Photosynthetic circadian rhythmicity patterns of Symbiodium,the coral endosymbiotic algae

Biological clocks are self-sustained endogenous timers that enable organisms (from cyanobacteria to humans) to anticipate daily environmental rhythms, and adjust their physiology and behaviour accordingly. Symbiotic corals play a central role in the creation of biologically rich ecosystems based on mutualistic symbioses between the invertebrate coral and dinoflagellate protists from the genus Symbiodinium. In this study, we experimentally establish that Symbiodinium photosynthesis, both as a free-living unicellular algae and as part of the symbiotic association with the coral Stylophora pistillata, is ‘wired’ to the circadian clock mechanism with a ‘free-run’ cycle close to 24 h. Associated photosynthetic pigments also showed rhythmicity under light/dark conditions and under constant light conditions, while the expression of the oxygen-evolving enhancer 1 gene (within photosystem II) coincided with photosynthetically evolved oxygen in Symbiodinium cultures. Thus, circadian regulation of the Symbiodinium photosynthesis is, however, complicated as being linked to the coral/host that have probably profound physiochemical influence on the intracellular environment. The temporal patterns of photosynthesis demonstrated here highlight the physiological complexity and interdependence of the algae circadian clock associated in this symbiosis and the plasticity of algae regulatory mechanisms downstream of the circadian clock.     

Task-induced deactivation from rest extends beyond the default mode brain network

Activity decreases, or deactivations, of midline and parietal cortical brain regions are routinely observed in human functional neuroimaging studies that compare periods of task-based cognitive performance with passive states, such as rest. It is now widely held that such task-induced deactivations index a highly organized 'default-mode network' (DMN): a large-scale brain system whose discovery has had broad implications in the study of human brain function and behavior. In this work, we show that common task-induced deactivations from rest also occur outside of the DMN as a function of increased task demand. Fifty healthy adult subjects performed two distinct functional magnetic resonance imaging tasks that were designed to reliably map deactivations from a resting baseline. As primary findings, increases in task demand consistently modulated the regional anatomy of DMN deactivation. At high levels of task demand, robust deactivation was observed in non-DMN regions, most notably, the posterior insular cortex. Deactivation of this region was directly implicated in a performance-based analysis of experienced task difficulty. Together, these findings suggest that task-induced deactivations from rest are not limited to the DMN and extend to brain regions typically associated with integrative sensory and interoceptive processes.     

Acetylation of Lysine 382 and Phosphorylation of Serine 392 in p53 Modulate the Interaction between p53 and MDC1 In Vitro

Occurrence of DNA damage in a cell activates the DNA damage response, a survival mechanism that ensures genomics stability. Two key members of the DNA damage response are the tumor suppressor p53, which is the most frequently mutated gene in cancers, and MDC1, which is a central adaptor that recruits many proteins to sites of DNA damage. Here we characterize the in vitro interaction between p53 and MDC1 and demonstrate that p53 and MDC1 directly interact. The p53-MDC1 interaction is mediated by the tandem BRCT domain of MDC1 and the C-terminal domain of p53. We further show that both acetylation of lysine 382 and phosphorylation of serine 392 in p53 enhance the interaction between p53 and MDC1. Additionally, we demonstrate that the p53-MDC1 interaction is augmented upon the induction of DNA damage in human cells. Our data suggests a new role for acetylation of lysine 382 and phosphorylation of serine 392 in p53 in the cellular stress response and offers the first evidence for an interaction involving MDC1 that is modulated by acetylation.     

Stability study of the human G-protein coupled receptor, Smoothened

Smoothened is a member of the G-protein coupled receptor (GPCR) family responsible for the transduction of the Hedgehog signal to the intracellular effectors of the Hedgehog signaling pathway. Aberrant regulation of this receptor is implicated in many cancers but also in neurodegenerative disorders. Despite the pharmacological relevance of this receptor, very little is known about its functional mechanism and its physiological ligand. In order to characterize this receptor for basic and pharmacological interests, we developed the expression of human Smoothened in the yeast Saccharomyces cerevisiae and Smoothened was then purified. Using Surface Plasmon Resonance technology, we showed that human Smoothened was in a native conformational state and able to interact with its antagonist, the cyclopamine, both at the yeast plasma membrane and after purification. Thermostability assays on purified human Smoothened showed that this GPCR is relatively stable in the classical detergent dodecyl-β-d-maltoside (DDM). The fluorinated surfactant C₈F₁₇TAC, which has been proposed to be less aggressive towards membrane proteins than classical detergents, increased Smoothened thermostability in solution. Moreover, the replacement of a glycine by an arginine in the third intracellular loop of Smoothened coupled to the use of the fluorinated surfactant C₈F₁₇TAC during the mutant purification increased Smoothened thermostability even more. These data will be very useful for future crystallization assays and structural characterization of the human receptor Smoothened.     

Uptake and turnover of acetate in hypersaline environments

Abstract: Acetate uptake and turnover rates were determined for the heterotrophic community in hypersaline environments (saltern crystallizer ponds, the Dead Sea) dominated by halpphilic Archaea. Acetate was formed from glycerol, which is potentially the major available carbon source for natural communities of halophilic Archaea. Values of [ K _t+ S _n] (the sum of the substrate affinity and the substrate concentration present in situ) for acetate measured in saltern crystallizer ponds were around 4.5–11.5 μM, while in the Dead Sea during a Dunaliella bloom values up to 12.8 μM were found. Maximal theoretical rates ( V _max) of acetate uptake in saltern crystallizer ponds were 12–56 nmol l⁻¹ h⁻¹, with estimated turnover times for acetate ( T _t) between 127–730 h at 35°C. V _max values measured in the Dead Sea were between 0.8 and 12.8 nmol l⁻¹ h⁻¹, with turnover times in the range of 320–2190 h. V _max values for acetate were much lower than those for glycerol. Comparisons with pure cultures of halophilic Archaea grown under different conditions showed that the natural communities were not adapted for preferential use of acetate. Both in natural brines and in pure cultures of halophilic Archaea, acetate incorporation rates rapidly decreased above the optimum pH value, probably since acetate enters the cell only in its unionized form. The low affinity for acetate, together with low potential utilization rates result in the long acetate turnover times, which explains the accumulation of acetate observed when low concentrations of glycerol are supplied as a nutrient to natural communities of halophilic Archaea.     

The Werner syndrome protein contributes to induction of p53 by DNA damage.

Mutations in the p53 tumor-suppressor gene promote increased genomic instability and cancer. Mutations in the WRN gene, encoding a DNA helicase, underlie the segmental progeroid Werner syndrome (WS). WS is also associated with increased genomic instability and elevated cancer risk. The p53 and WRN proteins can engage in direct protein-protein interactions. We report that excess WRN elicits increased cellular p53 levels and potentiates p53-mediated apoptosis. Importantly, cells derived from WS patients exhibit an attenuated and delayed induction of p53 by UV or by the topoisomerase I inhibitor camptothecin. These results suggest that WRN may participate in the activation of p53 in response to certain types of DNA damage. Furthermore, the failure to induce p53 effectively may contribute to enhanced genomic instability and elevated cancer risk in WS patients.