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3 Janelia Publications

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    Menon Lab
    11/24/11 | Multi-scale correlation structure of gene expression in the brain.
    Hawrylycz M, Ng L, Page D, Morris J, Lau C, Faber S, Faber V, Sunkin S, Menon V, Lein E, Jones A
    Neural networks : the official journal of the International Neural Network Society. 2011 Nov;24(9):933-42. doi: 10.1016/j.neunet.2011.06.012

    The mammalian brain is best understood as a multi-scale hierarchical neural system, in the sense that connection and function occur on multiple scales from micro to macro. Modern genomic-scale expression profiling can provide insight into methodologies that elucidate this architecture. We present a methodology for understanding the relationship of gene expression and neuroanatomy based on correlation between gene expression profiles across tissue samples. A resulting tool, NeuroBlast, can identify networks of genes co-expressed within or across neuroanatomic structures. The method applies to any data modality that can be mapped with sufficient spatial resolution, and provides a computation technique to elucidate neuroanatomy via patterns of gene expression on spatial and temporal scales. In addition, from the perspective of spatial location, we discuss a complementary technique that identifies gene classes that contribute to defining anatomic patterns.

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    Menon Lab
    11/01/11 | Frozen tissue can provide reproducible proteomic results of subcellular fractionation.
    Lim J, Menon V, Bitzer M, Miller LM, Madrid-Aliste C, Weiss LM, Fiser A, Angeletti RH
    Analytical biochemistry. 2011 Nov 1;418(1):78-84. doi: 10.1016/j.ab.2011.06.045

    Differential detergent fractionation (DDF) is frequently used to partition fresh cells and tissues into distinct compartments. We have tested whether DDF can reproducibly extract and fractionate cellular protein components from frozen tissues. Frozen kidneys were sequentially extracted with three different buffer systems. Analysis of the three fractions with liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified 1693 proteins, some of which were common to all fractions and others of which were unique to specific fractions. Normalized spectral index (SI(N)) values obtained from these data were compared to evaluate both the reproducibility of the method and the efficiency of enrichment. SI(N) values between replicate fractions demonstrated a high correlation, confirming the reproducibility of the method. Correlation coefficients across the three fractions were significantly lower than those for the replicates, supporting the capability of DDF to differentially fractionate proteins into separate compartments. Subcellular annotation of the proteins identified in each fraction demonstrated a significant enrichment of cytoplasmic, cell membrane, and nuclear proteins in the three respective buffer system fractions. We conclude that DDF can be applied to frozen tissue to generate reproducible proteome coverage discriminating subcellular compartments. This demonstrates the feasibility of analyzing cellular compartment-specific proteins in archived tissue samples with the simple DDF method.

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    Menon Lab
    04/01/11 | Hallmarks of molecular action of microtubule stabilizing agents: effects of epothilone B, ixabepilone, peloruside A, and laulimalide on microtubule conformation.
    Khrapunovich-Baine M, Menon V, Yang CH, Northcote PT, Miller JH, Angeletti RH, Fiser A, Horwitz SB, Xiao H
    The Journal of biological chemistry. 2011 Apr 1;286(13):11765-78. doi: 10.1074/jbc.M110.162214

    Microtubule stabilizing agents (MSAs) comprise a class of drugs that bind to microtubule (MT) polymers and stabilize them against disassembly. Several of these agents are currently in clinical use as anticancer drugs, whereas others are in various stages of development. Nonetheless, there is insufficient knowledge about the molecular modes of their action. Recent studies from our laboratory utilizing hydrogen-deuterium exchange in combination with mass spectrometry (MS) provide new information on the conformational effects of Taxol and discodermolide on microtubules isolated from chicken erythrocytes (CET). We report here a comprehensive analysis of the effects of epothilone B, ixabepilone (IXEMPRA(TM)), laulimalide, and peloruside A on CET conformation. The results of our comparative hydrogen-deuterium exchange MS studies indicate that all MSAs have significant conformational effects on the C-terminal H12 helix of α-tubulin, which is a likely molecular mechanism for the previously observed modulations of MT interactions with microtubule-associated and motor proteins. More importantly, the major mode of MT stabilization by MSAs is the tightening of the longitudinal interactions between two adjacent αβ-tubulin heterodimers at the interdimer interface. In contrast to previous observations reported with bovine brain tubulin, the lateral interactions between the adjacent protofilaments in CET are particularly strongly stabilized by peloruside A and laulimalide, drugs that bind outside the taxane site. This not only highlights the significance of tubulin isotype composition in modulating drug effects on MT conformation and stability but also provides a potential explanation for the synergy observed when combinations of taxane and alternative site binding drugs are used.

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