The elementary force generation process probed by temperature and length perturbations in muscle fibres from the rabbit.

Single chemically permeabilized fibres from rabbit psoas muscle were activated maximally at 5-6 degrees C and then exposed to a rapid temperature increase ('T-jump') up to 37 degrees C by passing a high-voltage pulse (40 kHz AC, 0.15 ms duration) through the fibre length. Fibre cooling after the T-jump was compensated by applying a warming (40 kHz AC, 200 ms) pulse.

Lithium and synaptic plasticity.

Lithium, a small cation, has been used in the treatment of bipolar disorders since its introduction in the 1950s by John Cade. Extensive research on the mechanism of action of lithium has revealed several possible targets. For some time, the most widely accepted action of lithium was its inhibitory effect on the synthesis of inositol, resulting in depletion of inositol with profound effects on neuronal signal transduction pathways.

Specificity and binding kinetics of murine lupus anti-DNA monoclonal antibodies implicate different stimuli for their production.

The origin and relative biological importance of the many different DNA-reactive antibodies that appear in systemic lupus erythematosus are not well understood. A detailed analysis of their fine specificity and binding characteristics with DNA is a necessary step in understanding their biology. We have examined here two monoclonal antibodies (mAb) IV-228 and V-88 that are, respectively, characteristic of antibodies, which bind exclusively to single-stranded (ss) DNA and to both double-stranded (ds) DNA and ssDNA.

Dishevelled-1 regulates microtubule stability: a new function mediated by glycogen synthase kinase-3beta.

Dishevelled has been implicated in the regulation of cell fate decisions, cell polarity, and neuronal function. However, the mechanism of Dishevelled action remains poorly understood. Here we examine the cellular localization and function of the mouse Dishevelled protein, DVL-1.

A role for GATA5 in Xenopus endoderm specification.

The endoderm gives rise to the gut and tissues that develop as outgrowths of the gut tube, including the lungs, liver and pancreas. Here we show that GATA5, a zinc-finger transcription factor, is expressed in the yolk-rich vegetal cells of Xenopus embryos from the early gastrula stage onwards, when these cells become committed to form endoderm. At mid-gastrula stages, GATA5 is restricted to the sub-blastoporal endoderm and is the first molecular marker for this subset of endodermal cells so far identified.

Evidence for differential post-translational modifications of slow myosin heavy chain during murine skeletal muscle development.

The contractile properties of muscle fibres are, in part, determined by the myosin heavy chain (MyHC) isoforms they express. Using monoclonal antibodies, we show that at least three forms of slow twitch MyHC accumulate sequentially during mouse fetal development and that slow MyHC maturation in slow fibres occurs before expression of the adult fast MyHCs in fast fibres. Expression of deletion derivatives of beta-cardiac MyHC cDNA shows that the slow MyHC epitopes that are detected in adult but not in young animals are located near the N-terminus.

A DNA-porphyrin minor-groove complex at atomic resolution: the structural consequences of porphyrin ruffling.

The crystal structure of a B-type DNA hexanucleotide duplex complexed with the porphyrin molecule nickel-[tetra-N-methyl-pyridyl] porphyrin has been solved by multiwavelength anomalous diffraction phasing and refined to an R factor of 11.5% at a resolution of 0.9 A.

The role of retinoic acid receptors in neurite outgrowth from different populations of embryonic mouse dorsal root ganglia.

Dorsal root ganglion (DRG) neurons can be categorised into at least three types, based upon their neurotrophin requirement for survival. We have analysed the expression of the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs) in NGF, NT-3 and BDNF dependent neurons isolated from embryonic day (E)13.5 mouse DRG.

Theories of rotary motors.

The bacterial flagellar motor and the ATP-hydrolysing F1 portion of the F1Fo-ATPase are known to be rotary motors, and it seems highly probable that the H+-translocating Fo portion rotates too. The energy source in the case of Fo and the flagellar motor is the flow of ions, either H+ (protons) or Na+, down an electrochemical gradient across a membrane. The fact that ions flow in a particular direction through a well-defined structure in these motors invites the possibility of a type of mechanism based on geometric constraints between the rotor position and the paths of ions flowing through the motor.

The role of retinoic acid in embryonic and post-embryonic development.

Retinoic acid (RA) is the bioactive metabolite of vitamin A (retinol) which acts on cells to establish or change the pattern of gene activity. Retinol is converted to RA by the action of two types of enzyme, retinol dehydrogenases and retinal dehydrogenases. In the nucleus RA acts as a ligand to activate two families of transcription factors, the RA receptors (RAR) and the retinoid X receptors (RXR) which heterodimerize and bind to the upstream sequences of RA-responsive genes.

Axonal remodeling and synaptic differentiation in the cerebellum is regulated by WNT-7a signaling.

Synapse formation requires changes in cell morphology and the upregulation and localization of synaptic proteins. In the cerebellum, mossy fibers undergo extensive remodeling as they contact several granule cells and form complex, multisynaptic glomerular rosettes. Here we show that granule cells secrete factors that induce axon and growth cone remodeling in mossy fibers.

Control of muscle fibre size: a crucial factor in ageing.

Force generation by skeletal muscle declines during ageing. This change contributes substantially to increased physical dependency in the aged. The decline in muscle mass is not entirely accounted for by a fall in muscle fibre number: fibres appear to lose volume.

Crystal structure of Escherichia coli UvrB C-terminal domain, and a model for UvrB-uvrC interaction.

A crystal structure of the C-terminal domain of Escherichia coli UvrB (UvrB') has been solved to 3.0 A resolution. The domain adopts a helix-loop-helix fold which is stabilised by the packing of hydrophobic side-chains between helices.

Comparison of IgE and IgG antibody-dependent cytotoxicity in vitro and in a SCID mouse xenograft model of ovarian carcinoma.

Allergic reactions are mediated by IgE antibodies bound to high-affinity receptors on mast cells in peripheral tissues and are characterized by their immediacy and hypersensitivity. These properties could also be advantageous in immunotherapy against cancer growth in peripheral tissues. We have constructed chimeric IgE and IgG1 antibodies with murine V regions and human C regions corresponding to the MOv18 monoclonal antibody against the human ovarian tumor-associated antigen, folate binding protein.

Role of actin-filament disassembly in lamellipodium protrusion in motile cells revealed using the drug jasplakinolide.

Background: In motile cells, protrusion of the lamellipodium (a type of cell margin) requires assembly of actin monomers into actin filaments at the tip of the lamellipodium. The importance of actin-filament disassembly in this process is less well understood, and is assessed here using the actin drug jasplakinolide, which has two known activities - inhibition of filament disassembly and induction of an increase in actin polymer.

Results: In cells the two activities of jasplakinolide were found to be separable; 1 microM jasplakinolide could permeate cells, bind cellular filamentous actin (F-actin) and inhibit filament disassembly within 3.

Glycogen synthase kinase 3beta phosphorylation of microtubule-associated protein 1B regulates the stability of microtubules in growth cones.

We have recently shown that glycogen synthase kinase 3beta (GSK3beta) phosphorylates the microtubule-associated protein (MAP) 1B in an in vitro kinase assay and in cultured cerebellar granule cells. Mapping studies identified a region of MAP1B high in serine-proline motifs that is phosphorylated by GSK3beta. Here we show that COS cells, transiently transfected with both MAP1B and GSK3beta, express high levels of the phosphorylated isoform of MAP1B (MAP1B-P) generated by GSK3beta.

Heads or tails? Retinoic acid will decide.

A recent study (Niederreither et al. Nat Genet 1999;21:444-448 [Ref. 1]) describes the phenotype of a gene knockout for an enzyme, retinaldehyde dehydrogenase 2 (RALDH-2), that synthesizes retinoic acid (RA) in the early embryo.

The nucleosomal response associated with immediate-early gene induction is mediated via alternative MAP kinase cascades: MSK1 as a potential histone H3/HMG-14 kinase.

The nucleosomal response refers to the rapid phosphorylation of histone H3 on serine 10 and HMG-14 on serine 6 that occurs concomitantly with immediate-early (IE) gene induction in response to a wide variety of stimuli. Using antibodies against the phosphorylated residues, we show that H3 and HMG-14 phosphorylation is mediated via different MAP kinase (MAPK) cascades, depending on the stimulus. The nucleosomal response elicited by TPA is ERK-dependent, whereas that elicited by anisomycin is p38 MAPK-dependent.

MAP kinase-mediated signalling to nucleosomes and immediate-early gene induction.

Extracellular signals are transduced into the nucleus through a variety of signalling mechanisms to elicit changes in patterns of gene expression. This review is focused in the MAP kinase cascades and the part they play in the induction of the immediate-early (IE) genes. We discuss the MAP kinases and their downstream effectors that are known to phosphorylate substrates in the nucleus.

NMR assignments and secondary structure of the UvrC binding domain of UvrB.

The 55 residue C-terminal domain of UvrB that interacts with UvrC during excision repair in Escherichia coli has been expressed and purified as a (His)6 fusion construct. The fragment forms a stable folded domain in solution. Heteronuclear NMR experiments were used to obtain extensive 15N, 13C and 1H NMR assignments.

Fetal myoblast clones contribute to both fast and slow fibres in developing rat muscle.

Retroviral cell lineage marking was used to investigate the role of cell lineage in fetal and neonatal rat muscle development. Clusters of infected cells, presumably myoblast clones, contribute cells to both slow primary and fast secondary fibres. Moreover, single clusters of marked cells contain both slow and fast primary fibres, suggesting that, at least during fetal life, single clones contribute nuclei to both fibres that are committed to remain slow and those that convert to a fast phenotype.

Myogenin induces a shift of enzyme activity from glycolytic to oxidative metabolism in muscles of transgenic mice.

Physical training regulates muscle metabolic and contractile properties by altering gene expression. Electrical activity evoked in muscle fiber membrane during physical activity is crucial for such regulation, but the subsequent intracellular pathway is virtually unmapped. Here we investigate the ability of myogenin, a muscle-specific transcription factor strongly regulated by electrical activity, to alter muscle phenotype.

Extrinsic influences on limb muscle organisation.

Skeletal muscle within the vertebrate limb originates from the somite. Much work has focussed upon the role of secreted signalling molecules of the Hedgehog, fibroblast growth factor (FGF), bone morphogenetic protein (BMP), and Wnt families plus their associated antagonists in establishing somitic cell types, yet there is no consensus on how these signals combine to influence muscle patterning. When somitic cells migrate into the limb bud, they become subject to a new set of guidance and patterning cues.

Control of muscle fibre and motoneuron diversification.

Recent studies have elucidated both the mechanism of early formation of diverse muscle fibre types and the matching of diverse populations of motoneurons to their appropriate muscle targets. Highlights include the demonstration that distinct signals are necessary for the formation of several distinct myoblast populations in the vertebrate somite, the identification of motoneuron subtypes, studies of how motoneurons target appropriate muscles, and rapid progress on the Drosophila neuromuscular system. We propose a model in which four classes of decision control the patterning of both motoneurons and muscles.

Model-independent analysis of the orientation of fluorescent probes with restricted mobility in muscle fibers.

The orientation of proteins in ordered biological samples can be investigated using steady-state polarized fluorescence from probes conjugated to the protein. A general limitation of this approach is that the probes typically exhibit rapid orientational motion ("wobble") with respect to the protein backbone. Here we present a method for characterizing the extent of this wobble and for removing its effects from the available information about the static orientational distribution of the probes.