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Nobel laureate Nikolaas Tinbergen provided clear criteria for declaring a neuroscience problem solved, criteria which despite the passage of more than 50 years and vastly expanded neuroscience tool kits remain applicable today. Tinbergen said for neuroscientists to claim that a behavior is understood, they must correspondingly understand its (i) development and its (ii) mechanisms and its (iii) function and its (iv) evolution. Now, all four of these domains represent hotbeds of current experimental work, each using arrays of new techniques which overlap only partly. Thus, as new methodologies come online, from single-nerve-cell RNA sequencing, for example, to smart FISH, large-scale calcium imaging from cortex and deep brain structures, computational ethology, and so on, one person, however smart, cannot master everything. Our response to the likely "fracturing" of neuroscience recognizes the value of ever larger consortia. This response suggests new kinds of problems for (i) funding and (ii) the fair distribution of credit, especially for younger scientists.

Hair cells, the sensory receptors of the inner ear, respond to mechanical forces originating from sounds and accelerations. An essential feature of each hair cell is an array of filamentous tip links, consisting of the proteins protocadherin 15 (PCDH15) and cadherin 23 (CDH23), whose tension is thought to directly gate the cell's transduction channels. These links are considered far too stiff to represent the gating springs that convert hair bundle displacement into forces capable of opening the channels, and no mechanism has been suggested through which tip-link stiffness could be varied to accommodate hair cells of distinct frequency sensitivity in different receptor organs and animals. Consequently, the gating spring's identity and mechanism of operation remain central questions in sensory neuroscience. Using a high-precision optical trap, we show that an individual monomer of PCDH15 acts as an entropic spring that is much softer than its enthalpic stiffness alone would suggest. This low stiffness implies that the protein is a significant part of the gating spring that controls a hair cell's transduction channels. The tip link's entropic nature then allows for stiffness control through modulation of its tension. We find that a PCDH15 molecule is unstable under tension and exhibits a rich variety of reversible unfolding events that are augmented when the Ca2+ concentration is reduced to physiological levels. Therefore, tip link tension and Ca2+ concentration are likely parameters through which nature tunes a gating spring's mechanical properties.

Histone methyltransferase MLL4 is centrally involved in transcriptional regulation and is often mutated in human diseases, including cancer and developmental disorders. MLL4 contains a catalytic SET domain that mono-methylates histone H3K4 and seven PHD fingers of unclear function. Here, we identify the PHD6 finger of MLL4 (MLL4-PHD6) as a selective reader of the epigenetic modification H4K16ac. The solution NMR structure of MLL4-PHD6 in complex with a H4K16ac peptide along with binding and mutational analyses reveal unique mechanistic features underlying recognition of H4K16ac. Genomic studies show that one third of MLL4 chromatin binding sites overlap with H4K16ac-enriched regions in vivo and that MLL4 occupancy in a set of genomic targets depends on the acetyltransferase activity of MOF, a H4K16ac-specific acetyltransferase. The recognition of H4K16ac is conserved in the PHD7 finger of paralogous MLL3. Together, our findings reveal a previously uncharacterized acetyllysine reader and suggest that selective targeting of H4K16ac by MLL4 provides a direct functional link between MLL4, MOF and H4K16 acetylation.

DEET (N, N-diethyl-meta-toluamide) is the most effective and widely used insect repellent, but its mechanism of action is both complex and controversial [1]. DEET acts on insect smell [2-6] and taste [7-11], and its olfactory mode of action requires the odorant coreceptor orco [2, 3, 6]. We previously observed that orco mutant female Aedes aegypti mosquitoes are strongly attracted to humans even in the presence of DEET, but they are rapidly repelled after contacting DEET-treated skin [6]. DEET inhibits food ingestion by Drosophila melanogaster flies, and this repellency is mediated by bitter taste neurons in the proboscis [9]. Similar neurons were identified in the mosquito proboscis, leading to the hypothesis that DEET repels on contact by activating an aversive bitter taste pathway [10]. To understand the basis of DEET contact chemorepellency, we carried out behavioral experiments and discovered that DEET acts by three distinct mechanisms: smell, ingestion, and contact. Like bitter tastants, DEET is a feeding deterrent when ingested, but its bitterness per se does not fully explain DEET contact chemorepellency. Mosquitoes blood fed on human arms treated with high concentrations of bitters, but rapidly avoided DEET-treated skin and did not blood feed. Insects detect tastants both through their proboscis and legs. We show that DEET contact chemorepellency is mediated exclusively by the tarsal segments of the legs and not the proboscis. This work establishes mosquito legs as the behaviorally relevant contact sensors of DEET. These results will inform the search for molecular mechanisms mediating DEET contact chemorepellency and novel contact-based insect repellents.

Integrative structure determination is a powerful approach to modeling the structures of biological systems based on data produced by multiple experimental and theoretical methods, with implications for our understanding of cellular biology and drug discovery. This Primer introduces theory and methods of integrative approaches, emphasizing the kinds of data that can be effectively included in developing models and using the nuclear pore complex as an example to illustrate the practice and challenges involved. These guidelines are intended to aid the researcher in understanding and applying integrative structural methods to systems of their interest and thus take advantage of this rapidly evolving field.

A search is presented for the production of a Higgs boson in association with a single top quark, based on data collected in 2016 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, which corresponds to an integrated luminosity of 35.9 fb(-1). The production cross section for this process is highly sensitive to the absolute values of the top quark Yukawa coupling, y(t); the Higgs boson coupling to vector bosons, g(HVV); and, uniquely, their relative sign. Analyses using multilepton signatures, targeting H -> WW, H -> tau tau, and H -> ZZ decay modes, and signatures with a single lepton and a b (b) over bar pair, targeting the H -> b (b) over bar decay, are combined with a reinterpretation of a measurement in the H -> gamma gamma channel to constrain y(t). For a standard model-like value of g(HVV), the data favor positive values of y(t) and exclude values of y(t) below about -0.9y(t)(SM).

In this issue of Neuron, Du et al. (2019) demonstrate that the bicistronic CACNA1A gene encodes a transcription factor alpha 1ACT, mutations in which are associated with SCA6, that controls expression of genes important for cerebellar Purkinje cell development and excitability. Reduction of alpha 1ACT in the adult is well tolerated, suggesting a potential new therapy for SCA6.

Spastin is a microtubule-severing AAA (ATPases associated with diverse cellular activities) protein needed for cell division and intracellular vesicle transport. Currently, we lack chemical inhibitors to probe spastin function in such dynamic cellular processes. To design a chemical inhibitor of spastin, we tested selected heterocyclic scaffolds against wild-type protein and constructs with engineered mutations in the nucleotide-binding site that do not substantially disrupt ATPase activity. These data, along with computational docking, guided improvements in compound potency and selectivity and led to spastazoline, a pyrazolyl-pyrrolopyrimidine-based cell-permeable probe for spastin. These studies also identified spastazoline-resistance-conferring point mutations in spastin. Spastazoline, along with the matched inhibitor-sensitive and inhibitor-resistant cell lines we generated, were used in parallel experiments to dissect spastin-specific phenotypes in dividing cells. Together, our findings suggest how chemical probes for AAA proteins, along with inhibitor resistance-conferring mutations, can be designed and used to dissect dynamic cellular processes.

The precise control of CRISPR-Cas9 activity is required for a number of genome engineering technologies. Here, we report a generalizable platform that provided the first synthetic small-molecule inhibitors of Streptococcus pyogenes Cas9 (SpCas9) that weigh <500 Da and are cell permeable, reversible, and stable under physiological conditions. We developed a suite of high-throughput assays for SpCas9 functions, including a primary screening assay for SpCas9 binding to the protospacer adjacent motif, and used these assays to screen a structurally diverse collection of natural-product-like small molecules to ultimately identify compounds that disrupt the SpCas9-DNA interaction. Using these synthetic anti-CRISPR small molecules, we demonstrated dose and temporal control of SpCas9 and catalytically impaired SpCas9 technologies, including transcription activation, and identified a pharmacophore for SpCas9 inhibition using structure-activity relationships. These studies establish a platform for rapidly identifying synthetic, miniature, cell-permeable, and reversible inhibitors against both SpCas9 and next-generation CRISPR-associated nucleases.

Associative learning of food cues that link location in space to food availability guides feeding behavior in mammals. However, the function of specific neurons that are elements of the higher-order, cognitive circuitry controlling feeding behavior is largely unexplored. Here, we report that hippocampal dopamine 2 receptor (hD2R) neurons are specifically activated by food and that both acute and chronic modulation of their activity reduces food intake in mice. Upstream projections from the lateral entorhinal cortex (LEC) to the hippocampus activate hD2R cells and can also decrease food intake. Finally, activation of hD2R neurons interferes with the encoding of a spatial memory linking food to a specific location via projections from the hippocampus to the septal area. Altogether these data describe a previously unidentified LEC > hippocampus > septal higher-order circuit that regulates feeding behavior.