DnaK-facilitated ribosome assembly in Escherichia coli revisited

Assembly helpers exist for the formation of ribosomal subunits. Such a function has been suggested for the DnaK system of chaperones (DnaK, DnaJ, GrpE). Here we show that 50S and 30S ribosomal subunits from an Escherichia coli dnaK-null mutant (containing a disrupted dnaK gene) grown at 30 degrees C are physically and functionally identical to wild-type ribosomes. Furthermore, ribosomal components derived from mutant 30S and 50S subunits are fully competent for in vitro reconstitution of active ribosomal subunits. On the other hand, the DnaK chaperone system cannot circumvent the necessary heat-dependent activation step for the in vitro reconstitution of fully active 30S ribosomal subunits. It is therefore questionable whether the requirement for DnaK observed during in vivo ribosome assembly above 37 degrees C implicates a direct or indirect role for DnaK in this process.     

A Large-Scale Distribution of Milk-Based Fortified Spreads: Evidence for a New Approach in Regions with High Burden of Acute Malnutrition

Background

There are 146 million underweight children in the developing world, which contribute to up to half of the world''s child deaths. In high burden regions for malnutrition, the treatment of individual children is limited by available resources. Here, we evaluate a large-scale distribution of a nutritional supplement on the prevention of wasting.

Methods and Findings

A new ready-to-use food (RUF) was developed as a diet supplement for children under three. The intervention consisted of six monthly distributions of RUF during the 2007 hunger gap in a district of Maradi region, Niger, for approximately 60,000 children (length: 60–85 cm). At each distribution, all children over 65 cm had their Mid-Upper Arm Circumference (MUAC) recorded. Admission trends for severe wasting (WFH<70% NCHS) in Maradi, 2002–2005 show an increase every year during the hunger gap. In contrast, in 2007, throughout the period of the distribution, the incidence of severe acute malnutrition (MUAC<110 mm) remained at extremely low levels. Comparison of year-over-year admissions to the therapeutic feeding program shows that the 2007 blanket distribution had essentially the same flattening effect on the seasonal rise in admissions as the 2006 individualized treatment of almost 60,000 children moderately wasted.

Conclusions

These results demonstrate the potential for distribution of fortified spreads to reduce the incidence of severe wasting in large population of children 6–36 months of age. Although further information is needed on the cost-effectiveness of such distributions, these results highlight the importance of re-evaluating current nutritional strategies and international recommendations for high burden areas of childhood malnutrition.     

Immunolocalization of Na+,K+-ATPase in the organs of the branchial cavity of the European lobster Homarus gammarus (Crustacea, Decapoda)

The localization of Na+,K(+)-ATPase in epithelia of the organs of the branchial cavity of Homarus gammarus exposed to seawater and dilute seawater was examined by immunofluorescence microscopy and immunogold electron microscopy with a monoclonal antibody IgG alpha 5 raised against the avian alpha-subunit of the Na-,K(+)-ATPase. In juveniles held in seawater, fluorescent staining was observed only in the epithelial cells of epipodites. In juveniles held in dilute seawater, heavier immunoreactivity was observed in the epithelial cells of epipodites, and positive immunostaining was also observed along the inner-side epithelial layer of the branchiostegites. No fluorescent staining was observed in the gill epithelia. At the ultrastructural level, the Na+,K(+)-ATPase was localized in the basolateral infolding systems of the epipodite and inner-side branchiostegite epithelia of juveniles held in dilute seawater, mostly along the basal lamina. The expression of Na+,K(+)-ATPase therefore differs within tissues of the branchial cavity and according to the external salinity. These and previous ultrastructural observations suggest that the epipodites, and to a lesser extent the inner-side epithelium of the branchiostegites, are involved in the slight hyper-regulation displayed by lobsters at low salinity. Enhanced Na+,K(+)-ATPase activity and de novo synthesis of Na+,K(+)-ATPase within the epipodite and branchiostegite epithelia may be key points enabling lobsters to adapt to low salinity environments.     

PP2A targeting by viral proteins: a widespread biological strategy from DNA/RNA tumor viruses to HIV-1

Protein phosphatase 2A (PP2A) is a large family of holoenzymes that comprises 1% of total cellular proteins and accounts for the majority of Ser/Thr phosphatase activity in eukaryotic cells. Although initially viewed as constitutive housekeeping enzymes, it is now well established that PP2A proteins represent a family of highly and sophistically regulated phosphatases. The past decade, multiple complementary studies have improved our knowledge about structural and functional regulation of PP2A holoenzymes. In this regard, after summarizing major cellular regulation, this review will mainly focus on discussing a particulate biological strategy, used by various viruses, which is based on the targeting of PP2A enzymes by viral proteins in order to specifically deregulate, for their own benefit, cellular pathways of their hosts. The impact of such PP2A targeting for research in human diseases, and in further therapeutic developments, is also discussed.     

Late steps of ribosome assembly in E. coli are sensitive to a severe heat stress but are assisted by the HSP70 chaperone machine

The late stages of 30S and 50S ribosomal subunits biogenesis have been studied in a wild-type (wt) strain of Escherichia coli (MC4100) subjected to a severe heat stress (45-46°C). The 32S and 45S ribosomal particles (precursors to 50S subunits) and 21S ribosomal particles (precursors to 30S subunits) accumulate under these conditions. They are authentic precursors, not degraded or dead-end particles. The 21S particles are shown, by way of a modified 3'5' RACE procedure, to contain 16S rRNA unprocessed, or processed at its 5' end, and not at the 3' end. This implies that maturation of 16S rRNA is ordered and starts at its 5'-terminus, and that the 3'-terminus is trimmed at a later step. This observation is not limited to heat stress conditions, but it also can be verified in bacteria growing at a normal temperature (30°C), supporting the idea that this is the general pathway. Assembly defects at very high temperature are partially compensated by plasmid-driven overexpression of the DnaK/DnaJ chaperones. The ribosome assembly pattern in wt bacteria under a severe heat stress is therefore reminiscent of that observed at lower temperatures in E. coli mutants lacking the chaperones DnaK or DnaJ.     

Preserved central memory and activated effector memory CD4+ T-cell subsets in human immunodeficiency virus controllers: an ANRS EP36 study

Human immunodeficiency virus (HIV) controllers are rare individuals who spontaneously control HIV type 1 replication for 10 years or more in the absence of antiretroviral treatment. In the present study, HIV controllers (n = 11) maintained potent HIV-specific CD4 responses in spite of very low antigenic loads. Their CD4⁺ central memory T (T_CM) cells were characterized by near-normal numbers and preserved interleukin-2 (IL-2) secretion in response to HIV antigens and uniformly high expression of the survival receptor IL-7 receptor α (IL-7Rα). Controllers expressed CCR7 at higher levels than uninfected controls, suggesting differences in T_CM-cell homing patterns. CD4⁺ effector memory T (T_EM)-cell responses were polyfunctional in HIV controllers, while IL-2 secretion was lost in viremic patients. Cytokine production was three times higher in controllers than in treated patients with undetectable viral loads, suggesting an intrinsically more efficient response in the former group. The total CD4⁺ T_EM-cell pool underwent immune activation in controllers, as indicated by increased HLA-DR expression, decreased IL-7Rα expression, a bias towards gamma interferon production upon polyclonal stimulation, and increased macrophage inflammatory protein 1β secretion associated with chronic CCR5 down-regulation. Thus, HIV controllers showed a preserved CD4⁺ T_CM-cell compartment and signs of potent functional activation in the CD4⁺ T_EM-cell compartment. While controllers did not show the generalized immune activation pattern associated with disease progression, they had signs of immune activation restricted to the effector compartment. These findings suggest the induction of an efficient, nondetrimental type of immune activation in patients who spontaneously control HIV.     

Spatial Structure and Distribution of Small Pelagic Fish in the Northwestern Mediterranean Sea

Understanding the ecological and anthropogenic drivers of population dynamics requires detailed studies on habitat selection and spatial distribution. Although small pelagic fish aggregate in large shoals and usually exhibit important spatial structure, their dynamics in time and space remain unpredictable and challenging. In the Gulf of Lions (north-western Mediterranean), sardine and anchovy biomasses have declined over the past 5 years causing an important fishery crisis while sprat abundance rose. Applying geostatistical tools on scientific acoustic surveys conducted in the Gulf of Lions, we investigated anchovy, sardine and sprat spatial distributions and structures over 10 years. Our results show that sardines and sprats were more coastal than anchovies. The spatial structure of the three species was fairly stable over time according to variogram outputs, while year-to-year variations in kriged maps highlighted substantial changes in their location. Support for the McCall''s basin hypothesis (covariation of both population density and presence area with biomass) was found only in sprats, the most variable of the three species. An innovative method to investigate species collocation at different scales revealed that globally the three species strongly overlap. Although species often co-occurred in terms of presence/absence, their biomass density differed at local scale, suggesting potential interspecific avoidance or different sensitivity to local environmental characteristics. Persistent favourable areas were finally detected, but their environmental characteristics remain to be determined.     

Postprandial morphological response of the intestinal epithelium of the Burmese python (Python molurus)

The postprandial morphological changes of the intestinal epithelium of Burmese pythons were examined using fasting pythons and at eight time points after feeding. In fasting pythons, tightly packed enterocytes possess very short microvilli and are arranged in a pseudostratified fashion. Enterocyte width increases by 23% within 24 h postfeeding, inducing significant increases in villus length and intestinal mass. By 6 days postfeeding, enterocyte volume had peaked, following as much as an 80% increase. Contributing to enterocyte hypertrophy is the cellular accumulation of lipid droplets at the tips and edges of the villi of the proximal and middle small intestine, but which were absent in the distal small intestine. At 3 days postfeeding, conventional and environmental scanning electron microscopy revealed cracks and lipid extrusion along the narrow edges of the villi and at the villus tips. Transmission electron microscopy demonstrated the rapid postprandial lengthening of enterocyte microvilli, increasing 4.8-fold in length within 24 h, and the maintaining of that length through digestion. Beginning at 24 h postfeeding, spherical particles were found embedded apically within enterocytes of the proximal and middle small intestine. These particles possessed an annular-like construction and were stained with the calcium-stain Alizarine red S suggesting that they were bone in origin. Following the completion of digestion, many of the postprandial responses were reversed, as observed by the atrophy of enterocytes, the shortening of villi, and the retraction of the microvilli. Further exploration of the python intestine will reveal the underlying mechanisms of these trophic responses and the origin and fate of the engulfed particles.     

Complementation of an Escherichia coli DnaK defect by Hsc70-DnaK chimeric proteins

Escherichia coli DnaK and rat Hsc70 are members of the highly conserved 70-kDa heat shock protein (Hsp70) family that show strong sequence and structure similarities and comparable functional properties in terms of interactions with peptides and unfolded proteins and cooperation with cochaperones. We show here that, while the DnaK protein is, as expected, able to complement an E. coli dnaK mutant strain for growth at high temperatures and lambda phage propagation, Hsc70 protein is not. However, an Hsc70 in which the peptide-binding domain has been replaced by that of DnaK is able to complement this strain for both phenotypes, suggesting that the peptide-binding domain of DnaK is essential to fulfill the specific functions of this protein necessary for growth at high temperatures and for lambda phage replication. The implications of these findings on the functional specificities of the Hsp70s and the role of protein-protein interactions in the DnaK chaperone system are discussed.