p53 and its main negative regulator, Mdm2, are key players in mammalian cancer development. Activation of the transcription factor p53 through DNA damage or other stresses can result in cell cycle arrest, apoptosis, or both. Because of the absence of characterized p53 signaling in zebrafish (Danio rerio), we have studied the roles of Mdm2 and p53 in zebrafish by generating early embryonic knockdowns and examined the involvement of p53 in DNA damage-induced apoptosis. p53-deficient embryos, induced by injection of antisense morpholinos, were morphologically indistinguishable from control embryos, when unperturbed, whereas Mdm2 knockdown embryos were severely apoptotic and arrested very early in development. Double knockdowns showed that p53 deficiency rescued Mdm2-deficient embryos completely, similar to observations in mice. p53 deficiency also markedly decreased DNA damage-induced apoptosis, elicited by ultraviolet irradiation or by the anti-cancer compound camptothecin. p21/Waf/Cip-1 appeared to be a downstream target of zebrafish p53, as revealed relative p21 mRNA levels determined via TaqMan analysis. In contrast to mammals, zebrafish may regulate p53 activity by using an internal polyA signal site. We conclude that zebrafish represents a promising model organism for future compound-based and genetic screens and believe that it will help to identify and characterize new anticancer drugs and new targets for cancer treatment.

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Zebrafish is recognized as one of the most important vertebrate model organisms; however, its value in pharmacological studies has not been extensively explored and exploited. In this review, I summarize significant findings about the effects of drugs and medicines on important physiological processes in zebrafish. Our experiments have shown that cardiovascular, anti-angiogenic and anti-cancer drugs elicit comparable responses in zebrafish embryos to those in mammalian systems. Similar observations have been reported by other laboratories, exposing zebrafish to a variety of pharmaceutical active compounds affecting a range of different processes. All the data summarized indicate that zebrafish represents a very valuable organism for different kinds of pharmacological studies, such as screenings of chemical libraries, lead validation and optimization, mode-of-action studies, analysis of gene function, predictive toxicology and teratogenicity, pharmacogenomics and toxicogenomics. Zebrafish pharmacological assays have specific advantages compared to in vitro cell culture studies and in vivo experiments using mice, complementing these assays to give valuable guides for future tests of new drugs for human therapy.

The present study was designed to test if microvascular coronary endothelial cells express ATP–sensitive K+ channels (KATP channels). We performed microfluorometric measurements of the membrane potential of freshly isolated guinea‐pig coronary capillaries equilibrated with the voltage–sensitive dye bis‐oxonol (bis‐[1,3–dibutylbarbituric acid] trimethineoxonol, [DiBAC4(3)]). The resting membrane potential of capillaries in physiological salt solution was −46±4.2 mV (n= 8) at room temperature (22 °C) as determined after calibration of the fluorescence using the Na+–K+ ionophore gramicidin in the presence of different K+ concentrations. Spontaneous membrane potential fluctuations of 10–20 mV amplitude were often observed. A reversible, sustained hyperpolarization to a new membrane potential close to the K+ equilibrium potential (EK) could be induced by application of the K+ channel openers HOE 234 (100 nm to 1 μM), diazoxide (10 pm to 100 nM) or pinacidil (100 nM). Subsequent addition of glibenclamide (200 nm to 2 μM) reversed this hyperpolarization. A glibenclamide–sensitive hyperpolarization of coronary capillaries to values near EK was also observed upon omission of D‐glucose (10 mM) from the superfusing solution or by substituting L‐glucose for D‐glucose. Maximum hyperpolarization was reached in less than 10 min. Our results suggest that microvascular coronary endothelial cells express KATP channels which may be activated during hypoglycaemia.

Bark, wood, and root tissues of several Populus species contain a 32-and a 36-kilodalton polypeptide which undergo seasonal fluctuations and are considered to be storage proteins. These two proteins are abundant in winter and not detectable in summer as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunodetection. An antibody raised against the 32-kilodalton storage protein of Populus trichocarpa (T. & G.) cross-reacts with the 36-kilodalton protein of this species. The synthesis of the 32-and 36-kilodalton proteins can be induced in micropropagated plants by short-day conditions in the growth chamber. These proteins are highly abundant in structural roots, bark, and wood and combined represent >25% of the total soluble proteins in these tissues. Nitrate concentration in the leaves and nitrate uptake rate decreased dramatically when LD plants were transferred to short-day conditions; the protein content in leaves was unaffected. A decrease of the 32-and 36-kilodalton polypeptides occurs after transferring induced plants back to LD conditions. Both polypeptides are glycosylated and can be efficiently purified by affinity chromatography using concanavalin A-Sepharose 4B. The 32-and the 36-kilodalton polypeptides have identical basic isoelectric points and both consist of at least three isoforms. The storage proteins show a loss in apparent molecular mass after deglycosylation with trifluoromethanesulfonic acid. It is concluded that the 32-and 36-kilodalton polypeptides are glycoforms differing only in the extent of glycosylation. The relative molecular mass of the native storage protein was estimated to be 58 kilodalton, using gel filtration. From the molecular mass and the elution pattern it is supposed that the storage protein occurs as a heterodimer composed of one 32-and one 36-kilodalton subunit. Preliminary data suggest the involvement of the phytochrome system in the induction process of the 32-and 36-kilodalton polypeptides.Most deciduous, woody perennials exhibit a seasonal variation in the nitrogen levels in many of their tissues. The seasonal fluctuation of nitrogen reserves has been reported in several earlier studies (6,8,22 (17) showed that poplar is extremely efficient at nitrogen conservation. More than 80% of the whole-tree nitrogen content is conserved during dormancy, and the majority of stored nitrogen can be found in the roots. It might be possible to increase biomass production of poplar through clonal selection for a minimal loss of nitrogen during the winter.In this paper, we characterize a 32-and a 36-kD storage protein in vegetative tissues of poplar which show seasonal fluctuations and are supposed to occur as glycoforms. We also demonstrate the induction of these two proteins in micropropagated plants under SDs and their disappearance under LDs using a 32-kD antibody. Involvement of the phytochrome system in the induction process is discussed. MATERIALS AND METHODS Plant MaterialBark and wood from first-order twigs and bark of structural roots were...