NDC1: a nuclear periphery component required for yeast spindle pole body duplication

Abstract

Abstract. The spindle pole body (SPB) of Saccharomyces cerevisiae serves as the centrosome in this organism, undergoing duplication early in the cell cycle to generate the two poles of the mitotic spindle. The conditional lethal mutation ndcl-1 has previously been shown to cause asymmetric segregation, wherein all the chromosomes go to one pole of the mitotic spindle (Thomas, J. H., and D. Botstein. 1986. Cell. 44:65-76). Examination by electron microscopy of mutant cells subjected to the nonpermissive temperature reveals a defect in SPB duplication. Although duplication is seen to occur, the nascent SPB fails to undergo insertion into the nuclear envelope. The parental SPB remains functional, organizing a monopolar spindle to which all the chromosomes are presumably attached. Order-of-function experiments reveal that the NDC1 function is required in (31 after a-factor arrest but before the arrest caused by cdc34. Molecular analysis shows that the NDC1 gene is essential and that it encodes a 656 amino acid protein (74 kD) with six or seven putative transmembrane domains. This evidence for membrane association is further supported by immunofluorescent localization of the NDC1 product to the vicinity of the nuclear envelope. These findings suggest that the NDC1 protein acts within the nuclear envelope to mediate insertion of the nascent SPB.SEMBLY of the mitotic spindle in a eucaryotic cell is dependent on the formation of two centrosomelike organelles from which spindle microtubules emanate. The apparent duplication of centrosomal components to generate spindle poles is well described cytologically (reviewed by McIntosh, 1983;Brinkley, 1985;Sluder, 1989), but few molecular details of the underlying mechanism are known. The relevant organeLle in the yeast Saccharomyces cerevisiae is the spindle pole body (SPB)/ which is situated within the nuclear envelope (reviewed by Winey and Byers, 1992). As the sole microtubule organizing center in S. cerevisiae, the SPB forms microtubular arrays in both the cytoplasm and the nucleus. Electron microscopy of wild-type and mutant yeast strains has permitted description of the SPB duplication pathway and spindle formation (Byers, 1981a;Winey et al., 1991). A crucial early step in this pathway is the formation of the satellite on the outer surface of the half-bridge structure adjacent to the extant SPB. At START in G1, the satellite-bearing SPB is transformed

The SESA network links duplication of the yeast centrosome with the protein translation machinery

“…This model is consistent with the activation of mammalian 4E-BPs by external stimuli (Gingras et al 1999) or of yeast Eap1 by membrane defects (Deloche et al 2004). In addition, elevated gene levels of SMY2, may arise due to chromosome missegregation in mutants with SPB duplication defects, which are genetically unstable (Winey et al 1991(Winey et al , 1993Schramm et al 2000;Araki et al 2006). Increased gene dosage of SMY2 then likely makes the SESA network more sensitive to defects (Fig.…”

“…(Step 1) Pom34, Pom152, and Ndc1 form a complex that functions in NPC biogenesis (Chial et al 1998;Madrid et al 2006;Alber et al 2007a,b;Onischenko et al 2009). (Step 3) Ndc1 has a dual role and together with Mps2, Bbp1, and Nbp1 it also functions in SPB duplication (Winey et al 1993;Araki et al 2006). (Step 2) Deletion of POM34 or POM152 or mutations in ndc1 rescue SPB duplication defects ( Fig.…”

“…An intermediate in this duplication process, the duplication plaque, develops on the cytoplasmic side of the nuclear envelope as an extension of the pre-existing SPB. The duplication plaque then becomes inserted into the nuclear envelope as a consequence of the action of the essential NDC1, MPS2, BBP1, and NBP1 genes (Winey et al 1991(Winey et al , 1993Adams and Kilmartin 1999;Schramm et al 2000;Araki et al 2006). A defect in these genes leads to a failure in SPB duplication such that the insertion of the duplication plaque into the nuclear envelope is either fully or partially compromised.…”

“…The integral membrane protein Mps2 forms a tight complex with the cytoplasmic Bbp1. For SPB duplication the Mps2-Bbp1 complex cooperates with the Nbp1 protein, and the highly conserved integral membrane protein Ndc1 (Winey et al 1993;Adams and Kilmartin 1999;Schramm et al 2000;Araki et al 2006;Mansfeld et al 2006).…”

Mps1p Regulates Meiotic Spindle Pole Body Duplication in Addition to Having Novel Roles during Sporulation

“…The effects of two mutations that disrupt the process of SPB duplication in mitotic cells have been studied in meiotic cells. In vegetatively growing cells, both cdc31-1 and ndc1-1, which define the early and late steps, respectively, of SPB duplication, prevent mitotic SPB duplication and trigger cell cycle arrest by activating the spindle assembly checkpoint (Winey et al, 1993;Weiss and Winey, 1996). The meiotic effects of the cdc31-1 and ndc1-1 mutations result in viable dyads (two-spored asci) as a result of the failure in the second of the two rounds of SPB duplication (Byers, 1981;Thomas and Botstein, 1986).…”