title: Gamma-tubulin can both nucleate microtubule assembly and self-assemble into novel tubular structures in mammalian cells.
abstract: alpha-, beta-, and gamma-tubulins are evolutionarily highly conserved members of the tubulin gene superfamily. While the abundant members, alpha- and beta-tubulins, constitute the building blocks of cellular microtubule polymers, gamma-tubulin is a low abundance protein which localized to the pericentriolar material and may play a role in microtubule assembly. To test whether gamma-tubulin mediates the nucleation of microtubule assembly in vivo, and co-assembles with alpha- and beta-tubulins into microtubules or self-assembles into macro-molecular structures, we experimentally elevated the expression of gamma-tubulin in the cell cytoplasm. In most cells, overexpression of gamma-tubulin causes a dramatic reorganization of the cellular microtubule network. Furthermore, we show that when overexpressed, gamma-tubulin causes ectopic nucleation of microtubules which are not associated with the centrosome. In a fraction of cells, gamma-tubulin self-assembles into novel tubular structures with a diameter of approximately 50 nm (named gamma-tubules). Furthermore, unlike microtubules, gamma-tubules are resistant to cold or drug induced depolymerization. These data provide evidence that gamma-tubulin can cause nucleation of microtubule assembly and can self-assemble into novel tubular structures.
authors.affiliation: Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: H B
authors.initials: HB
authors.lastname: Shu
authors.forename: H C
authors.initials: HC
authors.lastname: Joshi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured / Q000166:cytology; D018385:Centrosome / Q000502:physiology; D003593:Cytoplasm / Q000502:physiology; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D000882:Haplorhini; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D015739:Nocodazole / Q000494:pharmacology; D011108:Polymers / Q000378:metabolism; D011817:Rabbits; D013816:Thermodynamics; D014404:Tubulin / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*
chemical_list: D011108:Polymers; D014404:Tubulin; D015739:Nocodazole