Organization of perinuclear actin in live tobacco cells observed by PALM with optical sectioning.

Actin performs a wide variety of different tasks. This functional diversity may be accomplished either by the formation of different isotypes or by suitable protein decoration that regulates structure and dynamics of actin filaments. To probe for such a potential differential decoration, the actin-binding peptide Lifeact was fused to different photoactivatable fluorescent proteins. These fusions were stably expressed in Nicotiana tabacum L. cv. Bright Yellow 2 cells to follow dynamic reorganization of the actin cytoskeleton during the cell cycle. The Lifeact-monomeric variant of IrisFP fusion protein was observed to indiscriminately label both, central and cortical, actin filaments, whereas the tetrameric Lifeact-photoswitchable red fluorescent protein fusion construct selectively labeled only a specific perinuclear sub-population of actin. By using photoactivated localization microscopy, we acquired super-resolution images with optical sectioning to obtain a 3D model of perinuclear actin. This novel approach revealed that the perinuclear actin basket wraps around the nuclear envelope in a lamellar fashion and repartitions toward the leading edge of the migrating nucleus. Based on these data, we suggest that actin that forms the perinuclear basket differs from other actin assemblies by a reduced decoration with actin binding proteins, which is consistent with the differential decoration model.