title: Transmembrane agrin regulates filopodia in rat hippocampal neurons in culture.
abstract: Filopodia mediate axon guidance, neurite branching and synapse formation, but the membrane molecules that regulate neuronal filopodia in response to extracellular cues are largely unknown. The transmembrane isoform of the proteoglycan agrin, expressed predominantly in the CNS, may regulate neurite outgrowth, synapse formation and excitatory signaling. Here we demonstrate that agrin positively regulates neuronal filopodia. Over-expression of TM-agrin caused the formation of excess filopodia on neurites of hippocampal neurons cultured 1-6 days. Conversely, suppression of agrin expression by siRNA reduced the number of filopodia. Time lapse analysis indicated that endogenous TM-agrin regulates filopodia by increasing their stability and initiation. The N-terminal half of agrin was necessary for induction of filopodia, and over-expression of TM-agrin in a neuronal cell line increased Cdc42 activation, suggesting a role for Cdc42 downstream of agrin. By positively regulating filopodia in developing neurons, TM-agrin may influence the pattern of neurite outgrowth and synapse formation.
authors.affiliation: Laboratory of Cell Biology, National Heart Lung and Blood Institute, NIH, 50 South Drive, Bldg. 50, Rm 3318, Bethesda, MD 20892, USA.
authors.forename: Seumas
authors.initials: S
authors.lastname: McCroskery
authors.forename: Amal
authors.initials: A
authors.lastname: Chaudhry
authors.forename: Lin
authors.initials: L
authors.lastname: Lin
authors.forename: Mathew P
authors.initials: MP
authors.lastname: Daniels
mesh_terms: D018171:Agrin / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation; D006624:Hippocampus / Q000166:cytology*; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure*; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D018171:Agrin; D034741:RNA, Small Interfering; D020764:cdc42 GTP-Binding Protein