Glutamyl tRNA synthetases and glutamic acid induce sexual differentiation of Schizosaccharomyces pombe.

The moc3 gene was screened out as an inducer of sexual differentiation in fission yeast Schizosaccharomyces pombe. We isolated a novel gene, named ers2, encoding mitochondrial glutamyl tRNA synthetase (mGluRS) as a Moc3 interacting element by the yeast two-hybrid system. Cytoplasmic glutamyl tRNA synthetase (cGluRS) also interacted with Moc3 in a yeast two-hybrid system. Disruption of ers1 (cGluRS) and of ers2 (mGluRS) indicated that these genes are both essential for the cell growth of S. pombe. We found that ers2 severely affected cell growth and decreased viability, but induced sexual differentiation of S. pombe when it was over-expressed. Over-expression of ers1 also stimulated sexual differentiation in S. pombe. These observations led us to test the effects of various amino acids on sexual differentiation. We found that glutamic acid, as well as other specific amino acids, such as tryptophan, methionine, and threonine, efficiently induced sexual differentiation in S. pombe. Our findings suggest a new regulatory mechanism where GluRSs and glutamic acid are involved in sexual differentiation in S. pombe.

Involvement of Moc1 in sexual development and survival of Schizosaccharomyces pombe.

The moc1 gene in Schizosaccharomyces pombe was found as to overcome sterility caused by high expression of adenylyl cyclase. The moc1 gene was found to be identical with sds23 and psp1. Although psp1 has been reported to be essential for growth, sds23 has not been. To clarify this apparent discrepancy, we first assessed independently the phenotypes of the moc1 disruptant. We confirmed that the deletion mutant of moc1 is sterile, sensitive to high salt, and grows slowly at higher and lower temperatures, and that mutant cells are elongated. Besides these phenotypes, we found that viability of the moc1 disruptant was rapidly lost at the stationary phase. We confirmed that the Moc1 protein is phosphorylated in the stationary phase and also under nitrogen-starved conditions. We examined the significance of this phosphorylation of Moc1 by creating the S333A or S333D mutant Moc1. Interestingly, while S333D mutant Moc1 is lower in inducing sexual development, S333A mutant Moc1 is higher in this than the wild type, suggesting that phosphorylation of Moc1 affects sexual development. The other phenotypes, such as sensitivity to high salt and higher temperature and elongation of cells, were not affected by mutation of S333A nor S333D. We found that Moc1-GFP localized to both the cytosol and the nucleus during mitotic growth, but accumulated in the nucleus in mating cells and then enriched in spores, and that this localization shift was negatively regulated by the cAMP pathway. This and the observations above suggest that nuclear localized Moc1 is an inducer of sexual development. Thus, in addition to the roles of moc1/sds23/psp1 in mitosis and stress response, it is also important for the survival and sexual development of fission yeast, but phosphorylation of Moc1 only affects the sexual development.

zds1, a novel gene encoding an ortholog of Zds1 and Zds2, controls sexual differentiation, cell wall integrity and cell morphology in fission yeast.

While screening for genes that reverse the sporulation-deficient phenotype of the ras1delta diploid Schizosaccharomyces pombe strain, we identified zds1. This gene shares sequence homology with the ZDS1 and ZDS2 genes from Saccharomyces cerevisiae, which appear to be involved in multiple cellular events. Expression of Zds1 in ras1delta diploid cells elevated their sporulation rate from 0.3 to 11.2%. Expression of the Zds1 C-terminal region increased the sporulation rate further (to 21.9%) while introduction of the Zds1 N-terminal region had no effect. zds1 expression did not induce sporulation in strains with mutations in genes participating in the downstream MAP kinase cascade. The zds1-disrupted strain is sensitive to CaCl2, and this effect is suppressed by the C-terminal region of Zds1. The growth of the zds1delta strain is markedly inhibited by cold temperatures, while its viability decreased in the stationary phase. Moreover, the zds1delta strain is round in shape and very sensitive to zymolyase, and its cell wall becomes thicker than that of wild type. Thus, zds1 must be required to maintain cell wall integrity. The Zds1-GFP fusion protein localized to the cytosol, the septum, and the cell cortex. Its localization in the septum was dependent on its C-terminal region. Overexpression of the C-terminal region of Zds1 induced multi-septa and abnormal zygotes. We propose that the C-terminal region is the functional domain of Zds1 while the N-terminal region is a negative regulatory region. Thus, Zds1 is involved in multiple cellular events in fission yeast, including sexual differentiation, Ca2+ tolerance, cell wall integrity, viability in the stationary phase, and cell morphology.