Catálogo de publicaciones - revistas

<jats:p>In vivo, cytoplasmic microtubules are nucleated and anchored by their minus ends at the centrosome and are believed to turn over by a mechanism termed dynamic instability: depolymerization and repolymerization at their plus ends. In cytoplasmic fragments of fish melanophores, microtubules were shown to detach from their nucleation site and depolymerize from their minus ends. Free microtubules moved toward the periphery by treadmilling—growth at one end and shortening from the opposite end. Frequent release from nucleation sites may be a general property of centrosomes and permit a minus-end mechanism of microtubule turnover and treadmilling.</jats:p>

<jats:p>Resveratrol, a phytoalexin found in grapes and other food products, was purified and shown to have cancer chemopreventive activity in assays representing three major stages of carcinogenesis. Resveratrol was found to act as an antioxidant and antimutagen and to induce phase II drug-metabolizing enzymes (anti-initiation activity); it mediated anti-inflammatory effects and inhibited cyclooxygenase and hydroperoxidase functions (antipromotion activity); and it induced human promyelocytic leukemia cell differentiation (antiprogression activity). In addition, it inhibited the development of preneoplastic lesions in carcinogen-treated mouse mammary glands in culture and inhibited tumorigenesis in a mouse skin cancer model. These data suggest that resveratrol, a common constituent of the human diet, merits investigation as a potential cancer chemopreventive agent in humans.</jats:p>

<jats:p>Cortical neurons receive synaptic inputs from thousands of afferents that fire action potentials at rates ranging from less than 1 hertz to more than 200 hertz. Both the number of afferents and their large dynamic range can mask changes in the spatial and temporal pattern of synaptic activity, limiting the ability of a cortical neuron to respond to its inputs. Modeling work based on experimental measurements indicates that short-term depression of intracortical synapses provides a dynamic gain-control mechanism that allows equal percentage rate changes on rapidly and slowly firing afferents to produce equal postsynaptic responses. Unlike inhibitory and adaptive mechanisms that reduce responsiveness to all inputs, synaptic depression is input-specific, leading to a dramatic increase in the sensitivity of a neuron to subtle changes in the firing patterns of its afferents.</jats:p>

<jats:p> The long-standing supposition that the biological clock cannot function in cells that divide more rapidly than the circadian cycle was investigated. During exponential growth in which the generation time was 10 hours, the profile of bioluminescence from a reporter strain of the cyanobacterium <jats:italic>Synechococcus</jats:italic> (species PCC 7942) matched a model based on the assumption that cells proliferate exponentially and the bioluminescence of each cell oscillates in a cosine fashion. Some messenger RNAs showed a circadian rhythm in abundance during continuous exponential growth with a doubling time of 5 to 6 hours. Thus, the cyanobacterial circadian clock functions in cells that divide three or more times during one circadian cycle. </jats:p>