Are spatial memories strengthened in the human hippocampus during slow wave sleep?

In rats, the firing sequences observed in hippocampal ensembles during spatial learning are replayed during subsequent sleep, suggesting a role for posttraining sleep periods in the offline processing of spatial memories. Here, using regional cerebral blood flow measurements, we show that, in humans, hippocampal areas that are activated during route learning in a virtual town are likewise activated during subsequent slow wave sleep. Most importantly, we found that the amount of hippocampal activity expressed during slow wave sleep positively correlates with the improvement of performance in route retrieval on the next day. These findings suggest that learning-dependent modulation in hippocampal activity during human sleep reflects the offline processing of recent episodic and spatial memory traces, which eventually leads to the plastic changes underlying the subsequent improvement in performance.     

Spatial genetic structure within a metallicolous population of Arabidopsis halleri, a clonal, self-incompatible and heavy-metal-tolerant species

Arabidopsis halleri, a close wild relative of A. thaliana, is a clonal, insect-pollinated herb tolerant to heavy metals (Zn, Pd, Cd) and a hyperaccumulator of Zn and Cd. It is of particular interest in the study of evolutionary processes and phytoremediation. However, little is known about its population gene flow patterns and the structure of its genetic diversity. We used five microsatellite loci to investigate the genetic structure at a fine spatial scale (10 cm to 500 m) in a metallicolous population of A. halleri. We also studied the contributions made by clonal propagation and sexual reproduction (seed and pollen dispersal) to the genetic patterns. Clonal diversity was high (D(G) > 0.9). Clonal spread occurs only at short distances (< 1 m). Both clonal spread and limited dispersal, associated with sexual reproduction, contribute to the significant spatial genetic structure revealed by spatial autocorrelation analysis. The shape of the autocorrelogram suggests that seed dispersal is restricted and pollen flow extensive, which may be related to intense activity by insect pollinators. Clonal spread was more extensive in the lowly polluted zone than in the highly polluted zone. This cannot be interpreted as a strategy for promoting the propagation of adapted genotypes under the harshest ecological constraints (highest heavy metal concentrations). The higher fine-scale spatial genetic structure found in the lowly polluted zone can be ascribed to plant densities that were lower than in the highly polluted zone. No evidence of genetic divergence due to spatial heavy metal heterogeneity was found between lowly and highly polluted zones.     

In vivo homodimerisation of HTLV-1 Gag and MA gives clues to the retroviral capsid and TM envelope protein arrangement

During retroviral particle formation, the capsid precursors (Gag) associate with the cell membrane via their matrix (MA) domain to form viral assembling particles. After budding, Gag and its proteolytically matured MA, form a shell in the released immature and mature particles, respectively. Although the arrangement of Gag domains in vitro and their radial organisation in retroviral particles have been extensively studied, little is known concerning Gag inter-subunit interactions in authentic retroviruses. We report that human T-cell leukemia virus type 1 Gag homodimerises in the cell via a disulphide bonding at cysteine 61 in the MA domain. Most Gags are homodimeric after budding and MAs are also dimeric in mature authentic virions. Molecular modelling of the MA domain indicates that non-covalent interactions at the MA dimer interface may also be important for Gag (and MA) dimerisation. In addition, all amino acids previously reported to be involved in MA-transmembrane (TM) interactions are located on the MA face opposite to the dimer interface. The model reveals that homodimerisation is compatible with a hexameric network of Gag and MA dimers that look like the hexameric networks observed for other retroviruses. These data, together with previous studies, lead us to propose a supra-molecular arrangement model in which the transmembrane glycoproteins of the virion envelope are anchored in a hexameric cage hole formed by the MA.     

Specific regulation of cyclins D1 and D2 by FGF and Shh signaling coordinates cell cycle progression, patterning, and differentiation during early steps of spinal cord development

In the vertebrate embryo, spinal cord elongation requires FGF signaling that promotes the continuous development of the posterior nervous system by maintaining a stem zone of proliferating neural progenitors. Those escaping the caudal neural stem zone, which is expressed to Shh signal, initiate ventral patterning in the neural groove before starting neuronal differentiation in the neural tube. Here we investigated the integration of D-type cyclins, known to govern cell cycle progression under the control of extracellular signals, in the program of spinal cord maturation. In chicken embryo, we find that cyclin D2 is preferentially expressed in the posterior neural plate, whereas cyclin D1 appears in the neural groove. We demonstrated by loss- and gain-of-function experiments that FGF signaling maintains cyclin D2 in the immature caudal neural epithelium, while Shh activates cyclin D1 in the neural groove. Moreover, forced maintenance of cyclin D1 or D2 in the neural tube favors proliferation at the expense of neuronal differentiation. These results contribute to our understanding of how the cell cycle control can be linked to the patterning programs to influence the balance between proliferation and neuronal differentiation in discrete progenitors domains.     

Biosynthesis of mucin type <Emphasis Type="Italic">O</Emphasis>-glycans: Lack of correlation between glycosyltransferase and sulfotransferase activities and CFTR expression

Structural differences have been reported in the glycosylation patterns of cystic fibrosis glycoproteins. Although the gene mutated in cystic fibrosis (CFTR) has been cloned and characterized as a chloride channel, its relationship to the highly viscous mucus and structural glycoprotein and mucin abnormalities in cystic fibrosis still remains to be defined. We have evaluated O-glycan biosynthesis in CHO and BHK cells that express CFTR and F508 CFTR as in vitro models, and utilized the cftr knockout mouse as an in vivo model of CFTR dysfunction. Activities of glycosyltransferases and sulfotransferases synthesizing mucin type O-glycan chains were determined in these models. Differences in transferase activity levels were found between tissues and cell types and during mouse development. No specific patterns of activities were associated with the lack of CFTR or with F508CFTR expression. This suggests that it is not the presence or absence of normal CFTR, or the presence of mutant CFTR alone, but rather cell specific additional factors or pathophysiological consequences that determine the changes in mucin glycosylation in cystic fibrosis.     

Disruption of target cell adhesion structures by the Yersinia effector YopH requires interaction with the substrate domain of p130Cas

The docking protein p130Cas has, together with FAK, been found as a target of the Yersinia virulence effector YopH. YopH is a protein tyrosine phosphatase that is delivered into host cells via the bacterial type III secretion machinery, and the outcome of its activity is inhibition of host cell phagocytosis. In the present study using p130Cas-/- cells, and p130Cas-/- cells expressing variants of GFPp130Cas, we show that this docking protein, via its substrate domain, is responsible for subcellular targeting of YopH in eukaryotic cells. Since YopH inhibits phagocytosis, p130Cas was expected to be critical for signalling mediating bacterial internalization. However, p130Cas-/- cells did not exhibit reduced capacity to internalize Yersinia. On the other hand, when a dominant negative variant of p130Cas was expressed in these cells, the phagocytic capacity was severely impaired. Moreover, the p130Cas-/- cells displayed a marked reduced sensitivity towards YopH-mediated detachment compared to wild-type cells. Transfecting these cells with full-length p130Cas rendered cells hypersensitive to both mechanical and Yersinia-mediated detachment. This hypersensitivity was not seen upon transfection with the dominant negative substrate domain-deleted variant of p130Cas. This implicates p130Cas as a prominent regulator of cell adhesion, where its substrate-binding domain has a significant function.     

On the DNA cleavage mechanism of Type I restriction enzymes

Although the DNA cleavage mechanism of Type I restriction–modification enzymes has been extensively studied, the mode of cleavage remains elusive. In this work, DNA ends produced by EcoKI, EcoAI and EcoR124I, members of the Type IA, IB and IC families, respectively, have been characterized by cloning and sequencing restriction products from the reactions with a plasmid DNA substrate containing a single recognition site for each enzyme. Here, we show that all three enzymes cut this substrate randomly with no preference for a particular base composition surrounding the cleavage site, producing both 5′- and 3′-overhangs of varying lengths. EcoAI preferentially generated 3′-overhangs of 2–3 nt, whereas EcoKI and EcoR124I displayed some preference for the formation of 5′-overhangs of a length of ~6–7 and 3–5 nt, respectively. A mutant EcoAI endonuclease assembled from wild-type and nuclease-deficient restriction subunits generated a high proportion of nicked circular DNA, whereas the wild-type enzyme catalyzed efficient cleavage of both DNA strands. We conclude that Type I restriction enzymes require two restriction subunits to introduce DNA double-strand breaks, each providing one catalytic center for phosphodiester bond hydrolysis. Possible models for DNA cleavage are discussed.     

Association between anti-nucleophosmin and anti-cardiolipin antibodies in (NZW x BXSB)F1 mice and human systemic lupus erythematosus

We showed previously that nucleophosmin (NPM), a nucleolar phosphoprotein, is recognized by sera from (NZW x BXSB)F1 (WB) mice, a model of systemic lupus erythematosus (SLE) and anti-phospholipid syndrome. In the present study we analysed the prevalence and kinetics of anti-NPM autoantibodies in WB mice by a solid-phase ELISA with recombinant human (rh) NPM as the antigen and showed that most male WB mouse sera had anti-NPM antibodies that were responsible for their indirect immunofluorescence staining pattern on Hep-2 cells. Anti-NPM antibodies were significantly associated with anti-cardiolipin (aCL) antibodies. This antibody profile mirrored that observed in certain human SLE sera because anti-NPM antibodies were detected in 28% of the sera from patients with SLE and were similarly associated with aCL antibodies. The demonstration that rhNPM bound to cardiolipin (CL) in vitro and increased the CL-binding activity of a WB-derived aCL monoclonal antibody indicates that NPM can interact with CL to form SLE-related immunogenic particles that might be responsible for the concomitant production of anti-NPM and aCL antibodies.