A second high-frequency switching system was identified in selected pathogenic strains in the dimorphic yeast Candida albicans. In the characterized strain WO-1, cells switched heritably, reversibly, and at a high frequency (-10-2) between two phenotypes readily distinguishable by the size, shape, and color of colonies formed on agar at 25°C. In this system, referred to as the "white-opaque transition," cells formed either "white" hemispherical colonies, which were similar to the ones formed by standard laboratory strains of C. albicans, or "opaque" colonies, which were larger, flatter, and grey. At least three other heritable colony phenotypes were generated by WO-1 and included one irregular-wrinkle and two fuzzy colony phenotypes. The basis of the white-opaque transition appears to be a fundamental difference in cellular morphology. White cells were similar in shape, size, and budding pattern to cells of common laboratory strains. In dramatic contrast, opaque cells were bean shaped and exhibited three times the volume and twice the mass of white cells, even though these alternative phenotypes contained the same amount of DNA and a single nucleus in the log phase. In addition to differences in morphology, white and opaque cells differed in their generation time, in their sensitivity to low and high temperatures, and in their capacity to form hypae. The possible molecular mechanisms involved in high-frequency switching in the white-opaque transition are considered.Recently, we demonstrated that a common laboratory strain of the dimorphic yeast Candida albicans was capable of switching heritably, reversibly, and at a high frequency among at least seven general phenotypes distinguishable by colony morphology (17; D. R. Soll, B. Slutsky, S. Mackenzie, C. Langtimm, and M. Staebell, J. Oral Pathol., in press). In this system, cells of the parent strain switched spontaneously at a frequency of roughly io-4. A low dose of UV light, which killed less than 10% of the cell population, stimulated a 200-fold increase in this initial frequency. Whether spontaneous or UV induced, once the original strain switched, it continued to switch spontaneously and reversibly between variant colony phenotypes at a frequency of 10-2. Revertants to the original colony phenotype which exhibited a decrease in switching frequency from 10-2 to i0' were also obtained (17; Soll et al., in press).In examining the switching capabilities of strains of C. albicans isolated from patients with systemic infections, we have discovered a second switching system, which we will refer to as the "white-opaque transition." In this system, cells switch heritably, at a high frequency, and reversibly between two phenotypes which generate alternative colony morphologies distinguishable by colony size, shape, and color. In the "white" phenotype, cells form colonies which are white and hemispherical. In the "opaque" phenotype, cells form colonies which are larger, flatter, and opaque, or grey. The differences in colony shape and tone appear to be the result of a...

Select strains of Candida albicans switch reversibly and at extremely high frequency between a white and an opaque colony-forming phenotype, which has been referred to as the white-opaque transition. Cells in the white phase exhibit a cellular phenotype indistinguishable from that of most standard strains of C. albicans, but cells in the opaque phase exhibit an unusually large, elongate cellular shape. In comparing the white and opaque cellular phenotypes, the following findings are demonstrated. (i) The surface of the cell wall of maturing opaque cells when viewed by scanning electron microscopy exhibits a unique pimpled, or punctate, pattern not observed in white cells or standard strains of C. albicans. (ii) The dynamics of actin localization which accompanies opaque-cell growth first follows the pattern of budding cells during early opaque-bud growth and then the pattern of hypha-forming cells during late opaque-bud growth. (iii) A hypha-specific cell surface antigen is also expressed on the surface of opaque budding cells. (iv) An opaque-specific surface antigen is distributed in a punctate pattern.Most strains of Candida albicans are capable of switching at a high frequency between a number of phenotypes distinguishable by colony form on agar (11,12,22 Oral Mucosa, in press). There are at least three distinguishable switching systems which are strain specific and give rise to multiple colony phenotypes (22), but only one system, the white-opaque transition, has been demonstrated to affect the basic cellular form of the budding cell (12). In the whiteopaque transition, cells switch reversibly at frequencies of roughly 10-2 to i10 between two major colony-forming phenotypes. Cells in the white phase generate a smooth white colony which is indistinguishable from the common colony form of other C. albicans strains, and cells in the opaque phase generate a larger, flatter grey colony which is uncharacteristic of standard strains of C. albicans (12). It has been demonstrated that although white and opaque budding cells contain roughly the same quantity of DNA, they differ in mass, volume, shape, budding pattern, constraints on the bud-to-hypha transition, generation time, and sensitivities to both low and high temperature (12; B. Slutsky, Ph.D. thesis, University of Iowa, Iowa City, 1986; Soll et al., in press). White cells in the budding form are round and bud with a pattern similar to that of common laboratory strains of C. albicans (4,8,14,19). When challenged to form hyphae under the regime of pH-regulated dimorphism (5, 14, 17), they form hyphae in a fashion indistinguishable from that of common laboratory strains (17,24 (ii) The dynamics of actin localization (2) accompanying opaque cell growth follows the white budding cell pattern early in bud growth and the white hypha pattern later in bud growth. (iii) A hyphaspecific cell surface antigen is expressed in opaque cells. (iv) An opaque-specific antigen is distributed in a punctate pattern in association with the cell surface of opaque cells. These results...

Cells of Candida albicans WO-1 switch frequently and reversibly between two colony-forming phenotypes, white and opaque. In the white form, budding cells appear similar to those of most other strains of C. albicans, but in the opaque form, budding cells are larger, are bean shaped, and possess pimples on the wall. These pimples exhibit a unique and complex morphology. With scanning electron microscopy, a central pit can be discerned, and in many cases, a bleb can be observed emerging from the pimple center. With transmission electron microscopy, channels are evident in some pimples and vesicles are apparent under the pimple in the cytoplasm, in the actual wall of the pimple, or emerging from the tip of the pimple. A large vacuole predominates in the opaque-cell cytoplasm. This vacuole is usually filled with spaghettilike membranous material and in a minority of cases is filled with vesicles, many of which exhibit a relatively uniform size. An antiserum to opaque cells recognizes three opaque-cell-specific antigens with molecular masses of approximately 14.5, 21, and 31 kilodaltons (kDa). Absorption with nonpermeabilized opaque cells demonstrated that only the 14.5-kDa antigen is on the cell surface; indirect immunogold labeling demonstrated that it is localized in or on the pimple. The possibility is suggested that the vacuole of opaque cells is the origin of membrane-bound vesicles which traverse the wall through specialized pimple structures and emerge from the pimple with an intact outer double membrane, a unique phenomenon in yeast cells. The opaque-cell-specific 14.5-kDa antigen either is in the pimple channel or is a component of the emerging vesicle. The functions of the unique opaque-cell pimple and emerging vesicle are not known.Candida albicans and related species are capable of switching at high frequencies between a number of general phenotypes distinguishable by colony morphology (18,20,21,24). There are a number of different switching systems in the species C. albicans and Candida tropicalis, which differ from one another in phenotypic repertoire (18,20,21,26,27). Thus far, all of the systems tested share characteristics of high-and low-frequency modes of switching, heritability, reversibility, a limited number of phenotypes, and stimulation by low doses of UV irradiation (24,25). One of these switching systems, the white-opaque transition, involves a dramatic change not only in colony morphology but also in the basic phenotypes of cells in the budding growth form (1,2,19,21). In the white phase, cells produce smooth white colony domes in all respects similar to those produced by most other strains of C. albicans (2,21 large and sometimes multiple vacuoles (21) as well as unique pimples on the mature cell wall (1, 2). In addition, it has been demonstrated that opaque cells possess one or more opaquecell-specific antigens distributed in the cell wall in a punctate fashion similar to pimple distribution (1, 2).We present here scanning electron microscopy (SEM) and transmission electron microscopy (TE...

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.

Background The perioperative management of patients who take a direct oral anticoagulant (DOAC) for atrial fibrillation and require treatment interruption for an elective surgery/procedure is a common clinical scenario for which best practices are uncertain. The Perioperative Anticoagulant Use for Surgery Evaluation (PAUSE) study is designed to address this unmet clinical need. We discuss the rationale for the PAUSE design and analysis plan as well as the rationale supporting the perioperative DOAC protocol. Methods PAUSE is a prospective study with three parallel cohorts, one for each DOAC, to assess a standardized but patient-specific perioperative management protocol for DOAC-treated patients with atrial fibrillation. The perioperative protocol accounts for DOAC type, patient's renal function and surgery/procedure-related bleeding risk. The primary study aim is to demonstrate the safety of the PAUSE protocol for the perioperative management of each DOAC. The secondary aim is to determine the effect of the pre-procedure interruption on residual anticoagulation when measured by the dilute thrombin time for dabigatran and anti-factor Xa levels for rivaroxaban and apixaban. The study hypothesis is that the perioperative management protocol for each DOAC is safe for patient care, defined by expected risks for major bleeding of 1% (80% power to exclude 2%), and for arterial thromboembolism of 0.5% (80% power to exclude 1.5%) in each DOAC group. Conclusion The PAUSE study has the potential to establish a standard-of-care approach for the perioperative management of DOAC-treated patients. The PAUSE management protocol is designed to be easily applied in clinical practice, as it is standardized and also patient specific.

Cells of Candida albicans WO-1 switch spontaneously and frequently between a white and an opaque CFU. Recently, an opaque-phase-specific cDNA, PEP), was cloned and was demonstrated to code for a pepsinogen. By using a differential hybridization screen, a second opaque-phase-specific cDNA, Op4, has been isolated and its corresponding gene has been cloned. Op4 is coordinately regulated with PEP) but resides on a different chromosome. During temperature-induced mass conversion from opaque to white, transcription of PEP) and Op4 is immediately inhibited by the increase in temperature, but transcription of both genes can be rapidly reestablished by a downshift in temperature prior to phenotypic commitment. However, the capacity to rapidly induce both PEP) and Op4 is lost coincidentally with the second semisynchronous round of cell division and phenotypic commitment during mass conversion. Op4 shows no significant base or amino acid sequence homology with a known gene or protein, respectively. However, the deduced Op4 protein exhibits several

Cells of Candida albicans strain WO-1 and related strains switch frequently and reversibly between a white-colony-forming unit (white phase) and a gray-colony-forming unit (opaque phase). Cells in the budding white phase exhibit the usual smooth round phenotype observed in other C. albicans strains, but cells in the budding opaque phase exhibit a unique elongate shape with surface pimples or protrusions. In this study, it was demonstrated that opaque cells formed hyphae at low to negligible levels in suspension cultures but could be induced to form hyphae at high levels when anchored to the chamber wall of a perfusion chamber or to a monolayer of human skin epithelial cells. Variability in the proportion of hyphae formed between experiments appeared to be due to variability between individual opaque clones. The hyphae formed by opaque cells were morphologically identical to hyphae formed by white cells (i.e., they were devoid of pimples or protrusions and exhibited the same shape and septal locations). They also did not stain with an opaque-specific antiserum which differentially stained opaque budding cells in a punctate fashion. However, when stimulated to form buds, opaque hyphae formed opaque-shaped daughter buds, demonstrating that although they are morphologically similar to hyphae formed by white cells, they are genetically opaque.

1201Most strains of Candida albicans are capable of switching spontaneously and at high frequency between a number of phenotypes distinguishable by colony morphology. The switching frequency of Candida albicans strain WO-1 between two predominant phenotypes, 'white' and 'opaque', and a minor phenotype, 'fuzzy', increased dramatically with low doses of ultraviolet irradiation that killed less than 20% of the population. The ultraviolet irradiation effect continued to be expressed over many generations as evidenced by stimulated sectoring. Ultraviolet irradiation stimulated switching in both the white-to-opaque and opaque-to-white direction, suggesting that a common mechanism functions in both directions.