PROCEEDINGS |
To elucidate the existence of MTOCs in adult cardiocytes, where MT network densification reduces cell contractility via viscous loading1), we sought the existence and localization of gamma-tubulin (gTB) as a MTOC marker in cardiocytes. Enzymatically isolated adult feline cardiocytes and 3T3 fibroblasts were used for immunoblotting, confocal micrographs and electron micrographs. gTB was present at low levels in cardiocyte immunoblots. Confocal micrographs showed several gTB-marked MTOCs at the nuclear poles and in the internuclear region, with coincident staining with pericentrin, which is one of the MTOC proteins. These gTB signals were completely blocked by antibody pre-incubation with a gTB synthetic peptide. To show MTOC-based MT nucleation, MTs were depolymerized with nocodazole, and MT asters were allowed to form after nocodazole washout. The asters and gTB colocalized upon MT regrowth. Immunogold electron micrographs showed gold particles at the centrosomal structure and electron dense sites at the nuclear membrane. Thus, MTOCs exist in adult cardiocytes; the centrosomal structure and the nuclear membrane are suggested to be MT nucleation sites.
1) Tagawa et al. 1997. Cytoskeletal mechanics in pressure-overload cardiac hypertrophy. Cir Res. 80:281-289.