title: Colocalization of α-actinin and synaptopodin in the pyramidal cell axon initial segment.
abstract: The cisternal organelle that resides in the axon initial segment (AIS) of neocortical and hippocampal pyramidal cells is thought to be involved in regulating the Ca(2+) available to maintain AIS scaffolding proteins, thereby preserving normal AIS structure and function. Through immunocytochemistry and correlative light and electron microscopy, we show here that the actin-binding protein α-actinin is present in the typical cistenal organelle of rodent pyramidal neurons as well as in a large structure in the AIS of a subpopulation of layer V pyramidal cells that we have called the "giant saccular organelle." Indeed, this localization of α-actinin in the AIS is dependent on the integrity of the actin cytoskeleton. Moreover, in the cisternal organelle of cultured hippocampal neurons, α-actinin colocalizes extensively with synaptopodin, a protein that interacts with both actin and α-actinin, and they appear concomitantly during the development of these neurons. Together, these results indicate that α-actinin and the actin cytoskeleton are important components of the cisternal organelle that are probably required to stabilize the AIS.
authors.affiliation: Department of Functional and Systems Neurobiology, Instituto Cajal, CSIC, 28002 Madrid, Spain.
authors.forename: Diana
authors.initials: D
authors.lastname: Sánchez-Ponce
authors.forename: Lidia
authors.initials: L
authors.lastname: Blázquez-Llorca
authors.forename: Javier
authors.initials: J
authors.lastname: DeFelipe
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Garrido
authors.forename: Alberto
authors.initials: A
authors.lastname: Muñoz
mesh_terms: D000185:Actinin / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008840:Microfilament Proteins / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism*; D017966:Pyramidal Cells / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D008840:Microfilament Proteins; C503968:Synpo protein, mouse; C503969:Synpo protein, rat; D000185:Actinin