Genes that cause aberrant cell morphology by overexpression in fission yeast: a role of a small GTP-binding protein Rho2 in cell morphogenesis.

To identify the genes involved in cell morphogenesis in Schizosaccharomyces pombe, we screened for the genes that cause aberrant cell morphology by overexpression. The isolated genes were classified on the basis of morphology conferred. One of the genes causing a rounded morphology was identified as the rho2+ gene encoding a small GTP-binding protein. The overexpression of rho2+ resulted in a randomized distribution of cortical F-actin and formation of a thick cell wall. Analyses using cdc mutants suggested that the overexpression of rho2+ prevents the establishment of growth polarity in G1. The rho2+ gene was not essential, but among cells deleted for rho2+, those with an irregular shape were observed. The disruptant also showed a defect in cell wall integrity. An HA-Rho2 expressed in the cell was suggested to be present as a membrane-bound form by a cell fractionation experiment. A GFP-Rho2 was localized at the growing end(s) of the cell and the septation site. The localization of GFP-Rho2 during interphase was partially dependent on sts5+. These results indicate that Rho2 is involved in cell morphogenesis, control of cell wall integrity, control of growth polarity, and maintenance of growth direction. Analysis of functional overlapping between Rho2 and Rho1 revealed that their functions are distinct from each other, with partial overlapping.