Main Menu (Mobile)- Block

Main Menu - Block

janelia7_blocks-janelia7_fake_breadcrumb | block
Koyama Lab / Publications
general_search_page-panel_pane_1 | views_panes

18 Publications

Showing 1-10 of 18 results
Your Criteria:
    12/13/98 | Initiation of mitochondrial DNA replication by transcription and R-loop processing.
    Lee DY, Clayton DA
    The Journal of Biological Chemistry. 1998 Nov 13;273(46):30614-21. doi: 10.1101/gad.1352105

    The mitochondrial genome of eukaryotic cells is maintained by a mechanism distinct from that employed in the nucleus. Mitochondrial DNA replication at the leading-strand origin is coupled to transcription through the formation of an RNA-DNA hybrid known as an R-loop. In vivo and in vitro evidence has implicated an RNA processing enzyme, RNase MRP, in primer maturation. In our investigation of mammalian RNase MRP, we have analyzed its specific endoribonuclease activity on model R-loops. We demonstrate here that human RNase MRP cleaves this distinctly configured substrate at virtually all of the major DNA replication sites previously mapped in vivo. We further show that the processed RNA products remain stably base-paired to the template DNA strand and are functional for initiating DNA synthesis on a closed circular plasmid. Thus, in vitro initiation of leading-strand mtDNA synthesis requires only the actions of RNA polymerase and RNase MRP for the generation of replication primers.

    View Publication Page
    12/03/98 | A role of Ultrabithorax in morphological differences between Drosophila species.
    Stern DL
    Nature. 1998 Dec 3;396(6710):463-6. doi: 10.1038/24863

    The mechanisms underlying the evolution of morphology are poorly understood. Distantly related taxa sometimes exhibit correlations between morphological differences and patterns of gene expression, but such comparisons cannot establish how mechanisms evolve to generate diverse morphologies. Answers to these questions require resolution of the nature of developmental evolution within and between closely related species. Here I show how the detailed regulation of the Hox gene Ultrabithorax patterns trichomes on the posterior femur of the second leg in Drosophila melanogaster, and that evolution of Ultrabithorax has contributed to divergence of this feature among closely related species. The cis-regulatory regions of Ultrabithorax, and not the protein itself, appear to have evolved. This study provides experimental evidence that cis-regulatory evolution is one way in which conserved proteins have promoted morphological diversity.

    View Publication Page

    Several early studies suggested that spikes can be generated in the dendrites of CA1 pyramidal neurons, but their functional significance and the conditions under which they occur remain poorly understood. Here, we provide direct evidence from simultaneous dendritic and somatic patch-pipette recordings that excitatory synaptic inputs can elicit dendritic sodium spikes prior to axonal action potential initiation in hippocampal CA1 pyramidal neurons. Both the probability and amplitude of dendritic spikes depended on the previous synaptic and firing history of the cell. Moreover, some dendritic spikes occurred in the absence of somatic action potentials, indicating that their propagation to the soma and axon is unreliable. We show that dendritic spikes contribute a variable depolarization that summates with the synaptic potential and can act as a trigger for action potential initiation in the axon.

    View Publication Page
    Sternson Lab
    10/08/98 | An acid- and base-stable o-nitrobenzyl photolabile linker for solid phase organic synthesis.
    Sternson SM, Schreiber SL
    Tetrahedron Letters. 1998 Oct 8;39:7451-54

    The synthesis of an o-nitrobenzyl photolabile linker (1) from o-nitrobenzaldehyde is described, and the efficiency of its light-mediated (365 nm) cleavage is found to be comparable to related, previously developed systems. In contrast, 1 is shown to be stable to acid, base, and Lewis acid/amine combinations while the previously developed linker 2 is shown to degrade under the latter two conditions.

    View Publication Page
    09/01/98 | The Drosophila genome project: a progress report.
    Rubin GM
    Trends in Genetics. 1998 Sep;14(9):340-3
    06/12/98 | Ethanol intoxication in Drosophila: genetic and pharmacological evidence for regulation by the cAMP signaling pathway.
    Moore MS, DeZazzo J, Luk AY, Tully T, Singh CM, Heberlein U
    Cell. 1998 Jun 12;93(6):997-1007

    Upon exposure to ethanol, Drosophila display behaviors that are similar to ethanol intoxication in rodents and humans. Using an inebriometer to measure ethanol-induced loss of postural control, we identified cheapdate, a mutant with enhanced sensitivity to ethanol. Genetic and molecular analyses revealed that cheapdate is an allele of the memory mutant amnesiac. amnesiac has been postulated to encode a neuropeptide that activates the cAMP pathway. Consistent with this, we find that enhanced ethanol sensitivity of cheapdate can be reversed by treatment with agents that increase cAMP levels or PKA activity. Conversely, genetic or pharmacological reduction in PKA activity results in increased sensitivity to ethanol. Taken together, our results provide functional evidence for the involvement of the cAMP signal transduction pathway in the behavioral response to intoxicating levels of ethanol.

    View Publication Page
    06/01/98 | Drosophila EcR-B ecdysone receptor isoforms are required for larval molting and for neuron remodeling during metamorphosis.
    Schubiger M, Wade AA, Carney GE, Truman JW, Bender M
    Development. 1998 Jun;125(11):2053-62

    During the metamorphic reorganization of the insect central nervous system, the steroid hormone 20-hydroxyecdysone induces a wide spectrum of cellular responses including neuronal proliferation, maturation, cell death and the remodeling of larval neurons into their adult forms. In Drosophila, expression of specific ecdysone receptor (EcR) isoforms has been correlated with particular responses, suggesting that different EcR isoforms may govern distinct steroid-induced responses in these cells. We have used imprecise excision of a P element to create EcR deletion mutants that remove the EcR-B promoter and therefore should lack EcR-B1 and EcR-B2 expression but retain EcR-A expression. Most of these EcR-B mutant animals show defects in larval molting, arresting at the boundaries between the three larval stages, while a smaller percentage of EcR-B mutants survive into the early stages of metamorphosis. Remodeling of larval neurons at metamorphosis begins with the pruning back of larval-specific dendrites and occurs as these cells are expressing high levels of EcR-B1 and little EcR-A. This pruning response is blocked in the EcR-B mutants despite the fact that adult-specific neurons, which normally express only EcR-A, can progress in their development. These observations support the hypothesis that different EcR isoforms control cell-type-specific responses during remodeling of the nervous system at metamorphosis.

    View Publication Page
    06/01/98 | Ecdysteroids govern two phases of eye development during metamorphosis of the moth, Manduca sexta.
    Champlin DT, Truman JW
    Development. 1998 Jun;125(11):2009-18

    The eye primordium of the moth, Manduca sexta, shows two different developmental responses to ecdysteroids depending on the concentration to which it is exposed. Tonic exposure to moderate levels of 20-hydroxyecdysone (20E) or its precursor, ecdysone, are required for progression of the morphogenetic furrow across the primordium. Proliferation, cell-type specification and organization of immature ommatidial clusters occur in conjunction with furrow progression. These events can be reversibly started or stopped in cultured primordia simply by adjusting levels of ecdysteroid to be above or below a critical threshold concentration. In contrast, high levels of 20E cause maturation of the photoreceptors and the support cells that comprise the ommatidia. Ommatidial maturation normally occurs after the furrow has crossed the primordium, but premature exposure to high levels of 20E at any time causes precocious maturation. In such cases, the furrow arrests irreversibly and cells behind the furrow produce a well-formed, but miniature, eye. Precocious and catastrophic metamorphosis occurs throughout such animals, suggesting that ecdysteroids control development of other tissues in a manner similar to the eye. The threshold concentrations of 20E required for furrow progression versus ommatidial maturation differ by about 17-fold. This capacity to regulate distinct phases of development by different concentrations of a single hormone is probably achieved by differential sensitivity of target gene promoters to induction by the hormone-bound receptor(s).

    View Publication Page
    05/15/98 | Determinants of voltage attenuation in neocortical pyramidal neuron dendrites.
    Stuart G, Spruston N
    J Neurosci. 1998 May 15;18(10):3501-10

    How effectively synaptic and regenerative potentials propagate within neurons depends critically on the membrane properties and intracellular resistivity of the dendritic tree. These properties therefore are important determinants of neuronal function. Here we use simultaneous whole-cell patch-pipette recordings from the soma and apical dendrite of neocortical layer 5 pyramidal neurons to directly measure voltage attenuation in cortical neurons. When combined with morphologically realistic compartmental models of the same cells, the data suggest that the intracellular resistivity of neocortical pyramidal neurons is relatively low ( approximately 70 to 100 Omegacm), but that voltage attenuation is substantial because of nonuniformly distributed resting conductances present at a higher density in the distal apical dendrites. These conductances, which were largely blocked by bath application of CsCl (5 mM), significantly increased steady-state voltage attenuation and decreased EPSP integral and peak in a manner that depended on the location of the synapse. Together these findings suggest that nonuniformly distributed Cs-sensitive and -insensitive resting conductances generate a "leaky" apical dendrite, which differentially influences the integration of spatially segregated synaptic inputs.

    View Publication Page
    05/15/98 | Mutual regulation of decapentaplegic and hedgehog during the initiation of differentiation in the Drosophila retina.
    Borod ER, Heberlein U
    Devopemental Biology. 1998 May 15;197(2):187-97. doi: 10.1006/dbio.1998.8888

    Neuronal differentiation in the Drosophila retinal primordium, the eye imaginal disc, begins at the posterior tip of the disc and progresses anteriorly as a wave. The morphogenetic furrow (MF) marks the boundary between undifferentiated anterior cells and differentiating posterior cells. Anterior progression of differentiation is driven by Hedgehog, synthesized by cells located posterior to the MF. We report here that hedgehog (hh), which is expressed prior to the start of differentiation along the disc's posterior margin, also plays a crucial role in the initiation of differentiation. Using a temperature-sensitive allele we show that hh is normally required at the posterior margin to maintain the expression of decapentaplegic (dpp) and of the proneural gene atonal. In addition, we find that ectopic differentiation driven by ectopic dpp expression or loss of wingless function requires hh. Consistent with this is our observation that ectopic dpp induces the expression of hh along the anterior margin even in the absence of differentiation. Taken together, these data reveal a novel positive regulatory loop between dpp and hh that is essential for the initiation of differentiation in the eye disc.

    View Publication Page