The fission yeast SPB component Cut12 links bipolar spindle formation to mitotic control

Abstract

During fission yeast mitosis, the duplicated spindle pole bodies (SPBs) nucleate microtubule arrays that interdigitate to form the mitotic spindle. cut12.1 mutants form a monopolar mitotic spindle, chromosome segregation fails, and the mutant undergoes a lethal cytokinesis. The cut12 + gene encodes a novel 62-kD protein with two predicted coiled coil regions, and one consensus phosphorylation site for p34 cdc2 and two for MAP kinase. Cut12 is localized to the SPB throughout the cell cycle, predominantly around the inner face of the interphase SPB, adjacent to the nucleus. cut12 + is allelic to stf1 + ; stf1.1 is a gain-of-function mutation bypassing the requirement for the Cdc25 tyrosine phosphatase, which normally dephosphorylates and activates the p34 cdc2 /cyclin B kinase to promote the onset of mitosis. Expressing a cut12 + cDNA carrying the stf1.1 mutation also suppressed cdc25.22. The spindle defect in cut12.1 is exacerbated by the cdc25.22 mutation, and stf1.1 cells formed defective spindles in a cdc25.22 background at high temperatures. We propose that Cut12 may be a regulator or substrate of the p34 cdc2 mitotic kinase.

cut11+: A Gene Required for Cell Cycle-dependent Spindle Pole Body Anchoring in the Nuclear Envelope and Bipolar Spindle Formation inSchizosaccharomyces pombe

“…The simplest model is that Cut11p redistribution at mitosis is a matter of accessibility to other components of the SPB. A strong candidate for this type of interaction is Cut12p because 1) it localizes to the SPB surface that is proximal to the nuclear envelope during interphase (Bridge et al, 1998), 2) cut12-1 has a phenotype that is similar to that of cut11 ts , and 3) cut12-1 is synthetically lethal with cut11 ts in an allele-specific manner.…”

“…This leads to an asymmetric separation of chromosomes, resulting in either aneuploidy or aploidy and cell death (Hirano et al, 1986;Samejima et al, 1993). Several cut mutants have been characterized; their gene products cover a broad range of functions, including components of the spindle pole body (Bridge et al, 1998) and the anaphase-promoting complex (Samejima and Yanagida, 1994a,b), enzymes involved in DNA topology (Hirano et al, 1986;Saka et al, 1994) and replication (Saka et al, 1994), and microtubule-dependent motors (Hagan and Yanagida, 1990). cut11 ϩ , on the other hand, appears to be an essential component of the mitotic spindle pole body as well as a component of the nuclear pore complex.…”

“…Additional evidence of a role for cut11 ϩ in SPB function was obtained via an examination of the genetic interactions between cut11 ts and other mutants that affect the SPB, particularly cut12-1 ts . The phenotype of cut12-1 ts at the restrictive temperature is similar to that of cut11 ts , and Cut12p has been localized to the nuclear proximal surface of the SPB by immunoelectron microscopy in wild-type cells (Bridge et al, 1998). The six cut11 ts alleles were crossed to cut12-1, and the resultant double mutants showed allele-specific, synthetic lethal interactions.…”

“…The simplest model is that Cut11p redistribution at mitosis is a matter of accessibility to other components of the SPB. A strong candidate for this type of interaction is Cut12p because 1) it localizes to the SPB surface that is proximal to the nuclear envelope during interphase (Bridge et al, 1998), 2) cut12-1 has a phenotype that is similar to that of cut11 ts , and 3) cut12-1 is synthetically lethal with cut11 ts in an allele-specific manner.The presence of two mRNAs for the cut11 ϩ gene suggests an alternative mechanism for regulating the behavior of the protein. The two mRNAs may be produced differentially as a function of time in the cell cycle, although how this would affect Cut11p is not clear, because the larger message appears to arise from the inclusion of 3Ј-untranslated sequence.…”

pkl1+andklp2+: Two Kinesins of the Kar3 Subfamily in Fission Yeast Perform Different Functions in Both Mitosis and Meiosis

“…12, November 2001Genetic Interactions between the KAR3 Motors and Temperature-sensitive Alleles of the Mitotic Genes, cut11 ؉ and cut12 ؉ Cut12p, also known as Skf1p, is a structural component of the fission yeast spindle pole body whose function is essential for mitotic progression (Bridge et al, 1998). Both pkl1⌬ and klp2⌬ show a synthetic phenotype with a temperaturesensitive allele of this gene, cut12-1 (Figure 5).…”