Coupling between taxonomic and functional diversity in protistan coastal communities

The study of protistan functional diversity is crucial to understand the dynamics of oceanic ecological processes. We combined the metabarcoding data of various coastal ecosystems and a newly developed trait-based approach to study the link between taxonomic and functional diversity across marine protistan communities of different size-classes. Environmental DNA was extracted and the V4 18S rDNA genomic region was amplified and sequenced. In parallel, we tried to annotate the operational taxonomic units (OTUs) from our metabarcoding dataset to 30 biological traits using published and accessible information on protists. We then developed a method to study trait correlations across protists (i.e. trade-offs) in order to build the best functional groups. Based on the annotated OTUs and our functional groups, we demonstrated that the functional diversity of marine protist communities varied in parallel with their taxonomic diversity. The coupling between functional and taxonomic diversity was conserved across different protist size classes. However, the smallest size-fraction was characterized by wider taxonomic and functional groups diversity, corroborating the idea that nanoplankton and picoplankton are part of a more stable ecological background on which larger protists and metazoans might develop.     

Decoupling the Roles of Cell Shape and Mechanical Stress in Orienting and Cueing Epithelial Mitosis

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Viscoelasticity of human whole saliva collected after acid and mechanical stimulation

The rheology of saliva is highly important due to its influence on oral health and physiochemical processes within the oral environment. While the rheology of human whole saliva (HWS) is considered important for its functionality, its measurement is often performed erroneously and/or limited to the viscosity at a single shear rate. To ensure accurate rheological measurements, it is necessary to test HWS immediately after expectoration and to apply a thin layer of surfactant solution around the rim of the rheometer plates so that protein adsorption is minimized at the air-liquid interface. It is shown for the first time that the viscosity and viscoelasticity of HWS depends greatly upon the method of stimulation. Mechanical action stimulates slightly shear-thinning and relatively inelastic saliva, while acidic solutions (e.g. 0.25% citric acid) stimulate secretion of saliva that is highly elastic and shear-thinning. However, both acidic solutions and mechanical action stimulate similar volumes of saliva. For acid-stimulated saliva, the ratio of the primary normal stress difference to the shear stress is of order 100 and the viscosity at high shear rates is only marginally above that of water. This extremely high stress ratio for such a low viscosity fluid indicates that saliva's elastic properties dominate its flow behavior and may assist in facilitating lubrication within the oral cavity. It is anticipated that the variation in saliva rheology arises because the individual glands secrete saliva of different rheology, with the proportion of saliva secreted from each gland depending on the method of stimulation. The steady-shear rheology and linear viscoelasticity of HWS are described reasonably well using a FENE-P constitutive model and a 3-mode Maxwell model respectively. These models indicate that there are several long relaxation modes within saliva, possibly arising from the presence of large flexible macromolecules such as mucin glycoproteins.     

RAC3 down-regulation sensitizes human chronic myeloid leukemia cells to TRAIL-induced apoptosis

The nuclear receptor coactivator RAC3 plays important roles in many biological processes and tumorigenesis. We found that RAC3 is over-expressed in human chronic myeloid leukemia cells K562, which are normally resistant to TRAIL-induced apoptosis. RAC3 down-regulation by siRNA rendered these cells sensitive to TRAIL-induced cell death. In addition to the up-regulation of TRAIL receptors, the process involves Bid, caspases and PARP activation, loss of mitochondrial membrane potential, and release of AIF, cytochrome c and Smac/DIABLO to the cytoplasm. We conclude that RAC3 is required for TRAIL resistance and that this anti-apoptotic function is independent of its role in hormone receptor signaling.     

Acute beta-adrenergic overload produces myocyte damage through calcium leakage from the ryanodine receptor 2 but spares cardiac stem cells

A hyperadrenergic state is a seminal aspect of chronic heart failure. Also, "Takotsubo stress cardiomyopathy," is associated with increased plasma catecholamine levels. The mechanisms of myocyte damage secondary to excess catecholamine exposure as well as the consequence of this neurohumoral burst on cardiac stem cells (CSCs) are unknown. Cardiomyocytes and CSCs were exposed to high doses of isoproterenol (ISO), in vivo and in vitro. Male Wistar rats received a single injection of ISO (5 mg kg-1) and were sacrificed 1, 3, and 6 days later. In comparison with controls, LV function was impaired in rats 1 day after ISO and started to improve at 3 days. The fraction of dead myocytes peaked 1 day after ISO and decreased thereafter. ISO administration resulted in significant ryanodine receptor 2 (RyR2) hyperphosphorylation and RyR2-calstabin dissociation. JTV519, a RyR2 stabilizer, prevented the ISO-induced death of adult myocytes in vitro. In contrast, CSCs were resistant to the acute neurohumoral overload. Indeed, CSCs expressed a decreased and inverted complement of beta1/beta2-adrenoreceptors and absence of RyR2, which may explain their survival to ISO insult. Thus, a single injection of ISO causes diffuse myocyte death through Ca2+ leakage secondary to the acutely dysfunctional RyR2. CSCs are resistant to the noxious effects of an acute hyperadrenergic state and through their activation participate in the response to the ISO-induced myocardial injury. The latter could contribute to the ability of the myocardium to rapidly recover from acute hyperadrenergic damage.     

Fast, efficient and reproducible genetic transformation of Phaseolus spp. by Agrobacterium rhizogenes

This transformation procedure generates, with high efficiency (70-90%), hairy roots in cultivars, landraces and accessions of Phaseolus vulgaris (common bean) and other Phaseolus spp. Hairy roots rapidly develop after wounding young plantlets with Agrobacterium rhizogenes, at the cotyledon node, and keeping the plants in high-humidity conditions. Callogenesis always precedes hairy-root formation, and after 15 days, when roots develop at wounded sites, the stem with the normal root is cleaved below the hairy root zone. Transgenic roots and nodules co-transformed with a binary vector can be easily identified using a reporter gene. This procedure, in addition to inducing robust transgenic hairy roots that are susceptible to being nodulated by rhizobia and to fixing nitrogen efficiently, sets the foundation for a high-throughput functional genomics approach on the study of root biology and root-microbe interactions. This protocol can be completed within 30 days.