The regulation and activities of the multifunctional serine/threonine kinase Akt/PKB

The serine/threonine kinase Akt, or protein kinase B (PKB), has recently been a focus of intense research. It appears that Akt/PKB lies in the crossroads of multiple cellular signaling pathways and acts as a transducer of many functions initiated by growth factor receptors that activate phosphatidylinositol 3-kinase (PI 3-kinase). Akt/PKB is particularly important in mediating several metabolic actions of insulin. Another major activity of Akt/PKB is to mediate cell survival. In addition, the recent discovery of the tumor suppressor PTEN as an antagonist of PI 3-kinase and Akt/PKB kinase activity suggests that Akt/PKB is a critical factor in the genesis of cancer. Thus, elucidation of the mechanisms of Akt/PKB regulation and its physiological functions should be important for the understanding of cellular metabolism, apoptosis, and cancer.     

Protection of Energy Transfer Process in Isolated Phycobilisome by "White Light" from Ultraviolet-B Induced Damage in the Cyanobacterium Spirulina Platensis

Effect of UV-B (1.9 W m^-2) alone or in combination with supplemental "white light". WL (20 W m^-2) exposure was studied on the energy transfer process of intact phycobilisomes isolated from Spirulina platensis. Exposure of UV-B or supplemental irradiation induced a decrease in room temperature fluorescence intensity and caused a shift towards shorter wavelengths. The low temperature fluorescence measurements showed that UV-B impairs energy transfer from phycocyanin to allophycocyanin B and the extent of damage may be reduced by the exposure to supplemental WL. This revised version was published online in June 2006 with corrections to the Cover Date.     

Increased attention to spatial context increases both place field stability and spatial memory

The hippocampal formation is critical for the acquisition and consolidation of memories. When recorded in freely moving animals, hippocampal pyramidal neurons fire in a location-specific manner: they are "place" cells, comprising a hippocampal representation of the animal's environment. To explore the relationship between place cells and spatial memory, we recorded from mice in several behavioral contexts. We found that long-term stability of place cell firing fields correlates with the degree of attentional demands and that successful spatial task performance was associated with stable place fields. Furthermore, conditions that maximize place field stability greatly increase orientation to novel cues. This suggests that storage and retrieval of place cells is modulated by a top-down cognitive process resembling attention and that place cells are neural correlates of spatial memory. We propose a model whereby attention provides the requisite neuromodulatation to switch short-term homosynaptic plasticity to long-term heterosynaptic plasticity, and we implicate dopamine in this process.     

Modulation of pigment profiles of Calothrix elenkenii in response to environmental changes

Cyanobacteria are versatile tetrapyrrole synthesizers that can regulate their tetrapyrrole content and composition in response to environmental signals. The present investigation analyses the interplay between light and dark regimes (continuous light, light-dark cycles (16:8) and continuous darkness) and aerobic, air-tight, and anaerobic environments (argon-enriched), on the relative composition of various pigments and growth attributes of Calothrix elenkenii as a prelude to exploiting C. elenkenii's bioindustrial potential as a source of pigments. Incubation in an anaerobic environment stimulated hormogonia formation and induced colouration/thickening of cells. Aerobically grown cultures of Calothrix, under continuous illumination produced the maximum amount of total phycobiliproteins and sugars, although chlorophyll accumulation and nitrogenase activity were highest in the light-dark environment. However, the beta-carotene content was observed to vary under anaerobic conditions with different light-dark regimes. This C. elenkenii strain can be a valuable source of pigments under optimized environmental conditions.     

Evaluation of<Emphasis Type="Italic">Tolypothrix</Emphasis> germplasm for phycobiliprotein content

Twenty Tolypothrix strains, including 15 strains of T. tenuis, three strains of T. ceylonica and one strain each of T. nodosa and T. bouteillei, were evaluated for their phycobiliprotein content and composition. Significant differences among the Tolypothrix strains were found at both inter- and intra-specific levels in the production of phycobiliprotein constituents--phycocyanin (PC), allophycocyanin (APC) and phycoerythrin (PE). Four specific parameters, viz. PC or PE content, total phycobiliprotein and total protein content, and percentage of phycobiliproteins, in a mixture of total proteins were used to select four T. tenuis and one T. ceylonica strain as useful for phycobiliproteins production.     

Inducible and reversible enhancement of learning, memory, and long-term potentiation by genetic inhibition of calcineurin

The threshold for hippocampal-dependent synaptic plasticity and memory storage is thought to be determined by the balance between protein phosphorylation and dephosphorylation mediated by the kinase PKA and the phosphatase calcineurin. To establish whether endogenous calcineurin acts as an inhibitory constraint in this balance, we examined the effect of genetically inhibiting calcineurin on plasticity and memory. Using the doxycycline-dependent rtTA system to express a calcineurin inhibitor reversibly in the mouse brain, we find that the transient reduction of calcineurin activity facilitates LTP in vitro and in vivo. This facilitation is PKA dependent and persists over several days in vivo. It is accompanied by enhanced learning and strengthened short- and long-term memory in several hippocampal-dependent spatial and nonspatial tasks. The LTP and memory improvements are reversed fully by suppression of transgene expression. These results demonstrate that endogenous calcineurin constrains LTP and memory.