Biomedical subjects

Takayoshi Kuno

Publications and source records attributed to Takayoshi Kuno.

21 records · Page 2Linked to original sources

PubMed2002

Calcineurin is implicated in the regulation of the septation initiation network in fission yeast.

BACKGROUND: In fission yeast, calcineurin has been implicated in cytokinesis because calcineurin-deleted cells form multiple septa and cell separation is impeded. However, this mechanism remains unclear. RESULTS: We screened for mutations that confer synthetic lethality with calcineurin deletion and isolated a mutant, its 10-1/cdc7-i10, a novel allele of the cdc7+ gene involved in the septation initiation network (SIN). The mutation created a termination codon, resulting in the truncation of Cdc7 by 162 amino acids, which is not localized in the spindle pole body. Following treatment with the immune suppressive drug FK506, cdc7-i10 and the original cdc7-24 mutant cells showed highly elongated multinuclear morphology with few visible septa, closely resembling the phenotype at the restrictive temperature. Other SIN mutants, cdc11, spg1, sid2 and mob1 showed similar phenotypes following FK506 treatment. Consistent with this, expression of the constitutively active calcineurin suppressed the growth defects and septum initiation deficiency of these SIN mutants at the restrictive temperature. Moreover, electron microscopy revealed that calcineurin-deleted cells had very thick multiple septa which were partially and ectopically formed. CONCLUSION: These results suggest that calcineurin is involved in the regulation of the SIN pathway, and is required for the proper formation and maturation of the septum in fission yeast.

Alleles↗

PubMed2002

Role of the Rab GTP-binding protein Ypt3 in the fission yeast exocytic pathway and its connection to calcineurin function.

A genetic screen for mutations synthetically lethal with fission yeast calcineurin deletion led to the identification of Ypt3, a homolog of mammalian Rab11 GTP-binding protein. A mutant with the temperature-sensitive ypt3-i5 allele showed pleiotropic phenotypes such as defects in cytokinesis, cell wall integrity, and vacuole fusion, and these were exacerbated by FK506-treatment, a specific inhibitor of calcineurin. Green fluorescent protein (GFP)-tagged Ypt3 showed cytoplasmic staining that was concentrated at growth sites, and this polarized localization required the actin cytoskeleton. It was also detected as a punctate staining in an actin-independent manner. Electron microscopy revealed that ypt3-i5 mutants accumulated aberrant Golgi-like structures and putative post-Golgi vesicles, which increased remarkably at the restrictive temperature. Consistently, the secretion of GFP fused with the pho1(+) leader peptide (SPL-GFP) was abolished at the restrictive temperature in ypt3-i5 mutants. FK506-treatment accentuated the accumulation of aberrant Golgi-like structures and caused a significant decrease of SPL-GFP secretion at a permissive temperature. These results suggest that Ypt3 is required at multiple steps of the exocytic pathway and its mutation affects diverse cellular processes and that calcineurin is functionally connected to these cellular processes.

Actins↗

PubMed2002

Genetic interaction between calcineurin and type 2 myosin and their involvement in the regulation of cytokinesis and chloride ion homeostasis in fission yeast.

Calcineurin plays a critical role in Ca(2+) signaling in various cell types. In fission yeast, calcineurin is required for cytokinesis and chloride ion homeostasis. However, most of its physiological functions remain obscure. A genetic screen was performed to identify genes that share an essential function with calcineurin. We screened for mutations that confer sensitivity to the calcineurin inhibitor FK506 and to a high concentration of chloride ion and isolated a mutant, cis2-1/myp2-c2, which contains a novel allele of the myp2(+)/myo3(+) gene that encodes a type 2 myosin heavy chain. The myp2-c2 mutant showed morphological defects similar to those associated with a calcineurin deletion mutant, such as multiseptated and branched cells. Consistently, myp2-null cells were hypersensitive to chloride ion and showed the multiseptated phenotype in the presence of immunosuppressants or at high chloride concentrations. Overexpression of constitutively active calcineurin suppressed the chloride ion-sensitive growth defect and cytokinesis abnormality of the myp2-c2 mutant and myp2-null cells. Interestingly, the essential myosin light chain mutant cdc4-8 failed to grow and could not form a normal contractile ring in the presence of immunosuppressants. Furthermore, calcineurin-null cells exhibited aberrant contractile rings, suggesting impaired contraction of the rings. These results indicate that calcineurin is involved in the regulation of cytokinesis and that chloride ion homeostasis is mediated by type 2 myosin.

Calcineurin↗