Characterization of ypa1 and ypa2, the Schizosaccharomyces pombe Orthologs of the Peptidyl Proyl Isomerases That Activate PP2A, Reveals a Role for Ypa2p in the Regulation of Cytokinesis

Abstract

The Schizosaccharomyces pombe septation initiation network (SIN) regulates cytokinesis. Cdc7p is the first kinase in the core SIN; we have screened genetically for SIN regulators by isolating cold-sensitive suppressors of cdc7-24. Our screen yielded a mutant in SPAC1782.05, one of the two fission yeast orthologs of mammalian phosphotyrosyl phosphatase activator. We have characterized this gene and its ortholog SPAC4F10.04, which we have named ypa2 and ypa1, respectively. We find that Ypa2p is the major form of protein phosphatase type 2A activator in S. pombe. A double ypa1-D ypa2-D null mutant is inviable, indicating that the two gene products have at least one essential overlapping function. Individually, the ypa1 and ypa2 genes are essential for survival only at low temperatures. The ypa2-D mutant divides at a reduced cell size and displays aberrant cell morphology and cytokinesis. Genetic analysis implicates Ypa2p as an inhibitor of the septation initiation network. We also isolated a cold-sensitive allele of ppa2, the major protein phosphatase type 2A catalytic subunit, implicating this enzyme as a regulator of the septation initiation network. SCHIZOSACCHAROMYCES pombe cells take the form of a cylinder capped by hemispherical ends. During interphase, cells grow mainly at their tips. Cell elongation ceases after mitotic commitment, and the cytoskeleton is reorganized in preparation for nuclear and cell division (reviewed by McCully and Robinow 1971;Mitchison and Nurse 1985;Marks et al. 1986;Hagan and Hyams 1988;Hagan 1998). The cell divides by fission after forming a septum in the middle of the cell. The site of division is defined at the onset of mitosis (Daga and Chang 2005), by the formation of an actomyosin contractile ring (CAR), whose assembly continues throughout mitosis (Wu et al. 2003;Pollard 2008;Pollard and Wu 2010). At the end of anaphase, the CAR is thought to guide synthesis of the multilayered division septum (reviewed by (Ishiguro 1998;Sipiczki 2007). Septation Initiation NetworkThe S. pombe septation initiation network (SIN) is a network of protein kinases that is essential for cytokinesis in the mitotic cycle; reviewed by (Gould and Simanis 1997;Simanis 2003;Wolfe and Gould 2005;Goyal et al. 2011). It is tightly regulated through the mitotic cell cycle to assure proper coordination of mitosis and cytokinesis, and during meiosis, where it is essential for spore formation (Krapp et al. 2006). Signaling requires the activity of three protein kinases, each of which has a regulatory subunit (kinase regulator); Cdc7p-Spg1p (Fankhauser and Simanis 1994;Schmidt et al. 1997;Mehta and Gould 2006), Sid1p-Cdc14p (Fankhauser and Simanis 1993;Guertin et al. 2000;Guertin and McCollum 2001), and Sid2p-Mob1p (Sparks et al. 1999;Hou et al. 2000;Salimova et al. 2000). SIN signaling is modulated by the nucleotide status of the GTPase Spg1p (Schmidt et al. 1997;Sohrmann et al. 1998), which is determined by the balance of spontaneous nucleotide exchange, a putative GEF, Etd1p Garcia-Cortes and McCollu...

Dma1-dependent degradation of Septation Initiation Network proteins during meiosis inSchizosaccharomyces pombe

“…The failure of cdc14-118 to form spores is consistent with the requirement for its partner Sid1p in spore formation (Krapp et al, 2006), and the results for spg1, cdc11 and sid4 confirm those of earlier studies (Krapp et al, 2006;Yan et al, 2008). The ability of sid2-250 to form spores has been documented and explained previously (see Introduction), but it was surprising to find that mob1-R4 and cdc7-24 formed spores, because these mutant proteins are inactive in vegetative cells at 32˚C (Goyal and Simanis, 2012). This not due to a partial suppression of these alleles by pat1-114, because a similar result was observed for diploids of cdc7-24, cdc7-A20 and mob1-R4 in a pat1 + background (data not shown).…”

Analysis ofS. pombeSIN protein SPB-association reveals two genetically separable states of the SIN

“…6F). This indicates that the proposed feedback loop promoting SIN protein asymmetry in anaphase does not require Sid2p to phosphorylate (Goyal and Simanis, 2012). Mutation of the PP2A B9 subunit par1 rescues some SIN mutants (Jiang and Hallberg, 2001;Le Goff et al, 2001).…”

“…Previous studies have shown that mutation of the regulatory B subunit Pab1p does not affect the appearance of Cdc7p-GFP at one SPB in anaphase (Lahoz et al, 2010), suggesting that that PP2A-Par1p is involved in promoting the asymmetry of Cdc7p-GFP in anaphase. Previous studies have implicated other PP2A complexes and regulators in promoting the asymmetry of Cdc7p (Goyal and Simanis, 2012;Singh et al, 2011).…”

“…This might indicate that the individual proteins that influence asymmetry cooperate to bring about asymmetry. In this context, it is noteworthy that there is a negative genetic interaction between a SIP-complex-null mutant and cdc16-116 (Singh et al, 2011), and PP2A subunits and cdc16-116 (Goyal and Simanis, 2012;Le Goff et al, 2001).…”

Pombe's thirteen – control of fission yeast cell division by the septation initiation network

“…These include the phosphatase complex PP2A (Goyal and Simanis, 2012;Jiang and Hallberg, 2001;Lahoz et al, 2010;Le Goff et al, 2001), Clp1p Trautmann et al, 2001), calcineurin (also known as PP2B) (Lu et al, 2002) and the PP2A-related SIN-inhibitory phosphatase (SIP) complex (Singh et al, 2011), which is the counterpart of the mammalian striatin interacting phosphatase and kinase (STRIPAK) complexes (Hwang and Pallas, 2014). Loss of calcineurin or Clp1p function is deleterious in SIN mutant backgrounds, suggesting that they promote SIN signalling.…”