Journal of Electron Microscopy Advance Access published online on October 8, 2009
Journal of Electron Microscopy, doi:10.1093/jmicro/dfp050
Ultrastructural disorder of the secretory pathway in temperature-sensitive actin mutants of Saccharomyces cerevisiae
1 Medical Mycology Research Centre, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8673, Japan
2 Department of Biology, Faculty of Medicine, Masaryk University, Kamenice 5, A7, 62500 Brno, Czech Republic
* To whom correspondence should be addressed. E-mail: yama{at}faculty.chiba-u.jp
Phenotypes of the two temperature-sensitive actin mutants of Saccharomyces cerevisiae act1-1 and act1-2 at permissive, restrictive and semi-restrictive temperatures were studied by freeze fracture and thin section electron microscopy, and fluorescent microscopy. In contrast to secretory mutants where accumulations of either secretory vesicles, Golgi apparatus, or endoplasmic reticulum were reported, act1-1 and act1-2 mutants revealed accumulation of all the three components, even at permissive temperature. However, more distinct accumulation of secretory organelles was evident during cultivation at the sub-restrictive temperature of 30°C. At the restrictive temperature of 37°C, many cells died, and their empty cell walls remained. Some of the few living cells showed features of apoptosis. From the present study, actin cables are concluded to be necessary for (i) correct spatial positioning and orientation of secretary pathway to the bud and septum, and (ii) vectorial movement of vesicles of the secretory pathway along the actin cables to the bud and septum.
Keywords actin mutant, freeze-fracturing, freeze-substitution, secretory pathway, Golgi apparatus
Received 9 July 2009, accepted 10 September 2009
This paper is dedicated to the memory of our co-worker and friend, Miroslav Gabriel, M.D., Ph.D., Associate Professor of Department of Biology, Faculty of Medicine, Brno, Czech Republic, who died suddenly on 7 June 2008 before we finished this paper.