Inn1 couples contraction of the actomyosin ring to membrane ingression during cytokinesis in budding yeast

Abstract

By rapidly depleting each of the essential budding yeast proteins of unknown function, we identified a novel factor that we call Inn1, which associates with the contractile actomyosin ring at the end of mitosis and is needed for cytokinesis. We show that Inn1 has a C2 domain at the amino terminus of the protein that is required for ingression of the plasma membrane, whereas the remainder of the protein recruits Inn1 to the actomyosin ring. The lethal effects of deleting the INN1 gene can be suppressed by artificial fusion of the C2 domain to other components of the actomyosin ring, restoring membrane ingression on contraction of the actomyosin ring. Our data indicate that recruitment of the C2 domain of Inn1 to the contractile actomyosin ring is crucial for ingression of the plasma membrane during cytokinesis in budding yeast.

Cdk1-dependent phosphorylation of Iqg1 governs actomyosin ring assembly prior to cytokinesis

“…Iqg1 interaction with Inn1 has been demonstrated previously (Sanchez-Diaz et al, 2008), and Iqg1 interacts genetically with another Inn1-regulating protein, Cyk3 (Korinek et al, 2000). Our evidence for a physical interaction between Iqg1 and Hof1 provides further support for the notion that Iqg1 contributes to the regulation of primary septum deposition.…”

“…A secondary septum is then deposited along the primary septum and becomes the cell wall upon digestion of the primary septum. Like AMR assembly, primary septum deposition follows the sequential bud neck localization of several organizing proteins, most importantly Hof1, Cyk3 and Inn1 (Devrekanli et al, 2012;Kamei et al, 1998;Korinek et al, 2000;Lippincott and Li, 1998a;Nishihama et al, 2009;Sanchez-Diaz et al, 2008).…”

Mechanisms of cytokinesis in budding yeast

“…Because cyk3D is synthetically lethal with either myo1D or hof1D [Korinek et al, 2000], Cyk3 and Hof1 likely share an essential role in promoting PS formation in AMR-independent cytokinesis. Inn1 localizes to the division site after Iqg1 but before Cyk3, whereas Hof1 displays a complex pattern of localization during the cell cycle [Vallen et al, 2000;Sanchez-Diaz et al, 2008;Jendretzki et al, 2009;Nishihama et al, 2009;Meitinger et al, 2010]. Together, these observations suggest that Iqg1-Inn1-Hof1/ Cyk3 defines another level of AMR-PS coordination that presumably acts downstream of Iqg1.…”

Mitotic Exit and Separation of Mother and Daughter Cells

“…This complex localizes to the actomyosin ring before it contracts, a process that involves coordinated phosphorylation of Hof1 by Mob1-Dbf2, Cdc5, and mitotic CDK. The overall effect of this regulation is to shift Hof1 from a septin-bound pool to an actomyosin association (Korinek et al 2000;Vallen et al 2000;Sanchez-Diaz et al 2008;Meitinger et al 2010Meitinger et al , 2011. As a result, Inn1 and Cyk3 promote the localized activity of Chs2 and thus growth of the primary septum in concert with actomyosin ring contraction.…”