? Actin filaments and microtubules are dynamic cytoskeletal polymers that have important roles in cell physiology and determine cell morphology. The complex cellular morphology of neurons is directly related to the function of neurons in the nervous system. Thus, neurons provide an excellent model system for investigating the dynamics of the cytoskeleton as it relates to cellular functions. Actin filaments are of fundamental importance to the development and maintenance of connectivity patterns between neurons, and the formation and function of synapses. Neurons constantly deliver new cytoskeletal proteins synthesized in the cell body to the distal axon through axonal transport. The process of axonal transport is required for maintenance of a functional nervous system and is impaired in a variety of disease states. Filopodia are slender finger-like cellular projections that are strictly dependent on actin filaments and are required for axon guidance and synapse formation. Understanding the mechanisms responsible for filopodial initiation is thus of direct relevance to the understanding of regeneration and the maintenance of nervous system function. This proposal presents studies aimed at (1) determining the form (e.g., filaments versus monomers) of actin transport in axons, and (2) determining the actin-based mechanism of filopodia initiation. The form in which cytoskeletal proteins are transported is controversial. From in vitro studies using neurons transfected with EGFP-actin, we provide preliminary descriptive evidence suggestive of the transport of actin filaments and experimental evidence in favor of the transport of monomeric actin. A series of studies is detailed to experimentally test the hypothesis that actin filaments are the form of actin transport. Additionally, based on live imaging of EGFP-actin in axons and growth cones we have identified the presence of spontaneously formed actin puncta that serve as precursors to filopodial formation. These observations provide a model system for investigating the dynamic cytoskeletal basis of filopodial formation in living neurons. We present studies aimed at determining the role of extra-cellular signals, signaling pathways, and microtubules in regulating the earliest events in filopodial initiation. ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS048090-02
Application #
6989085
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Riddle, Robert D
Project Start
2004-12-06
Project End
2009-11-30
Budget Start
2005-12-01
Budget End
2006-11-30
Support Year
2
Fiscal Year
2006
Total Cost
$303,349
Indirect Cost
Name
Drexel University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
002604817
City
Philadelphia
State
PA
Country
United States
Zip Code
19104
Gallo, Gianluca (2013) Mechanisms underlying the initiation and dynamics of neuronal filopodia: from neurite formation to synaptogenesis. Int Rev Cell Mol Biol 301:95-156
Donnelly, Christopher J; Park, Michael; Spillane, Mirela et al. (2013) Axonally synthesized ?-actin and GAP-43 proteins support distinct modes of axonal growth. J Neurosci 33:3311-22
Greif, Karen F; Asabere, Nana; Lutz, Gordon J et al. (2013) Synaptotagmin-1 promotes the formation of axonal filopodia and branches along the developing axons of forebrain neurons. Dev Neurobiol 73:27-44
Hu, Jianli; Bai, Xiaobo; Bowen, Jonathan R et al. (2012) Septin-driven coordination of actin and microtubule remodeling regulates the collateral branching of axons. Curr Biol 22:1109-15
Spillane, Mirela; Ketschek, Andrea; Donnelly, Chris J et al. (2012) Nerve growth factor-induced formation of axonal filopodia and collateral branches involves the intra-axonal synthesis of regulators of the actin-nucleating Arp2/3 complex. J Neurosci 32:17671-89
Bowen, Jonathan R; Hwang, Daniel; Bai, Xiaobo et al. (2011) Septin GTPases spatially guide microtubule organization and plus end dynamics in polarizing epithelia. J Cell Biol 194:187-97
Spillane, Mirela; Ketschek, Andrea; Jones, Steven L et al. (2011) The actin nucleating Arp2/3 complex contributes to the formation of axonal filopodia and branches through the regulation of actin patch precursors to filopodia. Dev Neurobiol 71:747-58
DeMay, Bradley S; Bai, Xiaobo; Howard, Louisa et al. (2011) Septin filaments exhibit a dynamic, paired organization that is conserved from yeast to mammals. J Cell Biol 193:1065-81
Gallo, Gianluca (2011) The cytoskeletal and signaling mechanisms of axon collateral branching. Dev Neurobiol 71:201-20
Ketschek, Andrea; Gallo, Gianluca (2010) Nerve growth factor induces axonal filopodia through localized microdomains of phosphoinositide 3-kinase activity that drive the formation of cytoskeletal precursors to filopodia. J Neurosci 30:12185-97

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