Periodic signaling controlled by an oscillatory circuit that includes protein kinases ERK2 and PKA

Self-regulating systems often use robust oscillatory circuits. One such system controls the chemotactic signaling mechanism of Dictyostelium, where pulses of adenosine 3',5'-monophosphate (cAMP) are generated with a periodicity of 7 minutes. We have observed spontaneous oscillations in activation of the mitogen-activated protein (MAP) kinase ERK2 that occur in phase with peaks of cAMP, and we show that ERK2 modulates cAMP levels through the phosphodiesterase RegA. Computer modeling and simulations of the underlying circuit faithfully account for the ability of the cells to spontaneously generate periodic pulses during specific stages of development. Similar oscillatory processes may occur in cells of many different species.     

High-density electron anions in a nanoporous single crystal: [Ca24Al28O64]4+(4e-)

We removed approximately 100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO.7Al2O3, leading to the formation of high-density (approximately 2 x 10(21) cm-3) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F+ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity approximately 100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca24Al28O64]4+(4e-) may be regarded as a thermally and chemically stable single crystalline "electride."     

Inhibition of carbonic anhydrase by anions in the carbon dioxide-bicarbonate system

Chloride and iodide ions exhibit noncompetitive inhibition of carbon dioxide hydration catalyzed by bovine carbonic anhydrase and competitive inhibition of bicarbonate dehydration. Consideration of the net velocity at equilibrium leads to a satisfactory resolution of the dilemma concerning the different concentrations of such anions required to halve the initial reaction rate for each substrate.     

A prediction of Mars seismicity from surface faulting

The shallow seismicity of Mars has been estimated by measurement of the total slip on faults visible on the surface of the planet throughout geologic time. Seismicity was calibrated with estimates based on surface structures on the moon and measured lunar seismicity that includes the entire seismogenic lithosphere. Results indicate that Mars is seismically active today, with a sufficient number of detectable marsquakes to allow seismic investigations of its interior.     

Horsfield's hawk-cuckoo nestlings simulate multiple gapes for begging

Nestlings of some brood parasitic birds evict hosts' eggs and young soon after hatching, thereby avoiding discrimination by hosts while monopolizing parental care. Eviction carries a cost, however, because lone parasitic nestlings attract a reduced provisioning rate. Here we describe a form of visual signaling used by the evicting Horsfield's hawk-cuckoo (Cuculus fugax) to obtain sufficient food. The chick displays a gape-colored patch on the wing to the host parents as they deliver food, simulating the gaping display of more than one nestling.     

CO_2施肥时树脂膜培养容器在文心兰试管苗培养中的应用

采用在培养室内CO2 施肥的方法 ,以C3植物文心兰 (Oncidium)品种‘AlohaIwanaga’试管苗为实验植物材料 ,分别以氟乙烯树脂膜容器 (CP)和三角瓶作为培养容器进行培养 .结果表明 :CO2 施肥时 ,树脂膜培养容器 (CP)内生长的试管苗在株高、叶数、叶长、叶幅、根数、根长、鲜重、干物重、干物率、叶绿素指数 (SPAD值 )等生长指标上高于无CO2施肥处理 .采用SSR法进行比较 (显著水平P≤ 0 0 5 ) ,其中在株高、叶长、叶幅、根数、鲜重、干物重等重要生长指标之间存在显著性差异 .以三角瓶为培养容器时其生长虽优于无CO2 施肥处理 ,但多数指标差异并不显著 .实验证明 ,使用CP作为培养容器 ,培养室内CO2 施肥对促进文心兰试管苗的生长和提高其品质效果明显 .     

Regulation of mammalian tooth cusp patterning by ectodin

Mammalian tooth crowns have precise functional requirements but cannot be substantially remodeled after eruption. In developing teeth, epithelial signaling centers, the enamel knots, form at future cusp positions and are the first signs of cusp patterns that distinguish species. We report that ectodin, a secreted bone morphogenetic protein (BMP) inhibitor, is expressed as a "negative" image of mouse enamel knots. Furthermore, we show that ectodin-deficient mice have enlarged enamel knots, highly altered cusp patterns, and extra teeth. Unlike in normal teeth, excess BMP accelerates patterning in ectodin-deficient teeth. We propose that ectodin is critical for robust spatial delineation of enamel knots and cusps.     

GaN photonic-crystal surface-emitting laser at blue-violet wavelengths

Shorter-wavelength surface-emitting laser sources are important for a variety of fields, including photonics, information processing, and biology. We report on the creation of a current-driven blue-violet photonic-crystal surface-emitting laser. We have developed a fabrication method, named "air holes retained over growth," in order to construct a two-dimensional gallium nitride (GaN)/air photonic-crystal structure. The resulting periodic structure has a photonic-crystal band-edge effect sufficient for the successful operation of a current-injection surface-emitting laser. This represents an important step in the development of laser sources that could be focused to a size much less than the wavelength and be integrated two-dimensionally at such short wavelengths.     

A planar rhombic charge-separated tetrasilacyclobutadiene

The cyclobutadiene (CBD) molecule C(4)H(4) deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si(4)(EMind)(4) (1), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr(3) with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si(4) four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large (29)Si chemical shift differences (Δδ > 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.