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1.  Krüppel Mediates the Selective Rebalancing of Ion Channel Expression 
Neuron  2014;82(3):537-544.
Ion channel gene expression can vary substantially among neurons of a given type, even though neuron-type-specific firing properties remain stable and reproducible. The mechanisms that modulate ion channel gene expression and stabilize neural firing properties are unknown. In Drosophila, we demonstrate that loss of the Shal potassium channel induces the compensatory rebalancing of ion channel expression including, but not limited to, the enhanced expression and function of Shaker and slowpoke. Using genomic and network modeling approaches combined with genetic and electrophysiological assays, we demonstrate that the transcription factor Krüppel is necessary for the homeostatic modulation of Shaker and slowpoke expression. Remarkably, Krüppel induction is specific to the loss of Shal, not being observed in five other potassium channel mutants that cause enhanced neuronal excitability. Thus, homeostatic signaling systems responsible for rebalancing ion channel expression can be selectively induced after the loss or impairment of a specific ion channel.
PMCID: PMC4104505  PMID: 24811378
2.  Nmnat exerts neuroprotective effects in dendrites and axons 
Dendrites can be maintained for extended periods of time after they initially establish coverage of their receptive field. The long-term maintenance of dendrites underlies synaptic connectivity, but how neurons establish and then maintain their dendritic arborization patterns throughout development is not well understood. Here, we show that the NAD synthase Nicotinamide mononucleotide adenylyltransferase (Nmnat) is cell-autonomously required for maintaining type-specific dendritic coverage of Drosophila dendritic arborization (da) sensory neurons. In nmnat heterozygous mutants, dendritic arborization patterns of class IV da neurons are properly established before increased retraction and decreased growth of terminal branches lead to progressive defects in dendritic coverage during later stages of development. Although sensory axons are largely intact in nmnat heterozygotes, complete loss of nmnat function causes severe axonal degeneration, demonstrating differential requirements for nmnat dosage in the maintenance of dendritic arborization patterns and axonal integrity. Overexpression of Nmnat suppresses dendrite maintenance defects associated with loss of the tumor suppressor kinase Warts (Wts), providing evidence that Nmnat, in addition to its neuroprotective role in axons, can function as a protective factor against progressive dendritic loss. Moreover, motor neurons deficient for nmnat show progressive defects in both dendrites and axons. Our studies reveal an essential role for endogenous Nmnat function in the maintenance of both axonal and dendritic integrity and present evidence of a broad neuroprotective role for Nmnat in the central nervous system.
PMCID: PMC3152617  PMID: 21596138
Nmnat; dendrite; axon; motor neuron; neurodegeneration; Drosophila
3.  Optimized high-throughput screen for Hepatitis C virus translation inhibitors 
Journal of Biomolecular Screening  2011;16(2):211-220.
Hepatitis C virus (HCV) is a considerable global health problem for which new classes of therapeutics are needed. We developed a high-throughput assay to identify compounds that selectively block translation initiation from the HCV internal ribosome entry site (HCV IRES). Rabbit reticulocyte lysate conditions were optimized to faithfully report on authentic HCV IRES-dependent translation relative to a 5′ capped mRNA control. We screened a library of ~430,000 small molecules for IRES inhibition, leading to ~1,700 initial hits. After secondary counter screening the vast majority of hits proved to be luciferase and general translation inhibitors. Despite well-optimized in vitro translation conditions, in the end we found no selective HCV IRES inhibitors but did discover a new scaffold of general translation inhibitor. The analysis of these molecules, and the finding that a large fraction of false positives resulted from off-target effects, highlights the challenges inherent in screens for RNA-specific inhibitors.
PMCID: PMC3260011  PMID: 21297107
Hepatitis C virus (HCV); IRES; luciferase; high-throughput screen; rabbit reticulocyte lysate
4.  Synthesis and Preliminary Evaluation of Duocarmycin Analogues Incorporating the 1,2,11,11a-Tetrahydrocyclopropa[c]naphtho[2,3-e]indol-4-one (CNI) and 1,2,11,11a-Tetrahydrocyclopropa[c]naphtho[1,2-e]indol-4-one (iso-CNI) Alkylation Subunits 
Tetrahedron  2009;65(33):6591-6599.
Efficient syntheses and a preliminary evaluation of 1,2,11,11a-tetrahydrocyclopropa[c]-naphtho[2,3-e]indole (CNI) and 1,2,11,11a-tetrahydrocyclopropa[c]naphtho[1,2-e]indole (iso-CNI), and their derivatives containing an anthracene and phenanthrene variant of the CC-1065 or duocarmycin alkylation subunit are detailed.
PMCID: PMC2713043  PMID: 20161204
5.  The microRNA bantam functions in epithelial cells to regulate scaling growth of dendrite arbors in Drosophila sensory neurons 
Neuron  2009;63(6):788-802.
In addition to establishing dendritic coverage of the receptive field, neurons need to adjust their dendritic arbors to match changes of the receptive field. Here we show that dendrite arborization (da) sensory neurons establish dendritic coverage of the body wall early in Drosophila larval development and then grow in precise proportion to their substrate, the underlying body wall epithelium, as the larva more than triples in length. This phenomenon, referred to as scaling growth of dendrites, requires the function of the microRNA (miRNA) bantam (ban) in the epithelial cells rather than the da neurons themselves. We further show that ban in epithelial cells dampens Akt kinase activity in adjacent neurons to influence dendrite growth. This signaling between epithelial cells and neurons receiving sensory input from the body wall synchronizes their growth to ensure proper dendritic coverage of the receptive field.
PMCID: PMC2772869  PMID: 19778508

Results 1-5 (5)