FAK-MAPK-dependent adhesion disassembly downstream of L1 contributes to semaphorin3A-induced collapse

Axonal receptors for class 3 semaphorins (Sema3s) are heterocomplexes of neuropilins (Nrps) and Plexin-As signalling coreceptors. In the developing cerebral cortex, the Ig superfamily cell adhesion molecule L1 associates with Nrp1. Intriguingly, the genetic removal of L1 blocks axon responses of cortical neurons to Sema3A in vitro despite the expression of Plexin-As in the cortex, suggesting either that L1 substitutes for Plexin-As or that L1 and Plexin-A are both required and mediate distinct roles. We report that association of Nrp1 with L1 but not Plexin-As mediates the recruitment and activation of a Sema3A-induced focal adhesion kinase-mitogen-activated protein kinase cascade. This signalling downstream of L1 is needed for the disassembly of adherent points formed in growth cones and subsequently their collapse response to Sema3A. Plexin-As and L1 are coexpressed and present in common complexes in cortical neurons and both dominant-negative forms of Plexin-A and L1 impair their response to Sema3A. Consistently, Nrp1-expressing cortical projections are defective in mice lacking Plexin-A3, Plexin-A4 or L1. This reveals that specific signalling activities downstream of L1 and Plexin-As cooperate for mediating the axon guidance effects of Sema3A.     

Genetic immunisation by liver stage antigen 3 protects chimpanzees against malaria despite low immune responses

Background

The true interest of genetic immunisation might have been hastily underestimated based on overall immunogenicity data in humans and lack of parallelism with other, more classical immunisation methods.

Principal Findings

Using malaria Liver Stage Antigen-3 (LSA-3), we report that genetic immunization induces in chimpanzees, the closest relative of humans, immune responses which are as scarce as those reported using other DNA vaccines in humans, but which nonetheless confer strong, sterile and reproducible protection. The pattern was consistent in 3/4 immunized apes against two high dose sporozoite challenges performed as late as 98 and 238 days post-immunization and by a heterologous strain.

Conclusions

These results should, in our opinion, lead to a revisiting of the value of this unusual means of immunisation, using as a model a disease, malaria, in which virulent challenges of volunteers are ethically acceptable.     

Isotope Ratio Measurements of Iron in Blood Samples by Multi-collector ICP-MS to Support Nutritional Investigations in Humans

With the perspective of embarking on a human study using a double iron (Fe) stable isotope tracer protocol to assess iron bioavailability, investigations were conducted on Fe isotope ratios in blood samples using a VG Axiom Multi-collector ICP-MS. The factors affecting the precision and accuracy of Fe isotopic ratios, such as spectral- and matrix-induced interferences and Fe recoveries from sample preparation, have been identified and optimized. Major polyatomic interferences (e.g., Ar-O, Ar-OH, and FeH) were significantly reduced by using an Aridus nebulizer and desolvating system. Isobaric metal (e.g., ⁵⁴Cr⁺ on ⁵⁴Fe⁺ and ⁵⁸Ni⁺ on ⁵⁸Fe⁺) interferences and Ca-oxides and hydroxides were quantitatively removed during chemical purification of blood samples and selective isolation of Fe by anion-exchange resin, after mineralization of the blood samples by microwave digestion. Quantitative recoveries of Fe from different steps of sample preparation were verified using whole blood reference material. Fe isotopic compositions of the samples were corrected for instrumental mass bias by the standard-sample bracketing method using the certified reference standard IRMM-014. External precisions on the order of 0.008–0.05 (% RSD), 0.007–0.015 (% RSD), and 0.03–0.09 (% RSD) were obtained for ⁵⁴Fe/⁵⁶Fe, ⁵⁷Fe/⁵⁶Fe, and ⁵⁸Fe/⁵⁶Fe, respectively, in the blood for three replicate measurements. The level of precision obtained in this work enables the detection of low enrichments of Fe in blood, which is highly desired in nutrition tracer studies.     

Out-of-school experience categories influencing interest in biology of secondary school students by gender: exploration on an Abu Dhabi sample

This study employed the international Relevance of Science Education questionnaire to survey the interest in biology and the out-of-school experiences of Abu Dhabi secondary school students (median age 17, mean age 17.53 and mode age of 16) in the third semester of 2014. It included 3100 participants. An exploratory factor analysis was used to categorise the items for both interest in biology and out-of-school experience. Ten interest in biology and 12 out-of-school experience factors were extracted. The summated means for each factor indicated that ‘health and fitness’ and ‘disease control’ enjoyed highest interests among students. For out-of-school experiences, the two factors of ‘digital applications’ and ‘medical treatment’ received the highest scores. Multivariate analysis of variance revealed that all factors for both interest in biology and out-of-school experience exhibited significant differences between boys and girls. More girls than boys were interested in disease control, reproduction (human biology), alternative science, health and fitness, zoology, and applied cosmetic biology. No significant differences were observed for the remaining five other categories. Furthermore, analysis of variance revealed significant differences between boys and girls with regard to individual items comprising each of the factors. The highest correlations were between the two factors of out-of-school experiences of ‘the natural world’ and ‘learning through observation’ and the interest in biology factor related to ‘plant and animal farming and agriculture’. Results suggested that more emphasis must be placed on students’ out-of-school experience and their engagement in informal learning in contextual outdoor environments to enhance their interest in learning more about biology and the living environment in general.     

Beta-Actin Is Required for Proper Mouse Neural Crest Ontogeny

The mouse genome consists of six functional actin genes of which the expression patterns are temporally and spatially regulated during development and in the adult organism. Deletion of beta-actin in mouse is lethal during embryonic development, although there is compensatory expression of other actin isoforms. This suggests different isoform specific functions and, more in particular, an important function for beta-actin during early mammalian development. We here report a role for beta-actin during neural crest ontogeny. Although beta-actin null neural crest cells show expression of neural crest markers, less cells delaminate and their migration arrests shortly after. These phenotypes were associated with elevated apoptosis levels in neural crest cells, whereas proliferation levels were unchanged. Specifically the pre-migratory neural crest cells displayed higher levels of apoptosis, suggesting increased apoptosis in the neural tube accounts for the decreased amount of migrating neural crest cells seen in the beta-actin null embryos. These cells additionally displayed a lack of membrane bound N-cadherin and dramatic decrease in cadherin-11 expression which was more pronounced in the pre-migratory neural crest population, potentially indicating linkage between the cadherin-11 expression and apoptosis. By inhibiting ROCK ex vivo, the knockout neural crest cells regained migratory capacity and cadherin-11 expression was upregulated. We conclude that the presence of beta-actin is vital for survival, specifically of pre-migratory neural crest cells, their proper emigration from the neural tube and their subsequent migration. Furthermore, the absence of beta-actin affects cadherin-11 and N-cadherin function, which could partly be alleviated by ROCK inhibition, situating the Rho-ROCK signaling in a feedback loop with cadherin-11.     

αB-Crystallin Interacts with Cytoplasmic Intermediate Filament Bundles during Mitosis

The small heat-shock protein αB-crystallin interacts with intermediate filament proteins. Using cosedimentation assay, we showed previously that in vitro binding of αB-crystallin to peripherin and vimentin was temperature-dependent. Furthermore, when NIH 3T3 cells were submitted to different stress conditions a dynamic reorganization of the intermediate filament network was observed concomitantly with the recruitment of αB-crystallins on the intermediate filament proteins. Thus, the intracellular state of αB-crystallin correlated directly with the remodeling of the intermediate filament network in response to stress. Here, we show data suggesting that αB-crystallin is implicated in remodeling of intermediate filaments during cell division. We investigated the intracellular distribution of αB-crystallin in naturally occurring mitotic NIH 3T3 cells and in neuroblastoma N2a and N1E115 cells. In NIH 3T3 cells, αB-crystallin remained diffused throughout the cell cycle. Subcellular fractionation of αB-crystallin showed that αB-crystallin remained in the cytosolic compartment during mitosis. Furthermore, αB-crystallin accumulated in mitotically arrested NIH 3T3 cells. This increased level of αB-crystallin protein was due to an increased level of αB-crystallin mRNA in mitotic NIH 3T3 cells. In the neuroblastoma cells, the intermediate filaments were rearranged into thick cable-like structures and αB-crystallin was recruited onto them. In neuroblastoma N2a cells the level of expression did not change during the cell cycle. However, a small fraction of αB-crystallin switched onto the insoluble fraction in mitotically arrested N2a cells. Our results suggested that depending on the state of rearrangement of the intermediate filament network during mitosis αB-crystallin was either recruited onto the intermediate filaments or upregulated in the cytosolic compartment.     

Cuticular differences of the exoskeleton relative to habitat preferences among three terrestrial isopods

Terrestrial isopods have adapted to land life by diverse morphological, physiological and behavioral changes. Isopod species exhibit a large variety of preferences ranging from moist to dry habitats. Isopod cuticle is an interesting model for studying adaptations to terrestrial life. The cuticle consists of a hierarchically organized material which provides protection and sites for muscle attachment. The present paper aimed to investigate the structure of the cuticle in three isopod species in order to relate some peculiar features to an adaptive process to environmental constraints. Results showed that general thickness of Ligia italica cuticle was quite similar to that observed in Porcellio lamellatus. Nevertheless, this cuticle was half as thick as in Porcellio laevis. Although the positive relationship found between total body lengths and the total thickness of the cuticle, the exocuticle did not show any differences between the three species. However, it is the development of a thicker endocuticle in P. laevis which make its total cuticle thickness more important.     

Analysis of Cellular Mutants Resistant to Theiler’s Virus Infection: Differential Infection of L929 Cells by Persistent and Neurovirulent Strains

Theiler's murine encephalomyelitis virus (TMEV) is a natural pathogen of the mouse and belongs to the Picornaviridae family. TMEV strains are divided into two subgroups on the basis of their pathogenicity. The first group contains two neurovirulent strains, FA and GDVII, which cause a rapid fatal encephalitis. The second group includes persistent strains, like DA and BeAn, which produce a biphasic neurological disease in susceptible mice. Persistence of these viruses in the white matter of the spinal cord leads to chronic inflammatory demyelination. L929 cells, which are susceptible to TMEV infection, were subjected to physicochemical mutagenesis. Cellular clones that became resistant to TMEV infection were selected by viral infection. Three such mutants resistant to strain GDVII were characterized to determine the step of the virus cycle that was inhibited. The mutation present in one of these mutant cell lines inhibited, by more than 1,000-fold, the entry of strain GDVII but hardly decreased infection by strain DA. In the two other cellular mutants, replication of the viral genome was slowed down. Interestingly, one of these mutant cell lines resisted infection by both the persistent and neurovirulent strains while the second cell line resisted infection by strain GDVII but remained susceptible to the persistent virus. These results show that although they have 95% identity at the amino acid sequence level, neurovirulent and persistent viruses use partly distinct pathways for both entry into cells and genome replication.     

The integrative role of cryo electron microscopy in molecular and cellular structural biology

After gradually moving away from preparation methods prone to artefacts such as plastic embedding and negative staining for cell sections and single particles, the field of cryo electron microscopy (cryo‐EM) is now heading off at unprecedented speed towards high‐resolution analysis of biological objects of various sizes. This ‘revolution in resolution’ is happening largely thanks to new developments of new‐generation cameras used for recording the images in the cryo electron microscope which have much increased sensitivity being based on complementary metal oxide semiconductor devices. Combined with advanced image processing and 3D reconstruction, the cryo‐EM analysis of nucleoprotein complexes can provide unprecedented insights at molecular and atomic levels and address regulatory mechanisms in the cell. These advances reinforce the integrative role of cryo‐EM in synergy with other methods such as X‐ray crystallography, fluorescence imaging or focussed‐ion beam milling as exemplified here by some recent studies from our laboratory on ribosomes, viruses, chromatin and nuclear receptors. Such multi‐scale and multi‐resolution approaches allow integrating molecular and cellular levels when applied to purified or in situ macromolecular complexes, thus illustrating the trend of the field towards cellular structural biology.     

<Emphasis Type="Italic">Blastococcus colisei</Emphasis> sp. nov,isolated from an archaeological amphitheatre

The taxonomic position of an actinobacterial isolate, designated strain BMG 822^T, isolated from limestone from the Amphitheater of El Jem (Coliseum Thysdrus), Tunisia, was established using a polyphasic approach. Strain BMG 822^T was found to grow well at 30 °C and pH 6.5–8.0, and to be coral-coloured, Gram-positive, catalase and oxidase negative. Whole cell hydrolysates contained meso-diaminopimelic acid as the diagnostic diamino acid, glucose, galactose and ribose. The phospholipids detected were diphosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, hydroxy-phosphatidylethanolamine, an unidentified glycophospholipid and six unidentified phospholipids. MK-9(H₄) was found to be the predominant menaquinone, followed by MK-9(H₂) and MK-9. The major cellular fatty acids were identified as iso-C_16:0, C_18:1 ω9c, C_17:1 ω8c and iso-H-C_16:1. The G+C content of the DNA (73.2%) is typical of the genus. High degrees of 16S rRNA gene sequence similarity were found with the type strains of the genus Blastococcus (97.1–98.3%) followed by the type strains of Modestobacter (96.8–97.8%). Based on the above data and the phenotypic differences from the type strains of Blastococcus species, it is proposed that the isolate BMG 822^T (=DSM 46837^T=CECT 8823^T) should be classified as the type strain of a novel species, Blastococcus colisei sp. nov.