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2433 Publications

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    Simpson LabRubin Lab
    06/01/11 | BrainAligner: 3D registration atlases of Drosophila brains.
    Peng H, Chung P, Long F, Qu L, Jenett A, Seeds AM, Myers EW, Simpson JH
    Nature Methods. 2011 Jun;8:493-500. doi: 10.1038/nmeth.1602

    Analyzing Drosophila melanogaster neural expression patterns in thousands of three-dimensional image stacks of individual brains requires registering them into a canonical framework based on a fiducial reference of neuropil morphology. Given a target brain labeled with predefined landmarks, the BrainAligner program automatically finds the corresponding landmarks in a subject brain and maps it to the coordinate system of the target brain via a deformable warp. Using a neuropil marker (the antibody nc82) as a reference of the brain morphology and a target brain that is itself a statistical average of data for 295 brains, we achieved a registration accuracy of 2 μm on average, permitting assessment of stereotypy, potential connectivity and functional mapping of the adult fruit fly brain. We used BrainAligner to generate an image pattern atlas of 2954 registered brains containing 470 different expression patterns that cover all the major compartments of the fly brain.

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    06/01/11 | Deletion of the betaine-GABA transporter (BGT1; slc6a12) gene does not affect seizure thresholds of adult mice.
    Lehre AC, Rowley NM, Zhou Y, Holmseth S, Guo C, Holen T, Hua R, Laake P, Olofsson AM, Poblete-Naredo I, Rusakov DA, Madsen KK, Clausen RP, Schousboe A, White HS, Danbolt NC
    Epilepsy Research. 2011 Jun;95(1-2):70-81. doi: 10.1016/j.eplepsyres.2011.02.014

    Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. Once released, it is removed from the extracellular space by cellular uptake catalyzed by GABA transporter proteins. Four GABA transporters (GAT1, GAT2, GAT3 and BGT1) have been identified. Inhibition of the GAT1 by the clinically available anti-epileptic drug tiagabine has been an effective strategy for the treatment of some patients with partial seizures. Recently, the investigational drug EF1502, which inhibits both GAT1 and BGT1, was found to exert an anti-convulsant action synergistic to that of tiagabine, supposedly due to inhibition of BGT1. The present study addresses the role of BGT1 in seizure control and the effect of EF1502 by developing and exploring a new mouse line lacking exons 3-5 of the BGT1 (slc6a12) gene. The deletion of this sequence abolishes the expression of BGT1 mRNA. However, homozygous BGT1-deficient mice have normal development and show seizure susceptibility indistinguishable from that in wild-type mice in a variety of seizure threshold models including: corneal kindling, the minimal clonic and minimal tonic extension seizure threshold tests, the 6Hz seizure threshold test, and the i.v. pentylenetetrazol threshold test. We confirm that BGT1 mRNA is present in the brain, but find that the levels are several hundred times lower than those of GAT1 mRNA; possibly explaining the apparent lack of phenotype. In conclusion, the present results do not support a role for BGT1 in the control of seizure susceptibility and cannot provide a mechanistic understanding of the synergism that has been previously reported with tiagabine and EF1502.

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    Riddiford Lab
    05/15/11 | When is weight critical?
    Riddiford LM
    The Journal of Experimental Biology. 2011 May 15;214(Pt 10):1613-5. doi: 10.1242/jeb.049098
    05/06/11 | Automated reconstruction of neuronal morphology based on local geometrical and global structural models.
    Zhao T, Xie J, Amat F, Clack N, Ahammad P, Peng H, Long F, Myers E
    Neuroinformatics. 2011 May 6;9(2-3):247-61. doi: 10.1007/s12021-011-9120-3

    Digital reconstruction of neurons from microscope images is an important and challenging problem in neuroscience. In this paper, we propose a model-based method to tackle this problem. We first formulate a model structure, then develop an algorithm for computing it by carefully taking into account morphological characteristics of neurons, as well as the image properties under typical imaging protocols. The method has been tested on the data sets used in the DIADEM competition and produced promising results for four out of the five data sets.

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    05/03/11 | Robo-3--mediated repulsive interactions guide R8 axons during Drosophila visual system development.
    Pappu KS, Morey M, Nern A, Spitzweck B, Dickson BJ, Zipursky SL
    Proc Natl Acad Sci U S A. 2011 May 03;108(18):7571-6. doi: 10.1073/pnas.1103419108

    The formation of neuronal connections requires the precise guidance of developing axons toward their targets. In the Drosophila visual system, photoreceptor neurons (R cells) project from the eye into the brain. These cells are grouped into some 750 clusters comprised of eight photoreceptors or R cells each. R cells fall into three classes: R1 to R6, R7, and R8. Posterior R8 cells are the first to project axons into the brain. How these axons select a specific pathway is not known. Here, we used a microarray-based approach to identify genes expressed in R8 neurons as they extend into the brain. We found that Roundabout-3 (Robo3), an axon-guidance receptor, is expressed specifically and transiently in R8 growth cones. In wild-type animals, posterior-most R8 axons extend along a border of glial cells demarcated by the expression of Slit, the secreted ligand of Robo3. In contrast, robo3 mutant R8 axons extend across this border and fasciculate inappropriately with other axon tracts. We demonstrate that either Robo1 or Robo2 rescues the robo3 mutant phenotype when each is knocked into the endogenous robo3 locus separately, indicating that R8 does not require a function unique to the Robo3 paralog. However, persistent expression of Robo3 in R8 disrupts the layer-specific targeting of R8 growth cones. Thus, the transient cell-specific expression of Robo3 plays a crucial role in establishing neural circuits in the Drosophila visual system by selectively regulating pathway choice for posterior-most R8 growth cones.

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    05/01/11 | PALM and STORM: unlocking live-cell super-resolution.
    Henriques R, Griffiths C, Hesper Rego E, Mhlanga MM
    Biopolymers. 2011 May;95(5):322-31. doi: 10.1002/bip.21586

    Live-cell fluorescence light microscopy has emerged as an important tool in the study of cellular biology. The development of fluorescent markers in parallel with super-resolution imaging systems has pushed light microscopy into the realm of molecular visualization at the nanometer scale. Resolutions previously only attained with electron microscopes are now within the grasp of light microscopes. However, until recently, live-cell imaging approaches have eluded super-resolution microscopy, hampering it from reaching its full potential for revealing the dynamic interactions in biology occurring at the single molecule level. Here we examine recent advances in the super-resolution imaging of living cells by reviewing recent breakthroughs in single molecule localization microscopy methods such as PALM and STORM to achieve this important goal.

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    05/01/11 | Rapid three-dimensional isotropic imaging of living cells using Bessel beam plane illumination.
    Planchon TA, Gao L, Milkie DE, Davidson MW, Galbraith JA, Galbraith CG, Betzig E
    Nature Methods. 2011 May;8(5):417-23. doi: 10.1038/nmeth.1586

    A key challenge when imaging living cells is how to noninvasively extract the most spatiotemporal information possible. Unlike popular wide-field and confocal methods, plane-illumination microscopy limits excitation to the information-rich vicinity of the focal plane, providing effective optical sectioning and high speed while minimizing out-of-focus background and premature photobleaching. Here we used scanned Bessel beams in conjunction with structured illumination and/or two-photon excitation to create thinner light sheets (<0.5 μm) better suited to three-dimensional (3D) subcellular imaging. As demonstrated by imaging the dynamics of mitochondria, filopodia, membrane ruffles, intracellular vesicles and mitotic chromosomes in live cells, the microscope currently offers 3D isotropic resolution down to \~{}0.3 μm, speeds up to nearly 200 image planes per second and the ability to noninvasively acquire hundreds of 3D data volumes from single living cells encompassing tens of thousands of image frames.

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    05/01/11 | Rapid three-dimensional isotropic imaging of living cells using Bessel beam plane illumination. (With commentary)
    Planchon TA, Gao L, Milkie DE, Davidson MW, Galbraith JA, Galbraith CG, Betzig E
    Nature Methods. 2011 May;8(5):417-23. doi: 10.1038/nmeth.1586

    A key challenge when imaging living cells is how to noninvasively extract the most spatiotemporal information possible. Unlike popular wide-field and confocal methods, plane-illumination microscopy limits excitation to the information-rich vicinity of the focal plane, providing effective optical sectioning and high speed while minimizing out-of-focus background and premature photobleaching. Here we used scanned Bessel beams in conjunction with structured illumination and/or two-photon excitation to create thinner light sheets (<0.5 μm) better suited to three-dimensional (3D) subcellular imaging. As demonstrated by imaging the dynamics of mitochondria, filopodia, membrane ruffles, intracellular vesicles and mitotic chromosomes in live cells, the microscope currently offers 3D isotropic resolution down to \~{}0.3 μm, speeds up to nearly 200 image planes per second and the ability to noninvasively acquire hundreds of 3D data volumes from single living cells encompassing tens of thousands of image frames.

    Commentary: Plane illumination microscopy has proven to be a powerful tool for studying multicellular organisms and their development at single cell resolution. However, the light sheets employed are usually too thick to provide much benefit for imaging organelles within single cultured cells. Here we introduce the use of scanned Bessel beams to create much thinner light sheets better suited to long-term dynamic live cell imaging. Such light sheets not only minimize photobleaching and phototoxicity at the sub-cellular level, but also provide axial resolution enhancement, yielding isotropic three dimensional spatial resolution. Numerous movies are provided to demonstrate the wealth of 4D information (x,y,x,t) that can be obtained from single living cells by the method. Besides providing an attractive alternative to spinning disk, AOD-driven, or line scan confocal microscopes for high speed live cell imaging, the Bessel microscope might serve as a valuable platform for superresolution microscopy (PALM, structured Illumination, or RESOLFT), since confinement of the excitation to the focal plane makes far better use of the limited fluorescence photon budget than does the traditional epi-illumination configuration.

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    Zlatic Lab
    04/28/11 | A combinatorial semaphorin code instructs the initial steps of sensory circuit assembly in the Drosophila CNS.
    Wu Z, Sweeney LB, Ayoob JC, Chak K, Andreone BJ, Ohyama T, Kerr R, Luo L, Zlatic M, Kolodkin AL
    Neuron. 2011 Apr 28;70(2):281-98. doi: 10.1016/j.neuron.2011.02.050

    Longitudinal axon fascicles within the Drosophila embryonic CNS provide connections between body segments and are required for coordinated neural signaling along the anterior-posterior axis. We show here that establishment of select CNS longitudinal tracts and formation of precise mechanosensory afferent innervation to the same CNS region are coordinately regulated by the secreted semaphorins Sema-2a and Sema-2b. Both Sema-2a and Sema-2b utilize the same neuronal receptor, plexin B (PlexB), but serve distinct guidance functions. Localized Sema-2b attraction promotes the initial assembly of a subset of CNS longitudinal projections and subsequent targeting of chordotonal sensory afferent axons to these same longitudinal connectives, whereas broader Sema-2a repulsion serves to prevent aberrant innervation. In the absence of Sema-2b or PlexB, chordotonal afferent connectivity within the CNS is severely disrupted, resulting in specific larval behavioral deficits. These results reveal that distinct semaphorin-mediated guidance functions converge at PlexB and are critical for functional neural circuit assembly.

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    04/22/11 | Real-time observation of transcription initiation and elongation on an endogenous yeast gene.
    Larson DR, Zenklusen D, Wu B, Chao JA, Singer RH
    Science. 2011 Apr 22;332(6028):475-8. doi: 10.1126/science.1202142

    Cellular messenger RNA levels are achieved by the combinatorial complexity of factors controlling transcription, yet the small number of molecules involved in these pathways fluctuates stochastically. It has not yet been experimentally possible to observe the activity of single polymerases on an endogenous gene to elucidate how these events occur in vivo. Here, we describe a method of fluctuation analysis of fluorescently labeled RNA to measure dynamics of nascent RNA–including initiation, elongation, and termination–at an active yeast locus. We find no transcriptional memory between initiation events, and elongation speed can vary by threefold throughout the cell cycle. By measuring the abundance and intranuclear mobility of an upstream transcription factor, we observe that the gene firing rate is directly determined by trans-activating factor search times.

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