Spindle assembly defects leading to the formation of a monopolar mitotic apparatus

Mitotic spindle formation in animal cells involves microtubule nucleation from two centrosomes that are positioned at opposite sides of the nucleus. Microtubules are captured by the kinetochores and stabilized. In addition, microtubules can be nucleated independently of the centrosome and stabilized by a gradient of Ran—GTP, surrounding the mitotic chromatin. Complex regulation ensures the formation of a bipolar apparatus, involving motor proteins and controlled polymerization and depolymerization of microtubule ends. The bipolar apparatus is, in turn, responsible for faithful chromosome segregation. During recent years, a variety of experiments has indicated that defects in specific motor proteins, centrosome proteins, kinases and other proteins can induce the assembly of aberrant spindles with a monopolar morphology or with poorly separated poles. Induction of monopolar spindles may be a useful strategy for cancer therapy, since ensuing aberrant mitotic exit will usually lead to cell death. In this review, we will discuss the various underlying molecular mechanisms that may be responsible for monopolar spindle formation.     

Vertebrate palaeohistology: Past and future

Vertebrate palaeohistology has been considered for a long time as a modest subdivision of Palaeontology. Starting in the 1930s and 1940s, comparative bone tissue histology and palaeohistology progressively demonstrated the multiple correlations between bone tissue distribution and numerous biological variables, such as ontogenetic origin, growth, size, shape, biomechanics, physiology, and ecology. During the last three decades, Palaeohistology has focussed on deciphering the numerous, complex causes explaining the patterns and processes of Vertebrate evolution. Palaeohistology is a powerful tool, in connection with Biology, for the reconstruction of fossil Vertebrates as living organisms.     

Effects of disturbance intensity and frequency on bacterial community composition and function

Disturbances influence community structure and ecosystem functioning. Bacteria are key players in ecosystems and it is therefore crucial to understand the effect of disturbances on bacterial communities and how they respond to them, both compositionally and functionally. The main aim of this study was to test the effect of differences in disturbance strength on bacterial communities. For this, we implemented two independent short-term experiments with dialysis bags containing natural bacterial communities, which were transplanted between ambient and 'disturbed' incubation tanks, manipulating either the intensity or the frequency of a salinity disturbance. We followed changes in community composition by terminal restriction fragment analysis (T-RFLP) and measured various community functions (bacterial production, carbon substrate utilization profiles and rates) directly after and after a short period of recovery under ambient conditions. Increases in disturbance strength resulted in gradually stronger changes in bacterial community composition and functions. In the disturbance intensity experiment, the sensitivity to the disturbance and the ability of recovery differed between different functions. In the disturbance frequency experiment, effects on the different functions were more consistent and recovery was not observed. Moreover, in case of the intensity experiment, there was also a time lag in the responses of community composition and functions, with functional responses being faster than compositional ones. To summarize, our study shows that disturbance strength has the potential to change the functional performance and composition of bacterial communities. It further highlights that the overall effects, rates of recovery and the degree of congruence in the response patterns of community composition and functioning along disturbance gradients depend on the type of function and the character of the disturbance.     

Postnatal gender-dependent maturation of cellular cysteine uptake

Background. In view of the functional capacity of glutathione synthesis in premature infants, and because the availability of cysteine is one the rate limiting steps in glutathione synthesis, we hypothesized that the low glutathione levels in premature infants may be due to immaturity of the active cellular uptake of cysteine.

Objective. To document in cells from newborn infants the effect of maturity and gender on cysteine uptake and consequently on glutathione levels.

Methods. Incorporation of L-[35S] cysteine was measured in leukocytes from cord blood and from tracheal aspirates (TAC) of newborn infants of varying (gestational as well as postnatal) ages and gender. Cysteine uptake was correlated with glutathione in TAC.

Results. The maturity of newborn girls positively influences cysteine uptake, which is responsible for 78% of the variation in their glutathione content. However, in newborn boys, gestational and postnatal ages did not influence the cysteine uptake.

Discussion. Cysteine uptake appears to be the limiting step explaining the reported gender-related differences in glutathione as well as the low levels of this central antioxidant found in premature infants. The immature cysteine uptake found in cells from premature infants raises questions about the bioavailability of this conditionally essential amino acid in regimens of parenteral nutrition for human neonates.     

An improved method for the generation and transfection of protoplasts from Cucumis sativus Cotyledons

Summary A protocol was developed for the preparation of Cucumis sativus var Straight 8 protoplasts that incorporates a two-step Ficoll^® gradient and results in a high percentage of viable, debris-free protoplasts suitable for the transient expression of foreign genes. Polyethylene glycol and electroporation were compared for their effect on protoplast transfection with commonly used reporter genes. Using a polyethylene glycol method, cucumber protoplasts transfected with a plasmid containing the -glucuronidase gene showed high expression levels, while protoplasts transfected with a plasmid containing the chloramphenicol acetyl transferase gene showed levels of activity that were barely distinguishable from mock-transfected controls. Tomato ringspot virus genomic RNA was also transfected into the protoplasts, and the assembly of viral particles was confirmed.     

Diversity surveys and evolutionary relationships of aoxB genes in aerobic arsenite-oxidizing bacteria

A new primer set was designed to specifically amplify ca. 1,100 bp of aoxB genes encoding the As(III) oxidase catalytic subunit from taxonomically diverse aerobic As(III)-oxidizing bacteria. Comparative analysis of AoxB protein sequences showed variable conservation levels and highlighted the conservation of essential amino acids and structural motifs. AoxB phylogeny of pure strains showed well-discriminated taxonomic groups and was similar to 16S rRNA phylogeny. Alphaproteobacteria-, Betaproteobacteria-, and Gammaproteobacteria-related sequences were retrieved from environmental surveys, demonstrating their prevalence in mesophilic As-contaminated soils. Our study underlines the usefulness of the aoxB gene as a functional marker of aerobic As(III) oxidizers.     

Inter-Annual Variability of Fledgling Sex Ratio in King Penguins

As the number of breeding pairs depends on the adult sex ratio in a monogamous species with biparental care, investigating sex-ratio variability in natural populations is essential to understand population dynamics. Using 10 years of data (2000–2009) in a seasonally monogamous seabird, the king penguin (Aptenodytes patagonicus), we investigated the annual sex ratio at fledging, and the potential environmental causes for its variation. Over more than 4000 birds, the annual sex ratio at fledging was highly variable (ranging from 44.4% to 58.3% of males), and on average slightly biased towards males (51.6%). Yearly variation in sex-ratio bias was neither related to density within the colony, nor to global or local oceanographic conditions known to affect both the productivity and accessibility of penguin foraging areas. However, rising sea surface temperature coincided with an increase in fledging sex-ratio variability. Fledging sex ratio was also correlated with difference in body condition between male and female fledglings. When more males were produced in a given year, their body condition was higher (and reciprocally), suggesting that parents might adopt a sex-biased allocation strategy depending on yearly environmental conditions and/or that the effect of environmental parameters on chick condition and survival may be sex-dependent. The initial bias in sex ratio observed at the juvenile stage tended to return to 1∶1 equilibrium upon first breeding attempts, as would be expected from Fisher’s classic theory of offspring sex-ratio variation.     

A revised annotation and comparative analysis of Helicobacter pylori genomes

Huge amounts of genomic information are currently being generated. Therefore, biologists require structured, exhaustive and comparative databases. The PyloriGene database (http://genolist.pasteur.fr/PyloriGene) was developed to respond to these needs, by integrating and connecting the information generated during the sequencing of two distinct strains of Helicobacter pylori. This led to the need for a general annotation consensus, as the physical and functional annotations of the two strains differed significantly in some cases. A revised functional classification system was created to accommodate the existing data and to make it possible to classify coding sequences (CDS) into several functional categories to harmonize CDS classification. The annotation of the two complete genomes was revised in the light of new data, allowing us to reduce the percentage of hypothetical proteins from approximately 40 to 33%. This resulted in the reassignment of functions for 108 CDS (approximately 7% of all CDS). Interestingly, the functions of only approximately 13% of CDS (222 out of 1658 CDS) were annotated as a result of work done directly on H.pylori genes. Finally, comparison of the two published genomes revealed a significant amount of size variation between corresponding (orthologous) CDS. Most of these size variations were due to natural polymorphisms, although other sources of variation were identified, such as pseudogenes, new genes potentially regulated by slipped-strand mispairing mechanism, or frame-shifts. 113 of these differences were due to different start codon assignments, a common problem when constructing physical annotations.     

Enzymatic hydrolysis of asymmetric heterocyclic amino acid derivatives

Summary 2-methyl-oxazolinones and thio-thiazolidones representative of aromatic and aliphatic amino acids were hydrolysed by -chymotrypsin and subtilisin. The parametric ratio k_cat/K_m, correlated with the enantiomeric enrichment of the reaction product, indicates that thio-thiazolidones are converted to free amino acids by enzyme with the higher degree of stereospecificity.