The malaria parasite cyclic GMP-dependent protein kinase plays a central role in blood-stage schizogony

A role for the Plasmodium falciparum cyclic GMP (cGMP)-dependent protein kinase (PfPKG) in gametogenesis in the malaria parasite was elucidated previously. In the present study we examined the role of PfPKG in the asexual blood-stage of the parasite life cycle, the stage that causes malaria pathology. A specific PKG inhibitor (compound 1, a trisubstituted pyrrole) prevented the progression of P. falciparum schizonts through to ring stages in erythrocyte invasion assays. Addition of compound 1 to ring-stage parasites allowed normal development up to 30 h postinvasion, and segmented schizonts were able to form. However, synchronized schizonts treated with compound 1 for ≥6 h became large and dysmorphic and were unable to rupture or liberate merozoites. To conclusively demonstrate that the effect of compound 1 on schizogony was due to its selective action on PfPKG, we utilized genetically manipulated P. falciparum parasites expressing a compound 1-insensitive PfPKG. The mutant parasites were able to complete schizogony in the presence of compound 1 but not in the presence of the broad-spectrum protein kinase inhibitor staurosporine. This shows that PfPKG is the primary target of compound 1 during schizogony and provides direct evidence of a role for PfPKG in this process. Discovery of essential roles for the P. falciparum PKG in both asexual and sexual development demonstrates that cGMP signaling is a key regulator of both of these crucial life cycle phases and defines this molecule as an exciting potential drug target for both therapeutic and transmission blocking action against malaria

Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation

An extended study of the superconducting and normal-state properties of various as-grown and post-annealed RbxFe2-ySe2 single crystals is presented. Magnetization experiments evidence that annealing of RbxFe2-ySe2 at 413 K, well below the onset of phase separation Tp=489 K, neither changes the magnetic nor the superconducting properties of the crystals. In addition, annealing at 563 K, well above Tp, suppresses the superconducting transition temperature Tc and leads to an increase of the antiferromagnetic susceptibility accompanied by the creation of ferromagnetic impurity phases, which are developing with annealing time. However, annealing at T=488K=Tp increases Tc up to 33.3 K, sharpens the superconducting transition, increases the lower critical field, and strengthens the screening efficiency of the applied magnetic field. Resistivity measurements of the as-grown and optimally annealed samples reveal an increase of the upper critical field along both crystallographic directions as well as its anisotropy. Muon spin rotation and scanning transmission electron microscopy experiments suggest the coexistence of two phases below Tp: a magnetic majority phase of Rb2Fe4Se5 and a non-magnetic minority phase of Rb0.5Fe2Se2. Both microscopic techniques indicate that annealing the specimens just at Tp does not affect the volume fraction of the two phases, although the magnetic field distribution in the samples changes substantially. This suggests that the microstructure of the sample, caused by mesoscopic phase separation, is modified by annealing just at Tp, leading to an improvement of the superconducting properties of RbxFe2-ySe2 and an enhancement of Tc.Comment: 13 pages, 12 figure

The malaria parasite cyclic GMP-dependent protein kinase plays a central role in blood-stage schizogony.

A role for the Plasmodium falciparum cyclic GMP (cGMP)-dependent protein kinase (PfPKG) in gametogenesis in the malaria parasite was elucidated previously. In the present study we examined the role of PfPKG in the asexual blood-stage of the parasite life cycle, the stage that causes malaria pathology. A specific PKG inhibitor (compound 1, a trisubstituted pyrrole) prevented the progression of P. falciparum schizonts through to ring stages in erythrocyte invasion assays. Addition of compound 1 to ring-stage parasites allowed normal development up to 30 h postinvasion, and segmented schizonts were able to form. However, synchronized schizonts treated with compound 1 for > or =6 h became large and dysmorphic and were unable to rupture or liberate merozoites. To conclusively demonstrate that the effect of compound 1 on schizogony was due to its selective action on PfPKG, we utilized genetically manipulated P. falciparum parasites expressing a compound 1-insensitive PfPKG. The mutant parasites were able to complete schizogony in the presence of compound 1 but not in the presence of the broad-spectrum protein kinase inhibitor staurosporine. This shows that PfPKG is the primary target of compound 1 during schizogony and provides direct evidence of a role for PfPKG in this process. Discovery of essential roles for the P. falciparum PKG in both asexual and sexual development demonstrates that cGMP signaling is a key regulator of both of these crucial life cycle phases and defines this molecule as an exciting potential drug target for both therapeutic and transmission blocking action against malaria

Coarse-grained ripples investigated by the Opportunity rover on Meridiani Planum, Mars

Aeolian coarse-grained ripples have been found in all regions investigated by Mars rovers: Meridiani Planum, Gusev crater, Gale crater, and Jezero crater. Therefore, it can be assumed that coarse-grained ripples are one of the most common landforms on Mars. Studying their formation and evolution gives us the opportunity to determine past and current wind patterns. They are also crucial for understanding the formation and evolution of larger aeolian bedforms. Of all locations studied in situ on Mars, coarse-grained ripples in extensive (∼100 $km^{2}$) ripple fields were found only on Meridiani Planum. As coarse-grained ripples on Mars are not well characterized in the literature, in this work, the morphometry, morphology, spatial distribution, and orientation of coarse-grained ripples investigated along the 45 km long traverse of the Opportunity rover were analyzed. The obtained results allowed for a more precise definition of coarse-grained ripples and for distinguishing three classes of coarse-grained ripples on Meridiani Planum: small, medium, and large. The coarse-grained ripple activity on Meridiani Planum is now limited due to low material supply, and the relatively strong induration of the ripple surfaces. Even though most of the coarse-grained ripples on Meridiani Planum were formed thousands of years ago, some smaller coarse-grained ripples were formed by modern winds

Differential Adhesive Properties of Sequestered Asexual and Sexual Stages of Plasmodium falciparum on Human Endothelial Cells Are Tissue Independent

The protozoan parasite Plasmodium falciparum, responsible for the most severe form of malaria, is able to sequester from peripheral circulation during infection. The asexual stage parasites sequester by binding to endothelial cell receptors in the microvasculature of various organs. P. falciparum gametocytes, the developmental stages responsible for parasite transmission from humans to Anopheles mosquitoes, also spend the almost ten days necessary for their maturation sequestered away from the peripheral circulation before they are released in blood mainstream. In contrast to those of asexual parasites, the mechanisms and cellular interactions responsible for immature gametocyte sequestration are largely unexplored, and controversial evidence has been produced so far on this matter. Here we present a systematic comparison of cell binding properties of asexual stages and immature and mature gametocytes from the reference P. falciparum clone 3D7 and from a patient parasite isolate on a panel of human endothelial cells from different tissues. This analysis includes assays on human bone marrow derived endothelial cell lines (HBMEC), as this tissue has been proposed as a major site of gametocyte maturation. Our results clearly demonstrate that cell adhesion of asexual stage parasites is consistently more efficient than that, virtually undetectable of immature gametocytes, irrespectively of the endothelial cell lines used and of parasite genotypes. Importantly, immature gametocytes of both lines tested here do not show a higher binding efficiency compared to asexual stages on bone marrow derived endothelial cells, unlike previously reported in the only study on this issue. This indicates that gametocyte-host interactions in this tissue are unlikely to be mediated by the same adhesion processes to specific endothelial receptors as seen with asexual forms

Influence of textural features on aeolian transport in selected dune fields of the northern Sahara

The aim of the study was to determine the influence of textural features of sand on aeolian transport in six designated fields in northern Sahara. An analysis of textural features such as: mineral composition, grain shape, mean grain size diameter and sorting were performed during a multi-year research on dune sediments. Information on the movement of small landforms (1.5m) in areas of similar physico-geographical environments was taken under consideration. It was revealed that the fastest movement, of about 90 my⁻¹, is characteristic for barchans on dune field no. 4. (where gypsum sand dominates). Barchans on dune field no. 1 are slower, with 50 my⁻¹ (where limestone dominates), and the slowest are those on dune field 6 (where quartz dominates), with about 30 my⁻¹. The result of the study proves that textural features have a significant influence on aeolian transport

Development of the dune field in the area of Douz (SE Margin of the Chott Jerid)

The article describes evolution of a dune field located in a vicinity of Douz on south-eastern margin of the Chott Jerid. The aim of the research was to assess the migration rate of dunes and to find determining factors. Between 1997 and 2000 location of selected dunes was measured every month. Textural features of dune sediments were analysed in order to determine dynamics of aeolian processes and a source of the sediment. The dunes, mostly barchans in a youthful stage of development, 1,5-2m high and 40 m wide, migrated generally in two directions: E and NE in spring and SW and W in autumn. In winter and in summer the migration rate was much lower which is explained by seasonal changes in wind direction and speed. The dunes migrated with an average rate of 80m/yr eastwards with a maximum rate of 40m/month and 2-3m/day. The dune sediment mostly consists of fine and very well to well sorted sand which testifies for a long-lasting aeolian process. A share of quartz, very resistant to mechanical abrasion, is high and a share of gypsum is low which is a result of multiple and long-lasting process of redeposition. This is also supported by an analysis of heavy minerals among which minerals highly resistant to mechanical abrasion dominate (mostly garnet and epidotes). Results of sedimentological analysis combined with a broad phypico-geographical view of the area allow to conclude that, the migration rate of the researched dunes is determined by textural features of dune sediments. Such a high migration rate, much higher comparing with other dune fields in the world, is an effect of finer and better sorted sand which can be easily transported by weaker winds

Physico-geographical characteristics of the Chott Jerid Region

The article includes physico-geographical characteristics of the Chott Jerid which was selected for detailed studies presented in following articles. The analysed region is in southern Tunisia and lies within the Great Chotts region. Surface lithology is dominated by Quaternary clayey sediments of fluvial and lacustrine origin and aeolian sands. Crataceous and calcareous rocks can be found along margins of the chott. The climate can be described as very arid continental subtropical. Surface drainage and lakes appear only seasonally in lowest parts of the Chott Jerid and the water is rich in salt. Underground aquifers are very water efficient therefore there are many artesian or subartesian wells allowing for irrigation. Soils in the region belong to Aridisols and are rich in gypsum or calcite. Salt-rich soils dominate in the region. Natural vegetation is sparse (mainly shrubs and halophites) because of arid climate, lack of surface waters and salty soils. Dactyl palms dominate on irrigated land