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4 Publications

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    09/25/19 | Rational design of fluorogenic and spontaneously blinking labels for super-resolution imaging.
    Zheng Q, Ayala AX, Chung I, Weigel AV, Ranjan A, Falco N, Grimm JB, Tkachuk AN, Wu C, Lippincott-Schwartz J, Singer RH, Lavis LD
    ACS Central Science. 2019 Sep 25;5(9):1602-1613. doi: 10.1021/acscentsci.9b00676

    Rhodamine dyes exist in equilibrium between a fluorescent zwitterion and a nonfluorescent lactone. Tuning this equilibrium toward the nonfluorescent lactone form can improve cell-permeability and allow creation of "fluorogenic" compounds-ligands that shift to the fluorescent zwitterion upon binding a biomolecular target. An archetype fluorogenic dye is the far-red tetramethyl-Si-rhodamine (SiR), which has been used to create exceptionally useful labels for advanced microscopy. Here, we develop a quantitative framework for the development of new fluorogenic dyes, determining that the lactone-zwitterion equilibrium constant () is sufficient to predict fluorogenicity. This rubric emerged from our analysis of known fluorophores and yielded new fluorescent and fluorogenic labels with improved performance in cellular imaging experiments. We then designed a novel fluorophore-Janelia Fluor 526 (JF)-with SiR-like properties but shorter fluorescence excitation and emission wavelengths. JF is a versatile scaffold for fluorogenic probes including ligands for self-labeling tags, stains for endogenous structures, and spontaneously blinking labels for super-resolution immunofluorescence. JF constitutes a new label for advanced microscopy experiments, and our quantitative framework will enable the rational design of other fluorogenic probes for bioimaging.

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    Singer Lab
    09/23/19 | Mamo decodes hierarchical temporal gradients into terminal neuronal fate.
    Liu L, Long X, Yang C, Miyares RL, Sugino K, Singer RH, Lee T
    Elife. 2019 Sep 23;8:. doi: 10.7554/eLife.48056

    Temporal patterning is a seminal method of expanding neuronal diversity. Here we unravel a mechanism decoding neural stem cell temporal gene expression and transforming it into discrete neuronal fates. This mechanism is characterized by hierarchical gene expression. First, neuroblasts express opposing temporal gradients of RNA-binding proteins, Imp and Syp. These proteins promote or inhibit translation, yielding a descending neuronal gradient. Together, first and second-layer temporal factors define a temporal expression window of BTB-zinc finger nuclear protein, Mamo. The precise temporal induction of Mamo is achieved via both transcriptional and post-transcriptional regulation. Finally, Mamo is essential for the temporally defined, terminal identity of α'/β' mushroom body neurons and identity maintenance. We describe a straightforward paradigm of temporal fate specification where diverse neuronal fates are defined via integrating multiple layers of gene regulation. The neurodevelopmental roles of orthologous/related mammalian genes suggest a fundamental conservation of this mechanism in brain development.

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    Truman LabSinger Lab
    03/26/19 | Neurotransmitter identity is acquired in a lineage-restricted manner in the Drosophila CNS.
    Lacin H, Chen H, Long X, Singer RH, Lee T, Truman JW
    Elife. 2019 Mar 26;8:. doi: 10.7554/eLife.43701

    The vast majority of the adult fly ventral nerve cord is composed of 34 hemilineages, which are clusters of lineally related neurons. Neurons in these hemilineages use one of the three fast-acting neurotransmitters (acetylcholine, GABA, or glutamate) for communication. We generated a comprehensive neurotransmitter usage map for the entire ventral nerve cord. We did not find any cases of neurons using more than one neurotransmitter, but found that the acetylcholine specific gene ChAT is transcribed in many glutamatergic and GABAergic neurons, but these transcripts typically do not leave the nucleus and are not translated. Importantly, our work uncovered a simple rule: All neurons within a hemilineage use the same neurotransmitter. Thus, neurotransmitter identity is acquired at the stem cell level. Our detailed transmitter- usage/lineage identity map will be a great resource for studying the developmental basis of behavior and deciphering how neuronal circuits function to regulate behavior.

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    03/08/19 | Neural evolution of context-dependent fly song.
    Ding Y, Lillvis JL, Cande J, Berman GJ, Arthur BJ, Long X, Xu M, Dickson BJ, Stern DL
    Current Biology : CB. 2019 Mar 08;29(7):1089-99. doi: 10.1016/j.cub.2019.02.019

    It is unclear where in the nervous system evolutionary changes tend to occur. To localize the source of neural evolution that has generated divergent behaviors, we developed a new approach to label and functionally manipulate homologous neurons across Drosophila species. We examined homologous descending neurons that drive courtship song in two species that sing divergent song types and localized relevant evolutionary changes in circuit function downstream of the intrinsic physiology of these descending neurons. This evolutionary change causes different species to produce divergent motor patterns in similar social contexts. Artificial stimulation of these descending neurons drives multiple song types, suggesting that multifunctional properties of song circuits may facilitate rapid evolution of song types.

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