Educational Activities

Graduate School: Molecular Biology, Functional Genomics

Research Activities

Research in our laboratory is aimed to study coordination of cell morphology with cell proriferation. It is believed that cell wall remodeling and cell morphogenesis are tightly coordinated with progression of the cell cycle in many organisms. In the budding yeast, Saccharomyces cerevisiae, a major cell wall component, 1,3- -glucan is synthesized at the budding site in the early stage of the cell cycle, and constructed in the primary septum before cytokinesis. Yeast possesses both forward and feedback system to achieve temporal and spatial regulation of cell wall construction, Forward system is composed of a cell cycle dependent morphological pathway that is regulated by small GTPase, Rho1p. In addition, the feedback regulatory system, called cell wall integrity checkpoint was recently studied and characterized in our laboratory.
We found that yeast cells stop growing at the specific stage of the cell cycle after perturbation of 1,3- -glucan synthesis. These cells arrest with post-replicative DNA but quite low level of Clb2p, and without forming bipolar spindles. Wall-checkpoint defective mutation (wac1) that abolishes this arrest causes the accumulation of Clb2p and CLB2 mRNA and leads to formation of bipolar spindles despite 1,3- -glucan-synthesis perturbation. These results indicate the existence of a novel cell cycle checkpoint to coordinate entry into mitosis, and suggest that Wac1p is required to achieve this checkpoint function through a transcriptional regulation of CLB2. We revealed that WAC1 is identical with ARP1 (actin-related protein). Arp1p, Nip100p and Jnm1p, which are components of the dynactin complex, are all required to achieve the G2 arrest while keeping cells highly viable. These results imply that the dynactin complex has a regulatory role in the novel checkpoint to monitor cell wall remodeling.
With regard to the high-dimensional and quantitative phenotypic traits of cell morphology, we have developed CalMorph system suitable for collecting cell morphology information (collaboration with Prof. Morishita's group). Using CalMorph we have recently shown that we can reflect the dispersion to the high-dimensional cluster analysis using the morphological data obtained from replicated experiments. Qualitative or categorical phenotypes have been used for classification of mutants without consideration of the dispersion of the data. However, more accurate and detailed phenotypic analyses can now be performed to identify classes of mutants with similar phenotypes based on probability. Our new method is applicable to any quantitative phenotype (even a categorical phenotype) that is obtained from replicated experiments. Therefore, this method will represent a powerful method for large-scale phenotypic analysis.


yeast cells with various morphology

Literature

1) Suzuki, M., Igrashi, R., Sekiya, M., Utsugi, T., Morishita, S., Yukawa, M., Ohya, Y. (2004) Dynactin is involved in a checkpoint to monitor cell wall synthesis in Saccharomyces cerevisiae. Nat Cell Biol. 6:861-71.

2) Ohya, Y., Sese, J., Yukawa, M., Sano, F., Nakatani, Y., Saito, TL., Saka. A., Fukuda, T., Ishihara, S., Oka, S., Suzuki, G., Watanabe, M., Hirata, A., Ohtani, M., Sawai, H., Fraysse, N., Latge, JP., Francois, JM., Aebi, M., Tanaka, S., Muramatsu, S., Araki, H., Sonoike, K., Nogami, S., Morishita, S. (2005) High-dimensional and large-scale phenotyping of yeast mutants. Proc Natl Acad Sci U S A. 2005 Dec 27;102(52):19015-20.

3) Ohnuki, S., Kanai, H., Nogami, S., Nakatani, Y., Morishita, S., Hirata, D., Ohya Y. (2007) Multiple Ca2+ regulatory pathways revealed by morphological phenotyping of calcium-sensitive mutants. Eukaryotic Cell 6:817-30.

Other Activities

Priority Committee Member of Riken, etc.

Future Plan

1) Cell cycle checkpoint
2) High dimensional quantitative trait analysis
3) Chemical genomics

Messages to Students

Our immediate goals are to determine how yeast cells proliferate at the right timing in a right way. A variety of molecular, genetic, and immunochemical approaches will be employed so that any talented young students can join our laboratory.