Colony-forming progenitors from mouse olfactory epithelium: evidence for feedback regulation of neuron production.

The mammalian olfactory epithelium (OE) supports continual neurogenesis throughout life, suggesting that a neuronal stem cell exists in this system. In tissue culture, however, the capacity of the OE for neurogenesis ceases after a few days. In an attempt to identify conditions that support the survival of neuronal stem cells, a population of neuronal progenitors was isolated from embryonic mouse OE and cultured in defined serum-free medium. The vast majority of cells rapidly gave rise to neurons, which died shortly thereafter. However, when purified progenitors were co-cultured with cells derived from the stroma underlying the OE, a small subpopulation (0.07-0.1%) gave rise to proliferative colonies. A morphologically identifiable subset of these colonies generated new neurons as late as 7 days in vitro. Interestingly, development of these neuronal colonies was specifically inhibited when purified progenitors were plated onto stromal feeder cells in the presence of a large excess of differentiated OE neurons. These results indicate that a rare cell type, with the potential to undergo prolonged neurogenesis, can be isolated from mammalian OE and that stroma-derived factors are important in supporting neurogenesis by this cell. The data further suggest that differentiated neurons provide a signal that feeds back to inhibit production of new neurons by their own progenitors.

Pore-forming toxins trigger shedding of receptors for interleukin 6 and lipopolysaccharide.

Cleavage of membrane-associated proteins with the release of biologically active macromolecules is an emerging theme in biology. However, little is known about the nature and regulation of the involved proteases or about the physiological inducers of the shedding process. We here report that rapid and massive shedding of the interleukin 6 receptor (IL-6R) and the lipopolysaccharide receptor (CD14) occurs from primary and transfected cells attacked by two prototypes of pore-forming bacterial toxins, streptolysin O and Escherichia coli hemolysin. Shedding is not induced by an streptolysin O toxin mutant which retains cell binding capacity but lacks pore-forming activity. The toxin-dependent cleavage site of the IL-6R was mapped to a position close to, but distinct from, that observed after stimulation with phorbol myristate acetate. Soluble IL-6R that was shed from toxin-treated cells bound its ligand and induced an IL-6-specific signal in cells that primarily lacked the IL-6R. Transsignaling by soluble IL-6R and soluble CD14 is known to dramatically broaden the spectrum of host cells for IL-6 and lipopolysaccharide, and is thus an important mechanism underlying their systemic inflammatory effects. Our findings uncover a novel mechanism that can help to explain the long-range detrimental action of pore-forming toxins in the host organism.

Z-DNA-forming sites within the human beta-globin gene cluster.

Agarose-encapsulated, metabolically active, permeabilized nuclei from human hematopoietic cell lines were tested for Z-DNA formation in the beta-globin gene cluster. Biotinylated monoclonal antibodies against Z-DNA were diffused into the nuclei and cross-linked to DNA with a 10-ns laser exposure at 266 nm. Following digestion with restriction enzymes, fragments that had formed Z-DNA were isolated. Seventeen regions with Z-DNA sequence motifs in the 73-kb region were studied by PCR amplification, and five were found in the Z conformation.

A second nitrogenase in vegetative cells of a heterocyst-forming cyanobacterium.

In many filamentous cyanobacteria nitrogen fixation occurs in differentiated cells called heterocysts. Filamentous strains that do not form heterocysts may fix nitrogen in vegetative cells, primarily under anaerobic conditions. We describe here two functional Mo-dependent nitrogenases in a single organism, the cyanobacterium Anabaena variabilis. Using a lacZ reporter with a fluorescent beta-galactoside substrate for in situ localization of gene expression, we have shown that the two clusters of nif genes are expressed independently. One nitrogenase functions only in heterocysts under either aerobic or anaerobic growth conditions, whereas the second nitrogenase functions only under anaerobic conditions in vegetative cells and heterocysts. Differences between the two nif clusters suggest that the nitrogenase that is expressed in heterocysts is developmentally regulated while the other is regulated by environmental factors.

Platelets roll on stimulated endothelium in vivo: an interaction mediated by endothelial P-selectin.

P-selectin, found in storage granules of platelets and endothelial cells, can be rapidly expressed upon stimulation. Mice lacking this membrane receptor exhibit a severe impairment of leukocyte rolling. We observed that, in addition to leukocytes, platelets were rolling in mesenteric venules of wild-type mice. To investigate the role of P-selectin in this process, resting or activated platelets from wild-type or P-selectin-deficient mice were fluorescently labeled and transfused into recipients of either genotype. Platelet-endothelial interactions were monitored by intravital microscopy. We observed rolling of either wild-type or P-selectin-deficient resting platelets on wild-type endothelium. Endothelial stimulation with the calcium ionophore A23187 increased the number of platelets rolling 4-fold. Activated P-selectin-deficient platelets behaved similarly, whereas activated wild-type platelets bound to leukocytes and were seen rolling together. Platelets of either genotype, resting or activated, interacted minimally with mutant endothelium even after A23187 treatment. The velocity of platelet rolling was 6- to 9-fold greater than that of leukocytes. Our results demonstrate that (i) platelets roll on endothelium in vivo, (ii) this interaction requires endothelial but not platelet P-selectin, and (iii) platelet rolling appears to be independent of platelet activation, indicating constitutive expression of a P-selectin ligand(s) on platelets. We have therefore observed an interesting parallel between platelets and leukocytes in that both of these blood cell types roll on stimulated vessel wall and that this process is dependent on the expression of endothelial P-selectin.

Redundant 3' end-forming signals for the yeast CYC1 mRNA.

The cyc1-512 mutation is a 38-bp deletion in the 3' untranslated region of the CYC1 gene, which encodes iso-1-cytochrome c in Saccharomyces cerevisiae. This deletion caused a 90% reduction in the levels of the CYC1 mRNA and protein because of the absence of the normal 3' end-forming signal. Although the 3' end-forming signal was not defined by previous analyses, we report that concomitant alteration by base-pair substitution of three 3' end-forming signals within and adjacent to the 38-bp region produced the same phenotype as the cyc1-512 mutation. Furthermore, these signals appear to be related to the previously identified 3' end-forming signal TATATA. A computer analysis revealed that TATATA and related sequences were present in the majority of 3' untranslated regions of yeast genes. Although TATATA may be the strongest and most frequently used signal in yeast genes, the CYC1+ gene concomitantly employed the weaker signals TT-TATA, TATGTT, and TATTTA, resulting in a strong signal.

Tyrosine-phosphorylated Stat1 and Stat2 plus a 48-kDa protein all contact DNA in forming interferon-stimulated-gene factor 3.

Interferon alpha induction of transcription operates through interferon-stimulated-gene factor 3 (ISGF), a transcription factor two components of which are members of the newly characterized Stat family of transcription factors. Interferon alpha induces tyrosine phosphorylation of Stat1 and Stat2 proteins that associate and, together with a 48-kDa protein, form ISGF3. Evidence is presented that a heterodimer of Stat1 and Stat2 is present in ISGF3 and that Stat1 and the 48-kDa protein make precise contact, while Stat2 makes general contact, with the interferon-stimulated response element, the binding site of the ISGF3.

Stathmin interaction with a putative kinase and coiled-coil-forming protein domains.

Stathmin is a ubiquitous, cytosolic 19-kDa protein, which is phosphorylated on up to four sites in response to many regulatory signals within cells. Its molecular characterization indicates a functional organization including an N-terminal regulatory domain that bears the phosphorylation sites, linked to a putative alpha-helical binding domain predicted to participate in coiled-coil, protein-protein interactions. We therefore proposed that stathmin may play the role of a relay integrating diverse intracellular regulatory pathways; its action on various target proteins would be a function of its combined phosphorylation state. To search for such target proteins, we used the two-hybrid screen in yeast, with stathmin as a "bait." We isolated and characterized four cDNAs encoding protein domains that interact with stathmin in vivo. One of the corresponding proteins was identified as BiP, a member of the hsp70 heat-shock protein family. Another is a previously unidentified, putative serine/threonine kinase, KIS, which might be regulated by stathmin or, more likely, be part of the kinases controlling its phosphorylation state. Finally, two clones code for subdomains of two proteins, CC1 and CC2, predicted to form alpha-helices participating in coiled-coil interacting structures. Their isolation by interaction screening further supports our model for the regulatory function of stathmin through coiled-coil interactions with diverse downstream targets via its presumed alpha-helical binding domain. The molecular and biological characterization of KIS, CC1, and CC2 proteins will give further insights into the molecular functions and mechanisms of action of stathmin as a relay of integrated intracellular regulatory pathways.

Caught in the act: gas and stellar velocity dispersions in a fast Quenching compact star-forming galaxy at z ~ 1.7

We present Keck I MOSFIRE spectroscopy in the Y and H bands of GDN-8231, a massive, compact, star-forming galaxy at a redshift of z ~ 1.7. Its spectrum reveals both Hα and [Nii] emission lines and strong Balmer absorption lines. The Hα and Spitzer MIPS 24 μm fluxes are both weak, thus indicating a low star-formation rate of SFR≲5-10 M_⨀ yr−1. This, added to a relatively young age of ~700 Myr measured from the absorption lines, provides the first direct evidence for a distant galaxy being caught in the act of rapidly shutting down its star formation. Such quenching allows GDN-8231 to become a compact, quiescent galaxy, similar to three other galaxies in our sample, by z ~ 1.5. Moreover, the color profile of GDN-8231 shows a bluer center, consistent with the predictions of recent simulations for an early phase of inside-out quenching. Its line-of-sight velocity dispersion for the gas, σ_LOG^gas = 127 ± 32 km s^−1, is nearly 40% smaller than that of its stars, σ_LOG^* = 215 ± 35 km s^−1. High-resolution hydro-simulations of galaxies explain such apparently colder gas kinematics of up to a factor of ~1.5 with rotating disks being viewed at different inclinations and/or centrally concentrated star-forming regions. A clear prediction is that their compact, quiescent descendants preserve some remnant rotation from their star-forming progenitors.

Multiwavelength study of star-forming galaxies in the local Universe

We have studied in detail the properties of local active star-forming galaxies from the UCM survey, and in particular their star-formation histories. We have quantified the relative importance of the current episode of star formation in comparison to the underlying older stellar populations. We have also determined the total stellar mass function and burst mass function for the UCM sample using the M/L calculated for each galaxy. Integrating this mass function we obtained the contribution of the star-forming galaxies to the total stellar mass density of the local Universe.

Large-scale clustering measurements with photometric redshifts: comparing the dark matter haloes of X-ray AGN, star-forming and passive galaxies at z ≈ 1

We combine multi-wavelength data in the AEGIS-XD and C-COSMOS surveys to measure the typical dark matter halo mass of X-ray selected active galactic nuclei (AGN) [L_X(2–10 keV) > 10^42 erg s^− 1] in comparison with far-infrared selected star-forming galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; L_IR > 10^11 L_⊙) and quiescent systems at z ≈ 1. We develop a novel method to measure the clustering of extragalactic populations that uses photometric redshift probability distribution functions in addition to any spectroscopy. This is advantageous in that all sources in the sample are used in the clustering analysis, not just the subset with secure spectroscopy. The method works best for large samples. The loss of accuracy because of the lack of spectroscopy is balanced by increasing the number of sources used to measure the clustering. We find that X-ray AGN, far-infrared selected star-forming galaxies and passive systems in the redshift interval 0.6 < z < 1.4 are found in haloes of similar mass, log M_DMH/(M_⊙ h^−1) ≈ 13.0. We argue that this is because the galaxies in all three samples (AGN, star-forming, passive) have similar stellar mass distributions, approximated by the J-band luminosity. Therefore, all galaxies that can potentially host X-ray AGN, because they have stellar masses in the appropriate range, live in dark matter haloes of log M_DMH/(M_⊙ h^−1) ≈ 13.0 independent of their star formation rates. This suggests that the stellar mass of X-ray AGN hosts is driving the observed clustering properties of this population. We also speculate that trends between AGN properties (e.g. luminosity, level of obscuration) and large-scale environment may be related to differences in the stellar mass of the host galaxies.

Palladium and Bimetallic Palladium–Nickel Nanoparticles Supported on Multiwalled Carbon Nanotubes: Application to Carbon–Carbon Bond-Forming Reactions in Water

Palladium and bimetallic Pd–Ni nanoparticles (NPs) protected by polyvinylpyrrolidone were prepared by the reduction-by-solvent method and deposited on multiwalled carbon nanotubes (MWCNTs). The catalytic activity of these NPs to carbon–carbon bond-forming reactions was studied by using 0.1 mol % Pd loading, at 120 °C for 1 h and water as a solvent under ligand-free conditions. The Suzuki–Miyaura reaction took place quantitatively for the cross-coupling of 4-bromoanisole with phenylboronic acid, better than those obtained with potassium phenyltrifluoroborate, with Pd50Ni50/MWCNTs as a catalyst and K2CO3 as a base and TBAB as an additive, with good recyclability during 4 cycles with some Ni leaching. The Hiyama reaction of 4-iodoanisole with trimethoxyphenylsilane, under fluoride-free conditions using 50 % aqueous NaOH solution, was performed with Pd/MWCNTs as a catalyst in 83 % yield with low recyclability. For the Mizoroki-Heck reaction 4-iodoanisole and styrene gave the corresponding 4-methoxystilbene quantitatively with Pd50Ni50/MWCNTs using K2CO3 as a base and TBAB as an additive although the recycle failed. In the case of the Sonogashira-Hagihara reaction, Pd/MWCNTs had to be used as a catalyst and pyrrolidine as a base for the coupling of 4-iodoanisole with phenylacetylene under copper-free conditions. The corresponding 4-methoxytolane was quantitatively obtained allowing the recycling of the catalyst during 3 cycles.