Regulation of Mitotic Spindle Disassembly by an Environmental Stress-Sensing Pathway in Budding Yeast

Abstract

Timely spindle disassembly is essential for coordination of mitotic exit with cytokinesis. In the budding yeast Saccharomyces cerevisiae, the microtubule-associated protein She1 functions in one of at least three parallel pathways that promote spindle disassembly. She1 phosphorylation by the Aurora kinase Ipl1 facilitates a role for She1 in late anaphase, when She1 contributes to microtubule depolymerization and shrinkage of spindle halves. By examining the genetic interactions of known spindle disassembly genes, we identified three genes in the environmental stress-sensing HOG (high-osmolarity glycerol response) pathway, SHO1, PBS2, and HOG1, and found they are necessary for proper localization of She1 to the anaphase spindle and for proper spindle disassembly. HOG pathway mutants exhibited spindle disassembly defects, as well as mislocalization of anillin-related proteins Boi1 and Boi2 from the bud neck. Moreover, Boi2, but not Boi1, plays a role in spindle disassembly that places Boi2 in a pathway with Sho1, Pbs2, and Hog1. Together, our data identify a process by which cells monitor events at the spindle and bud neck and describe a novel role for the HOG pathway in mitotic signaling. MICROTUBULE dynamics play important roles in every stage of mitosis. In early M phase, interpolar microtubules help drive the separation of the spindle pole bodies (SPBs) to establish a bipolar spindle. As these interpolar microtubules (ipMTs) lengthen, the SPBs separate due to sliding forces generated by opposing microtubules originating from the opposite poles. In addition to ipMTs, kinetochore microtubules (kMTs) are attached to the kinetochore of each chromatid. A third class of microtubules, astral microtubules (aMTs), attach the SPBs to the cell cortex and help position the spindle along the mother-bud axis in yeast or perpendicular to the division plane in mammalian cells. Together, these three classes of MTs form the mitotic spindle. Over the course of mitosis, the dynamics of microtubules are modulated by several classes of proteins including +TIP proteins such as EB1/Bim1, which stabilize microtubule plus ends and promote growth, crosslinking proteins such as Ase1, which stabilize lateral interactions between ipMTs of the midzone, motor proteins such as Cin8 and Kip1, which generate forces necessary to slide the ipMTs by each other, and other motor proteins such as Kar3 and dynein (reviewed in Westermann et al. 2007;Khmelinskii and Schiebel 2008) that are also responsible for generating forces on MTs.She1 is an important regulator of microtubule dynamics in budding yeast and it appears to have several functions in the cell Bergman et al. 2012;Markus et al. 2012). Beginning in G1, She1 localizes to the SPB and restricts the activity of dynein by inhibiting its interaction with dynactin until anaphase, when dynein is required for spindle positioning prior to elongation into the bud ). In M phase, She1 also localizes to the kinetochore and along spindle microtubules and to the bud neck . Upon completion of anaph...

The kinetic landscape and interplay of protein networks in cytokinesis

“…To achieve an accurate comparison of the accumulation kinetics of each GFP-tagged protein from different strains, we included two RFP-based cell cycle markers as the “clock” in each strain ( Figure 1 A). mRuby2-Tub1, an RFP-tagged alpha-tubulin, marks the mitotic spindle ( Markus, et al., 2015 ), and the spindle breakage is known to occur a few minutes before the onset of AMR constriction in wild-type (WT) cells ( Pigula, et al., 2014 ; Woodruff, et al., 2010 ). Except where noted, time “0” refers to the point of spindle breakage or disassembly in all the analyses.…”

A new identified suppressor of Cdc7p/SepH kinase, PomA, regulates fungal asexual reproduction via affecting phosphorylation of MAPK-HogA

“…In mammalian cells, the MAPK signaling pathway is critical for normal immune and inflammatory responses and contributes to cell cycle or cytoskeleton remodeling [18]. In model yeasts, the MAPK signaling pathway involves many biological processes, including cell wall integrity, cell separation and the regulation of mitotic spindle disassembly [15,19]. In most filamentous fungi, the high-osmolarity glycerol (HOG) gene hogA , which encodes a MAPK that sense osmotic and oxidative stress, is required for hyphal growth and conidiation under osmotic stress culture conditions [14,20].…”

The conserved histone deacetylase Rpd3 and the DNA binding regulator Ume6 repress BOI1's meiotic transcript isoform during vegetative growth in Saccharomyces cerevisiae

“…A detailed cytological analysis in budding yeast revealed a role for Boi1 and Boi2 in a pathway preventing chromosomes from being broken apart during late stages of mitosis in anaphase and telophase, when sister chromatids are separated and pulled to opposite poles before cells split during cytokinesis (Norden et al ., ). Recent work suggests only Boi2, but not Boi1, to be important for spindle disassembly (Pigula et al ., ). Direct evidence for a role in polar growth was also reported for the fission yeast Boi1/2 homolog Pob1p (Toya et al ., ).…”