TY - JOUR AU - Friml, Jirí AU - Benfey, Philip AU - Benková, Eva AU - Bennett, Malcolm AU - Berleth, Thomas AU - Geldner, Niko AU - Grebe, Markus AU - Heisler, Marcus AU - Hejátko, Jan AU - Jürgens, Gerd AU - Laux, Thomas AU - Lindsey, Keith AU - Lukowitz, Wolfgang AU - Luschnig, Christian AU - Offringa, Remko AU - Scheres, Ben AU - Swarup, Ranjan AU - Torres Ruiz, Ramón AU - Weijers, Dolf AU - Zažímalová, Eva ID - 3005 IS - 1 JF - Trends in Plant Science TI - Apical-basal polarity: Why plant cells don't stand on their heads VL - 11 ER - TY - JOUR AB - Plants and some animals have a profound capacity to regenerate organs from adult tissues. Molecular mechanisms for regeneration have, however, been largely unexplored. Here we investigate a local regeneration response in Arabidopsis roots. Laser-induced wounding disrupts the flow of auxin-a cell-fate-instructive plant hormone-in root tips, and we demonstrate that resulting cell-fate changes require the PLETHORA, SHORTROOT, and SCARECROW transcription factors. These transcription factors regulate the expression and polar position of PIN auxin efflux-facilitating membrane proteins to reconstitute auxin transport in renewed root tips. Thus, a regeneration mechanism using embryonic root stem-cell patterning factors first responds to and subsequently stabilizes a new hormone distribution. AU - Xu, Jian AU - Hofhuis, Hugo AU - Heidstra, Renze AU - Sauer, Michael AU - Jirí Friml AU - Scheres, Ben ID - 3008 IS - 5759 JF - Science TI - A molecular framework for plant regeneration VL - 311 ER - TY - JOUR AU - Paciorek, Tomasz AU - Friml, Jirí ID - 3009 IS - 7 JF - Journal of Cell Science TI - Auxin signaling VL - 119 ER - TY - JOUR AB - Plant development is characterized by a profound ability to regenerate and form tissues with new axes of polarity. An unsolved question concerns how the position within a tissue and cues from neighboring cells are integrated to specify the polarity of individual cells. The canalization hypothesis proposes a feedback effect of the phytohormone auxin on the directionality of intercellular auxin flow as a means to polarize tissues. Here we identify a cellular and molecular mechanism for canalization. Local auxin application, wounding, or auxin accumulation during de novo organ formation lead to rearrangements in the subcellular polar localization of PIN auxin transport components. This auxin effect on PIN polarity is cell-specific, does not depend on PIN transcription, and involves the Aux/IAA-ARF (indole-3-acetic acid-auxin response factor) signaling pathway. Our data suggest that auxin acts as polarizing cue, which links individual cell polarity with tissue and organ polarity through control of PIN polar targeting. This feedback regulation provides a conceptual framework for polarization during multiple regenerative and patterning processes in plants. AU - Sauer, Michael AU - Balla, Jozef AU - Luschnig, Christian AU - Wiśniewska, Justyna AU - Reinöhl, Vilém AU - Friml, Jirí AU - Benková, Eva ID - 3016 IS - 20 JF - Genes and Development TI - Canalization of auxin flow by Aux/IAA-ARF-dependent feedback regulation of PIN polarity VL - 20 ER - TY - JOUR AB - The plant hormone auxin plays crucial roles in regulating plant growth development, including embryo and root patterning, organ formation, vascular tissue differentiation and growth responses to environmental stimuli. Asymmetric auxin distribution patterns have been observed within tissues, and these so-called auxin gradients change dynamically during different developmental processes. Most auxin is synthesized in the shoot and distributed directionally throughout the plant. This polar auxin transport is mediated by auxin influx and efflux facilitators, whose subcellular polar localizations guide the direction of auxin flow. The polar localization of PIN auxin efflux carriers changes in response to developmental and external cues in order to channel auxin flow in a regulated manner for organized growth. Auxin itself modulates the expression and subcellular localization of PIN proteins, contributing to a complex pattern of feedback regulation. Here we review the available information mainly from studies of a model plant, Arabidopsis thaliana, on the generation of auxin gradients, the regulation of polar auxin transport and further downstream cellular events. AU - Tanaka, Hirokazu AU - Dhonukshe, Pankaj AU - Brewer, Philip AU - Friml, Jirí ID - 3017 IS - 23 JF - Cellular and Molecular Life Sciences TI - Spatiotemporal asymmetric auxin distribution: A means to coordinate plant development VL - 63 ER - TY - JOUR AB - The directional flow of the plant hormone auxin mediates multiple developmental processes, including patterning and tropisms. Apical and basal plasma membrane localization of AUXIN-RESISTANT1 (AUX1) and PIN-FORMED1 (PIN1) auxin transport components underpins the directionality of intercellular auxin flow in Arabidopsis thaliana roots. Here, we examined the mechanism of polar trafficking of AUX1. Real-time live cell analysis along with subcellular markers revealed that AUX1 resides at the apical plasma membrane of protophloem cells and at highly dynamic subpopulations of Golgi apparatus and endosomes in all cell types. Plasma membrane and intracellular pools of AUX1 are interconnected by actin-dependent constitutive trafficking, which is not sensitive to the vesicle trafficking inhibitor brefeldin A. AUX1 subcellular dynamics are not influenced by the auxin influx inhibitor NOA but are blocked by the auxin efflux inhibitors TIBA and PBA. Furthermore, auxin transport inhibitors and interference with the sterol composition of membranes disrupt polar AUX1 distribution at the plasma membrane. Compared with PIN1 trafficking, AUX1 dynamics display different sensitivities to trafficking inhibitors and are independent of the endosomal trafficking regulator ARF GEF GNOM. Hence, AUX1 uses a novel trafficking pathway in plants that is distinct from PIN trafficking, providing an additional mechanism for the fine regulation of auxin transport. AU - Kleine-Vehn, Jürgen AU - Dhonukshe, Pankaj AU - Swarup, Ranjan AU - Bennett, Malcolm AU - Jirí Friml ID - 3018 IS - 11 JF - Plant Cell TI - Subcellular trafficking of the Arabidopsis auxin influx carrier AUX1 uses a novel pathway distinct from PIN1 VL - 18 ER - TY - JOUR AB - High throughput microarray transcription analyses provide us with the expression profiles for large amounts of plant genes. However, their tissue and cellular resolution is limited. Thus, for detailed functional analysis, it is still necessary to examine the expression pattern of selected candidate genes at a cellular level. Here, we present an in situ mRNA hybridization method that is routinely used for the analysis of plant gene expression patterns. The protocol is optimized for whole mount mRNA localizations in Arabidopsis seedling tissues including embryos, roots, hypocotyls and young primary leaves. It can also be used for comparable tissues in other species. Part of the protocol can also be automated and performed by a liquid handling robot. Here we present a detailed protocol, recommended controls and troubleshooting, along with examples of several applications. The total time to carry out the entire procedure is ∼7 d, depending on the tissue used. AU - Hejátko, Jan AU - Blilou, Ikram AU - Brewer, Philip B AU - Jirí Friml AU - Scheres, Ben AU - Eva Benková ID - 3020 IS - 4 JF - Nature Protocols TI - In situ hybridization technique for mRNA detection in whole mount Arabidopsis samples VL - 1 ER - TY - JOUR AB - As the field of plant molecular biology is swiftly advancing, a need has been created for methods that allow rapid and reliable in situ localization of proteins in plant cells. Here we describe a whole-mount 'immunolocalization' technique for various plant tissues, including roots, hypocotyls, cotyledons, young primary leaves and embryos of Arabidopsis thaliana and other species. The detailed protocol, recommended controls and troubleshooting are presented, along with examples of applications. The protocol consists of five main procedures: tissue fixation, tissue permeation, blocking, primary and secondary antibody incubation. Notably, the first procedure (tissue fixation) includes several steps (4-12) that are absolutely necessary for protein localization in hypocotyls, cotyledons and young primary leaves but should be omitted for other tissues. The protocol is usually done in 3 days, but could also be completed in 2 days. AU - Sauer, Michael AU - Paciorek, Tomasz AU - Eva Benková AU - Jirí Friml ID - 3015 IS - 1 JF - Nature Protocols TI - Immunocytochemical techniques for whole mount in situ protein localization in plants VL - 1 ER - TY - JOUR AB - There is a growing demand for methods that allow rapid and reliable in situ localization of proteins in plant cells. The immunocytochemistry protocol presented here can be used routinely to observe protein localization patterns in tissue sections of various plant species. This protocol is especially suitable for plant species with more-complex tissue architecture (such as maize, Zea mays), which makes it difficult to use an easier whole-mount procedure for protein localization. To facilitate the antibody-antigen reaction, it is necessary to include a wax-embedding and tissue-sectioning step. The protocol consists of the following procedures: chemical fixation of tissue, dehydration, wax embedding, sectioning, dewaxing, rehydration, blocking and antibody incubation. The detailed protocol, recommended controls and troubleshooting are presented here, along with examples of applications. AU - Paciorek, Tomasz AU - Sauer, Michael AU - Balla, Jozef AU - Wiśniewska, Justyna AU - Jirí Friml ID - 3013 IS - 1 JF - Nature Protocols TI - Immunocytochemical technique for protein localization in sections of plant tissues VL - 1 ER - TY - JOUR AB - Plant biology is currently confronted with an overflow of expression profile data provided by high-throughput microarray transcription analyses. However, the tissue and cellular resolution of these techniques is limited. Thus, it is still necessary to examine the expression pattern of selected candidate genes at a cellular level. Here we present an in situ mRNA hybridization method that is routinely used in the analysis of gene expression patterns. The protocol is optimized for mRNA localizations in sectioned tissue of Arabidopsis seedlings including embryos, roots, hypocotyls, young primary leaves and flowers. The detailed protocol, recommended controls and troubleshooting are presented along with examples of application. The total time for the process is 10 days. AU - Brewer, Philip B AU - Heisler, Marcus G AU - Hejátko, Jan AU - Jirí Friml AU - Eva Benková ID - 3014 IS - 3 JF - Nature Protocols TI - In situ hybridization for mRNA detection in Arabidopsis tissue sections VL - 1 ER - TY - JOUR AB - The basic concepts of the molecular machinery that mediates cell migration have been gleaned from cell culture systems. However, the three-dimensional environment within an organism presents migrating cells with a much greater challenge. They must move between and among other cells while interpreting multiple attractive and repulsive cues to choose their proper path. They must coordinate their cell adhesion with their surroundings and know when to start and stop moving. New insights into the control of these remaining mysteries have emerged from genetic dissection and live imaging of germ cell migration in Drosophila, zebrafish, and mouse embryos. In this review, we first describe germ cell migration in cellular and mechanistic detail in these different model systems. We then compare these systems to highlight the emerging principles. Finally, we contrast the migration of germ cells with that of immune and cancer cells to outline the conserved and different mechanisms. AU - Kunwar, Prabhat S AU - Daria Siekhaus AU - Lehmann, Ruth ID - 3152 JF - Annual Review of Cell and Developmental Biology TI - In vivo migration A germ cell perspective VL - 22 ER - TY - CONF AB - This paper presents an algorithm capable of real-time separation of foreground from background in monocular video sequences. Automatic segmentation of layers from colour/contrast or from motion alone is known to be error-prone. Here motion, colour and contrast cues are probabilistically fused together with spatial and temporal priors to infer layers accurately and efficiently. Central to our algorithm is the fact that pixel velocities are not needed, thus removing the need for optical flow estimation, with its tendency to error and computational expense. Instead, an efficient motion vs non-motion classifier is trained to operate directly and jointly on intensity-change and contrast. Its output is then fused with colour information. The prior on segmentation is represented by a second order, temporal, Hidden Markov Model, together with a spatial MRF favouring coherence except where contrast is high. Finally, accurate layer segmentation and explicit occlusion detection are efficiently achieved by binary graph cut. The segmentation accuracy of the proposed algorithm is quantitatively evaluated with respect to existing ground-truth data and found to be comparable to the accuracy of a state of the art stereo segmentation algorithm. Fore-ground/background segmentation is demonstrated in the application of live background substitution and shown to generate convincingly good quality composite video. AU - Criminisi, Antonio AU - Cross, Geoffrey AU - Blake, Andrew AU - Vladimir Kolmogorov ID - 3189 TI - Bilayer segmentation of live video VL - 1 ER - TY - JOUR AB - Algorithms for discrete energy minimization are of fundamental importance in computer vision. In this paper, we focus on the recent technique proposed by Wainwright et al. (Nov. 2005)- tree-reweighted max-product message passing (TRW). It was inspired by the problem of maximizing a lower bound on the energy. However, the algorithm is not guaranteed to increase this bound - it may actually go down. In addition, TRW does not always converge. We develop a modification of this algorithm which we call sequential tree-reweighted message passing. Its main property is that the bound is guaranteed not to decrease. We also give a weak tree agreement condition which characterizes local maxima of the bound with respect to TRW algorithms. We prove that our algorithm has a limit point that achieves weak tree agreement. Finally, we show that, our algorithm requires half as much memory as traditional message passing approaches. Experimental results demonstrate that on certain synthetic and real problems, our algorithm outperforms both the ordinary belief propagation and tree-reweighted algorithm in (M. J. Wainwright, et al., Nov. 2005). In addition, on stereo problems with Potts interactions, we obtain a lower energy than graph cuts. AU - Vladimir Kolmogorov ID - 3190 IS - 10 JF - IEEE Transactions on Pattern Analysis and Machine Intelligence TI - Convergent tree reweighted message passing for energy minimization VL - 28 ER - TY - CONF AB - We introduce the term cosegmentation which denotes the task of segmenting simultaneously the common parts of an image pair. A generative model for cosegmentation is presented. Inference in the model leads to minimizing an energy with an MRF term encoding spatial coherency and a global constraint which attempts to match the appearance histograms of the common parts. This energy has not been proposed previously and its optimization is challenging and NP-hard. For this problem a novel optimization scheme which we call trust region graph cuts is presented. We demonstrate that this framework has the potential to improve a wide range of research: Object driven image retrieval, video tracking and segmentation, and interactive image editing. The power of the framework lies in its generality, the common part can be a rigid/non-rigid object (or scene), observed from different viewpoints or even similar objects of the same class. AU - Rother, Carsten AU - Vladimir Kolmogorov AU - Minka, Thomas P AU - Blake, Andrew ID - 3188 TI - Cosegmentation of image pairs by histogram matching - Incorporating a global constraint into MRFs ER - TY - CONF AB - The Feistel-network is a popular structure underlying many block-ciphers where the cipher is constructed from many simpler rounds, each defined by some function which is derived from the secret key. Luby and Rackoff showed that the three-round Feistel-network – each round instantiated with a pseudorandom function secure against adaptive chosen plaintext attacks (CPA) – is a CPA secure pseudorandom permutation, thus giving some confidence in the soundness of using a Feistel-network to design block-ciphers. But the round functions used in actual block-ciphers are – for efficiency reasons – far from being pseudorandom. We investigate the security of the Feistel-network against CPA distinguishers when the only security guarantee we have for the round functions is that they are secure against non-adaptive chosen plaintext attacks (nCPA). We show that in the information-theoretic setting, four rounds with nCPA secure round functions are sufficient (and necessary) to get a CPA secure permutation. Unfortunately, this result does not translate into the more interesting pseudorandom setting. In fact, under the so-called Inverse Decisional Diffie-Hellman assumption the Feistel-network with four rounds, each instantiated with a nCPA secure pseudorandom function, is in general not a CPA secure pseudorandom permutation. AU - Maurer, Ueli M AU - Oswald, Yvonne A AU - Krzysztof Pietrzak AU - Sjödin, Johan ID - 3214 TI - Luby Rackoff ciphers from weak round functions VL - 4004 ER - TY - CONF AB - Most cryptographic primitives such as encryption, authentication or secret sharing require randomness. Usually one assumes that perfect randomness is available, but those primitives might also be realized under weaker assumptions. In this work we continue the study of building secure cryptographic primitives from imperfect random sources initiated by Dodis and Spencer (FOCS’02). Their main result shows that there exists a (high-entropy) source of randomness allowing for perfect encryption of a bit, and yet from which one cannot extract even a single weakly random bit, separating encryption from extraction. Our main result separates encryption from 2-out-2 secret sharing (both in the information-theoretic and in the computational settings): any source which can be used to achieve one-bit encryption also can be used for 2-out-2 secret sharing of one bit, but the converse is false, even for high-entropy sources. Therefore, possibility of extraction strictly implies encryption, which in turn strictly implies 2-out-2 secret sharing. AU - Dodis, Yevgeniy AU - Krzysztof Pietrzak AU - Przydatek, Bartosz ID - 3215 TI - Separating sources for encryption and secret sharing VL - 3876 ER - TY - CONF AB - To prove that a secure key-agreement protocol exists one must at least show P ≠NP. Moreover any proof that the sequential composition of two non-adaptively secure pseudorandom functions is secure against at least two adaptive queries must falsify the decisional Diffie-Hellman assumption, a standard assumption from public-key cryptography. Hence proving any of this two seemingly unrelated statements would require a significant breakthrough. We show that at least one of the two statements is true. To our knowledge this gives the first positive cryptographic result (namely that composition implies some weak adaptive security) which holds in Minicrypt, but not in Cryptomania, i.e. under the assumption that one-way functions exist, but public-key cryptography does not. AU - Krzysztof Pietrzak ID - 3217 TI - Composition implies adaptive security in minicrypt VL - 4004 ER - TY - CONF AB - We prove a new upper bound on the advantage of any adversary for distinguishing the encrypted CBC-MAC (EMAC) based on random permutations from a random function. Our proof uses techniques recently introduced in [BPR05], which again were inspired by [DGH + 04]. The bound we prove is tight — in the sense that it matches the advantage of known attacks up to a constant factor — for a wide range of the parameters: let n denote the block-size, q the number of queries the adversary is allowed to make and ℓ an upper bound on the length (i.e. number of blocks) of the messages, then for ℓ ≤ 2 n/8 and q≥ł2 the advantage is in the order of q 2/2 n (and in particular independent of ℓ). This improves on the previous bound of q 2ℓΘ(1/ln ln ℓ)/2 n from [BPR05] and matches the trivial attack (which thus is basically optimal) where one simply asks random queries until a collision is found. AU - Krzysztof Pietrzak ID - 3216 TI - A tight bound for EMAC VL - 4052 ER - TY - JOUR AB - We observed sharp wave/ripples (SWR) during exploration within brief (< 2.4 s) interruptions of or during theta oscillations. CA1 network responses of SWRs occurring during exploration (eSWR) and SWRs detected in waking immobility or sleep were similar. However, neuronal activity during eSWR was location dependent, and eSWR-related firing was stronger inside the place field than outside. The eSPW-related firing increase was stronger than the baseline increase inside compared to outside, suggesting a “supralinear” summation of eSWR and place-selective inputs. Pairs of cells with similar place fields and/or correlated firing during exploration showed stronger coactivation during eSWRs and subsequent sleep-SWRs. Sequential activation of place cells was not required for the reactivation of waking co-firing patterns; cell pairs with symmetrical cross-correlations still showed reactivated waking co-firing patterns during sleep-SWRs. We suggest that place-selective firing during eSWRs facilitates initial associations between cells with similar place fields that enable place-related ensemble patterns to recur during subsequent sleep-SWRs. AU - Joseph O'Neill AU - Senior,Timothy AU - Jozsef Csicsvari ID - 3522 IS - 1 JF - Neuron TI - Place-selective firing of CA1 pyramidal cells during sharp wave/ripple network patterns in exploratory behavior VL - 49 ER - TY - JOUR AB - We apply new analytical methods to understand the consequences of population bottlenecks for expected additive genetic variance. We analyze essentially all models for multilocus epistasis that have been numerically simulated to demonstrate increased additive variance. We conclude that for biologically plausible models, large increases in expected additive variance–attributable to epistasis rather than dominance–are unlikely. Naciri-Graven and Goudet (2003) found that as the number of epistatically interacting loci increases, additive variance tends to be inflated more after a bottleneck. We argue that this result reflects biologically unrealistic aspects of their models. Specifically, as the number of loci increases, higher-order epistatic interactions become increasingly important in these models, with an increasing fraction of the genetic variance becoming nonadditive, contrary to empirical observations. As shown by Barton and Turelli (2004), without dominance, conversion of nonadditive to additive variance depends only on the variance components and not on the number of loci per se. Numerical results indicating that more inbreeding is needed to produce maximal release of additive variance with more loci follow directly from our analytical results, which show that high levels of inbreeding (F > 0.5) are needed for significant conversion of higher-order components. We discuss alternative approaches to modeling multilocus epistasis and understanding its consequences. AU - Turelli, Michael AU - Nicholas Barton ID - 3607 IS - 9 JF - Evolution; International Journal of Organic Evolution TI - Will population bottlenecks and multilocus epistasis increase additive genetic variance? VL - 60 ER -