title: Calcium-triggered exit of F-actin and IP(3) 3-kinase A from dendritic spines is rapid and reversible.
abstract: The structure of the actin cytoskeleton in dendritic spines is thought to underlie some forms of synaptic plasticity. We have used fixed and live-cell imaging in rat primary hippocampal cultures to characterize the synaptic dynamics of the F-actin binding protein inositol trisphosphate 3-kinase A (IP3K), which is localized in the spines of pyramidal neurons derived from the CA1 region. IP3K was intensely concentrated as puncta in spine heads when Ca(2+) influx was low, but rapidly and reversibly redistributed to a striated morphology in the main dendrite when Ca(2+) influx was high. Glutamate stimulated the exit of IP3K from spines within 10 s, and re-entry following blockage of Ca(2+) influx commenced within a minute; IP3K appeared to remain associated with F-actin throughout this process. Ca(2+)-triggered F-actin relocalization occurred in about 90% of the cells expressing IP3K endogenously, and was modulated by the synaptic activity of the cultures, suggesting that it is a physiological process. F-actin relocalization was blocked by cytochalasins, jasplakinolide and by the over-expression of actin fused to green fluorescent protein. We also used deconvolution microscopy to visualize the relationship between F-actin and endoplasmic reticulum inside dendritic spines, revealing a delicate microorganization of IP3K near the Ca(2+) stores. We conclude that Ca(2+) influx into the spines of CA1 pyramidal neurons triggers the rapid and reversible retraction of F-actin from the dendritic spine head. This process contributes to changes in spine F-actin shape and content during synaptic activity, and might also regulate spine IP3 signals.
authors.affiliation: Department of Pharmacology, University of Cambridge CB2 1PD, UK. mschell@usuhs.mil
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Schell
authors.forename: Robin F
authors.initials: RF
authors.lastname: Irvine
mesh_terms: D000199:Actins / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000648:ultrastructure; D049229:Dendritic Spines / Q000378:metabolism / Q000648:ultrastructure*; D003952:Diagnostic Imaging; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D009473:Neuronal Plasticity / Q000502:physiology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D051381:Rats; D014162:Transfection
chemical_list: D000199:Actins; D018698:Glutamic Acid; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D002118:Calcium