Ace2p Controls the Expression of Genes Required for Cell Separation inSchizosaccharomyces pombe

Abstract

Schizosaccharomyces pombe cells divide by medial fission through contraction of an actomyosin ring and deposition of a multilayered division septum that must be cleaved to release the two daughter cells. Here we describe the identification of seven genes (adg1؉ , and mid2 ؉ ) whose expression is induced by the transcription factor Ace2p. The expression of all of these genes varied during the cell cycle, maximum transcription being observed during septation. At least three of these proteins (Eng1p, Agn1p, and Cfh4p) localize to a ring-like structure that surrounds the septum region during cell separation. Deletion of the previously uncharacterized genes was not lethal to the cells, but produced defects or delays in cell separation to different extents. Electron microscopic observation of mutant cells indicated that the most severe defect is found in eng1⌬ agn1⌬ cells, lacking the Eng1p endo-␤-1,3-glucanase and the Agn1p endo-␣-glucanase. The phenotype of this mutant closely resembled that of ace2⌬ mutants, forming branched chains of cells. This suggests that these two proteins are the main activities required for cell separation to be completed.

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

“…Although the disruption of exocyst function does not show comparable rescue to that of mid2D, ace2D and double deletion of eng1D agn1D, it might be explained by the fact that the exocyst complex is involved in transporting numerous proteins for different purposes and is essential for viability . We did not observe rescue of sid2-250 by deletion of the transcription factor sep1 1 , which has ace2 1 as one of its targets (Rustici et al 2004;Alonso-Nunez et al 2005), although sep1D shows very strong cell-separation defects. This might be explained by the fact that sep1 1 regulates multiple targets, including sid2 1 , which may offset the effects of loss of ace2 1 transcription.…”

“…1 is a target of the Ace2p transcription factor (Rustici et al 2004;Alonso-Nunez et al 2005). We show that expression of mid2 1 from a heterologous promoter could reverse the ability of an ace2D mutant to suppress sid2-250, suggesting that ace2D suppression of sid2-250 is due to loss of mid2 1 expression.…”

“…One of the other targets of Ace2p is mid2 1 , an anillin homolog required for septin ring assembly and stability (Berlin et al 2003;Tasto et al 2003;Rustici et al 2004;Alonso-Nunez et al 2005). Mutant cells lacking mid2 1 show a cellseparation defect similar to that of sep1D and ace2D but less severe.…”

“…The expression of Eng1p and Agn1p, together with at least five other proteins required for cell separation during the last stages of the cell cycle, is transcriptionally regulated by the transcription factor Ace2p (Rustici et al 2004;Alonso-Nunez et al 2005). In addition, various other proteins have been directly or indirectly implicated in the process of cell separation in fission yeast, as several mutants affecting cell-cell separation have been isolated, including mutations in the forkhead transcription factor sep1 (Yoshida et al 1994;Longtine et al 1996;Toda et al 1996;Ribar et al 1997;Sugiura et al 1998;Jiang and Hallberg 2000;Le Goff et al 2001;Wang et al 2002;Berlin et al 2003;Nakano et al 2003;Santos et al 2003;Tasto et al 2003;An et al 2004;Dekker et al 2004;Alonso-Nunez et al 2005;Bahler 2005;Garcia et al 2005). It is unclear how all of these proteins promote cell separation, but the exocyst complex, along with Mid2p and septins, was recently shown to be required for targeting of enzymes involved in septum cleavage to the septum .…”

Does copper stress lead to spindle misposition-dependent cell cycle arrest?

“…A conserved fungal protein encoding gene, adg2, whose expression increased 1.4-fold in response to copper stress in our study is regulated by Ace2 transcription factor and thought to function in separating daughter cells at the end of cytokinesis (Alonso-Nunez et al, 2005). Ace2p also plays a regulatory role in the cell separation process after budding in S. cerevisiae.…”