title: Two synaptojanin 1 isoforms are recruited to clathrin-coated pits at different stages.
abstract: Phosphoinositides are thought to play an important role in clathrin-coated pit (CCP) dynamics. Biochemical and structural studies have shown a direct interaction of phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] with endocytic clathrin adaptors, whereas functional studies using cell-free systems or intact cells have demonstrated the importance of PI(4,5)P2 synthesis and dephosphorylation in clathrin coating and uncoating, respectively. Furthermore, genetic manipulations of kinases and phosphatases involved in PI(4,5)P2 metabolism result in major defects in synaptic vesicle recycling and other forms of clathrin-dependent endocytosis. However, live imaging studies of these enzymes at CCPs have not been conducted. We have used multicolor total internal reflection fluorescence microscopy (TIRFM) to visualize the spatial-temporal recruitment of synaptojanin 1 (SJ1), a polyphosphoinositide phosphatase, and its binding partner endophilin to CCPs. Strikingly, we observed differential temporal recruitment of the two major SJ1 splice variants to CCPs. The 145-kDa isoform, the predominant isoform expressed in the brain, was rapidly recruited as a "burst," together with endophilin, at a late stage of CCP formation. In contrast, the nonneuronal ubiquitously expressed 170-kDa isoform of SJ1 was present at all stages of CCP formation. These results raise the possibility that dynamic phosphoinositide metabolism may occur throughout the lifetime of a CCP.
authors.affiliation: Department of Cell Biology, Kavli Institute for Neuroscience and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: Rushika M
authors.initials: RM
authors.lastname: Perera
authors.forename: Roberto
authors.initials: R
authors.lastname: Zoncu
authors.forename: Louise
authors.initials: L
authors.lastname: Lucast
authors.forename: Pietro
authors.initials: P
authors.lastname: De Camilli
authors.forename: Derek
authors.initials: D
authors.lastname: Toomre
mesh_terms: D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D022163:Clathrin-Coated Vesicles / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D000217:Acyltransferases; C018764:2-acylglycerophosphate acyltransferase; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases