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39 Publications

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    10/25/02 | Sum-frequency spectroscopy of electronic resonances on a chiral surface monolayer of bi-naphthol.
    Ji N
    Physical Review B. 2002 Oct 25;66:165415. doi: 10.1103/PhysRevB.66.165415

    We study chiral response in optical sum-frequency generation near electronic resonances from a 1,1 ′ −bi−2  -naphthol (BN) monolayer adsorbed on water. The polarization dependence of the spectra indicates that the molecules are well oriented at the surface with their symmetry axis along the surface normal. Orientational ordering effectively enhances the chiral response per BN molecule. The results can be quantitatively understood with a simple coupled-oscillator model for BN.

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    10/01/02 | Basic transcription element binding protein is a thyroid hormone-regulated transcription factor expressed during metamorphosis in Xenopus laevis.
    Hoopfer ED, Huang L, Denver RJ
    Development, Growth & Differentiation. 2002 Oct;44:365-81

    Basic transcription element binding protein (BTEB) is a member of the Krüppel family of zinc finger transcription factors. It has been shown that BTEB plays a role in promoting neuronal process formation during postembryonic development. In the present study, the biochemical properties, transactivation function, and the developmental and hormone-regulated expression of BTEB in Xenopus laevis (xBTEB) are described. xBTEB binds the GC-rich basic transcription element (BTE) with high affinity and functions as a transcriptional activator on promoters containing multiple or single GC boxes. xBTEB mRNA levels increase in the tadpole brain, intestine and tail during metamorphosis, and are correlated with tissue-specific morphological and biochemical transformations. xBTEB mRNA expression can be induced precociously in premetamorphic tadpole tissues by treatment with thyroid hormone. In situ hybridization histochemistry showed that thyroid hormone upregulates xBTEB mRNA throughout the brain of premetamorphic tadpoles, with the highest expression found in the subventricular zones of the telencephalon, diencephalon, optic tectum, cerebellum and spinal cord. xBTEB protein parallels changes in its mRNA, and it was found that xBTEB is not expressed in mitotic cells in the developing brain, but is expressed just distal to the proliferative zone, supporting the hypothesis that this protein plays a role in neural cell differentiation.

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    Adult insects achieve their final form shortly after adult eclosion by the combined effects of specialized behaviors that generate increased blood pressure, which causes cuticular expansion, and hormones, which plasticize and then tan the cuticle. We examined the molecular mechanisms contributing to these processes in Drosophila by analyzing mutants for the rickets gene. These flies fail to initiate the behavioral and tanning processes that normally follow ecdysis. Sequencing of rickets mutants and STS mapping of deficiencies confirmed that rickets encodes the glycoprotein hormone receptor DLGR2. Although rickets mutants produce and release the insect-tanning hormone bursicon, they do not melanize when injected with extracts containing bursicon. In contrast, mutants do melanize in response to injection of an analog of cyclic AMP, the second messenger for bursicon. Hence, rickets appears to encode a component of the bursicon response pathway, probably the bursicon receptor itself. Mutants also have a behavioral deficit in that they fail to initiate the behavioral program for wing expansion. A set of decapitation experiments utilizing rickets mutants and flies that lack cells containing the neuropeptide eclosion hormone, reveals a multicomponent control to the activation of this behavioral program.

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    Tjian Lab
    09/01/02 | Redundant role of tissue-selective TAF(II)105 in B lymphocytes.
    Freiman RN, Albright SR, Chu LE, Zheng S, Liang H, Sha WC, Tjian R
    Molecular and Cellular Biology. 2002 Sep;22(18):6564-72. doi: 10.1073/pnas.1100640108

    Regulated gene expression is a complex process achieved through the function of multiple protein factors acting in concert at a given promoter. The transcription factor TFIID is a central component of the machinery regulating mRNA synthesis by RNA polymerase II. This large multiprotein complex is composed of the TATA box binding protein (TBP) and several TBP-associated factors (TAF(II)s). The recent discovery of multiple TBP-related factors and tissue-specific TAF(II)s suggests the existence of specialized TFIID complexes that likely play a critical role in regulating transcription in a gene- and tissue-specific manner. The tissue-selective factor TAF(II)105 was originally identified as a component of TFIID derived from a human B-cell line. In this report we demonstrate the specific induction of TAF(II)105 in cultured B cells in response to bacterial lipopolysaccharide (LPS). To examine the in vivo role of TAF(II)105, we have generated TAF(II)105-null mice by homologous recombination. Here we show that B-lymphocyte development is largely unaffected by the absence of TAF(II)105. TAF(II)105-null B cells can proliferate in response to LPS, produce relatively normal levels of resting antibodies, and can mount an immune response by producing antigen-specific antibodies in response to immunization. Taken together, we conclude that the function of TAF(II)105 in B cells is likely redundant with the function of other TAF(II)105-related cellular proteins.

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    07/19/02 | Oscillations and sparsening of odor representations in the mushroom body.
    Perez-Orive J, Mazor O, Turner GC, Cassenaer S, Wilson RI, Laurent G
    Science (New York, N.Y.). 2002 Jul 19;297(5580):359-65. doi: 10.1126/science.1070502

    In the insect olfactory system, oscillatory synchronization is functionally relevant and reflects the coherent activation of dynamic neural assemblies. We examined the role of such oscillatory synchronization in information transfer between networks in this system. The antennal lobe is the obligatory relay for olfactory afferent signals and generates oscillatory output. The mushroom body is responsible for formation and retrieval of olfactory and other memories. The format of odor representations differs significantly across these structures. Whereas representations are dense, dynamic, and seemingly redundant in the antennal lobe, they are sparse and carried by more selective neurons in the mushroom body. This transformation relies on a combination of oscillatory dynamics and intrinsic and circuit properties that act together to selectively filter and synthesize the output from the antennal lobe. These results provide direct support for the functional relevance of correlation codes and shed some light on the role of oscillatory synchronization in sensory networks.

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    07/18/02 | Dendritic spikes as a mechanism for cooperative long-term potentiation.
    Golding NL, Staff NP, Spruston N
    Nature. 2002 Jul 18;418(6895):326-31. doi: 10.1038/nature00854

    Strengthening of synaptic connections following coincident pre- and postsynaptic activity was proposed by Hebb as a cellular mechanism for learning. Contemporary models assume that multiple synapses must act cooperatively to induce the postsynaptic activity required for hebbian synaptic plasticity. One mechanism for the implementation of this cooperation is action potential firing, which begins in the axon, but which can influence synaptic potentiation following active backpropagation into dendrites. Backpropagation is limited, however, and action potentials often fail to invade the most distal dendrites. Here we show that long-term potentiation of synapses on the distal dendrites of hippocampal CA1 pyramidal neurons does require cooperative synaptic inputs, but does not require axonal action potential firing and backpropagation. Rather, locally generated and spatially restricted regenerative potentials (dendritic spikes) contribute to the postsynaptic depolarization and calcium entry necessary to trigger potentiation of distal synapses. We find that this mechanism can also function at proximal synapses, suggesting that dendritic spikes participate generally in a form of synaptic potentiation that does not require postsynaptic action potential firing in the axon.

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    Tjian Lab
    06/21/02 | Neurodegeneration. A glutamine-rich trail leads to transcription factors.
    Freiman RN, Tjian R
    Science . 2002 Jun 21;296(5576):2149-50. doi: 10.1073/pnas.1100640108
    06/18/02 | Evidence for large domains of similarly expressed genes in the Drosophila genome.
    Spellman PT, Rubin GM
    Journal of Biology. 2002 Jun 18;1(1):5. doi: 10.1186/gb-2007-8-7-r145

    Transcriptional regulation in eukaryotes generally operates at the level of individual genes. Regulation of sets of adjacent genes by mechanisms operating at the level of chromosomal domains has been demonstrated in a number of cases, but the fraction of genes in the genome subject to regulation at this level is unknown.

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    Magee Lab
    06/15/02 | Phosphorylation-dependent differences in the activation properties of distal and proximal dendritic Na+ channels in rat CA1 hippocampal neurons.
    Gasparini S, Magee JC
    The Journal of Physiology. 2002 Jun 15;541(Pt 3):665-72. doi: 10.1002/cbic.201000254

    {At distal dendritic locations, the threshold for action potential generation is higher and the amplitude of back-propagating spikes is decreased. To study whether these characteristics depend upon Na+ channels, their voltage-dependent properties at proximal and distal dendritic locations were compared in CA1 hippocampal neurons. Distal Na+ channels activated at more hyperpolarized voltages than proximal (half-activation voltages were -20.4 +/- 2.4 mV vs. -12.0 +/- 1.7 mV for distal and proximal patches, respectively

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    06/13/02 | Theoretical neuroscience: state of the art.
    Chklovskii DB
    Neuron. 2002 Jun 13;34:863-4