Roles of the fission yeast UNC-13/Munc13 protein Ync13 in late stages of cytokinesis

Abstract

Cytokinesis is a complicated yet conserved step of the cell-division cycle that requires the coordination of multiple proteins and cellular processes. Here we describe a previously uncharacterized protein, Ync13, and its roles during fission yeast cytokinesis. Ync13 is a member of the UNC-13/Munc13 protein family, whose animal homologues are essential priming factors for soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex assembly during exocytosis in various cell types, but no roles in cytokinesis have been reported. We find that Ync13 binds to lipids in vitro and dynamically localizes to the plasma membrane at cell tips during interphase and at the division site during cytokinesis. Deletion of Ync13 leads to defective septation and exocytosis, uneven distribution of cell-wall enzymes and components of cell-wall integrity pathway along the division site and massive cell lysis during cell separation. Interestingly, loss of Ync13 compromises endocytic site selection at the division plane. Collectively, we find that Ync13 has a novel function as an UNC-13/Munc13 protein in coordinating exocytosis, endocytosis, and cell-wall integrity during fission yeast cytokinesis.

Two S. pombe septation phases differ in ingression rate, septum structure, and response to F-actin loss

“…Our TEM analysis of 130 WT septa showed many septa where the PS edge is behind the septum membrane edge. These sharp-edge septa point to septum membrane ingression occurring with a reduced or nonexistent pushing force from the PS, likely by addition of exocytic vesicles and membrane edge expansion (Vjestica et al, 2008;Wang et al, 2016;Zhu et al, 2018), as has been shown in animal and plant cytokinesis (Albertson et al, 2005;Prekeris and Gould, 2008;Müller and Jürgens, 2016;Smertenko et al, 2017). The PS synthesis is not necessarily performed from the Bgs1 ring at the septum edge.…”

“…However, the observation that in cells depleted of Bgs4-dependent β(1,3)glucan, a defective PS can lag behind the septum membrane during ingression suggests that the addition of new membrane to the growing septum edge could be important for driving cytokinesis, at least in mutants with a defective PS (Muñoz et al, 2013;García Cortés et al, 2016). Since we have found the exocyst is essential for septum ingression without F-actin, and it has been suggested that an exocyst-dependent expansion of the septum membrane is required for cytokinesis (Wang et al, 2016;Zhu et al, 2018), we used TEM to carefully examine the membrane deposition and septum edge ultrastructure in a high number of WT cells. A total of 122 TEM images of ingressing septa obtained from cells grown in different media from this study and 8 images from our previous studies (Cortés et al, 2012(Cortés et al, , 2015 were analyzed.…”

Roles of Mso1 and the SM protein Sec1 in efficient vesicle fusion during fission yeast cytokinesis

“…Previous studies found that exocytosis is essential for cytokinesis in fission yeast ( Wang et al. , 2002 , 2016 ; Zhu et al. , 2018 ).…”

“…, 2016 ). This TRAPP-II mediated exocytosis depends in part on the UNC-13/Munc13 protein Ync13 ( Zhu et al. , 2018 ).…”

Molecular mechanisms of contractile-ring constriction and membrane trafficking in cytokinesis

“…Thus, the coordination between exocytosis and endocytosis is essential, but it is poorly understood. Ync13, an Unc-13/Munc13 protein, plays a role in organizing exocytosis and endocytosis during cytokinesis (Zhu et al 2018). Loss of Ync13 dramatically affects endocytic sites on the division plane (Zhu et al 2018).…”