255,571 research outputs found

    Hippocampal Infusion of Zeta Inhibitory Peptide Impairs Recent, but Not Remote, Recognition Memory in Rats.

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    Spatial memory in rodents can be erased following the infusion of zeta inhibitory peptide (ZIP) into the dorsal hippocampus via indwelling guide cannulas. It is believed that ZIP impairs spatial memory by reversing established late-phase long-term potentiation (LTP). However, it is unclear whether other forms of hippocampus-dependent memory, such as recognition memory, are also supported by hippocampal LTP. In the current study, we tested recognition memory in rats following hippocampal ZIP infusion. In order to combat the limited targeting of infusions via cannula, we implemented a stereotaxic approach for infusing ZIP throughout the dorsal, intermediate, and ventral hippocampus. Rats infused with ZIP 3-7 days after training on the novel object recognition task exhibited impaired object recognition memory compared to control rats (those infused with aCSF). In contrast, rats infused with ZIP 1 month after training performed similar to control rats. The ability to form new memories after ZIP infusions remained intact. We suggest that enhanced recognition memory for recent events is supported by hippocampal LTP, which can be reversed by hippocampal ZIP infusion

    A Petunia homeodomain-leucine zipper protein, PhHD-Zip, plays an important role in flower senescence.

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    Flower senescence is initiated by developmental and environmental signals, and regulated by gene transcription. A homeodomain-leucine zipper transcription factor, PhHD-Zip, is up-regulated during petunia flower senescence. Virus-induced gene silencing of PhHD-Zip extended flower life by 20% both in unpollinated and pollinated flowers. Silencing PhHD-Zip also dramatically reduced ethylene production and the abundance of transcripts of genes involved in ethylene (ACS, ACO), and ABA (NCED) biosynthesis. Abundance of transcripts of senescence-related genes (SAG12, SAG29) was also dramatically reduced in the silenced flowers. Over-expression of PhHD-Zip accelerated petunia flower senescence. Furthermore, PhHD-Zip transcript abundance in petunia flowers was increased by application of hormones (ethylene, ABA) and abiotic stresses (dehydration, NaCl and cold). Our results suggest that PhHD-Zip plays an important role in regulating petunia flower senescence

    The Wood & Canvas Canoe: A Complete Guide to Its History, Construction, Restoration, and Maintenance

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    Review of The Wood & Canvas Canoe: A Complete Guide to Its History, Construction, Restoration, and Maintenance by Jerry Stelmok and Rollin Thurlo

    Donor-strand exchange in chaperone-assisted pilus assembly revealed in atomic detail by molecular dynamics

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    Adhesive multi-subunit fibres are assembled on the surface of many pathogenic bacteria via the chaperone-usher pathway. In the periplasm, a chaperone donates a Ξ²-strand to a pilus subunit to complement its incomplete immunoglobulin-like fold. At the outer membrane, this is replaced with a Ξ²-strand formed from the N-terminal extension (Nte) of an incoming pilus subunit by a donorstrand exchange (DSE) mechanism. This reaction has previously been shown to proceed via a concerted mechanism, in which the Nte interacts with the chaperone:subunit complex before the chaperone has been displaced, forming a ternary intermediate. Thereafter, the pilus and chaperone Ξ²-strands have been postulated to undergo a strand swap by a β€˜zip-in-zip-out’ mechanism, whereby the chaperone strand zips out, residue by residue, as the Nte simultaneously zips in. Here, molecular dynamics simulations have been used to probe the DSE mechanism during formation of the Salmonella enterica Saf pilus at an atomic level, allowing the direct investigation of the zip-inzip- out hypothesis. The simulations provide an explanation of how the incoming Nte is able to dock and initiate DSE due to inherent dynamic fluctuations within the chaperone:subunit complex. The chaperone donor-strand is shown to unbind from the pilus subunit residue by residue, in direct support of the zip-in-zip-out hypothesis. In addition, an interaction of a residue towards the Nterminus of the Nte with a specific binding pocket (P*) on the adjacent pilus subunit is shown to stabilise the DSE product against unbinding, which also proceeds by a zippering mechanism. Together, the study provides an in-depth picture of DSE, including the first insights into the molecular events occurring during the zip-in-zip-out mechanism

    Algebraic zip data

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    An algebraic zip datum is a tuple \CZ := (G,P,Q,\phi) consisting of a reductive group GG together with parabolic subgroups PP and QQ and an isogeny ϕ ⁣:P/RuPβ†’Q/RuQ\phi\colon P/R_uP\to Q/R_uQ. We study the action of the group E:={(p,q)∈PΓ—Qβˆ£Ο•(Ο€P(p))=Ο€Q(q)}E := \{(p,q)\in P{\times}Q | \phi(\pi_{P}(p)) =\pi_Q(q)\} on GG given by ((p,q),g)↦pgqβˆ’1((p,q),g)\mapsto pgq^{-1}. We define certain smooth EE-invariant subvarieties of GG, show that they define a stratification of GG. We determine their dimensions and their closures and give a description of the stabilizers of the EE-action on GG. We also generalize all results to non-connected groups. We show that for special choices of \CZ the algebraic quotient stack [E\G][E \backslash G] is isomorphic to [G\Z][G \backslash Z] or to [G\Zβ€²][G \backslash Z'], where ZZ is a GG-variety studied by Lusztig and He in the theory of character sheaves on spherical compactifications of GG and where Zβ€²Z' has been defined by Moonen and the second author in their classification of FF-zips. In these cases the EE-invariant subvarieties correspond to the so-called "GG-stable pieces" of ZZ defined by Lusztig (resp. the GG-orbits of Zβ€²Z').Comment: 42 pages, added some references, to appear in Doc. Mat

    Discrete invariants of varieties in positive characteristic

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    If SS is a scheme of characteristic pp, we define an FF-zip over SS to be a vector bundle with two filtrations plus a collection of semi-linear isomorphisms between the graded pieces of the filtrations. For every smooth proper morphism X→SX\to S satisfying certain conditions the de Rham bundles HdRn(X/S)H^n_{{\rm dR}}(X/S) have a natural structure of an FF-zip. We give a complete classification of FF-zips over an algebraically closed field by studying a semi-linear variant of a variety that appears in recent work of Lusztig. For every FF-zip over SS our methods give a scheme-theoretic stratification of SS. If the FF-zip is associated to an abelian scheme over SS the underlying topological stratification is the Ekedahl-Oort stratification. We conclude the paper with a discussion of several examples such as good reductions of Shimura varieties of PEL type and K3-surfaces.Comment: 35 pages, minor changes in exposition, major changes to introductio

    Are Peer Effects Present in Residential Solar Installations? Evidence from Minnesota and Wisconsin

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    There are geographic differences in the rate of adoption of residential photovoltaic (PV) solar. Are adoption rates in small scale localities (counties and zip codes) influenced by previous, nearby adoptions? This paper adds to the literature on Peer Effects with an analysis of Minnesota and Wisconsin zip codes. I use residential adoption data from the OpenPV Project in an empirical analysis of social interactions. My findings indicate that there is a small but significant effect of nearby adoptions at the zip code level. These peer effects are shown to be nuanced by policy incentives such as the XCEL Solar Rewards Program. I additionally engage in a case study analysis of the relationship of some localities
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