@article{105, abstract = {Clinical Utility Gene Card. 1. Name of Disease (Synonyms): Pontocerebellar hypoplasia type 9 (PCH9) and spastic paraplegia-63 (SPG63). 2. OMIM# of the Disease: 615809 and 615686. 3. Name of the Analysed Genes or DNA/Chromosome Segments: AMPD2 at 1p13.3. 4. OMIM# of the Gene(s): 102771.}, author = {Marsh, Ashley and Novarino, Gaia and Lockhart, Paul and Leventer, Richard}, journal = {European Journal of Human Genetics}, pages = {161--166}, publisher = {Springer Nature}, title = {{CUGC for pontocerebellar hypoplasia type 9 and spastic paraplegia-63}}, doi = {10.1038/s41431-018-0231-2}, volume = {27}, year = {2019}, } @article{10619, abstract = {The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.}, author = {Serlin, M. and Tschirhart, C. L. and Polshyn, Hryhoriy and Zhang, Y. and Zhu, J. and Watanabe, K. and Taniguchi, T. and Balents, L. and Young, A. F.}, issn = {1095-9203}, journal = {Science}, keywords = {multidisciplinary}, number = {6480}, pages = {900--903}, publisher = {American Association for the Advancement of Science}, title = {{Intrinsic quantized anomalous Hall effect in a moiré heterostructure}}, doi = {10.1126/science.aay5533}, volume = {367}, year = {2019}, } @article{10620, abstract = {Partially filled Landau levels host competing electronic orders. For example, electron solids may prevail close to integer filling of the Landau levels before giving way to fractional quantum Hall liquids at higher carrier density1,2. Here, we report the observation of an electron solid with non-collinear spin texture in monolayer graphene, consistent with solidification of skyrmions3—topological spin textures characterized by quantized electrical charge4,5. We probe the spin texture of the solids using a modified Corbino geometry that allows ferromagnetic magnons to be launched and detected6,7. We find that magnon transport is highly efficient when one Landau level is filled (ν=1), consistent with quantum Hall ferromagnetic spin polarization. However, even minimal doping immediately quenches the magnon signal while leaving the vanishing low-temperature charge conductivity unchanged. Our results can be understood by the formation of a solid of charged skyrmions near ν=1, whose non-collinear spin texture leads to rapid magnon decay. Data near fractional fillings show evidence of several fractional skyrmion solids, suggesting that graphene hosts a highly tunable landscape of coupled spin and charge orders.}, author = {Zhou, H. and Polshyn, Hryhoriy and Taniguchi, T. and Watanabe, K. and Young, A. F.}, issn = {1745-2481}, journal = {Nature Physics}, keywords = {General Physics and Astronomy}, number = {2}, pages = {154--158}, publisher = {Springer Nature}, title = {{Solids of quantum Hall skyrmions in graphene}}, doi = {10.1038/s41567-019-0729-8}, volume = {16}, year = {2019}, } @article{10621, abstract = {Twisted bilayer graphene has recently emerged as a platform for hosting correlated phenomena. For twist angles near θ ≈ 1.1°, the low-energy electronic structure of twisted bilayer graphene features isolated bands with a flat dispersion1,2. Recent experiments have observed a variety of low-temperature phases that appear to be driven by electron interactions, including insulating states, superconductivity and magnetism3,4,5,6. Here we report electrical transport measurements up to room temperature for twist angles varying between 0.75° and 2°. We find that the resistivity, ρ, scales linearly with temperature, T, over a wide range of T before falling again owing to interband activation. The T-linear response is much larger than observed in monolayer graphene for all measured devices, and in particular increases by more than three orders of magnitude in the range where the flat band exists. Our results point to the dominant role of electron–phonon scattering in twisted bilayer graphene, with possible implications for the origin of the observed superconductivity.}, author = {Polshyn, Hryhoriy and Yankowitz, Matthew and Chen, Shaowen and Zhang, Yuxuan and Watanabe, K. and Taniguchi, T. and Dean, Cory R. and Young, Andrea F.}, issn = {1745-2481}, journal = {Nature Physics}, keywords = {general physics and astronomy}, number = {10}, pages = {1011--1016}, publisher = {Springer Nature}, title = {{Large linear-in-temperature resistivity in twisted bilayer graphene}}, doi = {10.1038/s41567-019-0596-3}, volume = {15}, year = {2019}, } @article{10622, abstract = {We demonstrate a method for manipulating small ensembles of vortices in multiply connected superconducting structures. A micron-size magnetic particle attached to the tip of a silicon cantilever is used to locally apply magnetic flux through the superconducting structure. By scanning the tip over the surface of the device and by utilizing the dynamical coupling between the vortices and the cantilever, a high-resolution spatial map of the different vortex configurations is obtained. Moving the tip to a particular location in the map stabilizes a distinct multivortex configuration. Thus, the scanning of the tip over a particular trajectory in space permits nontrivial operations to be performed, such as braiding of individual vortices within a larger vortex ensemble—a key capability required by many proposals for topological quantum computing.}, author = {Polshyn, Hryhoriy and Naibert, Tyler and Budakian, Raffi}, issn = {1530-6992}, journal = {Nano Letters}, keywords = {mechanical engineering, condensed matter physics, general materials science, general chemistry, bioengineering}, number = {8}, pages = {5476--5482}, publisher = {American Chemical Society}, title = {{Manipulating multivortex states in superconducting structures}}, doi = {10.1021/acs.nanolett.9b01983}, volume = {19}, year = {2019}, } @article{10625, abstract = {The discovery of superconductivity and exotic insulating phases in twisted bilayer graphene has established this material as a model system of strongly correlated electrons. To achieve superconductivity, the two layers of graphene need to be at a very precise angle with respect to each other. Yankowitz et al. now show that another experimental knob, hydrostatic pressure, can be used to tune the phase diagram of twisted bilayer graphene (see the Perspective by Feldman). Applying pressure increased the coupling between the layers, which shifted the superconducting transition to higher angles and somewhat higher temperatures.}, author = {Yankowitz, Matthew and Chen, Shaowen and Polshyn, Hryhoriy and Zhang, Yuxuan and Watanabe, K. and Taniguchi, T. and Graf, David and Young, Andrea F. and Dean, Cory R.}, issn = {1095-9203}, journal = {Science}, keywords = {multidisciplinary}, number = {6431}, pages = {1059--1064}, publisher = {American Association for the Advancement of Science (AAAS)}, title = {{Tuning superconductivity in twisted bilayer graphene}}, doi = {10.1126/science.aav1910}, volume = {363}, year = {2019}, } @inproceedings{11826, abstract = {The diameter, radius and eccentricities are natural graph parameters. While these problems have been studied extensively, there are no known dynamic algorithms for them beyond the ones that follow from trivial recomputation after each update or from solving dynamic All-Pairs Shortest Paths (APSP), which is very computationally intensive. This is the situation for dynamic approximation algorithms as well, and even if only edge insertions or edge deletions need to be supported. This paper provides a comprehensive study of the dynamic approximation of Diameter, Radius and Eccentricities, providing both conditional lower bounds, and new algorithms whose bounds are optimal under popular hypotheses in fine-grained complexity. Some of the highlights include: - Under popular hardness hypotheses, there can be no significantly better fully dynamic approximation algorithms than recomputing the answer after each update, or maintaining full APSP. - Nearly optimal partially dynamic (incremental/decremental) algorithms can be achieved via efficient reductions to (incremental/decremental) maintenance of Single-Source Shortest Paths. For instance, a nearly (3/2+epsilon)-approximation to Diameter in directed or undirected n-vertex, m-edge graphs can be maintained decrementally in total time m^{1+o(1)}sqrt{n}/epsilon^2. This nearly matches the static 3/2-approximation algorithm for the problem that is known to be conditionally optimal.}, author = {Ancona, Bertie and Henzinger, Monika H and Roditty, Liam and Williams, Virginia Vassilevska and Wein, Nicole}, booktitle = {46th International Colloquium on Automata, Languages, and Programming}, isbn = {978-3-95977-109-2}, issn = {1868-8969}, location = {Patras, Greece}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Algorithms and hardness for diameter in dynamic graphs}}, doi = {10.4230/LIPICS.ICALP.2019.13}, volume = {132}, year = {2019}, } @inbook{11847, abstract = {This paper serves as a user guide to the Vienna graph clustering framework. We review our general memetic algorithm, VieClus, to tackle the graph clustering problem. A key component of our contribution are natural recombine operators that employ ensemble clusterings as well as multi-level techniques. Lastly, we combine these techniques with a scalable communication protocol, producing a system that is able to compute high-quality solutions in a short amount of time. After giving a description of the algorithms employed, we establish the connection of the graph clustering problem to protein–protein interaction networks and moreover give a description on how the software can be used, what file formats are expected, and how this can be used to find functional groups in protein–protein interaction networks.}, author = {Biedermann, Sonja and Henzinger, Monika H and Schulz, Christian and Schuster, Bernhard}, booktitle = {Protein-Protein Interaction Networks}, editor = {Canzar, Stefan and Rojas Ringeling, Francisca}, isbn = {9781493998722}, issn = {1940-6029}, pages = {215–231}, publisher = {Springer Nature}, title = {{Vienna Graph Clustering}}, doi = {10.1007/978-1-4939-9873-9_16}, volume = {2074}, year = {2019}, } @inproceedings{11850, abstract = {Modern networked systems are increasingly reconfigurable, enabling demand-aware infrastructures whose resources can be adjusted according to the workload they currently serve. Such dynamic adjustments can be exploited to improve network utilization and hence performance, by moving frequently interacting communication partners closer, e.g., collocating them in the same server or datacenter. However, dynamically changing the embedding of workloads is algorithmically challenging: communication patterns are often not known ahead of time, but must be learned. During the learning process, overheads related to unnecessary moves (i.e., re-embeddings) should be minimized. This paper studies a fundamental model which captures the tradeoff between the benefits and costs of dynamically collocating communication partners on l servers, in an online manner. Our main contribution is a distributed online algorithm which is asymptotically almost optimal, i.e., almost matches the lower bound (also derived in this paper) on the competitive ratio of any (distributed or centralized) online algorithm.}, author = {Henzinger, Monika H and Neumann, Stefan and Schmid, Stefan}, booktitle = {SIGMETRICS'19: International Conference on Measurement and Modeling of Computer Systems}, isbn = {978-1-4503-6678-6}, location = {Phoenix, AZ, United States}, pages = {43–44}, publisher = {Association for Computing Machinery}, title = {{Efficient distributed workload (re-)embedding}}, doi = {10.1145/3309697.3331503}, year = {2019}, } @inproceedings{11851, abstract = {The minimum cut problem for an undirected edge-weighted graph asks us to divide its set of nodes into two blocks while minimizing the weighted sum of the cut edges. In this paper, we engineer the fastest known exact algorithm for the problem. State-of-the-art algorithms like the algorithm of Padberg and Rinaldi or the algorithm of Nagamochi, Ono and Ibaraki identify edges that can be contracted to reduce the graph size such that at least one minimum cut is maintained in the contracted graph. Our algorithm achieves improvements in running time over these algorithms by a multitude of techniques. First, we use a recently developed fast and parallel inexact minimum cut algorithm to obtain a better bound for the problem. Afterwards, we use reductions that depend on this bound to reduce the size of the graph much faster than previously possible. We use improved data structures to further lower the running time of our algorithm. Additionally, we parallelize the contraction routines of Nagamochi et al. . Overall, we arrive at a system that significantly outperforms the fastest state-of-the-art solvers for the exact minimum cut problem.}, author = {Henzinger, Monika H and Noe, Alexander and Schulz, Christian}, booktitle = {33rd International Parallel and Distributed Processing Symposium}, isbn = {978-1-7281-1247-3}, issn = {1530-2075}, location = {Rio de Janeiro, Brazil}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{Shared-memory exact minimum cuts}}, doi = {10.1109/ipdps.2019.00013}, year = {2019}, } @inproceedings{11853, abstract = {We present a deterministic dynamic algorithm for maintaining a (1+ε)f-approximate minimum cost set cover with O(f log(Cn)/ε^2) amortized update time, when the input set system is undergoing element insertions and deletions. Here, n denotes the number of elements, each element appears in at most f sets, and the cost of each set lies in the range [1/C, 1]. Our result, together with that of Gupta~et~al.~[STOC'17], implies that there is a deterministic algorithm for this problem with O(f log(Cn)) amortized update time and O(min(log n, f)) -approximation ratio, which nearly matches the polynomial-time hardness of approximation for minimum set cover in the static setting. Our update time is only O(log (Cn)) away from a trivial lower bound. Prior to our work, the previous best approximation ratio guaranteed by deterministic algorithms was O(f^2), which was due to Bhattacharya~et~al.~[ICALP`15]. In contrast, the only result that guaranteed O(f) -approximation was obtained very recently by Abboud~et~al.~[STOC`19], who designed a dynamic algorithm with (1+ε)f-approximation ratio and O(f^2 log n/ε) amortized update time. Besides the extra O(f) factor in the update time compared to our and Gupta~et~al.'s results, the Abboud~et~al.~algorithm is randomized, and works only when the adversary is oblivious and the sets are unweighted (each set has the same cost). We achieve our result via the primal-dual approach, by maintaining a fractional packing solution as a dual certificate. This approach was pursued previously by Bhattacharya~et~al.~and Gupta~et~al., but not in the recent paper by Abboud~et~al. Unlike previous primal-dual algorithms that try to satisfy some local constraints for individual sets at all time, our algorithm basically waits until the dual solution changes significantly globally, and fixes the solution only where the fix is needed.}, author = {Bhattacharya, Sayan and Henzinger, Monika H and Nanongkai, Danupon}, booktitle = {60th Annual Symposium on Foundations of Computer Science}, isbn = {978-1-7281-4953-0}, issn = {2575-8454}, location = {Baltimore, MD, United States}, pages = {406--423}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{A new deterministic algorithm for dynamic set cover}}, doi = {10.1109/focs.2019.00033}, year = {2019}, } @inproceedings{11865, abstract = {We present the first sublinear-time algorithm that can compute the edge connectivity λ of a network exactly on distributed message-passing networks (the CONGEST model), as long as the network contains no multi-edge. We present the first sublinear-time algorithm for a distributed message-passing network sto compute its edge connectivity λ exactly in the CONGEST model, as long as there are no parallel edges. Our algorithm takes Õ(n1−1/353D1/353+n1−1/706) time to compute λ and a cut of cardinality λ with high probability, where n and D are the number of nodes and the diameter of the network, respectively, and Õ hides polylogarithmic factors. This running time is sublinear in n (i.e. Õ(n1−є)) whenever D is. Previous sublinear-time distributed algorithms can solve this problem either (i) exactly only when λ=O(n1/8−є) [Thurimella PODC’95; Pritchard, Thurimella, ACM Trans. Algorithms’11; Nanongkai, Su, DISC’14] or (ii) approximately [Ghaffari, Kuhn, DISC’13; Nanongkai, Su, DISC’14]. To achieve this we develop and combine several new techniques. First, we design the first distributed algorithm that can compute a k-edge connectivity certificate for any k=O(n1−є) in time Õ(√nk+D). The previous sublinear-time algorithm can do so only when k=o(√n) [Thurimella PODC’95]. In fact, our algorithm can be turned into the first parallel algorithm with polylogarithmic depth and near-linear work. Previous near-linear work algorithms are essentially sequential and previous polylogarithmic-depth algorithms require Ω(mk) work in the worst case (e.g. [Karger, Motwani, STOC’93]). Second, we show that by combining the recent distributed expander decomposition technique of [Chang, Pettie, Zhang, SODA’19] with techniques from the sequential deterministic edge connectivity algorithm of [Kawarabayashi, Thorup, STOC’15], we can decompose the network into a sublinear number of clusters with small average diameter and without any mincut separating a cluster (except the “trivial” ones). This leads to a simplification of the Kawarabayashi-Thorup framework (except that we are randomized while they are deterministic). This might make this framework more useful in other models of computation. Finally, by extending the tree packing technique from [Karger STOC’96], we can find the minimum cut in time proportional to the number of components. As a byproduct of this technique, we obtain an Õ(n)-time algorithm for computing exact minimum cut for weighted graphs.}, author = {Daga, Mohit and Henzinger, Monika H and Nanongkai, Danupon and Saranurak, Thatchaphol}, booktitle = {Proceedings of the 51st Annual ACM SIGACT Symposium on Theory of Computing}, isbn = {978-1-4503-6705-9}, issn = {0737-8017}, location = {Phoenix, AZ, United States}, pages = {343–354}, publisher = {Association for Computing Machinery}, title = {{Distributed edge connectivity in sublinear time}}, doi = {10.1145/3313276.3316346}, year = {2019}, } @inproceedings{11871, abstract = {Many dynamic graph algorithms have an amortized update time, rather than a stronger worst-case guarantee. But amortized data structures are not suitable for real-time systems, where each individual operation has to be executed quickly. For this reason, there exist many recent randomized results that aim to provide a guarantee stronger than amortized expected. The strongest possible guarantee for a randomized algorithm is that it is always correct (Las Vegas), and has high-probability worst-case update time, which gives a bound on the time for each individual operation that holds with high probability. In this paper we present the first polylogarithmic high-probability worst-case time bounds for the dynamic spanner and the dynamic maximal matching problem. 1. For dynamic spanner, the only known o(n) worst-case bounds were O(n3/4) high-probability worst-case update time for maintaining a 3-spanner, and O(n5/9) for maintaining a 5-spanner. We give a O(1)k log3(n) high-probability worst-case time bound for maintaining a (2k – 1)-spanner, which yields the first worst-case polylog update time for all constant k. (All the results above maintain the optimal tradeoff of stretch 2k – 1 and Õ(n1+1/k) edges.) 2. For dynamic maximal matching, or dynamic 2-approximate maximum matching, no algorithm with o(n) worst-case time bound was known and we present an algorithm with O(log5 (n)) high-probability worst-case time; similar worst-case bounds existed only for maintaining a matching that was (2 + ∊)-approximate, and hence not maximal. Our results are achieved using a new approach for converting amortized guarantees to worst-case ones for randomized data structures by going through a third type of guarantee, which is a middle ground between the two above: an algorithm is said to have worst-case expected update time α if for every update σ, the expected time to process σ is at most α. Although stronger than amortized expected, the worst-case expected guarantee does not resolve the fundamental problem of amortization: a worst-case expected update time of O(1) still allows for the possibility that every 1/f(n) updates requires Θ(f(n)) time to process, for arbitrarily high f(n). In this paper we present a black-box reduction that converts any data structure with worst-case expected update time into one with a high-probability worst-case update time: the query time remains the same, while the update time increases by a factor of O(log2(n)). Thus we achieve our results in two steps: (1) First we show how to convert existing dynamic graph algorithms with amortized expected polylogarithmic running times into algorithms with worst-case expected polylogarithmic running times. (2) Then we use our black-box reduction to achieve the polylogarithmic high-probability worst-case time bound. All our algorithms are Las-Vegas-type algorithms.}, author = {Bernstein, Aaron and Forster, Sebastian and Henzinger, Monika H}, booktitle = {30th Annual ACM-SIAM Symposium on Discrete Algorithms}, location = {San Diego, CA, United States}, pages = {1899--1918}, publisher = {Society for Industrial and Applied Mathematics}, title = {{A deamortization approach for dynamic spanner and dynamic maximal matching}}, doi = {10.1137/1.9781611975482.115}, year = {2019}, } @article{11898, abstract = {We build upon the recent papers by Weinstein and Yu (FOCS'16), Larsen (FOCS'12), and Clifford et al. (FOCS'15) to present a general framework that gives amortized lower bounds on the update and query times of dynamic data structures. Using our framework, we present two concrete results. (1) For the dynamic polynomial evaluation problem, where the polynomial is defined over a finite field of size n1+Ω(1) and has degree n, any dynamic data structure must either have an amortized update time of Ω((lgn/lglgn)2) or an amortized query time of Ω((lgn/lglgn)2). (2) For the dynamic online matrix vector multiplication problem, where we get an n×n matrix whose entires are drawn from a finite field of size nΘ(1), any dynamic data structure must either have an amortized update time of Ω((lgn/lglgn)2) or an amortized query time of Ω(n⋅(lgn/lglgn)2). For these two problems, the previous works by Larsen (FOCS'12) and Clifford et al. (FOCS'15) gave the same lower bounds, but only for worst case update and query times. Our bounds match the highest unconditional lower bounds known till date for any dynamic problem in the cell-probe model.}, author = {Bhattacharya, Sayan and Henzinger, Monika H and Neumann, Stefan}, issn = {0304-3975}, journal = {Theoretical Computer Science}, pages = {72--87}, publisher = {Elsevier}, title = {{New amortized cell-probe lower bounds for dynamic problems}}, doi = {10.1016/j.tcs.2019.01.043}, volume = {779}, year = {2019}, } @article{11957, abstract = {Cross-coupling reactions mediated by dual nickel/photocatalysis are synthetically attractive but rely mainly on expensive, non-recyclable noble-metal complexes as photocatalysts. Heterogeneous semiconductors, which are commonly used for artificial photosynthesis and wastewater treatment, are a sustainable alternative. Graphitic carbon nitrides, a class of metal-free polymers that can be easily prepared from bulk chemicals, are heterogeneous semiconductors with high potential for photocatalytic organic transformations. Here, we demonstrate that graphitic carbon nitrides in combination with nickel catalysis can induce selective C−O cross-couplings of carboxylic acids with aryl halides, yielding the respective aryl esters in excellent yield and selectivity. The heterogeneous organic photocatalyst exhibits a broad substrate scope, is able to harvest green light, and can be recycled multiple times. In situ FTIR was used to track the reaction progress to study this transformation at different irradiation wavelengths and reaction scales.}, author = {Pieber, Bartholomäus and Malik, Jamal A. and Cavedon, Cristian and Gisbertz, Sebastian and Savateev, Aleksandr and Cruz, Daniel and Heil, Tobias and Zhang, Guigang and Seeberger, Peter H.}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {28}, pages = {9575--9580}, publisher = {Wiley}, title = {{Semi‐heterogeneous dual nickel/photocatalysis using carbon nitrides: Esterification of carboxylic acids with aryl halides}}, doi = {10.1002/anie.201902785}, volume = {58}, year = {2019}, } @article{11982, abstract = {A carbon nitride material can be combined with homogeneous nickel catalysts for light-mediated cross-couplings of aryl bromides with alcohols under mild conditions. The metal-free heterogeneous semiconductor is fully recyclable and couples a broad range of electron-poor aryl bromides with primary and secondary alcohols as well as water. The application for intramolecular reactions and the synthesis of active pharmaceutical ingredients was demonstrated. The catalytic protocol is applicable for the coupling of aryl iodides with thiols as well.}, author = {Cavedon, Cristian and Madani, Amiera and Seeberger, Peter H. and Pieber, Bartholomäus}, issn = {1523-7052}, journal = {Organic Letters}, number = {13}, pages = {5331--5334}, publisher = {American Chemical Society}, title = {{Semiheterogeneous dual nickel/photocatalytic (thio)etherification using carbon nitrides}}, doi = {10.1021/acs.orglett.9b01957}, volume = {21}, year = {2019}, } @article{11984, abstract = {Differentially protected galactosamine building blocks are key components for the synthesis of human and bacterial oligosaccharides. The azidophenylselenylation of 3,4,6-tri-O-acetyl-d-galactal provides straightforward access to the corresponding 2-nitrogenated glycoside. Poor reproducibility and the use of azides that lead to the formation of potentially explosive and toxic species limit the scalability of this reaction and render it a bottleneck for carbohydrate synthesis. Here, we present a method for the safe, efficient, and reliable azidophenylselenylation of 3,4,6-tri-O-acetyl-d-galactal at room temperature, using continuous flow chemistry. Careful analysis of the transformation resulted in reaction conditions that produce minimal side products while the reaction time was reduced drastically when compared to batch reactions. The flow setup is readily scalable to process 5 mmol of galactal in 3 h, producing 1.2 mmol/h of product.}, author = {Guberman, Mónica and Pieber, Bartholomäus and Seeberger, Peter H.}, issn = {1520-586X}, journal = {Organic Process Research and Development}, number = {12}, pages = {2764--2770}, publisher = {American Chemical Society}, title = {{Safe and scalable continuous flow azidophenylselenylation of galactal to prepare galactosamine building blocks}}, doi = {10.1021/acs.oprd.9b00456}, volume = {23}, year = {2019}, } @article{12190, abstract = {Meiotic crossover frequency varies within genomes, which influences genetic diversity and adaptation. In turn, genetic variation within populations can act to modify crossover frequency in cis and trans. To identify genetic variation that controls meiotic crossover frequency, we screened Arabidopsis accessions using fluorescent recombination reporters. We mapped a genetic modifier of crossover frequency in Col × Bur populations of Arabidopsis to a premature stop codon within TBP-ASSOCIATED FACTOR 4b (TAF4b), which encodes a subunit of the RNA polymerase II general transcription factor TFIID. The Arabidopsis taf4b mutation is a rare variant found in the British Isles, originating in South-West Ireland. Using genetics, genomics, and immunocytology, we demonstrate a genome-wide decrease in taf4b crossovers, with strongest reduction in the sub-telomeric regions. Using RNA sequencing (RNA-seq) from purified meiocytes, we show that TAF4b expression is meiocyte enriched, whereas its paralog TAF4 is broadly expressed. Consistent with the role of TFIID in promoting gene expression, RNA-seq of wild-type and taf4b meiocytes identified widespread transcriptional changes, including in genes that regulate the meiotic cell cycle and recombination. Therefore, TAF4b duplication is associated with acquisition of meiocyte-specific expression and promotion of germline transcription, which act directly or indirectly to elevate crossovers. This identifies a novel mode of meiotic recombination control via a general transcription factor.}, author = {Lawrence, Emma J. and Gao, Hongbo and Tock, Andrew J. and Lambing, Christophe and Blackwell, Alexander R. and Feng, Xiaoqi and Henderson, Ian R.}, issn = {0960-9822}, journal = {Current Biology}, keywords = {General Agricultural and Biological Sciences, General Biochemistry, Genetics and Molecular Biology}, number = {16}, pages = {2676--2686.e3}, publisher = {Elsevier BV}, title = {{Natural variation in TBP-ASSOCIATED FACTOR 4b controls meiotic crossover and germline transcription in Arabidopsis}}, doi = {10.1016/j.cub.2019.06.084}, volume = {29}, year = {2019}, } @article{12192, abstract = {Transposable elements (TEs), the movement of which can damage the genome, are epigenetically silenced in eukaryotes. Intriguingly, TEs are activated in the sperm companion cell – vegetative cell (VC) – of the flowering plant Arabidopsis thaliana. However, the extent and mechanism of this activation are unknown. Here we show that about 100 heterochromatic TEs are activated in VCs, mostly by DEMETER-catalyzed DNA demethylation. We further demonstrate that DEMETER access to some of these TEs is permitted by the natural depletion of linker histone H1 in VCs. Ectopically expressed H1 suppresses TEs in VCs by reducing DNA demethylation and via a methylation-independent mechanism. We demonstrate that H1 is required for heterochromatin condensation in plant cells and show that H1 overexpression creates heterochromatic foci in the VC progenitor cell. Taken together, our results demonstrate that the natural depletion of H1 during male gametogenesis facilitates DEMETER-directed DNA demethylation, heterochromatin relaxation, and TE activation.}, author = {He, Shengbo and Vickers, Martin and Zhang, Jingyi and Feng, Xiaoqi}, issn = {2050-084X}, journal = {eLife}, keywords = {General Immunology and Microbiology, General Biochemistry, Genetics and Molecular Biology, General Medicine, General Neuroscience}, publisher = {eLife Sciences Publications, Ltd}, title = {{Natural depletion of histone H1 in sex cells causes DNA demethylation, heterochromatin decondensation and transposon activation}}, doi = {10.7554/elife.42530}, volume = {8}, year = {2019}, } @article{12600, abstract = {The snow cover dynamics of High Mountain Asia are usually assessed at spatial resolutions of 250 m or greater, but this scale is too coarse to clearly represent the rugged topography common to the region. Higher-resolution measurement of snow-covered area often results in biased sampling due to cloud cover and deep shadows. We therefore develop a Normalized Difference Snow Index-based workflow to delineate snow lines from Landsat Thematic Mapper/Enhanced Thematic Mapper+ imagery and apply it to the upper Langtang Valley in Nepal, processing 194 scenes spanning 1999 to 2013. For each scene, we determine the spatial distribution of snow line altitudes (SLAs) with respect to aspect and across six subcatchments. Our results show that the mean SLA exhibits distinct seasonal behavior based on aspect and subcatchment position. We find that SLA dynamics respond to spatial and seasonal trade-offs in precipitation, temperature, and solar radiation, which act as primary controls. We identify two SLA spatial gradients, which we attribute to the effect of spatially variable precipitation. Our results also reveal that aspect-related SLA differences vary seasonally and are influenced by solar radiation. In terms of seasonal dominant controls, we demonstrate that the snow line is controlled by snow precipitation in winter, melt in premonsoon, a combination of both in postmonsoon, and temperature in monsoon, explaining to a large extent the spatial and seasonal variability of the SLA in the upper Langtang Valley. We conclude that while SLA and snow-covered area are complementary metrics, the SLA has a strong potential for understanding local-scale snow cover dynamics and their controlling mechanisms.}, author = {Girona‐Mata, Marc and Miles, Evan S. and Ragettli, Silvan and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {8}, pages = {6754--6772}, publisher = {American Geophysical Union}, title = {{High‐resolution snowline delineation from Landsat imagery to infer snow cover controls in a Himalayan catchment}}, doi = {10.1029/2019wr024935}, volume = {55}, year = {2019}, }