Anterior regions of monkey parietal cortex process visual 3D shape

The intraparietal cortex is involved in the control of visually guided actions, like reach-to-grasp movements, which require extracting the 3D shape and position of objects from 2D retinal images. Using fMRI in behaving monkeys, we investigated the role of the intraparietal cortex in processing stereoscopic information for recovering the depth structure and the position in depth of objects. We found that while several areas (CIP, LIP, and AIP on the lateral bank; PIP and MIP on the medial bank) are activated by stereoscopic stimuli, AIP and an adjoining portion of LIP are sensitive only to depth structure. Furthermore, only these two regions are sensitive to both the depth structure and the 2D shape of small objects. These results indicate that extracting 3D spatial information from stereo involves several intraparietal areas, among which AIP and anterior LIP are more specifically engaged in extracting the 3D shape of objects.     

Toxoplasma gondii uses unusual sorting mechanisms to deliver transmembrane proteins into the host-cell vacuole

A critical step in infection by the apicomplexan parasite Toxoplasma gondii is the formation of a membrane-bound compartment within which the parasite proliferates. This process relies on a set of secretory organelles that discharge their contents into the host cell upon invasion. Among these organelles, the dense granules are specialized in the export of transmembrane (TM) GRA proteins, which are major components of the mature parasitophorous vacuole (PV) membrane. How eukaryotic pathogens export and sort membrane-bound proteins destined for the host cell is still poorly understood at the mechanistic level. In this study, we show that soluble trafficking of the PV-targeted GRA5 TM protein is parasite specific: when expressed in mammalian cells, GRA5 is targeted to the plasma membrane and behaves as an integral membrane protein with a type I toplogy. We also demonstrate the dual role of the GRA5 N-terminal ectodomain, which is sufficient to prevent membrane integration within the parasite and is essential for both sorting and post-secretory membrane insertion into the vacuolar membrane. These results contrast with the general rule that states that information contained within the cytoplasmic tail and/or the TM domain of integral membrane proteins dictates their cellular localization. They also highlight the diversity of sorting mechanisms that leads to the specialization of secretory processes uniquely adapted to intracellular parasitism.     

Initial Characterization of the Pf-Int Recombinase from the Malaria Parasite Plasmodium falciparum

Background

Genetic variation is an essential means of evolution and adaptation in many organisms in response to environmental change. Certain DNA alterations can be carried out by site-specific recombinases (SSRs) that fall into two families: the serine and the tyrosine recombinases. SSRs are seldom found in eukaryotes. A gene homologous to a tyrosine site-specific recombinase has been identified in the genome of Plasmodium falciparum. The sequence is highly conserved among five other members of Plasmodia.

Methodology/Principal Findings

The predicted open reading frame encodes for a ∼57 kDa protein containing a C-terminal domain including the putative tyrosine recombinase conserved active site residues R-H-R-(H/W)-Y. The N-terminus has the typical alpha-helical bundle and potentially a mixed alpha-beta domain resembling that of λ-Int. Pf-Int mRNA is expressed differentially during the P. falciparum erythrocytic life stages, peaking in the schizont stage. Recombinant Pf-Int and affinity chromatography of DNA from genomic or synthetic origin were used to identify potential DNA targets after sequencing or micro-array hybridization. Interestingly, the sequences captured also included highly variable subtelomeric genes such as var, rif, and stevor sequences. Electrophoretic mobility shift assays with DNA were carried out to verify Pf-Int/DNA binding. Finally, Pf-Int knock-out parasites were created in order to investigate the biological role of Pf-Int.

Conclusions/Significance

Our data identify for the first time a malaria parasite gene with structural and functional features of recombinases. Pf-Int may bind to and alter DNA, either in a sequence specific or in a non-specific fashion, and may contribute to programmed or random DNA rearrangements. Pf-Int is the first molecular player identified with a potential role in genome plasticity in this pathogen. Finally, Pf-Int knock-out parasite is viable showing no detectable impact on blood stage development, which is compatible with such function.     

Trimethylamine and Organic Matter Additions Reverse Substrate Limitation Effects on the δ13C Values of Methane Produced in Hypersaline Microbial Mats

Methane production has been observed in a number of hypersaline environments, and it is generally thought that this methane is produced through the use of noncompetitive substrates, such as the methylamines, dimethylsulfide and methanol. Stable isotope measurements of the produced methane have also suggested that the methanogens are operating under conditions of substrate limitation. Here, substrate limitation in gypsum-hosted endoevaporite and soft-mat hypersaline environments was investigated by the addition of trimethylamine, a noncompetitive substrate for methanogenesis, and dried microbial mat, a source of natural organic matter. The δ¹³C values of the methane produced after amendments were compared to those in unamended control vials. At all hypersaline sites investigated, the δ¹³C values of the methane produced in the amended vials were statistically lower (by 10 to 71‰) than the unamended controls, supporting the hypothesis of substrate limitation at these sites. When substrates were added to the incubation vials, the methanogens within the vials fractionated carbon isotopes to a greater degree, resulting in the production of more ¹³C-depleted methane. Trimethylamine-amended samples produced lower methane δ¹³C values than the mat-amended samples. This difference in the δ¹³C values between the two types of amendments could be due to differences in isotope fractionation associated with the dominant methane production pathway (or substrate used) within the vials, with trimethylamine being the main substrate used in the trimethylamine-amended vials. It is hypothesized that increased natural organic matter in the mat-amended vials would increase fermentation rates, leading to higher H₂ concentrations and increased CO₂/H₂ methanogenesis.     

Expression of the skeletal muscle dystrophin-dystroglycan complex and syntrophin-nitric oxide synthase complex is severely affected in the type 2 diabetic Goto-Kakizaki rat

The inability of insulin to stimulate glucose metabolism in skeletal muscle fibres is a classic characteristic of type 2 diabetes. Using the non-obese Goto-Kakizaki rat as an established animal model of this type of diabetes, sucrose gradient centrifugation studies were performed and confirmed the abnormal subcellular location of the glucose transporter GLUT4. In addition, this analysis revealed an unexpected drastic reduction in the surface membrane marker beta-dystroglycan, a dystrophin-associated glycoprotein. Based on this finding, a comprehensive immunoblotting survey was conducted which showed a dramatic decrease in the Dp427 isoform of dystrophin and the alpha/beta-dystroglycan subcomplex, but not in laminin, sarcoglycans, dystrobrevin, and excitation-contraction-relaxation cycle elements. Thus, the backbone of the trans-sarcolemmal linkage between the extracellular matrix and the actin membrane cytoskeleton might be structurally impaired in diabetic fibres. Immunohistochemical studies revealed that the reduction in the dystrophin-dystroglycan complex does not induce obvious signs of muscle pathology, and is neither universal in all fibres, nor fibre-type specific. Most importantly, the expression of alpha-syntrophin and the syntrophin-associated neuronal isoform of nitric oxide synthase, nNOS, was demonstrated to be severely reduced in diabetic fibres. The loss of the dystrophin-dystroglycan complex and the syntrophin-nNOS complex in selected fibres suggests a weakening of the sarcolemma, abnormal signalling and probably a decreased cytoprotective mechanism in diabetes. Impaired anchoring of the cortical actin cytoskeleton via dystrophin might interfere with the proper recruitment of the glucose transporter to the surface membrane, following stimulation by insulin or muscle contraction. This may, at least partially, be responsible for the insulin resistance in diabetic skeletal muscles.     

Hyperhydricity of Prunus avium shoots cultured on gelrite: a controlled stress response.

Hyperhydricity is a physiological disorder frequently affecting shoots vegetatively propagated in vitro. Hyperhydric shoots are characterised by a translucent aspect due to a chlorophyll deficiency, a not very developed cell wall and a high water content. Hyperhydricity of Prunus avium shoots was expressed in vitro in one multiplication cycle by replacing the gelling agent agar (normal shoots: NS) by gelrite (hyperhydric shoots: HS). P. avium shoots evolving towards the hyperhydric state produced higher amounts of ethylene, polyamines (PAs) and proline, which are substances considered as stress markers. A higher activity of glutathione peroxidase (GPX; EC 1.11.1.9), involved in organic hydroperoxide elimination, suggested an increased production of these compounds in HS. The unchanged free fatty acid composition indicated no HS membrane damages compared to NS. The ploidy level of HS nuclei was not affected, but the bigger size and the lower percentage of nuclei during the S phase suggested a slowing down of the cell cycle. The results argued for a stress response of the HS, but no signs of oxidative damages of lipid membrane and nucleus were observed. The discussion points out paradoxical results in a classical analysis of stress and suggests an alternative way of defense mechanisms in HS, involving homeostatic regulation and controlled degradation processes to maintain integrity and vital functions of the cell.     

Whole genome sequence of an unusual Borrelia burgdorferi sensu lato isolate

Human Lyme disease is caused by a number of related Borrelia burgdorferi sensu lato species. We report here the complete genome sequence of Borrelia sp. isolate SV1 from Finland. This isolate is to date the closest known relative of B. burgdorferi sensu stricto, but it is sufficiently genetically distinct from that species that it and its close relatives warrant its candidacy for new-species status. We suggest that this isolate should be named "Borrelia finlandensis."