Extensive lesions were produced in cell walls of Saccharomyces cerevisiae by the bleomycin family of anticancer antibiotics (30 min to 4 h). Electron micrographs revealed that the alterations were most frequently large breaks and small interruptions or holes in cell walls, which sometimes extended into cell membranes. Large portions of cell walls were sometimes lost. Cell walls were frequently ruptured in one or more positions. More than 75% of bud scar regions in single-plane sections and all bud scars in serial sections exhibited many interruptions and breaks after 3 or 4 h of treatment. The discovery of extensive damage to cell walls was consistent with the preferential (approximately 70%) association of radiolabeled bleomycin with cell walls and perimeters of bud scar regions after short exposures (30 min). After longer exposures, the distribution of silver grains changed from a predominant association with cell walls (30 min) to an increased association with the cell cytoplasm (1 to 4 h). This correlated with increased ultrastructural damage, since damage to cell walls was generally more frequent and more severe with increasing length of treatment (30 min to 4 h) or dose (25 to 100 micrograms/ml). Although DNA lesions are believed to be the lethal properties of bleomycins, the lesions produced in cell walls are also lethal properties of the antibiotics. The distributions of lesions on cell walls suggested a generalized interaction of the antibiotic with a cell wall component. These results led us to hypothesize a mechanism of effective antifungal action for the bleomycin family of antibiotics.
When the essential and distinctive cell walls of either pathogenic or nonpathogenic fungi break, cytoplasmic membranes rupture and fungi die. This fungicidal activity was discovered previously on nonproliferating Saccharomyces cerevisiae cells treated briefly with the oxidative tool and anticancer drug family of bleomycins. The present studies investigated effects of bleomycin on growing fungal organisms. These included the medically important Aspergillus fumigatus and Cryptococcus neoformans, as well as the emerging human pathogen and fungal model, S. cerevisiae. Bleomycin had its highest potency against A. fumigatus. Scanning electron microscopy and thin-section transmission electron microscopy were used to study morphological growth characteristics. Killing and growth inhibition were also measured. Long, thin, and segmented hyphae were observed when A. fumigatus was grown without bleomycin but were never observed when the mold was grown with the drug. Bleomycin arrested conidial germination, hyphal development, and the progression and completion of cell wall septation. Similarly, the drug inhibited the construction of yeast cell wall septa, preventing cytokinesis and progression in the cell division cycle of S. cerevisiae. Even when cytoplasms of mother and daughter cells separated, septation and cell division did not necessarily occur. Bizarre cell configurations, abnormally thickened cell walls at mother-daughter necks, abnormal polarized growth, large undivided cells, fragmented cells, and empty cell ghosts were also produced. This is the first report of a fungicidal agent that arrests fungal growth and development, septum formation, and cytokinesis and that also preferentially localizes to cell walls and alters isolated cell walls as well as intact cell walls on nongrowing cells.The unique cell wall that surrounds fungal cells is absolutely essential for their survival. The cell wall of pathogenic fungi has evolved for survival from environmental factors and host defenses (7,16,18,21,60). The ability of cell walls to evade such factors contributes to the power of pathogenic fungi to cause a wide spectrum of clinical disease (45). Moreover, the unique arrangement of the molecular species forming the structure of the fungal cell wall makes it an excellent target for drug intervention (3,6,24,44,46,54). Thus, the elucidation of the mechanisms of action of agents that interact with the molecules forming the cell walls will yield new insights into fungal cell wall structure, formation of cell walls between dividing cells, and cell division. For fungal pathogens, an understanding of the mechanisms of action of cell wall-specific agents should assist in the design of wall-specific antifungal drugs.Saccharomyces cerevisiae has long been a unicellular fungal model for studies of basic mechanisms. Since this budding yeast is also an emerging opportunistic human pathogen (15,38,42) with properties frequently observed in pathogenic fungi (4,29,30), the yeast is also developing as a model fungal pathogen (12). The dis...
Rats were tested for spontaneous alternation in a variety of mazes differing in the angle between choice alleys. Uniformly high alternation rates were found at all angles from 330 down to 90 deg. At 45 or 0 deg, the rates approximated a chance 50%, and at angles between 45 and 90 deg the alternation rates were also intermediate. The hypothesis that the spatial distance between goal regions is the critical factor was rejected, and it was concluded that the angle between alleys is the principal factor determining alternation under these conditions. The results support the idea that alternation in the rat is basically a vestibular phenomenon.In a previous study (Douglas, Mitchell, & Kentala, 1972), it was found that the tendency of the rat to spontaneously visit opposite alleys in a two-choice maze depended upon the shape of the maze. The alternation rate dropped from about 85% in a T-maze down to a chance 50% rate in a maze in which the two choice alleys extended forward, side by side, from the choice point (Maze a in Fig. 1). The results could be explained equally well by either of two hypotheses. The first is that the choice alleys are not sufficiently distant in space in the parallel-arm maze, and the second is that the angle between choice alleys is too small. The data gathered in the study above did not allow a choice to be made between these hypotheses because distance and angle were confounded in the mazes employed in the experiment. In the present study rats were tested for spontaneous alternation in a variety of mazes which differed in the angle between choice alleys and in the distance between goals. The purposes of this study were to generate data which would allow one of the hypotheses to be rejected and to determine whether the alternation rate would be a systematic function of the angle between choice alleys. METHOD SubjectsMost of the data were gathered from a group of 20 male Wistar rats that were 4 months of age. All were housed in group cages with continuous access to food and water. They were handled twice a day for 10 days prior to testing. Data for the parallel-arm maze (a) were gathered from 22 hooded rats, while a third group of 24 hooded rats was employed for tests at the 60-deg angle (Maze c). The hooded rats were roughly 6 months of age and were individually housed but otherwise treated the same as the first groups of rats above. All three groups were tested in the 180-deg T-maze in order to insure that performance was comparable in this standard situation. As Fig. 2 shows, the three groups were in fact virtually identical in T-maze alternation. ApparatusEleven different mazes were constructed of 9-mm plywood in the various shapes shown in Fig.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.