Abstract #82A

Actin clumps in yeast quiescent cells: an immediately available actin reserve? Isabelle Sagot, Benoit Pinson, Benedicte Salin, Bertrand Daignan-Fornier. Inst Biochem & Genetique Cell, CNRS UMR 5095, Bordeaux, France.
   Most eukaryotic cells spend the majority of their life in a quiescent state, waiting for specific signals to proliferate. In the case of Saccharomyces cerevisiae, entry into and exit from quiescence are only dependent on the availability of nutrients in the environment. The transition from quiescence to proliferation requires not only drastic metabolic changes but also a complete remodelling of various cellular structures. Here, we describe an actin cytoskeleton organization specific of the quiescent state. When cells cease to divide, actin is reorganized into structures that we call “actin clumps”. These structures do not have a specific shape and do not localize in a particular region of the cytoplasm. We show that actin clumps contain F-actin and several actin binding proteins such as fimbrin and capping protein. Further, by contrast to actin patches or cables, actin clumps are mostly immobile and we could not detect any actin filaments turn over. Finally, we show that upon cells re-feeding, actin clumps disappear rapidly and actin cables and patches can be assembled independently of new protein synthesis. This lead us to speculate that actin clumps act as a reserve of actin that can be immediately mobilized for actin cable and patches formation upon re-entry into a proliferation cycle.

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