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Search Results: 1 - 10 of 45127 matches for " Michael Granato "
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Plexin A3 and Turnout Regulate Motor Axonal Branch Morphogenesis in Zebrafish
Rajiv Sainath, Michael Granato
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0054071
Abstract: During embryogenesis motor axons navigate to their target muscles, where individual motor axons develop complex branch morphologies. The mechanisms that control axonal branching morphogenesis have been studied intensively, yet it still remains unclear when branches begin to form or how branch locations are determined. Live cell imaging of individual zebrafish motor axons reveals that the first axonal branches are generated at the ventral extent of the myotome via bifurcation of the growth cone. Subsequent branches are generated by collateral branching restricted to their synaptic target field along the distal portion of the axon. This precisely timed and spatially restricted branching process is disrupted in turnout mutants we identified in a forward genetic screen. Molecular genetic mapping positioned the turnout mutation within a 300 kb region encompassing eight annotated genes, however sequence analysis of all eight open reading frames failed to unambiguously identify the turnout mutation. Chimeric analysis and single cell labeling reveal that turnout function is required cell non-autonomously for intraspinal motor axon guidance and peripheral branch formation. turnout mutant motor axons form the first branch on time via growth cone bifurcation, but unlike wild-type they form collateral branches precociously, when the growth cone is still navigating towards the ventral myotome. These precocious collateral branches emerge along the proximal region of the axon shaft typically devoid of branches, and they develop into stable, permanent branches. Furthermore, we find that null mutants of the guidance receptor plexin A3 display identical motor axon branching defects, and time lapse analysis reveals that precocious branch formation in turnout and plexin A3 mutants is due to increased stability of otherwise short-lived axonal protrusions. Thus, plexin A3 dependent intrinsic and turnout dependent extrinsic mechanisms suppress collateral branch morphogenesis by destabilizing membrane protrusions before the growth cone completes navigation into the synaptic target field.
Temporal and Spatial Requirements of unplugged/MuSK Function during Zebrafish Neuromuscular Development
Lili Jing,Laura R. Gordon,Elena Shtibin,Michael Granato
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0008843
Abstract: One of the earliest events in neuromuscular junction (NMJ) development is the accumulation of acetylcholine receptor (AChR) at the center of muscle cells. The unplugged/MuSK (muscle specific tyrosine kinase) gene is essential to initiate AChR clustering but also to restrict approaching growth cones to the muscle center, thereby coordinating pre- and postsynaptic development. To determine how unplugged/MuSK signaling coordinates these two processes, we examined the temporal and spatial requirements of unplugged/MuSK in zebrafish embryos using heat-shock inducible transgenes. Here, we show that despite its expression in muscle cells from the time they differentiate, unplugged/MuSK activity is first required just prior to the appearance of AChR clusters to simultaneously induce AChR accumulation and to guide motor axons. Furthermore, we demonstrate that ectopic expression of unplugged/MuSK throughout the muscle membrane results in wildtype-like AChR prepattern and neuromuscular synapses in the central region of muscle cells. We propose that AChR prepatterning and axonal guidance are spatio-temporally coordinated through common unplugged/MuSK signals, and that additional factor(s) restrict unplugged/MuSK signaling to a central muscle zone critical for establishing mid-muscle synaptogenesis.
The Tumor Suppressor Gene Retinoblastoma-1 Is Required for Retinotectal Development and Visual Function in Zebrafish
Michael Gyda equal contributor,Marc Wolman equal contributor,Kristin Lorent,Michael Granato
PLOS Genetics , 2012, DOI: 10.1371/journal.pgen.1003106
Abstract: Mutations in the retinoblastoma tumor suppressor gene (rb1) cause both sporadic and familial forms of childhood retinoblastoma. Despite its clinical relevance, the roles of rb1 during normal retinotectal development and function are not well understood. We have identified mutations in the zebrafish space cadet locus that lead to a premature truncation of the rb1 gene, identical to known mutations in sporadic and familial forms of retinoblastoma. In wild-type embryos, axons of early born retinal ganglion cells (RGC) pioneer the retinotectal tract to guide later born RGC axons. In rb1 deficient embryos, these early born RGCs show a delay in cell cycle exit, causing a transient deficit of differentiated RGCs. As a result, later born mutant RGC axons initially fail to exit the retina, resulting in optic nerve hypoplasia. A significant fraction of mutant RGC axons eventually exit the retina, but then frequently project to the incorrect optic tectum. Although rb1 mutants eventually establish basic retinotectal connectivity, behavioral analysis reveals that mutants exhibit deficits in distinct, visually guided behaviors. Thus, our analysis of zebrafish rb1 mutants reveals a previously unknown yet critical role for rb1 during retinotectal tract development and visual function.
Molecular-Genetic Mapping of Zebrafish Mutants with Variable Phenotypic Penetrance
Roshan A. Jain, Marc A. Wolman, Lauren A. Schmidt, Harold A. Burgess, Michael Granato
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0026510
Abstract: Forward genetic screens in vertebrates are powerful tools to generate models relevant to human diseases, including neuropsychiatric disorders. Variability in phenotypic penetrance and expressivity is common in these disorders and behavioral mutant models, making their molecular-genetic mapping a formidable task. Using a ‘phenotyping by segregation’ strategy, we molecularly map the hypersensitive zebrafish houdini mutant despite its variable phenotypic penetrance, providing a generally applicable strategy to map zebrafish mutants with subtle phenotypes.
A Novel Role for Lh3 Dependent ECM Modifications during Neural Crest Cell Migration in Zebrafish
Santanu Banerjee, Jesse Isaacman-Beck, Valerie A. Schneider, Michael Granato
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0054609
Abstract: During vertebrate development, trunk neural crest cells delaminate along the entire length of the dorsal neural tube and initially migrate as a non-segmented sheet. As they enter the somites, neural crest cells rearrange into spatially restricted segmental streams. Extracellular matrix components are likely to play critical roles in this transition from a sheet-like to a stream-like mode of migration, yet the extracellular matrix components and their modifying enzymes critical for this transition are largely unknown. Here, we identified the glycosyltransferase Lh3, known to modify extracellular matrix components, and its presumptive substrate Collagen18A1, to provide extrinsic signals critical for neural crest cells to transition from a sheet-like migration behavior to migrating as a segmental stream. Using live cell imaging we show that in lh3 null mutants, neural crest cells fail to transition from a sheet to a stream, and that they consequently enter the somites as multiple streams, or stall shortly after entering the somites. Moreover, we demonstrate that transgenic expression of lh3 in a small subset of somitic cells adjacent to where neural crest cells switch from sheet to stream migration restores segmental neural crest cell migration. Finally, we show that knockdown of the presumptive Lh3 substrate Collagen18A1 recapitulates the neural crest cell migration defects observed in lh3 mutants, consistent with the notion that Lh3 exerts its effect on neural crest cell migration by regulating post-translational modifications of Collagen18A1. Together these data suggest that Lh3–Collagen18A1 dependent ECM modifications regulate the transition of trunk neural crest cells from a non-segmental sheet like migration mode to a segmental stream migration mode.
Numerical study of resistivity scaling in pi junction granular superconductors
Granato, Enzo;
Brazilian Journal of Physics , 2003, DOI: 10.1590/S0103-97332003000400005
Abstract: numerical simulations based on monte carlo dynamics are used to investigate the resistivity behavior of granular superconductors containing a random distribution of p junctions, as in superconducting materials with d-wave symmetry. the presence of p junctions leads to quenched in circulating currents (chiralities) and to chiral glass behavior at low temperatures, even without an external magnetic field. an xy spin glass model in the phase representation is used to determine the current-voltage characteristics and critical exponents of the resistivity transition. in two dimensions, the linear resistivity is nonzero at finite temperatures and the dynamic scaling analysis of the nonlinear resistivity is consistent with a phase transition at zero temperature. in three dimensions, we find a transition at finite temperatures below which the linear resistivity vanishes and the corresponding critical exponents are determined from the scaling analysis. the results are in good agreement with langevin simulations in the phase representation. the dynamic exponent z is significantly different from previous results obtained in the vortex representation.
Zero-temperature superconducting transition in frustrated Josephson-junction arrays
Granato, Enzo;
Brazilian Journal of Physics , 2002, DOI: 10.1590/S0103-97332002000400006
Abstract: the critical behavior of zero-temperature superconducting transitions which can occur in disordered two-dimensional josephson-junction arrays are investigated by monte carlo calculation of ground-state excitation energies and dynamical simulation of the current-voltage characteristics at nonzero temperatures. two models of arrays in an applied magnetic field are considered: random dilution of junctions and random couplings with half-ux quantum per plaquette f = 1/2. abovea critical value of disorder, finite-size scaling of the excitation energies indicates a zero-temperature transition and allows an estimate of the critical disorder and the thermal correlation length exponent characterizing the transition. current-voltage scaling is consistent with the zero-temperature transition. the linear resistance is nonzero at finite temperatures but nonlinear behavior sets in at a characteristic current density determined by the thermal critical exponent. the zero-temperature transition provides an explanation of the washing out of structure for increasing disorder at f = 1/2 while it remains for f = 0, observed experimentally in supercondoucting wire networks.
A problemática da infec o pelo citomegalovírus em pacientes imunodeprimidos
Granato Celso
Revista Brasileira de Hematologia e Hemoterapia , 2001,
Abstract:
Zero-temperature superconducting transition in frustrated Josephson-junction arrays
Granato Enzo
Brazilian Journal of Physics , 2002,
Abstract: The critical behavior of zero-temperature superconducting transitions which can occur in disordered two-dimensional Josephson-junction arrays are investigated by Monte Carlo calculation of ground-state excitation energies and dynamical simulation of the current-voltage characteristics at nonzero temperatures. Two models of arrays in an applied magnetic field are considered: random dilution of junctions and random couplings with half-ux quantum per plaquette f = 1/2. Abovea critical value of disorder, finite-size scaling of the excitation energies indicates a zero-temperature transition and allows an estimate of the critical disorder and the thermal correlation length exponent characterizing the transition. Current-voltage scaling is consistent with the zero-temperature transition. The linear resistance is nonzero at finite temperatures but nonlinear behavior sets in at a characteristic current density determined by the thermal critical exponent. The zero-temperature transition provides an explanation of the washing out of structure for increasing disorder at f = 1/2 while it remains for f = 0, observed experimentally in supercondoucting wire networks.
Numerical study of resistivity scaling in p junction granular superconductors
Granato Enzo
Brazilian Journal of Physics , 2003,
Abstract: Numerical simulations based on Monte Carlo dynamics are used to investigate the resistivity behavior of granular superconductors containing a random distribution of pi junctions, as in superconducting materials with d-wave symmetry. The presence of pi junctions leads to quenched in circulating currents (chiralities) and to chiral glass behavior at low temperatures, even without an external magnetic field. An XY spin glass model in the phase representation is used to determine the current-voltage characteristics and critical exponents of the resistivity transition. In two dimensions, the linear resistivity is nonzero at finite temperatures and the dynamic scaling analysis of the nonlinear resistivity is consistent with a phase transition at zero temperature. In three dimensions, we find a transition at finite temperatures below which the linear resistivity vanishes and the corresponding critical exponents are determined from the scaling analysis. The results are in good agreement with Langevin simulations in the phase representation. The dynamic exponent z is significantly different from previous results obtained in the vortex representation.
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