| dc.description.abstract |
<p>The cells of the budding yeast Saccharomyces cerevisiae undergo a robust morphological
cycle, involving reorganization of the actin cytoskeleton, septin ring formation,
and polarized growth. These events are crucial to the formation of a fully-equipped
and properly-shaped bud, which gives rise to the daughter cell. The budding yeast,
as a well-established genetic model system, has attracted numerous investigations
aimed at uncovering the underlying principles of morphogenesis. </p><p>Despite the
important roles of the septin ring and collar in morphogenesis and cytokinesis, little
is known about how they are assembled. We found that septins are recruited to the
ring and collar following a tri-linear assembly/disassembly scheme. </p><p>Polarization
of actin cables enable directed secretion and growth. The formin Bni1p, an actin
nucleator, is thought to polarize actin cables in response to the direct regulation
by the master polarity regulator, Cdc42p. However, we found that all the known Bni1p-regulatory
pathways are dispensable, including the direct regulation by Cdc42p, and we uncovered
a novel pathway linking Bni1p to Cdc42p via the Cdc42p effector, Gic2p.</p><p>Yeast
morphogenesis is tightly coupled with the cell cycle. Contrary to the prevailing
model, we found that G1-CDK activity, albeit required for bud emergence, is not needed
to trigger polarization. This finding suggests that cells are in a default polarized
state, which is negatively regulated by the G2-CDK.</p>
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