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4 Janelia Publications

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    10/16/15 | Opposing intrinsic temporal gradients guide neural stem cell production of varied neuronal fates.
    Liu Z, Yang C, Sugino K, Fu C, Liu L, Yao X, Lee LP, Lee T
    Science (New York, N.Y.). 2015 Oct 16;350(6258):317-20. doi: 10.1126/science.aad1886

    Neural stem cells show age-dependent developmental potentials, as evidenced by their production of distinct neuron types at different developmental times. Drosophila neuroblasts produce long, stereotyped lineages of neurons. We searched for factors that could regulate neural temporal fate by RNA-sequencing lineage-specific neuroblasts at various developmental times. We found that two RNA-binding proteins, IGF-II mRNA-binding protein (Imp) and Syncrip (Syp), display opposing high-to-low and low-to-high temporal gradients with lineage-specific temporal dynamics. Imp and Syp promote early and late fates, respectively, in both a slowly progressing and a rapidly changing lineage. Imp and Syp control neuronal fates in the mushroom body lineages by regulating the temporal transcription factor Chinmo translation. Together, the opposing Imp/Syp gradients encode stem cell age, specifying multiple cell fates within a lineage.

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    Freeman LabSvoboda Lab
    04/21/15 | A cellular resolution map of barrel cortex activity during tactile behavior.
    Peron SP, Freeman J, Iyer V, Guo C, Svoboda K
    Neuron. 2015 Apr 21;86(3):783-99. doi: 10.1016/j.neuron.2015.03.027

    Comprehensive measurement of neural activity remains challenging due to the large numbers of neurons in each brain area. We used volumetric two-photon imaging in mice expressing GCaMP6s and nuclear red fluorescent proteins to sample activity in 75% of superficial barrel cortex neurons across the relevant cortical columns, approximately 12,000 neurons per animal, during performance of a single whisker object localization task. Task-related activity peaked during object palpation. An encoding model related activity to behavioral variables. In the column corresponding to the spared whisker, 300 layer (L) 2/3 pyramidal neurons (17%) each encoded touch and whisker movements. Touch representation declined by half in surrounding columns; whisker movement representation was unchanged. Following the emergence of stereotyped task-related movement, sensory representations showed no measurable plasticity. Touch direction was topographically organized, with distinct organization for passive and active touch. Our work reveals sparse and spatially intermingled representations of multiple tactile features.

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    03/11/15 | Dual-channel circuit mapping reveals sensorimotor convergence in the primary motor cortex.
    Hooks BM, Lin JY, Guo C, Svoboda K
    The Journal of Neuroscience. 2015 Mar 11;35(10):4418-26. doi: 10.1523/JNEUROSCI.3741-14.2015

    Cortical cells integrate synaptic input from multiple sources, but how these different inputs are distributed across individual neurons is largely unknown. Differences in input might account for diverse responses in neighboring neurons during behavior. We present a strategy for comparing the strengths of multiple types of input onto the same neuron. We developed methods for independent dual-channel photostimulation of synaptic inputs using ChR2 together with ReaChR, a red-shifted channelrhodopsin. We used dual-channel photostimulation to probe convergence of sensory information in the mouse primary motor cortex. Input from somatosensory cortex and thalamus converges in individual neurons. Similarly, inputs from distinct somatotopic regions of the somatosensory cortex are integrated at the level of single motor cortex neurons. We next developed a ReaChR transgenic mouse under the control of both Flp- and Cre-recombinases that is an effective tool for circuit mapping. Our approach to dual-channel photostimulation enables quantitative comparison of the strengths of multiple pathways across all length scales of the brain.

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    12/10/14 | Live imaging of endogenous PSD-95 using ENABLED: a conditional strategy to fluorescently label endogenous proteins.
    Fortin DA, Tillo SE, Yang G, Rah J, Melander JB, Bai S, Soler-Cedeño O, Qin M, Zemelman BV, Guo C, Mao T, Zhong H
    Journal of Neuroscience. 2014 Dec 10;34(50):16698-712. doi: 10.1523/JNEUROSCI.3888-14.2014

    Stoichiometric labeling of endogenous synaptic proteins for high-contrast live-cell imaging in brain tissue remains challenging. Here, we describe a conditional mouse genetic strategy termed endogenous labeling via exon duplication (ENABLED), which can be used to fluorescently label endogenous proteins with near ideal properties in all neurons, a sparse subset of neurons, or specific neuronal subtypes. We used this method to label the postsynaptic density protein PSD-95 with mVenus without overexpression side effects. We demonstrated that mVenus-tagged PSD-95 is functionally equivalent to wild-type PSD-95 and that PSD-95 is present in nearly all dendritic spines in CA1 neurons. Within spines, while PSD-95 exhibited low mobility under basal conditions, its levels could be regulated by chronic changes in neuronal activity. Notably, labeled PSD-95 also allowed us to visualize and unambiguously examine otherwise-unidentifiable excitatory shaft synapses in aspiny neurons, such as parvalbumin-positive interneurons and dopaminergic neurons. Our results demonstrate that the ENABLED strategy provides a valuable new approach to study the dynamics of endogenous synaptic proteins in vivo.

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