Targeted localization of Inn1, Cyk3 and Chs2 by the mitotic-exit network regulates cytokinesis in budding yeast

Abstract

SummaryThe mitotic-exit network (MEN) is a signaling pathway that is essential for the coordination of mitotic exit and cytokinesis. Whereas the role of the MEN in mitotic exit is well established, the molecular mechanisms by which MEN components regulate cytokinesis remain poorly understood. Here, we show that the MEN controls components involved in septum formation, including Inn1, Cyk3 and Chs2. MEN-deficient mutants, forced to exit mitosis as a result of Cdk1 inactivation, show defects in targeting Cyk3 and Inn1 to the bud-neck region. In addition, we found that the chitin synthase Chs2 did not efficiently localize at the bud neck in the absence of MEN activity. Ultrastructural analysis of the bud neck revealed that low MEN activity led to unilateral, uncoordinated extension of the primary and secondary septa. This defect was partially suppressed by increased levels of Cyk3. We therefore propose that the MEN directly controls cytokinesis via targeting of Inn1, Cyk3 and Chs2 to the bud neck.

Mechanisms of cytokinesis in budding yeast

“…Second, the MEN could control AMR constriction by controlling PS formation. The MEN activity is required for the proper localization of the proteins involved in PS formation such as Chs2, Inn1, Hof1, and Cyk3 (see more discussion on these proteins later) at the division site Meitinger et al, 2010]. Consistently, MEN mutants are defective in PS formation [Meitinger et al, 2010].…”

“…First, the MEN could control AMR constriction by controlling septin hourglass splitting [Cid et al, 2001;Lippincott et al, 2001]. However, in the MEN mutants forced to exit mitosis by overexpression of the CDK1 inhibitor Sic1, the septin hourglass is split into two cortical rings but AMR constriction still cannot occur [Meitinger et al, 2010;Meitinger et al, 2011], suggesting that the MEN controls AMR constriction independently of septin hourglass splitting. Second, the MEN could control AMR constriction by controlling PS formation.…”

Hippo signalling in the G2/M cell cycle phase: Lessons learned from the yeast MEN and SIN pathways

“…Nevertheless, recent evidence suggests that MEN signalling components have more direct roles in orchestrating the process of cytokinesis. On one hand, Dbf2p and Mob1p have been found at the actin-myosin ring (AMR) structure that is essential for abscission [35][36][37][38], and Cdc15p, Dbf2p and Mob1p are required for AMR contraction [39,40]. Moreover, current evidence suggests that the MEN components Dbf2p and Mob1p can regulate the cytokinetic components Chs2p, Hof1p, and Inn1p (summarised in [33,41]).…”

Microcompartments within the yeast plasma membrane

“…They orchestrate cell division and act as a signaling platform for cytokinesis Vrabioiu and Mitchison , 2006 ;McMurray and Thorner , 2009a ;Roncero and Sanchez , 2010 AMR (Myo1, Mlc1, Act1) AMR assembles during early mitosis Myo1; type II myosin of the AMR; Mcl1, type V myosin, light chain of Myo1; Act1, forming filamentous actin Vallen et al , 2000 Iqg1 ( = Cyk1) Ring-like structure at the bud neck Essential for actomyosin formation but has also a cytokinetic function that is independent from the AMR; interacts with Myo1 independently of septins Epp and Chant , 1997 ;Ko et al , 2007 Cyk3 Ring-like structure at the bud neck Recruits Inn1 to the bud neck; when overexpressed, Inn1 recruitment is AMR independent Jendretzki et al , 2009 ;Meitinger et al , 2010 Inn1 Localizes to the bud neck during late mitosis Required for plasma membrane ingression concomitant with AMR constriction; binds to Hof1 and Cyk3 Jendretzki et al , 2009 ;Meitinger et al , 2010 Hof1 Bud neck at anaphase; initially forms a double ring that fuses after AMR constriction Binds to the formin Bnr1 and triggers AMR constriction; then, it relocates to the septin filaments Vallen et al , 2000 ;Meitinger et al , 2011 Formins (Bni1, Bnr1) Bni1 localizes at the bud tip during bud growth and later at the bud neck; Bnr1 stably associates with septins at the bud neck Promote actin polymerization in a Rho1 dependent manner.…”