THE ROLE OF THE CYTOSKELETON IN THE POLARIZED GROWTH OF THE GERM TUBE IN CANDIDA-ALBICANS

Cells of the dimorphic yeast Candida albicans are easily induced to germinate in synchrony. Using germinating cells of strain FC18, we examined the effects of several drugs that are known to affect the cytoskeleton on growth and cytoskeletal organization. Cytochalasin A (CA), an inhibitor of actin function, inhibited the germination of the yeast cells and changed the cylindrical expansion of the apex of the germ tube to swelling growth. Effects of CA on the organization of actin were examined with rhodamine-phalloidin (Rh-Ph), which specifically stains F-actin. In CA-untreated cells, ph-ph staining resulted in condensed dot-like fluorescence at the growing tip, as well as filamentous fluorescence (actin cables) that ran from the apex to the basal region. In CA-treated cells, condensed dot-like fluorescence was still observed at the swelling tip, but actin cables had disappeared completely. This result indicates that CA does not affect the asymmetrical distribution of actin, and suggests that the actin cables are not required for maintenance of the polarized localization of actin. Benomyl, an anti-microtubule drug, inhibited the germination of yeast cells and the apical growth of germinated cells. Benomyl not only disrupted microtubules (MTs), but also affected the distribution of actin. In benomyl-treated cells, actin dots were randomly dispersed all over the cell. This result indicates that benomyl destroyed the mechanism that maintains the asymmetrical distribution of actin, and suggests that MTs are involved in such a mechanism. The polarized localization of organelles is one of the most important factors associated with dimorphism. Our data suggest that the cytoskeleton, composed of actin and MTs, is involved in the control of polarity in the hyphal growth of C. albicans, and that actin and MTs are interrelated in the establishment of polarity.