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.     

The formation of titan cells in Cryptococcus neoformans depends on the mouse strain and correlates with induction of Th2‐type responses

Cryptococcus neoformans is a pathogenic yeast that can form titan cells in the lungs, which are fungal cells of abnormal enlarged size. Little is known about the factors that trigger titan cells. In particular, it is not known how the host environment influences this transition. In this work, we describe the formation of titan cells in two mouse strains, CD1 and C57BL/6J. We found that the proportion of C. neoformans titan cells was significantly higher in C57BL/6J mice than in CD1. This higher proportion of titan cells was associated with a higher dissemination of the yeasts to the brain. Histology sections demonstrated eosinophilia in infected animals, although it was significantly lower in the CD1 mice which presented infiltration of lymphocytes. Both mouse strains presented infiltration of granulocytes, but the amount of eosinophils was higher in C57BL/6J. CD1 mice showed a significant accumulation of IFN‐γ, TNF‐α and IL17, while C57BL/BL mice had an increase in the anti‐inflammatory cytokine IL‐4. IgM antibodies to the polysaccharide capsule and total IgE were more abundant in the sera from C57BL/6J, confirming that these animals present a Th2‐type response. We conclude that titan cell formation in C. neoformans depends, not only on microbe factors, but also on the host environment.     

Behavioral response of manatees to variations in environmental sound levels

Florida manatees (Trichechus manatus latirostris) inhabit coastal regions because they feed on the aquatic vegetation that grows in shallow waters, which are the same areas where human activities are greatest. Noise produced from anthropogenic and natural sources has the potential to affect these animals by eliciting responses ranging from mild behavioral changes to extreme aversion. Sound levels were calculated from recordings made throughout behavioral observation periods. An information theoretic approach was used to investigate the relationship between behavior patterns and sound level. Results indicated that elevated sound levels affect manatee activity and are a function of behavioral state. The proportion of time manatees spent feeding and milling changed in response to sound level. When ambient sound levels were highest, more time was spent in the directed, goal‐oriented behavior of feeding, whereas less time was spent engaged in undirected behavior such as milling. This work illustrates how shifts in activity of individual manatees may be useful parameters for identifying impacts of noise on manatees and might inform population level effects.     

Environmental control and spatial structures in peatland vegetation

Question: What are the relative influences of environment and space in structuring the plant composition in a peatland complex? Location: Lakkasuo, southern boreal zone, Finland. Method: We used principal coordinates of neighbour matrices (PCNM) to model spatial structures in the plant composition of a peatland complex comprising ombrotrophic and minerotrophic, open and forested areas. We used redundancy analyses (RDA) and variation partitioning to assess the relative influences of chemical variables (peat and water characteristics), physical variables (hydrology, soil properties, shade), as well as broad‐scale (>350 m) and medium‐scale (100–350 m) spatial structures on vegetation assemblages. Results: We identified five different significant spatial patterns circumscribing (1) the minerotrophic–ombrotrophic gradient; (2) dry ombrotrophic and wet minerotrophic areas; (3) open and shaded areas; (4) dry open/shaded and wet patches within the ombrotrophic areas; and (5) dry open patches and dry forested patches. With spatial structures and environmental variables, we were able to model 30% of the variability in plant composition in the peatland complex, 13% of which was attributable to spatial structures alone. Conclusions: We demonstrated that in the peatland complex, the spatial dependence processes were more important at the broadest scale, and found that patterns at a medium scale might reflect finer‐scale patterns that were not investigated here. Spatial autocorrelation in vegetation composition in the peatland complex appeared to be driven by Sphagnum species. Our results emphasize that spatial modelling should be routinely implemented in studies looking at species composition, since they significantly increase the explained proportion of variance.     

Patterns of early succession on bare peat in a Swiss mire after a bog burst

Questions: How does plant diversity (species richness, species abundance and rate of change) evolve in early succession on bare peat? Does succession converge towards one equilibrium stage or end up in several stages? Is there a regular pattern in succession velocity? Location: A mire in the calcareous Jura Mountains of northwest Switzerland. Method: Twenty‐one 1‐m² permanent plots on bare peat were used to monitor temporal stages over a 21‐year period (1988 to 2008) in a Swiss mire where a slide occurred in 1987. Species diversity and life forms were analysed based on Shannon's equitability index and cover. We used classification and metric ordination techniques to investigate patterns of successional rates and trends. The high temporal resolution of the survey allowed the pattern of succession velocity to be analysed. Results: Species richness increased continuously over the 21 years of succession. The highest cover throughout the study period was the life form sedge. Time trajectories of the 21 plots revealed three alternative pathways towards intermediate equilibrium stages in the first years, still not converging in the later stages. Changes in succession velocity reached a first maximum about 6 years after the slide had occurred and a second maximum 12 years later.     

A novel light‐dependent selection marker system in plants

Photosensitizers are common in nature and play diverse roles as defense compounds and pathogenicity determinants and as important molecules in many biological processes. Toxoflavin, a photosensitizer produced by Burkholderia glumae, has been implicated as an essential virulence factor causing bacterial rice grain rot. Toxoflavin produces superoxide and H₂O₂ during redox cycles under oxygen and light, and these reactive oxygen species cause phytotoxic effects. To utilize toxoflavin as a selection agent in plant transformation, we identified a gene, tflA, which encodes a toxoflavin‐degrading enzyme in the Paenibacillus polymyxa JH2 strain. TflA was estimated as 24.56 kDa in size based on the amino acid sequence and is similar to a ring‐cleavage extradiol dioxygenase in the Exiguobacterium sp. 255‐15; however, unlike other extradiol dioxygenases, Mn²⁺and dithiothreitol were required for toxoflavin degradation by TflA. Here, our results suggested toxoflavin is a photosensitizer and its degradation by TflA serves as a light‐dependent selection marker system in diverse plant species. We examined the efficiencies of two different plant selection systems, toxoflavin/tflA and hygromycin/hygromycin phosphotransferase (hpt) in both rice and Arabidopsis. The toxoflavin/tflA selection was more remarkable than hygromycin/hpt selection in the high‐density screening of transgenic Arabidopsis seeds. Based on these results, we propose the toxoflavin/tflA selection system, which is based on the degradation of the photosensitizer, provides a new robust nonantibiotic selection marker system for diverse plants.