Three microtubule‐organizing centers are required for ascus growth and sporulation in the fungus Sordaria macrospora

Abstract

AbstractThe microtubule system of the Sordaria macrospora ascus was examined by antitubulin immunofluorescence, without the removal of the cell wall. The complex cytoskeleton revealed three possible microtubule‐organizing centers (MTOCs): the spindle pole body (SPB), the nuclear envelope, and an apical organizing center. MPM‐2, a mitotic phosphoprotein antibody which reacts with MTOCs, stained the apical center in a developmentally specific manner, and the nuclear envelope and SPB in a cell cycle‐dependent fashion. Nocodazole was used in both high (10–15 μg/ml) and low (0.5 μg/ml) concentrations to depolymerize the networks and reveal their points of origin and recovery. The apical center was active from prophase I to the end of first meiosis. The nuclear envelope was the site of microtubule nucleation in early prophase and at the telophase/interphase transition, while SPBs were active in both nuclear division and sporulation.Mutant strains deficient in sporulation and with aberrant morphology were analyzed by antitubulin and MPM‐2 immunofluorescence. Shape mutants showed abnormal or absent apical organizing centers and abnormal cortical microtubule patterns, indicating a possible role for the cortical network in the establishment and maintenance of ascus shape. © 1992 Wiley‐Liss, Inc.