Originally published as Genetics Published Articles Ahead of Print on January 16, 2006.

Genetics, Vol. 172, 2101-2112, April 2006, Copyright © 2006
doi:10.1534/genetics.105.050955

A Role for the Septation Initiation Network in Septum Assembly Revealed by Genetic Analysis of sid2-250 Suppressors

Quan-Wen Jin^*, Mian Zhou^*, Andrea Bimbo, Mohan K. Balasubramanian and Dannel McCollum^*,1

^* Department of Molecular Genetics and Microbiology, and the Program in Cell Dynamics, University of Massachusetts Medical School, Worcester, Massachusetts 01605 and Cell Division Laboratory, Temasek Life Sciences Laboratory and Department of Biological Sciences, National University of Singapore, Singapore 117604, Republic of Singapore

¹ Corresponding author: University of Massachusetts Medical School, 377 Plantation St., Biotech 4, Worcester, MA 01605.
E-mail: dannel.mccollum{at}umassmed.edu

In the fission yeast Schizosaccharomyces pombe the septation initiation network (SIN) is required for stabilization of the actomyosin ring in late mitosis as well as for ring constriction and septum deposition. In a genetic screen for suppressors of the SIN mutant sid2-250, we isolated a mutation, ace2-35, in the transcription factor Ace2p. Both ace2 and ace2-35 show defects in cell separation, and both can rescue the growth defects of some SIN mutants at low restrictive temperatures, where the SIN single mutants lyse at the time of cytokinesis. By detailed analysis of the formation and constriction of the actomyosin ring and septum in the sid2-250 mutant at low restrictive temperatures, we show that the lysis phenotype of the sid2-250 mutant is likely due to a weak cell wall and septum combined with enzymatic activity of septum-degrading enzymes. Consistent with the recent findings that Ace2p controls transcription of genes involved in cell separation, we show that disruption of some of these genes can also rescue sid2-250 mutants. Consistent with SIN mutants having defects in septum formation, many SIN mutants can be rescued at the low restrictive temperature by the osmotic stabilizer sorbitol. The small GTPase Rho1 is known to promote cell wall formation, and we find that Rho1p expressed from a multi-copy plasmid can also rescue sid2-250 at the low restrictive temperature. Together these results suggest that the SIN has a role in promoting proper cell wall formation at the division septa.

International Access Link

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
phone: 412-268-1812   fax: 412-268-1813   email: genetics-gsa{at}andrew.cmu.edu