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N A Gow

Publications and source records attributed to N A Gow.

10 recordsLinked to original sources
PubMed1992

Contact sensing in Candida albicans: a possible aid to epithelial penetration.

Hyphal development in the dimorphic pathogenic fungus Candida albicans is thought to facilitate the primary invasion of surface epithelia during superficial infections. When mycelia were grown on Nuclepore membrane filters that were placed over serum-containing agar, the hyphae grew over the membrane surface and through the pores thereby crossing to the other side of the membrane. Hyphae that did not contact the lip of a pore did not enter it. The response was likely to be due to contact guidance (thigmotropism) and not chemotropism towards the nutrients since hyphae growing on the underside of the membrane also entered the pores then grew away from the underlying nutrient agar. The response therefore seems to be due to sensation of the substrate topography, and tropic movement in relation to changes in contour. This behaviour may enable the hyphae to penetrate epithelia at microscopic wound sites, membrane invaginations and other foci where the integrity of the epithelium is weak.

Candida albicans↗
PubMed1992

Electric field-induced orientation of rat hippocampal neurones in vitro.

Rat hippocampal neurones in primary culture exhibited directional growth in response to DC electric fields. Neurites lay perpendicular to the field after exposure to 28, 80 or 219 mV/mm but there was no orientation effect at 9 mV/mm or in unexposed control cultures. Fields that evoked perpendicular responses also reduced the number of cathode-facing neurites. Orientation was the same for neurite initiation sites and the direction of overall neurite growth.

Animals↗
PubMed1991

Rates of germ tube formation from growing and non-growing yeast cells of Candida albicans.

The rates of germ tube formation from growing and non-growing yeast cells of Candida albicans were investigated using a protocol for dimorphism regulated by temperature and pH. Stationary-phase cells formed germ tubes less rapidly than yeast cells that were preincubated in fresh growth medium prior to induction of dimorphism by an upshift in temperature or pH. On the basis of experiments using inhibitors of macromolecular biosyntheses it is suggested that the accelerated growth kinetics required de novo RNA and protein biosynthesis, but not DNA synthesis. The results suggest that metabolically active yeast cells are better able to undergo dimorphism than non-growing cells.

Candida albicans↗
PubMed1990

Influence of applied electrical fields on yeast and hyphal growth of Candida albicans.

Yeast cells of Candida albicans which had been attached to polylysine-coated microscope slides were induced to form buds or germ tubes in the presence of external electrical fields. The sites of budding and germ tube formation and the growth of germ tubes and hyphal branches were polarized preferentially towards the cathode. Buds were not converted to pseudohyphae or germ tubes by the field and the field had no effect on the positioning of nuclei or septa in the yeast cell or germ tube. Buds were less polarized than germ tubes at any given applied voltage. The polarization of buds reached a peak at an electrical field of 12 mV per cell. Polarization of germ tubes was biphasic, increasing rapidly with increasing field strengths up to 5 mV per cell, and then more slowly in stronger fields. An electrical field was only required for a fraction of the time taken for germ tubes to start to form, so cells retained a memory of experiencing an electrical field which influenced the selection of sites of evagination. Increasing the electrical field delayed the time of germ tube evagination and inhibited the rate of germ tube extension. Unlike previous findings with other filamentous fungi, germ tubes grew unidirectionally towards the cathode for extended periods and did not deviate to a perpendicular orientation. This result suggests that the septal pore of the filamentous form may have high electrical resistance and would act as an effective barrier to solute transport between intercalary compartments.

Candida albicans↗
PubMed1989

Changes in internal and external pH accompanying growth of Candida albicans: studies of non-dimorphic variants.

Non-dimorphic variants of Candida albicans, which were unable to form germ tubes or mature hyphae in media containing amino acids, glucose and salts or N-acetylglucosamine or serum, were prepared from two hyphal positive laboratory strains using a physical separation method. The hyphal-minus phenotype was stable and may be due to mutations or phenotypic variation. The variant strains maintained their internal pH within narrower bounds as compared to their parental wild-types. When exposed to conditions that normally supported the induction of germ tubes the cytoplasmic pH of the wild type strains increased from 6.8 to over pH 8.0 within 5 min while in the variants the rise in internal pH was only about 0.3 pH units. The wild type strains acidified the growth medium more rapidly than the variants. The results suggest that the control of internal pH is directly or indirectly associated with the regulation of dimorphism. The variants had unaltered cell volumes and specific growth rates. The hyphal-minus phenotype was however fully reversible since revertants occurred spontaneously on serum containing agar.

Candida albicans↗
PubMed1988

Cytoplasmic alkalinization during germ tube formation in Candida albicans.

Weak acids were used to measure the internal pH of yeast cells of Candida albicans that had been induced to form buds or germ tubes. Under conditions that supported germ tube formation the internal pH rose from around 6.8 to over 8.0 after 30 min in two different induction media. Internal pH measured by 31P NMR confirmed this pattern and also showed that the internal pH fell to around 7.0 prior to the outgrowth of germ tubes. Conditions which led to budding induced less cytoplasmic alkalinization. This alkalinization was brought about when cells were inoculated into media of neutral pH and at an increased temperature. Increasing the temperature of the medium augmented the alkalinization of the cytoplasm induced by raising the external pH. Strains of C. albicans defective in the ability to produce germ tubes did not show this dramatic cytoplasmic alkalinization under conditions which normally supported filamentous growth. The raising of internal pH may be due to the activation of the plasma membrane proton-pumping ATPase since diethylstilboestrol inhibited the cytoplasmic alkalinization and germ tube formation without causing irreversible loss of cell viability. The results show that the induction of the dimorphic transition in this organism is accompanied by a steep rise in internal pH. It is not known whether these changes are the cause or consequence of morphogenesis.

Candida albicans↗
PubMed1987

Cytological aspects of dimorphism in Candida albicans.

From a comparison of the growth of yeast and hyphal cells of Candida albicans at 37 degrees C, the present authors suggest that the formation of hyphae is a response to nutrient stress. The major cytological evidence for this is that the formation of a germ tube is chiefly the result of the migration of cytoplasm out of the parent yeast cell, with little biosynthesis occurring other than DNA replication and wall assembly. This explains the linear outgrowth of the germ tube rather than an autocatalytic outgrowth. It is accompanied by the enlargement of the vacuole in the parent cell. Subsequent elongation of the hyphae is accompanied by vacuolation of subapical compartments, and branching only occurs from some of the subapical compartments after they have reformed sufficient cytoplasm.

Candida albicans↗
PubMed1986

Cytological interrelationships between the cell cycle and duplication cycle of Candida albicans.

The cytology of nuclear division and septation in the yeast and hyphal phases of Candida albicans growing at 37 degrees C has been studied by fluorescence microscopy after staining of specimens with 4'6-diaminido-2-phenylindole (DAPI) and Calcofluor. Yeast and hyphal cells replicated their nuclei at about 18 min after the emergence of a bud or germ-tube. The site of nuclear division coincided with the future location of the septum in both forms. This occurred at the junction of the bud and parent yeast cell or 6.0 micron from the parent yeast in germ tubes which were formed in medium containing serum. The filamentous forms of a range of clinical and laboratory strains grown in a variety of germ tube-inducing media were all extensively vacuolated. Germ tube extension in all of these media was linear. It is suggested that there is little biosynthesis of cytoplasm during the initial stages of germ tube growth in this organism and that this accounts for the development of the large vacuoles and the linear growth kinetics.

Candida albicans↗