Novel RNA chaperone domain of RNA-binding protein La is regulated by AKT phosphorylation

The cellular function of the cancer-associated RNA-binding protein La has been linked to translation of viral and cellular mRNAs. Recently, we have shown that the human La protein stimulates IRES-mediated translation of the cooperative oncogene CCND1 in cervical cancer cells. However, there is little known about the underlying molecular mechanism by which La stimulates CCND1 IRES-mediated translation, and we propose that its RNA chaperone activity is required. Herein, we show that La binds close to the CCND1 start codon and demonstrate that La''s RNA chaperone activity can change the folding of its binding site. We map the RNA chaperone domain (RCD) within the C-terminal region of La in close proximity to a novel AKT phosphorylation site (T389). Phosphorylation at T389 by AKT-1 strongly impairs its RNA chaperone activity. Furthermore, we demonstrate that the RCD as well as T389 is required to stimulate CCND1 IRES-mediated translation in cells. In summary, we provide a model whereby a novel interplay between RNA-binding, RNA chaperoning and AKT phosphorylation of La protein regulates CCND1 IRES-mediated translation.     

Resting site selection by large herbivores – The case of European bison (Bison bonasus) in Białowieża Primeval Forest

Resting site selection by European bison (Bison bonasus, L., 1758), the largest terrestrial mammal of Europe, was studied in the free-ranging population in Bia?owie?a Primeval Forest (Poland) in 2009–2010. In total, 104 sites of 21 bison (both collared and uncollared) were analysed to determine the most important microhabitat characteristics selected by resting bison during summer and winter and to study the influence of supplementary feeding on resting behaviour of this herbivore. Resting sites were identified on the basis of GPS locations and activity records collected by GPS collars, as well as direct observations of bison, and were compared with control sites. Microhabitat selection by bison did not differ significantly between the sexes. During summer and winter, bison resting sites displayed a high tree density, low visibility and high complexity (structures providing cover). Summer resting sites were also characterised by a significantly lower abundance of blood-sucking insects and denser canopy than control sites. Winter resting sites showed a lower complexity and higher visibility than summer sites, and were less often located in mixed forest habitats. During winter, bison rested more frequently in forest below 50 years of age than in older forest. Resting sites of non-fed bison were more often located in young coniferous forests, were lower in visibility and situated closer to open areas than sites of bison using supplementary winter feeding, suggesting a trade-off between food and cover. The results indicate that European bison select their resting sites in areas of mosaic habitat structure providing cover from disturbances with access to profitable natural forage grounds.     

On the connection between the T-system and the subsynaptic folds in the motor end plate of amphibians

Using lanthanum as an extracellular marker, the transition between the subsynaptic folds of the motor end plate and the T-system of frog muscle fibres is portrayed for the first time. On the lower segment of the subsynaptic folds of frogs, there are numerous caveolae which can connect with one another to form meandering, branching tubes. The T-system is in contact with these tubes (which run through the sarcoplasm) beneath the motor end plate. In those segments of the end plate with massed sarcoplasm and a cell nucleus, these tubes form networks in close proximity to the cellular organelles. The morphological findings obtained here are compared with findings from mammals. The physiological significance of the transition between the subsynaptic fold and the T-system is discussed.     

Plant chemical traits define functional and phylogenetic axes of plant biodiversity

To determine which types of plant traits might better explain ecosystem functioning and plant evolutionary histories, we compiled 42 traits for each of 15 perennial species in a biodiversity experiment. We used every possible combination of three traits to cluster species. Across these 11,480 combinations, clusters generated using tissue %Ca, %N and %K best mapped onto phylogeny. Moreover, for the 15 best combinations of three traits, 82% of traits were chemical, 16% morphological and 2% metabolic. The diversity-dependence of ecosystem productivity was better explained by the %Ca, %N and %K clusters: compared to adding a new species at random, adding a species from an absent cluster/clade better-explained gains in productivity. Species number impacted productivity only when all clusters were present. Our results suggest that tissue elemental chemistry might be more phylogenetically conserved and more strongly related to ecosystem functioning than commonly measured morphological and physiological traits, a possibility that merits exploration.     

Invasions of equilibria: tests of resource competition using two species of algae

Summary Single-species, steady-state chemostat cultures of two freshwater diatoms showed that Fragilaria crotonensis had a lower equilibrial requirement for silicate than did Tabellaria fenestratra. Using this information, resource competition theory predicts that Fragilaria should be able to invade silicate-limited equilibrium populations of Tabellaria, but Tabellaria should not be able to invade silicatelimited Fragilaria. This prediction was supported by a series of invasion experiments. The two species did not have detectable differences in their phosphate requirements. Invasion experiments showed that Fragilaria could invade Tabellaria cultures, but that Tabellaria could not invade Fragilaria cultures under phosphate-limited conditions. These results are consistent with predictions based on previous studies of the phosphate physiology of these genera.     

Seed and microsite limitation in a late-successional old field: the effects of water, adults, litter, and small mammals on seeds and seedlings

Many plant communities are recruitment limited, which may occur because there are either too few seeds to fill available microsites, too few available microsites, or both. In a recruitment-limited, Minnesota, USA old field, we tested among these alternatives in a three-phase study. In phase 1, we estimated the production of late-successional forb and C4 grass seeds. In phase 2, we experimentally modified field establishment conditions with rainfall amendment, adult plant thinning, litter reduction, and small mammal exclusion. We then measured recruitment. On average, of the nearly 2,600 seeds produced m^?2, only 164 seeds m^?2 were present and living after overwintering, as measured by field and greenhouse germination. Furthermore, on average, only 9 of those 164 seeds m^?2 germinated in the field, even under the relaxed establishment conditions of our four experimental treatments. Although adults of C4 grasses dominate the field, surprisingly few C4 grass seedlings germinated. To understand why, in phase 3, we added seed of the three dominant C4 grasses into the same plots the following year. Their ability to recruit into control plots compared with treated plots was relatively lower than for the ambiently recruited forbs from phase 2, suggesting that the competitively dominant C4 grasses have greater difficulty establishing in the extant community. Of the seeds that did germinate in the field in phases 2 and 3, all four experimental treatments significantly improved at least one stage of establishment, with the rainfall amendment having the greatest overall effect across species. In total, our results suggest that seed limitation was exacerbated by microsite limitation via multiple mechanisms.