Urinary bladder hyporeflexia and reduced pain-related behaviour in P2X3-deficient mice

Extracellular ATP is implicated in numerous sensory processes ranging from the response to pain to the regulation of motility in visceral organs. The ATP receptor P2X3 is selectively expressed on small diameter sensory neurons, supporting this hypothesis. Here we show that mice deficient in P2X3 lose the rapidly desensitizing ATP-induced currents in dorsal root ganglion neurons. P2X3 deficiency also causes a reduction in the sustained ATP-induced currents in nodose ganglion neurons. P2X3-null mice have reduced pain-related behaviour in response to injection of ATP and formalin. Significantly, P2X3-null mice exhibit a marked urinary bladder hyporeflexia, characterized by decreased voiding frequency and increased bladder capacity, but normal bladder pressures. Immunohistochemical studies localize P2X3 to nerve fibres innervating the urinary bladder of wild-type mice, and show that loss of P2X3 does not alter sensory neuron innervation density. Thus, P2X3 is critical for peripheral pain responses and afferent pathways controlling urinary bladder volume reflexes. Antagonists to P2X3 may therefore have therapeutic potential in the treatment of disorders of urine storage and voiding such as overactive bladder.     

Superconductivity at 52 K in hole-doped C60

Superconductivity in electron-doped C60 was first observed almost ten years ago. The metallic state and superconductivity result from the transfer of electrons from alkaline or alkaline-earth ions to the C60 molecule, which is known to be a strong electron acceptor. For this reason, it is very difficult to remove electrons from C60--yet one might expect to see superconductivity at higher temperatures in hole-doped than in electron-doped C60, because of the higher density of electronic states in the valence band than in the conduction band. We have used the technique of gate-induced doping in a field-effect transistor configuration to introduce significant densities of holes into C60. We observe superconductivity over an extended range of hole density, with a smoothly varying transition temperature Tc that peaks at 52 K. By comparison with the well established dependence of Tc on the lattice parameter in electron-doped C60, we anticipate that Tc values significantly in excess of 100 K should be achievable in a suitably expanded, hole-doped C60 lattice.     

Messenger RNA targeting of rice seed storage proteins to specific ER subdomains

Rice seeds, a rich reserve of starch and protein, are a major food source in many countries. Unlike the seeds of other plants, which typically accumulate one major type of storage protein, rice seeds use two major classes, prolamines and globulin-like glutelins. Both storage proteins are synthesized on the endoplasmic reticulum (ER) and translocated to the ER lumen, but are then sorted into separate intracellular compartments. Prolamines are retained in the ER lumen as protein bodies whereas glutelins are transported and stored in protein storage vacuoles. Mechanisms responsible for the retention of prolamines within the ER lumen and their assembly into intracisternal inclusion granules are unknown, but the involvement of RNA localization has been suggested. Here we show that the storage protein RNAs are localized to distinct ER membranes and that prolamine RNAs are targeted to the prolamine protein bodies by a mechanism based on RNA signal(s), a process that also requires a translation initiation codon. Our results indicate that the ER may be composed of subdomains that specialize in the synthesis of proteins directed to different compartments of the plant endomembrane system.     

Insights into SCF ubiquitin ligases from the structure of the Skp1-Skp2 complex

F-box proteins are members of a large family that regulates the cell cycle, the immune response, signalling cascades and developmental programmes by targeting proteins, such as cyclins, cyclin-dependent kinase inhibitors, IkappaBalpha and beta-catenin, for ubiquitination (reviewed in refs 1-3). F-box proteins are the substrate-recognition components of SCF (Skp1-Cullin-F-box protein) ubiquitin-protein ligases. They bind the SCF constant catalytic core by means of the F-box motif interacting with Skp1, and they bind substrates through their variable protein-protein interaction domains. The large number of F-box proteins is thought to allow ubiquitination of numerous, diverse substrates. Most organisms have several Skp1 family members, but the function of these Skp1 homologues and the rules of recognition between different F-box and Skp1 proteins remain unknown. Here we describe the crystal structure of the human F-box protein Skp2 bound to Skp1. Skp1 recruits the F-box protein through a bipartite interface involving both the F-box and the substrate-recognition domain. The structure raises the possibility that different Skp1 family members evolved to function with different subsets of F-box proteins, and suggests that the F-box protein may not only recruit substrate, but may also position it optimally for the ubiquitination reaction.     

Organoplatinum crystals for gas-triggered switches

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.     

Liquid crystal phase transitions in suspensions of polydisperse plate-like particles

Colloidal suspensions that form periodic self-assembling structures on sub-micrometre scales are of potential technological interest; for example, three-dimensional arrangements of spheres in colloidal crystals might serve as photonic materials, intended to manipulate light. Colloidal particles with non-spherical shapes (such as rods and plates) are of particular interest because of their ability to form liquid crystals. Nematic liquid crystals possess orientational order; smectic and columnar liquid crystals additionally exhibit positional order (in one or two dimensions respectively). However, such positional ordering may be inhibited in polydisperse colloidal suspensions. Here we describe a suspension of plate-like colloids that shows isotropic, nematic and columnar phases on increasing the particle concentration. We find that the columnar two-dimensional crystal persists for a polydispersity of up to 25%, with a cross-over to smectic-like ordering at very high particle concentrations. Our results imply that liquid crystalline order in synthetic mesoscopic materials may be easier to achieve than previously thought.     

Controlled surface charging as a depth-profiling probe for mesoscopic layers

Probing the structure of material layers just a few nanometres thick requires analytical techniques with high depth sensitivity. X-ray photoelectron spectroscopy (XPS) provides one such method, but obtaining vertically resolved structural information from the raw data is not straightforward. There are several XPS depth-profiling methods, including ion etching, angle-resolved XPS (ref. 2) and Tougaard's approach, but all suffer various limitations. Here we report a simple, non-destructive XPS depth-profiling method that yields accurate depth information with nanometre resolution. We demonstrate the technique using self-assembled multilayers on gold surfaces; the former contain 'marker' monolayers that have been inserted at predetermined depths. A controllable potential gradient is established vertically through the sample by charging the surface of the dielectric overlayer with an electron flood gun. The local potential is probed by measuring XPS line shifts, which correlate directly with the vertical position of atoms. We term the method 'controlled surface charging' and expect it to be generally applicable to a large variety of mesoscopic heterostructures.     

Elevated UV-B radiation reduces genome stability in plants

Long-term depletion of the stratospheric ozone layer contributes to an increase in terrestrial solar ultraviolet-B radiation. This has deleterious effects on living organisms, such as DNA damage. When exposed to elevated ultraviolet-B radiation (UV-B; 280-315 nm), plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation. Here we show, using special sun simulators, that elevated solar UV-B doses increase the frequency of somatic homologous DNA rearrangements in Arabidopsis and tobacco plants. Increases in recombination are accompanied by a strong induction of photolyase and Rad51 gene expression. These genes are putatively involved in major DNA repair pathways, photoreactivation and recombination repair. In mutant Arabidopsis plants that are deficient in photoreactivating ultraviolet-induced cyclobutane pyrimidine dimers, recombination under elevated UV-B regimes greatly exceeds wild-type levels. Our results show that homologous recombination repair pathways might be involved in eliminating UV-B-induced DNA lesions in plants. Thus, increases in terrestrial solar UV-B radiation as forecasted for the early 21st century may affect genome stability in plants.