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Search Results: 1 - 10 of 1352 matches for " Annette Schenck "
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Analysis of Adhesion Molecules and Basement Membrane Contributions to Synaptic Adhesion at the Drosophila Embryonic NMJ
Andre Koper, Annette Schenck, Andreas Prokop
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0036339
Abstract: Synapse formation and maintenance crucially underlie brain function in health and disease. Both processes are believed to depend on cell adhesion molecules (CAMs). Many different classes of CAMs localise to synapses, including cadherins, protocadherins, neuroligins, neurexins, integrins, and immunoglobulin adhesion proteins, and further contributions come from the extracellular matrix and its receptors. Most of these factors have been scrutinised by loss-of-function analyses in animal models. However, which adhesion factors establish the essential physical links across synaptic clefts and allow the assembly of synaptic machineries at the contact site in vivo is still unclear. To investigate these key questions, we have used the neuromuscular junction (NMJ) of Drosophila embryos as a genetically amenable model synapse. Our ultrastructural analyses of NMJs lacking different classes of CAMs revealed that loss of all neurexins, all classical cadherins or all glutamate receptors, as well as combinations between these or with a Laminin deficiency, failed to reveal structural phenotypes. These results are compatible with a view that these CAMs might have no structural role at this model synapse. However, we consider it far more likely that they operate in a redundant or well buffered context. We propose a model based on a multi-adaptor principle to explain this phenomenon. Furthermore, we report a new CAM-independent adhesion mechanism that involves the basement membranes (BM) covering neuromuscular terminals. Thus, motorneuronal terminals show strong partial detachment of the junction when BM-to-cell surface attachment is impaired by removing Laminin A, or when BMs lose their structural integrity upon loss of type IV collagens. We conclude that BMs are essential to tie embryonic motorneuronal terminals to the muscle surface, lending CAM-independent structural support to their adhesion. Therefore, future developmental studies of these synaptic junctions in Drosophila need to consider the important contribution made by BM-dependent mechanisms, in addition to CAM-dependent adhesion.
HSPC300 and its role in neuronal connectivity
Abrar Qurashi, H Bahar Sahin, Pilar Carrera, Alexis Gautreau, Annette Schenck, Angela Giangrande
Neural Development , 2007, DOI: 10.1186/1749-8104-2-18
Abstract: In the present study, we identify the HSPC300 gene and characterize its interaction with the WAVE/SCAR complex in the Drosophila animal model. On the basis of several lines of evidence, we demonstrate that HSPC300 is an indispensable component of the complex controlling axonal and neuromuscular junction (NMJ) growth. First, the Drosophila HSPC300 expression profile resembles that of other members of the WAVE/SCAR complex. Second, HSPC300 mutation, as well as mutations in the other complex subunits, results in identical axonal and NMJ growth defects. Third, like with other complex subunits, defects in NMJ architecture are rescued by presynaptic expression of the respective wild-type gene. Fourth, HSPC300 genetically interacts with another subunit of the WAVE/SCAR complex. Fifth, HSPC300 physically associates with CYFIP and SCAR.Present data provide the first evidence for HSPC300 playing a role in nervous system development and demonstrate in vivo that this small protein works in the context of the WAVE/SCAR complex.The evolutionarily conserved WAVE/SCAR complex has emerged as an important Rac1 small GTPase downstream effector that regulates several aspects of neuronal architecture. The mammalian WAVE/SCAR complex is composed of five proteins: CYFIP (PIR121 or Sra1), Kette (Nap1 or Hem2), Abi (or Abl interactor), SCAR (WAVE) and HSPC300 [1,2]. Whereas in the mouse nervous system WAVE function has so far been analyzed exclusively [3,4], Drosophila mutants are available for all but one subunit, HSPC300 [5-9]. Although our understanding is still far from complete, studies of these mutants and their protein partners have already uncovered that the WAVE/SCAR complex acts as a crucial hub, integrating and regulating various signaling pathways. The SCAR protein, probably the best-studied subunit, is a direct activator of the Arp2/3 actin nucleating complex [2,10], which is required for the formation of a branched actin network [11]. The other complex subunits physically inte
The Epigenetic Regulator G9a Mediates Tolerance to RNA Virus Infection in Drosophila
Sarah H. Merkling?,Alfred W. Bronkhorst?,Jamie M. Kramer?,Gijs J. Overheul?,Annette Schenck,Ronald P. Van Rij
PLOS Pathogens , 2015, DOI: 10.1371/journal.ppat.1004692
Abstract: Little is known about the tolerance mechanisms that reduce the negative effects of microbial infection on host fitness. Here, we demonstrate that the histone H3 lysine 9 methyltransferase G9a regulates tolerance to virus infection by shaping the response of the evolutionary conserved Jak-Stat pathway in Drosophila. G9a-deficient mutants are more sensitive to RNA virus infection and succumb faster to infection than wild-type controls, which was associated with strongly increased Jak-Stat dependent responses, but not with major differences in viral load. Genetic experiments indicate that hyperactivated Jak-Stat responses are associated with early lethality in virus-infected flies. Our results identify an essential epigenetic mechanism underlying tolerance to virus infection.
Taking the Guesswork Out of Curriculum Design: Learning to Engineer Explicit Grammar Curricula through the Analysis of Multiple Influences on the Acquisition Process  [PDF]
Andrew D. Schenck, Wonkyung Choi
Open Journal of Modern Linguistics (OJML) , 2012, DOI: 10.4236/ojml.2012.23015
Abstract: While a study by Goldschneider and DeKeyser (2005) was able to explain how factors such as phonological salience, frequency, morphological regularity, semantic complexity, and syntactic complexity influence acquisition order, the examination of six similar morphological features provided only a limited perspective. The purpose of this study was to see if causal variables, both individually and cumulatively, could be used to predict acquisition orders with more highly disparate morphological and syntactic features. Results of Spearman rank calculations revealed that the integration of causal factors yielded the highest correlation to both the Processability Theory (rs = 0.821; p = 0.007) and Natural Order Hypothesis (rs = 0.529; p = 0.143), suggesting that these factors have a synergistic influence on morphosyntactic development. Methods to predict the acquisition of both syntactic and morphological features are suggested, along with an empirically-based method to guide explicit grammar instruction.
Building a Better Mousetrap: Replacing Subjective Writing Rubrics with More Empirically-Sound Alternatives for EFL Learners  [PDF]
Andrew D. Schenck, Eoin Daly
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.38193
Abstract: Although writing rubrics can provide valuable feedback, the criteria they use are often subjective, which compels raters to employ their own tacit biases. The purpose of this study is to see if discreet empirical characteristics of texts can be used in lieu of the rubric to objectively assess the writing quality of EFL learners. The academic paragraphs of 38 participants were evaluated according to several empirically calculable criteria related to cohesion, content, and grammar. Values were then compared to scores obtained from holistic scoring by multiple raters using a multiple regression formula. The resulting correlation between variables (R = .873) was highly significant, suggesting that more empirical, impartial means of writing evaluation can now be used in conjunction with technology to provide student feedback and teacher training.
Unlocking the Secrets of Morphosyntactic Development by Examining Acquisition Order Disparities in an EFL Context  [PDF]
Andrew D. Schenck, Wonkyung Choi
Open Journal of Modern Linguistics (OJML) , 2013, DOI: 10.4236/ojml.2013.31006
Abstract:

This study examined acquisition order disparities and their associated causes in an EFL context, so that pedagogical means of enhancing the process of morphosyntactic development could be discovered. Twenty-six South Korean EFL middle school students were given an extensive timed writing test. Following the administration of this test, an acquisition order for 16 morphosyntactic features was constructed. The EFL order was first compared to others found in ESL contexts. It was then compared to six hypothesized causes of acquisition: EFL input frequency, L1 similarity, morphosyntactic variability, semantic complexity, sonority, and morphosyntactic complexity. Results suggest that while input frequency and L1 similarity are the most significant predictors, all causal variables have a role in the manifestation of acquisition order within an EFL context. Suggestions for curricular reform that utilize the unique causal characteristics of each morphosyntactic feature have been proposed.

Weyl laws for partially open quantum maps
Emmanuel Schenck
Physics , 2008, DOI: 10.1007/s00023-009-0421-0
Abstract: We study a toy model for "partially open" wave-mechanical system, like for instance a dielectric micro-cavity, in the semiclassical limit where ray dynamics is applicable. Our model is a quantized map on the 2-dimensional torus, with an additional damping at each time step, resulting in a subunitary propagator, or "damped quantum map". We obtain analogues of Weyl's laws for such maps in the semiclassical limit, and draw some more precise estimates when the classical dynamic is chaotic.
Linear systems on a special rational surface
Hal Schenck
Mathematics , 2003,
Abstract: We study the Hilbert series of a family of ideals J_\phi generated by powers of linear forms in k[x_1,...,x_n]. Using the results of Emsalem-Iarrobino, we formulate this as a question about fatpoints in P^{n-1}. In the three variable case this is equivalent to studying the dimension of a linear system on a blow up of P^2. The ideals that arise have the points in very special position, but because there are only seven points, we can apply results of Harbourne to obtain the classes of the negative curves. Reducing to an effective, nef divisor and using Riemann-Roch yields a formula for the Hilbert series. This proves the n=3 case of a conjecture of Postnikov and Shapiro, which they later showed true for all n. Postnikov and Shapiro observe that for a family of ideals closely related to J_\phi a similar result often seems to hold, although counterexamples exist for n=4 and n=5. Our methods allow us to prove that for n=3 an analogous formula is indeed true. We close with a counterexample to a conjecture Postnikov and Shapiro make about the minimal free resolution of these ideals.
Exponential stabilization without geometric control
Emmanuel Schenck
Mathematics , 2010,
Abstract: We present examples of exponential stabilization for the damped wave equation on a compact manifold in situations where the geometric control condition is not satisfied. This follows from a dynamical argument involving a topological pressure on a suitable uncontrolled set.
Resonance varieties via blowups of P^2 and scrolls
Hal Schenck
Mathematics , 2010,
Abstract: Conjectures of Suciu relate the fundamental group of the complement M = C^n\A of a hyperplane arrangement A to the first resonance variety of H^*(M,Z). We describe a connection between the first resonance variety and the Orlik-Terao algebra C(A) of the arrangement. In particular, we show that non-local components of R^1(A) give rise to determinantal syzygies of C(A). As a result, Proj(C(A)) lies on a scroll, placing geometric constraints on R^1(A). The key observation is that C(A) is the homogeneous coordinate ring associated to a nef but not ample divisor on the blowup of P^2 at the singular points of A.
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