A Highlights from MBoC Selection: Cell shape impacts on the positioning of the mitotic spindle with respect to the substratum

All known mechanisms of mitotic spindle orientation rely on astral microtubules. We report that even in the absence of astral microtubules, metaphase spindles in MDCK and HeLa cells are not randomly positioned along their x-z dimension, but preferentially adopt shallow β angles between spindle pole axis and substratum. The nonrandom spindle positioning is due to constraints imposed by the cell cortex in flat cells that drive spindles that are longer and/or wider than the cell''s height into a tilted, quasidiagonal x-z position. In rounder cells, which are taller, fewer cortical constraints make the x-z spindle position more random. Reestablishment of astral microtubule–mediated forces align the spindle poles with cortical cues parallel to the substratum in all cells. However, in flat cells, they frequently cause spindle deformations. Similar deformations are apparent when confined spindles rotate from tilted to parallel positions while MDCK cells progress from prometaphase to metaphase. The spindle disruptions cause the engagement of the spindle assembly checkpoint. We propose that cell rounding serves to maintain spindle integrity during its positioning.     

Effect of stocking density on the behavior of newly transformed juvenile Macrobrachium rosenbergii

This study characterized the behavioral activity of Macrobrachium rosenbergii in the early stages of development, under different stocking densities (25 and 40 animals/m²), and during the light and dark phases of a 24-h cycle. Observations of individuals were made in 8 aquariums. Behavioral recording lasted 15 min/aquarium, 4 times/day and 4 days/week, 4 weeks in total. Food was offered twice daily. Observational methods included a combination of behavioral sampling and scan sampling. During the light phase, inactivity, cleaning and remaining in a shelter were the most frequent behaviors. During the dark phase the subjects displayed a higher frequency of feeding, exploration, swimming, and digging. At low density, the animals gained more weight and exhibited greater growth overall. These results indicate a behavioral pattern that is more favorable to animals in the lower density cultivation environment that can also create better living conditions for these shrimp, favor survival rates and therefore improve management success.     

Astrocyte Resilience to Oxidative Stress Induced by Insulin-like Growth Factor I (IGF-I) Involves Preserved AKT (Protein Kinase B) Activity

Disruption of insulin-like growth factor I (IGF-I) signaling is a key step in the development of cancer or neurodegeneration. For example, interference of the prosurvival IGF-I/AKT/FOXO3 pathway by redox activation of the stress kinases p38 and JNK is instrumental in neuronal death by oxidative stress. However, in astrocytes, IGF-I retains its protective action against oxidative stress. The molecular mechanisms underlying this cell-specific protection remain obscure but may be relevant to unveil new ways to combat IGF-I/insulin resistance. Here, we describe that, in astrocytes exposed to oxidative stress by hydrogen peroxide (H₂O₂), p38 activation did not inhibit AKT (protein kinase B) activation by IGF-I, which is in contrast to our previous observations in neurons. Rather, stimulation of AKT by IGF-I was significantly higher and more sustained in astrocytes than in neurons either under normal or oxidative conditions. This may be explained by phosphorylation of the phosphatase PTEN at the plasma membrane in response to IGF-I, inducing its cytosolic translocation and preserving in this way AKT activity. Stimulation of AKT by IGF-I, mimicked also by a constitutively active AKT mutant, reduced oxidative stress levels and cell death in H₂O₂-exposed astrocytes, boosting their neuroprotective action in co-cultured neurons. These results indicate that armoring of AKT activation by IGF-I is crucial to preserve its cytoprotective effect in astrocytes and may form part of the brain defense mechanism against oxidative stress injury.     

The control of flower initiation by gibberellin in Helianthus annuus L. (sunflower), a non-photoperiodic plant

The involvement of gibberellins in the control of flowering of sunflower was studied by direct application of GA₃ to the apex of the plants, analysis of the endogenous levels of gibberellin-like substances at different plant ages, and indirectly by the application of paclobutrazol, an inhibitor of gibberellin synthesis. GA₃ speeded-up flower initiation and floral apex development. The time of GA₃ application was more critical than the amount of GA₃ applied. The endogenous levels of gibberellin-like compounds increased significantly by day 15 after sowing. The application of paclobutrazol markedly delayed floral initiation and this effect was also depedent on plant age. Both GA₃ and paclobutrazol had their greatest effects between 10 and 20 days after sowing suggesting that an increase in gibberellins in that time period plays a role in floral initiation.     

Control of water-use efficiency by florigen

A major issue in modern agriculture is water loss through stomata during photosynthetic carbon assimilation. In water-limited ecosystems, annual plants have strategies to synchronize their growth and reproduction to the availability of water. Some species or ecotypes of flowers are early to ensure that their life cycles are completed before the onset of late season terminal drought (“drought escape”). This accelerated flowering correlates with low water-use efficiency (WUE). The molecular players and physiological mechanisms involved in this coordination are not fully understood. We analyzed WUE using gravimetry, gas exchange, and carbon isotope discrimination in florigen deficient (sft mutant), wild-type (Micro-Tom), and florigen over-expressing (SFT-ox) tomato lines. Increased florigen expression led to accelerated flowering time and reduced WUE. The low WUE of SFT-ox was driven by higher stomatal conductance and thinner leaf blades. This florigen-driven effect on WUE appears be independent of abscisic acid (ABA). Our results open a new avenue to increase WUE in crops in an ABA-independent manner. Manipulation of florigen levels could allow us to produce crops with a life cycle synchronized to water availability.     

‘Cool’ adaptations to cold environments: globins in Notothenioidei (Actynopterygii,Perciformes)

Notothenioidei, the taxonomic group of teleosts that dominates the Southern Ocean and dwell in the Ross Sea at large, provide an example of marine species that underwent unique adaptations to life at low temperatures and high oxygen concentrations, resulting in morphological, physiological, genomic, and biochemical peculiarities in comparison with warm-water fish. Global Warming raises concerns over the fate of these stenothermal fish, as their adaptation has been accompanied by irreversible genomic losses, which suggest a poor genetic potential to adapt to warmer climates. Specifically, this review focuses on adaptation of proteins belonging to the globin superfamily, which include the respiratory proteins hemoglobin and myoglobin and the non-respiratory proteins neuroglobin and cytoglobin. Here, we describe their molecular adaptations to cold temperatures in the framework of the physiology of oxygen transport and management of oxidative stress in fish species largely populating the Ross Sea.     

When the same is not the same: phenotypic variation reveals different plant ecological strategies within species occurring in distinct Neotropical savanna habitats

Variations in abiotic characteristics such as soil water availability and fertility impose different selective pressures on plant populations. This may produce intraspecific variability in functional traits, even at a fine spatial scale. We investigated whether functional traits related to water-use efficiency, resource-retention strategy, soil nutrient acquisition, and fire tolerance differ in species that occur in two different habitats of Brazilian Cerrado: rocky savannas and savanna woodlands. Rocky savannas occur over sandstone, quartzite outcrops and have shallow nutrient-poor and low-moisture rocky soils, while savanna woodlands occur over well-drained and deep soils with frequent fire regimes. We measured nine functional traits of 40 tree species that occur in both habitats. Rocky savanna individuals exhibited a greater water-use efficiency strategy. The resource-retention strategy in rocky savanna individuals was corroborated by lower adult maximum height. However, despite the lower nutrient availability in rocky savanna soils, we only detected lower leaf phosphorus content in individuals from this habitat. Furthermore, individuals from both habitats had equally thick bark, suggesting that the fire-defense strategy is related to a stable, rather than plastic trait. Overall, our results highlight the central role of contrasting soil water availability patterns in driving phenotypic plasticity within species. We conclude that savanna species are responding to water and nutrient availabilities, via plasticity in traits related to the resource-retention strategy, and preparing for future fires, via uniformly thick bark. Wide plant distribution in contrasting habitats is possible for species that can shift ecological strategies to survive in nutrient- and water-limited habitats such as rocky savannas.