Genome-wide screen reveals novel mechanisms for regulating cobalt uptake and detoxification in fission yeast.

Cobalt is an essential micronutrient but is toxic when present in excess. To study cobalt homeostasis we performed a genome-wide screen for deletion strains that show sensitivity or resistance to CoCl(2). Among 54 cobalt-sensitive strains, 18 are supersensitive strains, which are involved in histidine biosynthetic process, ubiquitination, mitochondria function, membrane trafficking, transporter and a variety of other known functions or still unknown functions. Furthermore, we identified 56 cobalt-resistant deletion strains, which are mainly involved in mitochondria function, signal transduction, ubiquitination, and gene expression and chromatin remodeling. Notably, deletion of the zhf1(+) gene, encoding a zinc ion transporter, confers supersensitivity to cobalt and overexpression of the zhf1(+) gene confers marked tolerance to cobalt, indicating that Zhf1 play key roles in cobalt detoxification. Interestingly, all the histidine-auxotrophic mutants displayed cobalt sensitivity and deletion of cationic amino acid transporter Cat1, which was shown to be involved in histidine uptake, suppressed the CoCl(2)-sensitive growth defect of the his2 mutants, suggesting that CoCl(2) may be transported into the cell together with histidine via histidine transporters including Cat1. In addition, we obtained results suggesting that the E2 ubiquitin conjugating enzyme Rhp6 and Sty1 stress MAP kinase pathway are involved in the regulation of cobalt homeostasis. Altogether, our genome-wide study demonstrates for the first time the mechanisms of cobalt homeostasis, particularly its uptake and detoxification in fission yeast.

Genome-wide screening for genes associated with FK506 sensitivity in fission yeast.

We have been studying calcineurin signal transduction pathway in fission yeast Schizosaccharomyces pombe (S. pombe) by developing a genetic screen for mutants that show hypersensitivity to the immunosuppressive calcineurin inhibitor FK506 (tacrolimus). In the present study, to identify nonessential genes that are functionally related to the calcineurin signaling pathway, we performed a genome-wide screen of 3004 haploid deletion strains and confirmed 72 deletion strains to be FK506 sensitive. These 72 genes are classified into nine functional groups to include membrane trafficking (16 genes), signal transduction (10 genes), ubiquitination (8 genes), chromatin remodeling (6 genes), cytokinesis (4 genes), ribosomal protein (3 genes), RNA binding protein (3 genes), and a variety of other known functions (17 genes) or still unknown functions (5 genes) in the biological system. In our previous screening of FK506-sensitive mutants we isolated several membrane-trafficking mutants showing defective cell wall integrity. Here, we further examined the vacuolar fusion, the v-SNARE synaptobrevin Syb1 localization, and the sensitivity to the ß-glucan synthase inhibitor micafungin in these 72 FK506-sensitive strains. Results showed that 25 deletion strains exhibited abnormal vacuole fusion, 19 deletion strains exhibited Syb1 mislocalization, and 14 deletion strains exhibited both abnormal vacuole fusion and Syb1 mislocalization, while 42 deletion strains showed both normal vacuole fusion and Syb1 localization. Likewise, 16 deletion strains showed sensitivity to micafungin. Altogether, our present study indicates that calcineurin mediates a plethora of physiological processes in fission yeast, and that calcineurin is extensively involved in cross-talk between signaling pathways.