Showing papers by "Istituto Italiano di Tecnologia published in 2006"

Dynamic regulation of ERK2 nuclear translocation and mobility in living cells.

Abstract: The extracellular signal-regulated protein kinase ERK1/2 is a crucial effector linking extracellular stimuli to cellular responses: upon phosphorylation ERK [also known as mitogen-activated protein kinase P42/P44 (MAPK)] concentrates in the nucleus where it activates specific programs of gene expression. Notwithstanding the importance of this process, little is known about the modalities, time course and regulation of ERK exchange between nucleus and cytoplasm in living cells. We visualized the dynamic of nuclear translocation by expressing low levels (<150 nM) of fluorescently tagged ERK2 in living fibroblasts. Time-lapse imaging demonstrated that nuclear concentration can change bidirectionally with a time constant of a few minutes. The increase of nuclear concentration requires continuous MEK (also known as MAPK kinase) activity upstream of ERK and is rapidly reduced by the operation of phosphatases. We measured quantitatively the speed of ERK2 shuttling between nucleus and cytoplasm and determined that shuttling accelerated after ERK activation, becoming fast enough not to be rate-limiting for translocation. Finally, we demonstrated that ERK2 did not diffuse freely in the nucleus and that diffusion was further impeded after phosphorylation, suggesting the formation of complexes of low mobility. These results show that nucleocytoplasmic trafficking of ERK2 and its mobility are dynamically regulated in living cells.

James: A Humanoid Robot Acting over an Unstructured World

Abstract: The recent trend of humanoid robotics research has been deeply influenced by concepts such as embodiment, embodied interaction and emergence. In our view, these concepts, beside shaping the controlling intelligence, should guide the very design process of the modern humanoid robotic platforms. In this paper, we discuss how these principles have been applied to the design of a humanoid robot called James. James has been designed by considering an object manipulation scenario and by explicitly taking into account embodiment, interaction, and the exploitation of smart design solutions. The robot is equipped with moving eyes, neck, arm and hand, and a rich set of sensors, enabling proprioceptive, kinesthetic, tactile and visual sensing. A great deal of effort has been devoted to the design of the hand and touch sensors. Experiments, e.g., tactile object classification, have been performed, to validate the quality of the robot perceptual capabilities

The synapsin domain E accelerates the exoendocytotic cycle of synaptic vesicles in cerebellar Purkinje cells.

Abstract: Synapsins are synaptic-vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release and excitability of neuronal networks. Mutation of synapsin genes in mouse and human causes epilepsy. To understand the role of the highly conserved synapsin domain E in the dynamics of release from mammalian inhibitory neurons, we generated mice that selectively overexpress the most conserved part of this domain in cerebellar Purkinje cells. At Purkinje-cell-nuclear-neuron synapses, transgenic mice were more resistant to depression induced by short or prolonged high-frequency stimulations. The increased synaptic performance was accompanied by accelerated release kinetics and shorter synaptic delay. Despite a marked decrease in the total number of synaptic vesicles, vesicles at the active zone were preserved or slightly increased. The data indicate that synapsin domain E increases synaptic efficiency by accelerating both the kinetics of exocytosis and the rate of synaptic vesicle cycling and decreasing depression at the inhibitory Purkinje-cell-nuclear-neuron synapse. These effects may increase the sensitivity of postsynaptic neurons to inhibition and thereby contribute to the inhibitory control of network activity.

Implementation of Listing's Law for a Tendon Driven Robot Eye

Abstract: This paper presents a model for a tendon driven robot eye designed to emulate the actual saccadic and smooth pursuit movements performed by human eyes. Physiological saccadic motions obey the so called Listing's Law which constrains the admissible eye's angular velocities. The paper discusses conditions making possible to implement the Listing's Law on a purely mechanical basis, i.e. without active control.

Design of a Humanoid Robot Eye: Models and Experiments

Abstract: Eye movements have the goal of optimizing visual perception, therefore the investigation of eye motion strategies play an important role in the design of humanoid robot eye systems Saccades in humans and primates is a significant class of ocular motions, which obey the so called Listing's Law, which constrains the admissible eye's angular velocities and ensure zero torsion during motion In this paper we present a model of the eye plant proving that Listing's Law implementation is strongly related with the geometry of the eye and its actuation system (extraocular muscles) The proposed model has been used to provide the guidelines for the design of a tendon driven humanoid robot eye Experimental tests, presented in this paper, validate the model by performing a quantitative comparison of the performance of the robot eye with physiological data measured in humans and primates during saccades