Identification of a Second Myosin-II inSchizosaccharomyces pombe:

Abstract

As in many eukaryotic cells, fission yeast cytokinesis depends on the assembly of an actin ring. We clonedmyp2+ , a myosin-II inSchizosaccharomyces pombe, conditionally required for cytokinesis. myp2+ , the second myosin-II identified in S. pombe, does not completely overlap in function with myo2+ . The catalytic domain of Myp2p is highly homologous to known myosin-IIs, and phylogenetic analysis places Myp2p in the myosin-II family. The Myp2p sequence contains well-conserved ATP- and actin-binding motifs, as well as two IQ motifs. However, the tail sequence is unusual, since it is predicted to form two long coiled-coils separated by a stretch of sequence containing 19 prolines. Disruption of myp2+ is not lethal but under nutrient limiting conditions cells lackingmyp2+ function are multiseptated, elongated, and branched, indicative of a defect in cytokinesis. The presence of salt enhances these morphological defects. Additionally,Δmyp2 cells are cold sensitive in high salt, failing to form colonies at 17°C. Thus, myp2+ is required under conditions of stress, possibly linking extracellular growth conditions to efficient cytokinesis and cell growth. GFP-Myp2p localizes to a ring in the middle of late mitotic cells, consistent with a role in cytokinesis. Additionally, we constructed double mutants of Δmyp2 with temperature-sensitive mutant strains defective in cytokinesis. We observed synthetic lethal interactions between Δmyp2 and three alleles ofcdc11ts, as well as more modest synthetic interactions with cdc14ts and cdc16ts, implicatingmyp2+ function for efficient cytokinesis under normal conditions.

Mid1/anillin and the spatial regulation of cytokinesis in fission yeast

“…Once compacted, the contractile ring still needs to mature by the addition of several new components such as the unconventional myosin II Myp2 [Bezanilla et al, 1997;Wu et al, 2003], the F-BAR protein Imp2 and paxillin, a modulator of Rho1 [Ge and Balasubramanian, 2008;Pinar et al, 2008] which together with the C2-domain protein Fic1 confers structural integrity to the contractile ring, preventing its fragmentation when it constricts [Roberts-Galbraith et al, 2009]. Constriction requires an active SIN pathway and is finely tuned by phosphorylation of myosin II heavy and light chains [Loo and Balasubramanian, 2008;Sladewski et al, 2009].…”

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

“…However, one significant difference is in the relative importance of the actomyosin contractile ring during cytokinesis. Although myosin II and the contractile ring are essential for cytokinesis in S. pombe (Bezanilla et al, 1997;Kitayama et al, 1997;May et al, 1997;Motegi et al, 1997), they are not essential in S. cerevisiae (Bi et al, 1998;Lippincott and Li, 1998). A possible explanation for this difference is that the primary role of the contractile ring is to guide septum deposition (Hales et al, 1999;Vallen et al, 2000) and that the need for such guidance is greater in forming the ϳ3-m-diameter septum in S. pombe than in forming the ϳ1-m-diameter septum in S. cerevisiae.…”

“…First, Ain1p was detected exclusively in this structure. Second, ain1 deletion cells display cell division defects under stress conditions, much as do cells lacking the nonessential myosin II Myp2p/Myo3p (Bezanilla et al, 1997;Motegi et al, 1997). Third, cells overexpressing Ain1p have defects in cell division.…”

Take five: A myosin class act in fission yeast

“…It is not clear why S. pombe requires two class II myosins for cytokinesis. Myo2 is an essential gene whereas cells lacking Myp2 display only subtle cytokinetic defects that are exacerbated when cells are stressed [Bezanilla et al, 1997;Motegi et al, 1997;Mulvihill et al, 2000]. Combining myp2⌬ with the temperature-sensitive myo2 mutation myo2-E1 creates a double mutant that displays exaggerated cytokinetic de- Fig.…”