Fission Yeast Schizosaccharomyces Research Articles

Posttranslational Regulatory Control of Trehalase Induced by Nutrients, Metabolic Inhibitors, and Physical Agents inPachysolen tannophilus

Soto, T., Fernandez, J., Vicente-Soler, J., Cansado, J., and Gacto, M. 1996. Posttranslational regulatory control of trehalase induced by nutrients, metabolic inhibitors, and physical agents inPachysolen tannophilus. Fungal Genetics and Biology20,143–151. Trehalase activity in the yeastPachysolen tannophilusis due to a single enzyme with highest activity during exponential growth on glucose. Derepressed cells enhanced markedly the level of trehalase activity upon addition of glucose, 2,4-dinitrophenol, nitrogen sources, protein-synthesis inhibitors, or azide. The increase induced by the last three types of compounds required the presence of an energy source in the incubation assay. In glucose-repressed cells, only nitrogen sources and azide were able to produce trehalase activation. The increase in trehalase was preceded by a cAMP signal, suggesting that cAMP may be involved as second messenger in a signaling pathway for trehalase stimulation. When cells from either repressed or derepressed growing cultures were temperature shifted from 28 to 40°C, trehalase activity increased with negligible change in the cAMP level. This type of activation was not produced in cells from resting cultures. The increase in trehalase triggered by heating was independent on bothde novoprotein synthesis and the presence of glucose. Treatment by phosphatase of trehalase activated by either glucose or heat shock resulted in trehalase deactivation, indicating that phosphorylation of the enzyme protein occurs during activation. These data support that at least two independent mechanisms, involving different phosphorylation pathways, can promote trehalase activation inPa. tannophilus.Some functional features of these signaling pathways appear closer to those present in the fission yeastSchizosaccharomyces pombethan to those found in other budding yeasts likeSaccharomyces cerevisiaeorCandida utilis.

New arrays of cytoplasmic microtubules in the fission yeastSchizosaccharomyces pombe

New arrays of microtubules in the fission yeastSchizosaccharomyces pombe, which distribute in the cell in a cell cycle-dependent manner, were characterized using conventional and confocal laser scanning immunofluorescence microscopy. During the interphase and prophase, we observed abundant cytoplasmic microtubules between cell poles, a peripheral network of randomly and helically distributed cortical microtubules, and perinuclear microtubules surrounding the nucleus. At the anaphase and telophase, an equatorial ring containing tubulin was visualized. This ring colocalized with an actin contractile ring, suggesting that they may control the plane of cell division cooperatively.

Mating-type gene switching in a homothallic fission yeast

When single cells of a homothallic strain of the fission yeast ( Schizosaccharomyces pombe 968h 90 ) are plated upon sporulation agar, a couple of cell divisions yield four preconjugal cells ordered in a line. Within a line, conjugation occurs either between sibs (the pair at either end of the line) or between cousins (the central pair of cells) or not at all. Miyata & Miyata (1981) have shown that sib matings are favored over cousin matings, the ratio of sib:cousin:sterile being 96:23:10. To have mating within these 4-cell clones means that the mating types of some of the cells have switched. In a further analysis of their data, we come to a series of deductions, one of which is that switching of mating-type genes in the fission yeast must be asymmetrical. We propose a random model and a deterministic model based upon asymmetrical switching. Either model could generate the ratios provided, but the models are sufficiently different that experimental tests should be able to discriminate between the two.

Regeneration of the cell wall of protoplasts of the fission yeastSchizosaccharomyces versatilis in liquid media and their reversion to cells

Regeneration of the cell wall and reversion of protoplasts with a completely regenerated cell wall to cells were studied by light and electron microscopy in protoplasts of the fission yeastsSchizosaccharomyces versatilis. On their surface the protoplasts regenerated a complete new wall even m liquid media The wall regeneration began with the formation of a thin irregular net of flat bundles of long microfibrils and the net was gradually filled with aggregates of short straight microfibrils and small piles of amorphous material. Osmotically resistant organisms with regenerated walls were detected after a 4–6 h cultivation Depending on the nutrient medium used 10–80 % of protoplasts with the regenerated wall were obtained that reverted subsequently to cells. The high percentage of the wall regeneration and reversion to cells was reached by combining cultivation in a poor medium with that in a rich medium Reversion to cells could only occur after the protoplasts had regenerated rigid cell walls These walled protoplasts underwent septation, and, by polar growth, produced cylindrical cells, further dividing by fission.

Interdependence of cell cycle events inSchizosaccharomyces pombe. Terminal phenotypes of cell division cycle mutants arrested during dna synthesis and nuclear division

Temperature-sensitive cell division cycle (cdc) mutants of the fission yeastSchizosaccharomyces pombe, previously characterized as defective in nuclear division were examined by thin section electron microscopy. All of the mutants failed to enter mitosis, rather they accumulated at one of four distinct terminal phenotypes. Class one were arrested with a nucleus rectangular in cross-section and a laterally situated spindle pole body (SPB). The second group had spherical or rectangular nuclei with a single SPB. The sole member of the third group wascdc 27. K 3, which had a spherical crenated nucleus with a single SPB from which microtubules emerged and extended into the cytoplasm. Allelic variants ofcdc 25 comprised the fourth group all of which displayed aberrant nuclear morphologies. Utilizing this ultrastructural data together with a knowledge of the transition points of these mutants a model for the interdependence of certain cell cycle event is proposed in which the initiation of DNA synthesis is uncoupled from the replication and separation of the SPB. This paper also provides new information on SPB structure inS. pombe. This is discussed in connection with the transient assembly of both spindle and cytoplasmic microtubules.

The isolation of protoplasts of the fission yeast Schizosaccharomyces by Trichoderma viride and snail enzymes.

The formation of protoplasts of the fission yeasts Schizosaccharomyces pombe and Schizosaccharomyces versatilis after the combined application of snail enzymes and Trichoderma viride enzymes in an osmotic stabilizer (0.4M KCl, pH 5.5) was studied by light and electron microscopy. The effect of the enzymes used leads during 30 min to the formation of 100% protoplast population. Using electron microscopy no original walls or wall remnants were detected in the suspension of protoplasts. Protoplasts are viable and in liquid nutrient medium they regenerate cell walls and revert into normal cells. Such a protoplast population may be useful for biochemical study of protoplast metabolism by quantitative methods as well as for the chemical study of regenerating cell walls.

Utilization and interconversions of purine derivatives in the fission yeastSchizosaccharomyces pombe

SUMMARYIn the fission yeastSchizosaccharomyces pombe, growth responses of mutants strains in the de novo purine synthesis pathway, in the purine interconversion system, and of various double mutants, have been studied upon different purine-supplemented media. The results show that exogenous purine utilization as nucleotide source is based exclusively upon pyrophosphorylation of purine bases, and they make it possible to identify most of the enzymic steps acting, in this organism, upon a purine ring to give another purine ring.A scheme of the interconversion system inSchizosaccharomyces pombeis given.