and development of the nematode. With very few exceptions, the identities of these secretions are unknown, and the mechanisms of cyst nematode parasitism, therefore, remain obscure. The most direct and efficient approach for cloning parasitism genes and rapidly advancing our understanding of the molecular interactions during nematode parasitism of plants is to create gland cell-specific cDNA libraries using cytoplasm microaspirated from the esophageal gland cells of various parasitic stages. By combining expressed sequence tag analysis of a gland cell cDNA library with high throughput in situ expression localization of clones encoding secretory proteins, we obtained the first comprehensive parasitome profile for a parasitic nematode. We identified 51 new H. glycines gland-expressed candidate parasitism genes, of which 38 genes constitute completely novel sequences. Individual parasitome members showed distinct gland cell expression patterns throughout the parasitic cycle. The parasitome complexity discovered paints a more elaborate picture of host cellular events under specific control by the nematode parasite than previously hypothesized.     

Malaria parasite colonisation of the mosquito midgut--placing the Plasmodium ookinete centre stage

Vector-borne diseases constitute an enormous burden on public health across the world. However, despite the importance of interactions between infectious pathogens and their respective vector for disease transmission, the biology of the pathogen in the insect is often less well understood than the forms that cause human infections. Even with the global impact of Plasmodium parasites, the causative agents of malarial disease, no vaccine exists to prevent infection and resistance to all frontline drugs is emerging. Malaria parasite migration through the mosquito host constitutes a major population bottleneck of the lifecycle and therefore represents a powerful, although as yet relatively untapped, target for therapeutic intervention. The understanding of parasite-mosquito interactions has increased in recent years with developments in genome-wide approaches, genomics and proteomics. Each development has shed significant light on the biology of the malaria parasite during the mosquito phase of the lifecycle. Less well understood, however, is the process of midgut colonisation and oocyst formation, the precursor to parasite re-infection from the next mosquito bite. Here, we review the current understanding of cellular and molecular events underlying midgut colonisation centred on the role of the motile ookinete. Further insight into the major interactions between the parasite and the mosquito will help support the broader goal to identify targets for transmission-blocking therapies against malarial disease.     

Moderate and exhaustive endurance exercise influences the interferon-γ levels in whole-blood culture supernatants

The aim of this study was to investigate whether moderate or exhaustive endurance exercise influences cytokine levels in whole-blood culture supernatants after stimulation. Therefore, eight healthy subjects were first exposed to moderate exercise on a cycle ergometer for 30 min at 70% of their 4-mmol/l lactic acid (anaerobic) threshold, and 1 week later to exhaustion (for 90 min) at their anaerobic threshold. Blood samples were taken before, 30 min after and 24 h after each exercise bout. The following lymphocyte subpopulations were determined: CD14-positive(+)/CD45+, CD4+, CD8+, and CD16+. Cytokine levels in the supernatants were measured by enzyme-linked immunosorbent assay (ELISA). Production of interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α were induced with lipopolysaccharides (LPS), and that of IL-2 and interferon (IFN)-γ with staphylococcal enterotoxin B (SEB) and phytohaemagglutinin (PHA). Cortisol levels were also determined by ELISA. The lymphocyte subset distribution was observed to be unchanged after moderate exercise. Thirty minutes after exhaustive exercise, the CD16+ count was found to be significantly lower, whereas 24 h later the CD4+ count was significantly higher than pre-exercise counts. Moderate exercise influenced the IFN-γ production (PHA-stimulated), which increased significantly from 974 (391) pg/ml before exercise to 1450 (498) pg/ml 24 h later. Thirty minutes after exhaustive exercise the IFN-γ level in the supernatants (SEB-stimulated) was significantly decreased (from 14470 (11840) pg/ml before exercise to 6000 (4950) pg/ml after exercise). The IL-1β and TNF-α production per monocyte was also significantly reduced. Accepted: 19 February 1997     

Active uptake of cyst nematode parasitism proteins into the plant cell nucleus

Cyst nematodes produce parasitism proteins that contain putative nuclear localisation signals (NLSs) and, therefore, are predicted to be imported into the nucleus of the host plant cell. The in planta localisation patterns of eight soybean cyst nematode (Heterodera glycines) parasitism proteins with putative NLSs were determined by producing these proteins as translational fusions with the GFP and GUS reporter proteins. Two parasitism proteins were found to be imported into the nuclei of onion epidermal cells as well as Arabidopsis protoplasts. One of these two parasitism proteins was further transported into the nucleoli. Mutations introduced into the NLS domains of these two proteins abolished nuclear import and caused a cytoplasmic accumulation. Furthermore, we observed active nuclear uptake for three additional parasitism proteins, however, only when these proteins were synthesised as truncated forms. Two of these proteins were further transported into nucleoli. We hypothesise that nuclear uptake and nucleolar localisation are important mechanisms for H. glycines to modulate the nuclear biology of parasitised cells of its host plant.     

Trypanosoma cruzi: inhibition by spirogermanium hydrochloride

Spirogermanium is an antineoplastic agent that has been shown to be useful for the treatment of a variety of solid tumors and Plasmodium falciparum infection. We found that this agent, at concentrations of 1-10 micrograms/ml, markedly inhibited the growth of epimastigotes of Trypanosoma cruzi. This inhibition of growth was seen in liver infusion tryptose cultures as well as on agar where colonial growth was inhibited markedly. Ultrastructural studies demonstrated that affected organisms were round and swollen and contained vacuoles, lamellar structures, and multivesicular bodies. Spirogermanium also significantly decreased the growth of intracellular amastigotes in myotubes. Pretreatment of myotubes with the agent protected them from infection with trypomastigotes but tachyzoites of Toxoplasma sp. readily infected pretreated cells. These data suggest that spirogermanium may be useful as a chemotherapeutic agent against T. cruzi.     

The 5S DNA units of bread wheat (Triticum aestivum)

A collection of 44 cloned 5S DNA units fromTriticum aestivum cv. Chinese Spring were grouped into 12 sequence-types based on sequence similarity and the respective consensus sequences were then produced. The relationship between these 12 consensus sequences (T. aestivum S 1-S 8 andT. aestivum L 1-L 4), together with two clones sequenced byGerlach andDyer, and the 5S DNA consensus sequences from diploidTriticum spp. were then determined by numerical methods. Both phenetic and cladistic analyses were carried out. The following wheat 5S DNA sequences were found to group with respective sequences from diploidTriticum spp.:T. aestivum S 4, S 6 withT. tauschii S;T. aestivum S 3 withT. monococcum S andT. monococcum S-Rus 7;T. aestivum L 1 andT. aestivum L-G&D withT. speltoides L;T. aestivum L 2, L 3 withT. tauschii L;T. aestivum L 4 withT. monococcum L andT. monococcum L-Rus 12. The analyses suggested that 5 out of the 65S Dna loci present in wheat were identified at the sequence level. The locus that could not be identified in this analysis was the5S Dna-B 1 locus. A group ofT. aestivum sequences (T. aestivum S 1, S 7, S 8, S-G&D) were found to be distinct from the other 5S DNA sequences in the data base. The existence of the distinct group of 5S DNA sequences suggests that there is a gap in our current understanding of wheat evolution with respect to the5S Dna loci.     

Calpain-mediated AQP2 proteolysis in inner medullary collecting duct

Vitamin D-elicited hypercalcemia/hypercalciuria is associated with polyuria in humans and in animal models. In rats, dihydrotachysterol (DHT) induces AQP2 water channel downregulation despite unaltered AQP2 mRNA expression and thus we investigated the mechanism of AQP2 degradation. Incubation of AQP2-containing inner medullary collecting duct (IMCD) endosomes with Ca(2+) or calpain elicited AQP2 proteolysis, an effect abolished by leupeptin. This endogenous, Ca(2+)-sensitive protease activity exhibited a different proteolytic digest pattern from trypsin, which also degraded AQP2 in vitro. IMCDs contain abundant micro-calpain protein and functional calpain proteolytic activity as demonstrated by immunohistochemistry, immunoblotting, and gel zymography. Furthermore, by small particle flow cytometry we demonstrated that micro-calpain colocalizes with apical IMCD endosomes. DHT does not appear to elicit general proteolysis, however, in addition to AQP2 degradation, DHT treatment also diminished micro-calpain and calpastatin expression although whether these changes contributed to the AQP2 instability remains unclear. Together, these data show for the first time that AQP2 is a substrate for calpain-mediated proteolysis and that furthermore, micro-calpain, like AQP2, is both highly expressed in renal inner medulla and localized to apical IMCD endosomes.