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179 Janelia Publications

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    12/31/20 | An unbiased template of the Drosophila brain and ventral nerve cord.
    Bogovic JA, Otsuna H, Heinrich L, Ito M, Jeter J, Meissner G, Nern A, Colonell J, Malkesman O, Ito K, Saalfeld S
    PLoS One. 2020 Dec 31;15(12):e0236495. doi: 10.1371/journal.pone.0236495

    The fruit fly Drosophila melanogaster is an important model organism for neuroscience with a wide array of genetic tools that enable the mapping of individual neurons and neural subtypes. Brain templates are essential for comparative biological studies because they enable analyzing many individuals in a common reference space. Several central brain templates exist for Drosophila, but every one is either biased, uses sub-optimal tissue preparation, is imaged at low resolution, or does not account for artifacts. No publicly available Drosophila ventral nerve cord template currently exists. In this work, we created high-resolution templates of the Drosophila brain and ventral nerve cord using the best-available technologies for imaging, artifact correction, stitching, and template construction using groupwise registration. We evaluated our central brain template against the four most competitive, publicly available brain templates and demonstrate that ours enables more accurate registration with fewer local deformations in shorter time.

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    The prefrontal cortex (PFC)'s functions are thought to include working memory, as its activity can reflect information that must be temporarily maintained to realize the current goal. We designed a flexible spatial working memory task that required rats to navigate - after distractions and a delay - to multiple possible goal locations from different starting points and via multiple routes. This made the current goal location the key variable to remember, instead of a particular direction or route to the goal. However, across a broad population of PFC neurons, we found no evidence of current-goal-specific memory in any previously reported form - that is differences in the rate, sequence, phase, or covariance of firing. This suggests that such patterns do not hold working memory in the PFC when information must be employed flexibly. Instead, the PFC grouped locations representing behaviorally equivalent task features together, consistent with a role in encoding long-term knowledge of task structure.

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    11/23/20 | The structural basis of Rubisco phase separation in the pyrenoid.
    He S, Chou H, Matthies D, Wunder T, Meyer MT, Atkinson N, Martinez-Sanchez A, Jeffrey PD, Port SA, Patena W, He G, Chen VK, Hughson FM, McCormick AJ, Mueller-Cajar O, Engel BD, Yu Z, Jonikas MC
    Nature Plants. 2020 Nov 23:. doi: 10.1038/s41477-020-00811-y

    Approximately one-third of global CO fixation occurs in a phase-separated algal organelle called the pyrenoid. The existing data suggest that the pyrenoid forms by the phase separation of the CO-fixing enzyme Rubisco with a linker protein; however, the molecular interactions underlying this phase separation remain unknown. Here we present the structural basis of the interactions between Rubisco and its intrinsically disordered linker protein Essential Pyrenoid Component 1 (EPYC1) in the model alga Chlamydomonas reinhardtii. We find that EPYC1 consists of five evenly spaced Rubisco-binding regions that share sequence similarity. Single-particle cryo-electron microscopy of these regions in complex with Rubisco indicates that each Rubisco holoenzyme has eight binding sites for EPYC1, one on each Rubisco small subunit. Interface mutations disrupt binding, phase separation and pyrenoid formation. Cryo-electron tomography supports a model in which EPYC1 and Rubisco form a codependent multivalent network of specific low-affinity bonds, giving the matrix liquid-like properties. Our results advance the structural and functional understanding of the phase separation underlying the pyrenoid, an organelle that plays a fundamental role in the global carbon cycle.

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    12/16/20 | DNA damage alters nuclear mechanics through chromatin reorganization.
    Dos Santos Á, Cook AW, Gough RE, Schilling M, Olszok NA, Brown I, Wang L, Aaron J, Martin-Fernandez ML, Rehfeldt F, Toseland CP
    Nucleic Acids Research. 2020 Dec 16:. doi: 10.1093/nar/gkaa1202

    DNA double-strand breaks drive genomic instability. However, it remains unknown how these processes may affect the biomechanical properties of the nucleus and what role nuclear mechanics play in DNA damage and repair efficiency. Here, we have used Atomic Force Microscopy to investigate nuclear mechanical changes, arising from externally induced DNA damage. We found that nuclear stiffness is significantly reduced after cisplatin treatment, as a consequence of DNA damage signalling. This softening was linked to global chromatin decondensation, which improves molecular diffusion within the organelle. We propose that this can increase recruitment for repair factors. Interestingly, we also found that reduction of nuclear tension, through cytoskeletal relaxation, has a protective role to the cell and reduces accumulation of DNA damage. Overall, these changes protect against further genomic instability and promote DNA repair. We propose that these processes may underpin the development of drug resistance.

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    12/15/20 | In situ differentiation of iridophore crystallotypes underlies zebrafish stripe patterning.
    Gur D, Bain EJ, Johnson KR, Aman AJ, Pasoili HA, Flynn JD, Allen MC, Deheyn DD, Lee JC, Lippincott-Schwartz J, Parichy DM
    Nature Communications. 2020 Dec 15;11(1):6391. doi: 10.1038/s41467-020-20088-1

    Skin color patterns are ubiquitous in nature, impact social behavior, predator avoidance, and protection from ultraviolet irradiation. A leading model system for vertebrate skin patterning is the zebrafish; its alternating blue stripes and yellow interstripes depend on light-reflecting cells called iridophores. It was suggested that the zebrafish's color pattern arises from a single type of iridophore migrating differentially to stripes and interstripes. However, here we find that iridophores do not migrate between stripes and interstripes but instead differentiate and proliferate in-place, based on their micro-environment. RNA-sequencing analysis further reveals that stripe and interstripe iridophores have different transcriptomic states, while cryogenic-scanning-electron-microscopy and micro-X-ray diffraction identify different crystal-arrays architectures, indicating that stripe and interstripe iridophores are different cell types. Based on these results, we present an alternative model of skin patterning in zebrafish in which distinct iridophore crystallotypes containing specialized, physiologically responsive, organelles arise in stripe and interstripe by in-situ differentiation.

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    12/14/20 | Structure of the radial spoke head and insights into its role in mechanoregulation of ciliary beating.
    Grossman-Haham I, Coudray N, Yu Z, Wang F, Zhang N, Bhabha G, Vale RD
    Nature Structural Molecular Biology. 2020 Dec 14:. doi: 10.1038/s41594-020-00519-9

    Motile cilia power cell locomotion and drive extracellular fluid flow by propagating bending waves from their base to tip. The coordinated bending of cilia requires mechanoregulation by the radial spoke (RS) protein complexes and the microtubule central pair (CP). Despite their importance for ciliary motility across eukaryotes, the molecular function of the RSs is unknown. Here, we reconstituted the Chlamydomonas reinhardtii RS head that abuts the CP and determined its structure using single-particle cryo-EM to 3.1-Å resolution, revealing a flat, negatively charged surface supported by a rigid core of tightly intertwined proteins. Mutations in this core, corresponding to those involved in human ciliopathies, compromised the stability of the recombinant complex, providing a molecular basis for disease. Partially reversing the negative charge on the RS surface impaired motility in C. reinhardtii. We propose that the RS-head architecture is well-suited for mechanoregulation of ciliary beating through physical collisions with the CP.

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    12/13/20 | Two-parameter single-molecule analysis for measurement of chromatin mobility.
    Lerner J, Gomez-Garcia PA, McCarthy RL, Liu Z, Lakadamyali M, Zaret KS
    STAR Protocols. 2020 Dec 13;1(3):100223. doi: 10.1016/j.xpro.2020.100223

    This protocol provides a two-parameter analysis of single-molecule tracking (SMT) trajectories of Halo-tagged histones in living adherent cell lines and unveils a chromatin mobility landscape composed of five chromatin types, ranging from low to high mobility. When the analysis is applied to Halo-tagged, chromatin-binding proteins, it associates chromatin interaction properties with known functions in a way that previously used SMT parameters did not. For complete information on the use and execution of this protocol, please refer to Lerner et al. (2020).

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    12/07/20 | The claustrum.
    Smith JB, Lee AK, Jackson J
    Current Biology. 2020 Dec 07;30(23):R1401-R1406. doi: 10.1016/j.cub.2020.09.069

    The claustrum is a brain region that has been investigated for over 200 years, yet its precise function remains unknown. In the final posthumously released article of Francis Crick, written with Christof Koch, the claustrum was suggested to be critically linked to consciousness. Though the claustrum remained relatively obscure throughout the last half century, it has enjoyed a renewed interest in the last 15 years since Crick and Koch's article. During this time, the claustrum, like many other brain regions, has been studied with the myriad of modern systems neuroscience tools that have been made available by the intersection of genetic and viral technologies. This has uncovered new information about its anatomical connectivity and physiological properties and begun to reveal aspects of its function. From these studies, one clear consensus has emerged which supports Crick and Koch's primary interest in the claustrum: the claustrum has widespread extensive connectivity with the entire cerebral cortex, suggesting a prominent role in 'higher order processes'.

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    12/02/20 | Central processing of leg proprioception in Drosophila.
    Agrawal S, Dickinson ES, Sustar A, Gurung P, Shepherd D, Truman JW, Tuthill JC
    eLife. 2020 Dec 02;9:. doi: 10.7554/eLife.60299

    Proprioception, the sense of self-movement and position, is mediated by mechanosensory neurons that detect diverse features of body kinematics. Although proprioceptive feedback is crucial for accurate motor control, little is known about how downstream circuits transform limb sensory information to guide motor output. Here, we investigate neural circuits in that process proprioceptive information from the fly leg. We identify three cell-types from distinct developmental lineages that are positioned to receive input from proprioceptor subtypes encoding tibia position, movement, and vibration. 13Bα neurons encode femur-tibia joint angle and mediate postural changes in tibia position. 9Aα neurons also drive changes in leg posture, but encode a combination of directional movement, high frequency vibration, and joint angle. Activating 10Bα neurons, which encode tibia vibration at specific joint angles, elicits pausing in walking flies. Altogether, our results reveal that central circuits integrate information across proprioceptor subtypes to construct complex sensorimotor representations that mediate diverse behaviors, including reflexive control of limb posture and detection of leg vibration.

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    12/02/20 | Cryo-EM structure of the inhibited (10S) form of myosin II.
    Yang S, Tiwari P, Lee KH, Sato O, Ikebe M, Padrón R, Craig R
    Nature. 2020 Dec 02;588(7838):521-25. doi: 10.1038/s41586-020-3007-0

    Myosin II is the motor protein that enables muscle cells to contract and nonmuscle cells to move and change shape. The molecule has two identical heads attached to an elongated tail, and can exist in two conformations: 10S and 6S, named for their sedimentation coefficients. The 6S conformation has an extended tail and assembles into polymeric filaments, which pull on actin filaments to generate force and motion. In 10S myosin, the tail is folded into three segments and the heads bend back and interact with each other and the tail, creating a compact conformation in which ATPase activity, actin activation and filament assembly are all highly inhibited. This switched-off structure appears to function as a key energy-conserving storage molecule in muscle and nonmuscle cells, which can be activated to form functional filaments as needed-but the mechanism of its inhibition is not understood. Here we have solved the structure of smooth muscle 10S myosin by cryo-electron microscopy with sufficient resolution to enable improved understanding of the function of the head and tail regions of the molecule and of the key intramolecular contacts that cause inhibition. Our results suggest an atomic model for the off state of myosin II, for its activation and unfolding by phosphorylation, and for understanding the clustering of disease-causing mutations near sites of intramolecular interaction.

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