title: SPAR2, a novel SPAR-related protein with GAP activity for Rap1 and Rap2.
abstract: Spine-associated RapGAP 2 (SPAR2) is a novel GTPase activating protein (GAP) for the small GTPase Rap that shows significant sequence homology to SPAR, a synaptic RapGAP that was reported to regulate spine morphology in hippocampal neurons. SPAR2, like SPAR, interacts with the recently described synaptic scaffolding protein ProSAP-interacting protein (ProSAPiP), which in turn binds to the PDZ domain of ProSAP/Shank post-synaptic density proteins. In subcellular fractionation experiments, SPAR2 is enriched in synaptosomes and post-synaptic density fractions indicating that it is a synaptic protein. Furthermore, we could show using in vitro GAP assays that SPAR2 has GAP activity for Rap1 and Rap2. Expression in COS-7 cells, however, revealed different actin-binding properties of SPAR2 and SPAR. Additionally, over-expression of SPAR2 in cultured hippocampal neurons did not affect spine morphology as it was reported for SPAR. In situ hybridization studies also revealed a differential tissue distribution of SPAR and SPAR2 with SPAR2 transcripts being mainly expressed in cerebellar and hippocampal granule cells. Moreover, in the cerebellum SPAR2 is developmentally regulated with a peak of expression around the period of synapse formation. Our results imply that SPAR2 is a new RapGAP with specific functions in cerebellar and hippocampal granule cells.
authors.affiliation: Project Group Neuroplasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany. spilker@ifn-magdeburg.de
authors.forename: Christina
authors.initials: C
authors.lastname: Spilker
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Acuña Sanhueza
authors.forename: Tobias M
authors.initials: TM
authors.lastname: Böckers
authors.forename: Michael R
authors.initials: MR
authors.lastname: Kreutz
authors.forename: Eckart D
authors.initials: ED
authors.lastname: Gundelfinger
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular / Q000379:methods; D004622:Embryo, Mammalian; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D047468:Immunoprecipitation / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D009474:Neurons / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000378:metabolism; D013569:Synapses / Q000378:metabolism; D014162:Transfection / Q000379:methods; D020668:rap GTP-Binding Proteins / Q000378:metabolism*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; C479629:Sipa1l1 protein, rat; C116756:RAP2A protein, human; D020668:rap GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins