Role of endoplasmic reticulum-derived vesicles in the formation of golgi elements insec23andsec18Saccharomyces Ccerevisiae mutants
✍ Scribed by Morin-Ganet, M.N. ;Rambourg, A. ;Clermont, Y. ;Képès, F.
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 566 KB
- Volume
- 251
- Category
- Article
- ISSN
- 0003-276X
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✦ Synopsis
Background: In the yeast Saccharomyces cerevisiae, the Golgi apparatus consists of individual networks of membranous tubules interspersed throughout the cytoplasm. When sec23 and sec18 mutants are shifted from the permissive (20°C) to the restrictive (37°C) temperature, the secretory pathway is blocked between endoplasmic reticulum (ER) and Golgi elements. When examined with an electron microscope, sec23 displays an excess of ER membranes, whereas sec18 accumulates small vesicles. The present investigation describes the kinetics of the ultrastructural modifications of the Golgi and vesicular elements when sec23 and sec18 mutants are shifted for 10 min to restrictive temperature and then returned to permissive temperature for various time intervals.
Methods: S. cerevisiae sec23 and sec18 mutants from exponentially growing cultures at 20°C were maintained for 10 min at the restrictive temperature of 37°C and returned to the permissive temperature of 20°C for different time intervals. Following fixation in glutaraldehyde and postfixation in potassium ferrocyanide reduced osmium, 80-to 200-nm-thick sections were prepared from Epon-embedded yeast cells. Using the thicker sections, stereopairs of electron microscopy photographs were prepared and used to visualize the three-dimensional configuration of the organelles. To follow the modifications of cell organelles, cell sections were selected at random in thinner sections and cell organelles were scored.
Results: At permissive temperature (20°C), the Golgi apparatus consisted of individual networks of tubules dispersed in the cytoplasm, as in the wild type strain. When both mutants were shifted for 10 min at the restrictive temperature (37°C), the main structural feature was the disappearance of all Golgi networks. In sec23 mutant cells, there was an increase in number of tubular, nonnodular networks corresponding to terminal portions of the endoplasmic reticulum; in sec18 cells, small 20-to 50-nm tubules and vesicles accumulated in the cytoplasm. Within minutes after the return of sec23 cells to permissive temperature (20°C), small vesicles and tubules started to accumulate to reach a number similar or greater than that noted in sec18 cells observed under the same conditions. At later time intervals and in both mutants, the small tubules and vesicles decreased in number. This decrease Grant sponsor: Centre National de la Recherche Scientifique.