Heterogeneity and Convergence of Olfactory First-Order Neurons Account for the High Speed and Sensitivity of Second-Order Neurons

In the olfactory system of male moths, a specialized subset of neurons detects and processes the main component of the sex pheromone emitted by females. It is composed of several thousand first-order olfactory receptor neurons (ORNs), all expressing the same pheromone receptor, that contact synaptically a few tens of second-order projection neurons (PNs) within a single restricted brain area. The functional simplicity of this system makes it a favorable model for studying the factors that contribute to its exquisite sensitivity and speed. Sensory information—primarily the identity and intensity of the stimulus—is encoded as the firing rate of the action potentials, and possibly as the latency of the neuron response. We found that over all their dynamic range, PNs respond with a shorter latency and a higher firing rate than most ORNs. Modelling showed that the increased sensitivity of PNs can be explained by the ORN-to-PN convergent architecture alone, whereas their faster response also requires cell-to-cell heterogeneity of the ORN population. So, far from being detrimental to signal detection, the ORN heterogeneity is exploited by PNs, and results in two different schemes of population coding based either on the response of a few extreme neurons (latency) or on the average response of many (firing rate). Moreover, ORN-to-PN transformations are linear for latency and nonlinear for firing rate, suggesting that latency could be involved in concentration-invariant coding of the pheromone blend and that sensitivity at low concentrations is achieved at the expense of precise encoding at high concentrations.     

β1 Integrin Is Essential for Teratoma Growth and Angiogenesis

Teratomas are benign tumors that form after ectopic injection of embryonic stem (ES) cells into mice and contain derivatives of all primitive germ layers. To study the role of β1 integrin during teratoma formation, we compared teratomas induced by normal and β1-null ES cells. Injection of normal ES cells gave rise to large teratomas. In contrast, β1-null ES cells either did not grow or formed small teratomas with an average weight of <5% of that of normal teratomas. Histological analysis of β1-null teratomas revealed the presence of various differentiated cells, however, a much lower number of host-derived stromal cells than in normal teratomas. Fibronectin, collagen I, and nidogen were expressed but, in contrast to normal teratomas, diffusely deposited in β1-null teratomas. Basement membranes were present but with irregular shape and detached from the cell surface.

Normal teratomas had large blood vessels with a smooth inner surface, containing both host- and ES cell–derived endothelial cells. In contrast, β1-null teratomas had small vessels that were loosely embedded into the connective tissue. Furthermore, endothelial cells were always of host-derived origin and formed blood vessels with an irregular inner surface. Although β1- deficient endothelial cells were absent in teratomas, β1-null ES cells could differentiate in vitro into endothelial cells. The formation of a complex vasculature, however, was significantly delayed and of poor quality in β1-null embryoid bodies. Moreover, while vascular endothelial growth factor induced proliferation of endothelial cells as well as an extensive branching of blood vessels in normal embryoid bodies, it had no effect in β1-null embryoid bodies.

     

Sodium sensing induces different changes in free cytosolic calcium concentration and pH in salt-tolerant and -sensitive rice (Oryza sativa) cultivars

Perception of salt stress in plant cells induces a change in the free cytosolic Ca²⁺, [Ca²⁺]_cyt, which transfers downstream reactions toward salt tolerance. Changes in cytosolic H⁺ concentration, [H⁺]_cyt, are closely linked to the [Ca²⁺]_cyt dynamics under various stress signals. In this study, salt‐induced changes in [Ca²⁺]_cyt, and [H⁺]_cyt and vacuolar [H⁺] concentrations were monitored in single protoplasts of rice (Oryza sativa L. indica cvs. Pokkali and BRRI Dhan29) by fluorescence microscopy. Changes in cytosolic [Ca²⁺] and [H⁺] were detected by use of the fluorescent dyes acetoxy methyl ester of calcium‐binding benzofuran and acetoxy methyl ester of 2′, 7′‐bis‐(2‐carboxyethyl)‐5‐(and‐6) carboxyfluorescein, respectively, and for vacuolar pH, fluorescent 6‐carboxyfluorescein and confocal microscopy were used. Addition of NaCl induced a higher increase in [Ca²⁺]_cyt in the salt‐tolerant cv. Pokkali than in the salt‐sensitive cv. BRRI Dhan29. From inhibitor studies, we conclude that the internal stores appear to be the major source for [Ca²⁺]_cyt increase in Pokkali, although the apoplast is more important in BRRI Dhan29. The [Ca²⁺]_cyt measurements in rice also suggest that Na⁺ should be sensed inside the cytosol, before any increase in [Ca²⁺]_cyt occurs. Moreover, our results with individual mesophyll protoplasts suggest that ionic stress causes an increase in [Ca²⁺]_cyt and that osmotic stress sharply decreases [Ca²⁺]_cyt in rice. The [pH]_cyt was differently shifted in the two rice cultivars in response to salt stress and may be coupled to different activities of the H⁺‐ATPases. The changes in vacuolar pH were correlated with the expressional analysis of rice vacuolar H⁺‐ATPase in these two rice cultivars.     

Fine mapping of the Autosomal Dominant Split Hand/Split Foot Locus on Chromosome 7, Band q21.3-q22.1

Split hand/split foot (SHFD) is a human developmental defect characterized by missing digits, fusion of remaining digits, and a deep median cleft in the hands and feet. Cytogenetic studies of deletions and translocations associated with this disorder have indicated that an autosomal dominant split hand/split foot locus (gene SHFD1) maps to 7q21-q22. To characterize the SHFD1 locus, somatic cell hybrid lines were constructed from cytogenetically abnormal individuals with SHFD. Molecular analysis resulted in the localization of 93 DNA markers to one of 10 intervals surrounding the SHFD1 locus. The translocation breakpoints in four SHFD patients were encompassed by the smallest region of overlap among the SHFD-associated deletions. The order of DNA markers in the SHFD1 critical region has been defined as PON–D7S812–SHFD1–D7S811–ASNS. One DNA marker, D7S811, detected altered restriction enzyme fragments in three patients with translocations when examined by pulsed-field gel electro-phoresis (PFGE). These data map SHFD1, a gene that is crucial for human limb differentiation, to a small interval in the q21.3-q22.1 region of human chromosome 7.     

Transgenic apple plants overexpressing the Lc gene of maize show an altered growth habit and increased resistance to apple scab and fire blight

Transgenic apple plants (Malus × domestica cv. ‘Holsteiner Cox’) overexpressing the Leaf Colour (Lc) gene from maize (Zea mays) exhibit strongly increased production of anthocyanins and flavan-3-ols (catechins, proanthocyanidins). Greenhouse plants investigated in this study exhibit altered phenotypes with regard to growth habit and resistance traits. Lc-transgenic plants show reduced size, transversal gravitropism of lateral shoots, reduced trichome development, and frequently reduced shoot diameter and abnormal leaf development with fused leaves. Such phenotypes seem to be in accordance with a direct or an indirect effect on polar-auxin-transport in the transgenic plants. Furthermore, leaves often develop necrotic lesions resembling hypersensitive response lesions. In tests, higher resistance against fire blight (caused by the bacterium Erwinia amylovora) and against scab (caused by the fungus Venturia inaequalis) is observed. These phenotypes are discussed with respect to the underlying altered physiology of the Lc-transgenic plants. The results are expected to be considered in apple breeding strategies.     

Connexin43 and pannexin1 channels in osteoblasts: who is the "hemichannel"?

Osteoblasts sense and respond to mechanical stimuli in a process involving influx and release of large ions and signaling molecules. Unapposed gap junction hemichannels formed of connexin43 (Cx43) have been proposed as a major route for such exchange, in particular for release of ATP and prostaglandin E₂ (PGE₂) in osteocytes. However, we have found that Cx43-null osteoblasts have unaltered, mechanically induced PGE₂ release and ATP-induced YoPro dye uptake. In contrast, PGE₂ release in response to fluid shear stress is abolished in P2X₇ receptor (P2X₇R)–null osteoblasts, and ATP-induced dye uptake is attenuated following treatment of wild-type cells with a P2X₇R or Pannexin1 (Panx1) channel blocker. These data indicate that Panx1 channels, in concert with P2X₇R, likely form a molecular complex that performs the hemichannel function in osteoblast mechanosignaling.     

17β-Estradiol regulation of protein kinase C activity in chondrocytes is sex-dependent and involves nongenomic mechanisms

17β-Estradiol (E₂) regulates growth plate chondrocyte differentiation in both a sex- and cell maturation–dependent manner, and the sex-specific effects of E₂ appear to be mediated in part by membrane events. In this study, we examined whether E₂ regulates protein kinase C (PKC) in a cell-maturation and sex-specific manner and whether E₂ uses a nongenomic mechanism in regulating this enzyme. In addition, we determined if PKC mediates the E₂-dependent stimulation of alkaline phosphatase activity seen in chondrocytes. Confluent, fourth passage resting zone (RC) and growth zone (GC) chondrocytes from male and female rat costochondral cartilage were treated with 10⁻¹⁰ to 10⁻⁷ M E₂. E₂ caused a dose-dependent increase in PKC in RC and GC cells from female rats. Peak stimulation was at 90 min. Increased PKC was evident by 3 min in both RC and GC and was still evident in RC cells at 720 min, but in GC cells activity returned to baseline by 270 min. Actinomycin D had no effect at 9, 90, 270, or 720 min, but there was a small decrease in E₂-stimulated PKC in RC treated with cycloheximide at 90 and 270 min and in GC treated for 90 min. E₂ increased cytosolic and membrane PKC at 9 min and by 90 min promoted translocation of PKC activity from the cytosol to the membranous compartment of female RC cells. Antibodies specific for the α, β, δ, ε, and ζ isoforms of PKC revealed that PKCα in female GC and RC cells is activated by E₂. There was a small, but statistically significant, increase in PKC in male RC cells in response to E₂, but it was not dose-dependent, and no effect of E₂ was noted in male GC cells. 17α-estradiol, an inactive isomer of E₂, did not affect PKC specific activity in RC or GC cells from either female or male rats. Chelerythrine, a specific inhibitor of PKC, inhibited E₂-dependent alkaline phosphatase activity, indicating that E₂ mediates its rapid effects on alkaline phosphatase via PKC. J. Cell. Physiol. 176:435–444, 1998. © 1998 Wiley-Liss, Inc.     

Mechanism for Cd2+ inhibition of (K++ Mg2+)ATPase activity and K+ (86Rb+) uptake join roots of sugar beet (Beta vulgaris)

Steady state kinetics were used to examine the influence of Cd²⁺ both on K⁺ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K⁺(⁸⁶Rb⁺) uptake in intact or excised beet roots. The in vitro effect of Cd²⁺ was studied both on a 12000–25000 g root fraction of the (Na⁺+K⁺+Mg²⁺)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd²⁺ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd²⁺ at concentrations <100 μM inhibits the specific K⁺ activation at both high and low affinity sites for K⁺. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K⁺ <5 mM, the inhibition by Cd²⁺ with respect to K⁺ is uncompetitive. In the presence of MgATP and K⁺ >10 μM, the inhibition by Cd²⁺ is competitive. 3) At the low concentrations of K⁺, Cd²⁺ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K⁺(⁸⁶Rb⁺) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K⁺(⁸⁶Rb⁺) uptake is little influenced by Cd²⁺. As Cd²⁺ inhibits the metabolic uptake of K⁺(⁸⁶Rb⁺) and the K⁺ activation of the ATPase in the same way at low concentrations of K⁺, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K⁺ is low, the presence of Cd²⁺ could be disadvantageous.     

EPR investigation of the role of B10 phenylalanine in neuroglobin - evidence that B10Phe mediates structural changes in the heme region upon disulfide-bridge formation

The function of neuroglobin, a member of the vertebrate globin family, is still unknown. In human neuroglobin (NGB), the formation of a disulfide bridge between the CysCD7 and CysD5 is known to affect the heme environment and its ligand-binding kinetics. Here, we show by means of EPR that the PheB10 residue plays a key role in transmitting the structural information from the disulfide bridge to the heme-pocket region. While formation of a disulfide bridge in ferric wild-type NGB leads to a considerable change of its EPR parameters, only minor changes are observed in the case of ferric PheB10Leu NGB. Furthermore, wild-type NGB is found to be much more stable in the presence of H₂O₂ than its PheB10Leu or its HisE7Leu mutants. While tyrosyl radicals are induced in HisE7Leu NGB by the addition of H₂O₂, this is not the case for wild-type and PheB10Leu NGB. The results will be discussed in terms of the protein's putative functions.