Direct induction of homozygous diploidization in the fission yeastSchizosaccharomyces pombeby pressure stress

Regulation of cell cycle and stress responses to hydrostatic pressure in fission yeast

We have investigated the cellular responses to hydrostatic pressure by using the fission yeast Schizosaccharomyces pombe as a model system. Exposure to sublethal levels of hydrostatic pressure resulted in G2 cell cycle delay. This delay resulted from Cdc2 tyrosine-15 (Y-15) phosphorylation, and it was abrogated by simultaneous disruption of the Cdc2 kinase regulators Cdc25 and Wee1. However, cell cycle delay was independent of the DNA damage, cytokinesis, and cell size checkpoints, suggesting a novel mechanism of Cdc2-Y15 phosphorylation in response to hydrostatic pressure. Spc1/Sty1 mitogen-activated protein (MAP) kinase, a conserved member of the eukaryotic stress-activated p38, mitogen-activated protein (MAP) kinase family, was rapidly activated after pressure stress, and it was required for cell cycle recovery under these conditions, in part through promoting polo kinase (Plo1) phosphorylation on serine 402. Moreover, the Spc1 MAP kinase pathway played a key role in maintaining cell viability under hydrostatic pressure stress through the bZip transcription factor, Atf1. Further analysis revealed that prestressing cells with heat increased barotolerance, suggesting adaptational cross-talk between these stress responses. These findings provide new insight into eukaryotic homeostasis after exposure to pressure stress.

Effects of pressure stress on the fission yeast Schizosaccharomyces pombe cold-sensitive mutant nda3

To investigate the influence of pressure stress on the cell cycle of Schizosaccharomyces pombe, we used a cold-sensitive nda3-KM311 mutant which arrests cell division at a step similar to the mitotic prophase, proposed by Hiraoka and colleagues (Cell 39 (1984) 349-358), under the restrictive temperature, 20 degrees C. The nda3-KM311 cells were first aerobically grown at 30 degrees C, transferred to 20 degrees C for 4 h and shifted to a permissive temperature of 36 degrees C for 15 min. The cells were treated with 100-200 MPa pressure and studied by electron and fluorescence microscopy. At 100 MPa, the nuclear membrane was damaged and the matrix of mitochondria had an electron-dense area. At 150 MPa, the nuclear membrane was broken over broad areas; numerous small vacuoles had fused into large pieces. Actin patches were concentrated in the central region and actin rings were seen in the 20 degrees C-grown cells. Even at 100 MPa, specific actin distribution was lost. Although at 100 MPa, long and fine actin cables were seen all over the cells, large actin patches and the actin rings remained in the center of the cell. They changed into thick and short cables at 150 MPa and above 200 MPa they decomposed but the actin ring was visible even with faint fluorescence. Immunoelectron microscopic observation confirmed this phenomenon.