The conserved Schizosaccharomyces pombe kinase plo1, required to form a bipolar spindle, the actin ring, and septum, can drive septum formation in G1 and G2 cells.

Abstract

We have identified a Schizosaccharomyces pombe gene with homology to the budding yeast gene CDCS, the Drosophila gene polo, and the mammalian family of genes encoding polo-like kinases. Disruption of this gene, plol +, indicates that it is essential. Loss of plol + function leads to a mitotic arrest in which condensed chromsomes are associated with a monopolar spindle or to the failure of septation following the completion of nuclear division. In the latter case, cells show a failure both in the formation of an F-actin ring and in the deposition of septal material, suggesting that plol + function is required high in the regulatory cascade that controls septation. The overexpression of plol + in wild-type cells also results in the formation of monopolar spindles but also induces the formation of multiple septa without nuclear division. Septation can also be induced in the absence of mitotic commitment and concomitant spindle formation by the overexpression of plol + in cdc25-22 or cdc2-33 cells arrested in G2; in GI cells arrested at Start by the cdclO-V50 mutation, or in cells lacking the cyclin B homolog cdcl3 that undergo repeated S phases in the absence of mitosis.[Key Words: S. pombe; polo homolog; bipolar spindle; actin ring; septum; plol kinase] Received January 20, 1995; revised version accepted March 16, 1995.The polo ~ mutation of Drosophila was first identified as a maternal-effect mutant giving rise to embryos that show abnormal networks of microtubules associated with condensed chromosomes, in which the centrosomal antigen CP190 {formerly called Bx63; Frasch et al. 1986;Whitfield et al. 1988) fails to become organized into centrosomes with microtubule-organizing capability (Sunkel and Glover 1988). The mutation results in multipolar spindles and nondisjunction in male meiosis leading to reduced fertility. There is a high mitotic index in larval neuroblasts, with a wide range of defects including monopolar spindles and spindles with broad poles (Sunkel and Glover 1988;Llamazares et al. 1991).polo encodes a 576-amino-acid protein that has an amino-terminal putative kinase domain and a 300-residue carboxy-terminal domain (Llamazares et al. 1991). The polo kinase is highly conserved. The budding yeast and murine genes, CDC5 (Kitada et al. 1993) and mouse Plk (polo-like kinase; Clay et al. 1993;Lake and Jelinek 1993;Hamanaka et al. 1994), for example, show 52% and 65% identity in the kinase domain and 33% and 43% in the carboxy-terminal domain, with the latter homolo3Corresponding author. gies lying in distinct blocks. The human Plk has also been identified (Golsteyn et al. 1994;Hamanaka et al. 1994;Holtrich et al. 1994), and studies in the mouse suggest that there is another closely related kinase, Snk (serum-induced kinase; Simmons et al. 1992), that falls into the same gene family. These mammalian genes are expressed only in proliferating cells or tissues suggesting a cell cycle role.In mutants of the budding yeast gene CDC5, nuclear division is arrested at a late stage and the spindle is elongated (Ha...

Protein kinases in control of the centrosome cycle

“…The same result is seen in ¢ssion yeast where loss of Plo1, the Schizosaccharomyces pombe Plk, also induces monopolar spindle formation with unseparated spindle poles [20]. Plk activation in di¡erent organisms coincides with the time of centrosome separation and the identi¢cation of some candidate Plk substrates lends further support to an active role in this process.…”

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

“…Indeed, although Mid1 starts localizing at medial cortical nodes very early in interphase, even before NETO [Paoletti and Chang, 2000;Celton-Morizur et al, 2006], predefining the division site, it only starts recruiting contractile ring components at mitotic onset, triggering contractile ring assembly. As discussed earlier, Plo1 activity is necessary for the proper positioning of the division plane and for contractile ring assembly [Ohkura et al, 1995;]. In particular, Plo1 promotes Mid1 nuclear export at the beginning of mitosis ].…”

“…Contractile ring assembly is then strictly dependent on the activity of the SIN, [septation initiation network; Hachet and Simanis, 2008]. This signalling cascade, essential for cytokinesis, is activated by Plo1 kinase and controlled from the spindle pole body by the small GTPase Spg1 [Ohkura et al, 1995; Schmidt et al, 1997;Sohrmann et al, 1998; see Goyal et al, 2011 for a review]. The SIN, whose activation can bypass the requirement for Plo1 for contractile ring assembly, induces the dephosphorylation of the F-BAR protein Cdc15 [Hachet and Simanis, 2008].…”

A ‘marker switch’ approach for targeted mutagenesis of genes in Schizosaccharomyces pombe

“…pombe plo1 + gene offers a good example of this phenomenon. When the phenotype of the original deletion allele was described, it was found that cells went through two or three nuclear divisions in the absence of cell division and then were unable to form a mitotic spindle (Ohkura et al, 1995). Thus, cytokinesis was more sensitive than spindle formation to Plo1 levels.…”

“…For many proteins, altering gene dosage can have a direct phenotypic consequence (e.g. Ohkura et al, 1995) and increasing the copy number of a gene encoding a mutant protein can suppress or enhance the mutant phenotype. However, for the majority of processes, the most incisive studies will probably be those in which the mutant allele is present as a single copy and is the only allele of this gene in the cell.…”