Bone morphogenetic proteins (BMPs) can either promote growth of embryonic muscle by expanding the Pax-3-expressing muscle precursor population or restrict its development by inducing apoptosis. Follistatin, a proposed BMP antagonist, is expressed in embryonic muscle. Deficiency in Follistatin results in muscle defects and postnatal asphyxia. Here, we report that during chick limb development Follistatin enhances BMP-7 action to induce muscle growth but prevents the ability of BMP-7 to induce apoptosis and muscle loss. Follistatin, unlike another BMP-binding protein, Noggin, promotes Pax-3 expression and transiently delays muscle differentiation and thus exerts proliferative signalling during muscle development. We provide data which show that Follistatin binds BMP-7 and BMP-2 at low affinities and that the binding is reversible. These data suggest that Follistatin acts to present BMPs to myogenic cells at a concentration that permits stimulation of embryonic muscle growth.

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Small molecule fluorochromes (synonyms: biosensors, chemosensors, fluorescent probes, vital stains) are widely used to investigate the structure, composition, physicochemical properties and biological functions of living cells, tissues and organisms. Selective entry and accumulation within particular cells and cellular structures are key processes for achieving these diverse objectives. Despite the complexities, probes routinely are applied using standard protocols, often without experimenter awareness of what factors that control accumulation and localization. The mechanisms of many such selective accumulations, however, now are known. Moreover, the influence of physicochemical properties of probes on their uptake and localization often can be defined numerically, hence predicted, using quantitative structure activity relations (QSAR) models with its required numerical structure parameters (or "descriptors"). The state of the art of this approach is described. Available QSAR models are summarized for uptake into cells and localization in the cytosol, endoplasmic reticulum, generic biomembranes, Golgi apparatus, lipid droplets, lysosomes/endosomes, mitochondria, eukaryotic nuclei (histones and DNA), plasma membrane, and ribosomal RNA (cytoplasmic and nucleolar). Integration of such core models to both aid understanding and troubleshooting of current fluorescent probes and to assist the design of novel probes is outlined and illustrated using case examples. Limitations and generic problems arising with this approach and comments on application of such approaches to xenobiotics other than probes, e.g., drugs and herbicides, together with a brief note about an alternative approach to prediction, are given.

Selectivity of nuclear probes is controlled by competitive accumulation of the probe by cellular organelles as well as the high affinity for nucleic acids. Physicochemical features of probes which favor nucleic acid binding include cationic character and a planar aromatic system above a minimum size. Features of probes which permit entry into cells are low protein and lipid binding. Features which reduce accumulation in non-nuclear sites include high base strength and hydrophilicity of the cation. The overall quantitative structure-activity (QSAR) model specifying nuclear accumulation may be expressed as follows: CBN<40; 8>log P (neutral species)>0; AI<8; Z>0; -510; LCF>17; LCF/CBN>0.70 (where CBN is the conjugated bond number, log P (x )the logarithm of the water-octanol partition coefficient of species x, AI the amphilicity index, Z the electric charge, pK ( a ) the negative logarithm of the equilibrium constant for the free base-protonated base reaction, and LCF the largest conjugated fragment). Preliminary applications of the QSAR model--to the selection of anticancer drugs, minimization of dye and drug toxicity and the designed synthesis of fluorescent probes-are outlined.

The basis of the selectivity of fluorochromes routinely used to visualize the endoplasmic reticulum (ER) in live cells remains obscure. To clarify this, interactions of living cells with fluorochromes of varied physicochemical properties were analyzed experimentally and numerically using a quantitative structure activity relationship analysis (QSAR). Routine selective ER probes were found to be amphipathic, lipophilic cations with moderate-sized conjugated systems. The moderately lipophilic character permits probe uptake by passive diffusion without nonspecific accumulation in biomembranes. The moderately amphipathic character favors uptake into the ER, perhaps owing to its high concentration of zwitterionic lipid head-groups. The QSAR model rationalizes the impractical character of some ER probes mentioned in the literature, and could permit design of novel ER probes with different emission colors. The possibility of using the QSAR model as a tool to predict the accumulation of xenobiotics in the ER of living cells is illustrated by the localization of certain antipsychotic drugs in cultured cells.

ObjectiveThe aims of this study were to describe the experiences of senior students using mobile devices in a clinical setting while learning and interacting with clinical teachers, patients and each other, and to identify challenges that facilitated or impeded the use of such devices in the hospital.DesignInterpretative phenomenology was chosen to guide our enquiry. Semi-structured interviews were conducted to examine the experiences of five senior medical students using mobile devices in the clinical setting.Setting and participantsSenior medical students at an international medical school in the Middle East.ResultsThree main themes emerged from the data analysis: learning; professional identity and transitioning from student to doctor. The findings showed that using mobile devices in the clinical area as a learning tool was not a formalised process. Rather, it was opportunistic learning at the bedside and on occasion a source of distraction from clinical teaching. Students needed to negotiate relationships between themselves, the clinical teacher and patients in order to ensure that they maintained an acceptable professional image. Participants experienced and negotiated the change from student to doctor making them mindful of using their devices at the bedside.ConclusionsMobile devices are part of daily life for a medical student and there is a need to adapt medical education in the clinical setting, to allow the students to use their devices in a sensitive manner.

We describe the practical issues and the methodological procedures that must be carried out to construct and use QSAR models for predicting localization of probes in single cells. We address first the determination of probe factors starting with a consideration of the chemical nature of probe molecules present. What is their identity? Do new compounds arise in incubation media or intracellularly? For each probe, how many distinct chemical species are present? For each probe species, the derivation of the following numerical structure parameters, or descriptors, is set out with worked examples of electric charge and acid/base strength (Z and pKa); hydrophilicity/lipophilicity (log P); amphiphilicity (AI and HGH); conjugated bond number and largest conjugated fragment (CBN and LCF); width and length (W and L); and molecular and ionic weights, head group size and substituent bulk (MW, IW, HGS and SB). Next, protocol factors are specified by focusing separately on the mode of introduction of the probe to the cells, other application phenomena, and factors that influence directly observations of outcomes. Cell factors then are specified by considering separately structural and functional aspects. The next step is to select appropriate QSAR models and to integrate probe, protocol and cell factors to predict the interactions of the probe with the cell. Finally, we use an extended case example to explore the intracellular localization of certain photodynamic therapy dyes to illustrate these procedures.

Small-molecule fluorochromes are used in biology and medicine to generate informative microscopic and macroscopic images, permitting identification of cell structures, measurement of physiological/physicochemical properties, assessment of biological functions and assay of chemical components. Modes of uptake and precise intracellular localisation of a probe are typically significant factors in its successful application. These processes and localisations can be predicted using quantitative structure activity relations (QSAR) models, which correlate aspects of the physicochemical properties of the probes (expressed numerically) with the uptake/localisation. Pay-offs of such modelling include better understanding and trouble-shooting of current and novel probes, and easier design of future probes ("guided synthesis"). Uptake models discussed consider adsorptive (to lipid or protein domains), phagocytic and pinocytotic endocytosis, as well as passive diffusion. Localisation models discussed include those for cytosol, endoplasmic reticulum, Golgi apparatus, lipid droplets, lysosomes, mitochondria, nucleus and plasma membrane. A case example illustrates how such QSAR modelling of probe interactions can clarify localisation and mode of binding of probes to intracellular nucleic acids of living cells, including not only eukaryotic chromatin DNA and ribosomal RNA, but also prokaryote chromosomes.