Differences in Actin Localization during Bud and Hypha Formation in the Yeast Candida albicans

Abstract

Stationary phase cells of Candida albicans can form either a bud or a hypha, depending upon the pH of the medium into which they are released. At low pH, cells form an ellipsoidal bud and at high pH, cells form an elongated hypha. By staining cells with rhodamine-conjugated phalloidin, we have compared the dynamics of actin localization during the formation of buds and hyphae. Before evagination, actin granules were distributed throughout the cytoplasmic cortex in both budding and hypha-forming cells. Just before evagination, actin granules clustered at the site of evagination, then filled the early evagination in both budding and hypha-forming cells. With continued bud growth, the actin granules then redistributed throughout the cytoplasmic cortex. In marked contrast, with continued hyphal growth, the majority of actin granules clustered at the hyphal apex. This distinct difference in actin granule localization may be related to the distinct differences in the expansion zones of the cell wall recently demonstrated between growing buds and hyphae. The spatial and temporal dynamics of the large neck actin granules and of actin fibres are also described.

Hyphal Elongation Is Regulated Independently of Cell Cycle inCandida albicans

“…Polarization of the actin cytoskeleton at the tips of hyphae was reported previously and is probably required for hyphal elongation (Anderson and Soll, 1986;Yokoyama et al, 1990). We observed that the actin polarization at the hyphal tip appeared 30 min after hyphal induction in G 1 cells, ϳ70 min before SPB duplication, DNA replication, and chitin ring formation, and that it persisted throughout the cell cycle (Figures 3B, bottom; and 4B).…”

“…Hyphal-associated polarization of the actin cytoskeleton is located exclusively at the tip of each hypha (Anderson and Soll, 1986). It coexists with the cell cycle-regulated actin assemblies in the apical cells of each hypha ( Figure 4B), and both contribute to cell shape.…”

“…The localization of the actin cytoskeleton in yeast and hyphal cells reflects these differences in morphogenesis. Polarization of the actin cytoskeleton to the hyphal tip is observed in all hyphal cells (Anderson and Soll, 1986). However, in yeast-form cells, the cortical actin patches are observed at the area of apical expansion only in small budded cells but not in large budded cells (Anderson and Soll, 1986).…”

“…Polarization of the actin cytoskeleton to the hyphal tip is observed in all hyphal cells (Anderson and Soll, 1986). However, in yeast-form cells, the cortical actin patches are observed at the area of apical expansion only in small budded cells but not in large budded cells (Anderson and Soll, 1986). It has been suggested that the actin cytoskeleton is essential for polarized apical growth because chloropropham, a drug affecting actin microfilament organization, has been shown to inhibit hyphal growth (Yokoyama et al, 1990(Yokoyama et al, , 1994.…”

Transcript Profiles of Candida albicans Cortical Actin Patch Mutants Reflect Their Cellular Defects: Contribution of the Hog1p and Mkc1p Signaling Pathways

“…The actin cytoskeleton of the fungal pathogen C. albicans plays a key role in morphogenesis and hyphal formation (1,4,5,32,41,55,58). In yeasts, this cytoskeleton is comprised of cortical actin patches found at sites of polarized growth and actin cables that serve as tracks for secretion of vesicles to sites of polarized growth (11,45,46).…”