The Septation Apparatus, an Autonomous System in Budding Yeast

Abstract

Actomyosin ring contraction and chitin primary septum deposition are interdependent processes in cell division of budding yeast. By fusing Myo1p, as representative of the contractile ring, and Chs2p for the primary septum, to different fluorescent proteins we show herein that the two processes proceed essentially at the same location and simultaneously. Chs2p differs from Myo1p in that it reflects the changes in shape of the plasma membrane to which it is attached and in that it is packed after its action into visible endocytic vesicles for its disposal. To ascertain whether this highly coordinated system could function independently of other cell cycle events, we reexamined the septum-like structures made by the septin mutant cdc3 at various sites on the cell cortex at the nonpermissive temperature. With the fluorescent fusion proteins mentioned above, we observed that in cdc3 at 37°C both Myo1p and Chs2p colocalize at different spots of the cell cortex. A contraction of the Myo1p patch could also be detected, as well as that of a Chs2p patch, with subsequent appearance of vesicles. Furthermore, the septin Cdc12p, fused with yellow or cyan fluorescent protein, also colocalized with Myo1p and Chs2p at the aberrant locations. The formation of delocalized septa did not require nuclear division. We conclude that the septation apparatus, composed of septins, contractile ring, and the chitin synthase II system, can function at ectopic locations autonomously and independently of cell division, and that it can recruit the other elements necessary for the formation of secondary septa.

The yeast endocytic protein Epsin 2 functions in a cell-division signaling pathway

“…Since these latter processes depend on chitin synthase regulation, particularly of Chs2 (Cabib et al, 2001), we examined the localization and dynamics of Chs2-GFP in empty vector transformants, ENTH1-and ENTH2-overexpressing cells. In agreement with normal Chs2-GFP behavior as described by others (Roh et al, 2002), ENTH1-overexpressing and empty-vectortransformed cells had dynamic punctate structures and transient localization at the bud neck during cytokinesis (supplementary material Fig. S4 and supplementary material Movies 3 and 4, respectively).…”

Architecture and Biosynthesis of the Saccharomyces cerevisiae Cell Wall

“…Chs2 resides at the site of primary septum formation for only 7-8 min (Roh et al 2002a;Zhang et al 2006). The protein is degraded upon endocytosis and delivery to the vacuole Schmidt et al 2002;VerPlank and Li 2005), and optimal endocytic turnover of Chs2 requires components of the endosomal sorting complexes required for transport (ESCRT) pathway (McMurray et al 2011).…”

Mitotic Exit and Separation of Mother and Daughter Cells

“…Indeed, defects in protein mannosylation affect septation; this process occurs as proteins that span the plasma membrane or are secreted move through the endomembrane system, and is broadly important for the function of cell wall components (Schmidt et al 2005). A forthcoming YeastBook chapter by Orlean and Strahl will discuss cell wall organization mechanisms in detail; additionally, the process by which this septum is built is the subject of a number of excellent reviews (Cabib et al 2001;Roh et al 2002;Roncero and Sanchez 2010).…”