Cdc15 Is Required for Spore Morphogenesis Independently of Cdc14 in Saccharomyces cerevisiae

Abstract

In Saccharomyces cerevisiae exit from mitosis requires the Cdc14 phosphatase to reverse CDK-mediated phosphorylation. Cdc14 is released from the nucleolus by the Cdc14 early anaphase release (FEAR) and mitotic exit network (MEN) pathways. In meiosis, the FEAR pathway is essential for exit from anaphase I. The MEN component Cdc15 is required for the formation of mature spores. To analyze the role of Cdc15 during sporulation, a conditional mutant in which CDC15 expression was controlled by the CLB2 promoter was used. Cdc15-depleted cells proceeded normally through the meiotic divisions but were unable to properly disassemble meiosis II spindles. The morphology of the prospore membrane was aberrant and failed to capture the nuclear lobes. Cdc15 was not required for Cdc14 release from the nucleoli, but it was essential to maintain Cdc14 released and for its nucleo-cytoplasmic transport. However, cells carrying a CDC14 allele with defects in nuclear export (Cdc14-DNES) were able to disassemble the spindle and to complete spore formation, suggesting that the Cdc14 nuclear export defect was not the cause of the phenotypes observed in cdc15 mutants. MEIOSIS is a specialized cell division that produces the haploid cells needed for sexual reproduction, and the completion of meiosis is normally coupled to differentiation programs that produce gametes. In Saccharomyces cerevisiae, sporulation is initiated when diploid cells are grown in the absence of nitrogen and the presence of a nonfermentable carbon source such as acetate (Esposito and Klapholtz 1981). When triggered to enter the sporulation program, cells exit the mitotic cycle from the G1 phase. This is followed by one round of S phase and two meiotic divisions that generate four haploid nuclei, which are packaged into individual spores. As a consequence of this process, four haploid gametes (spores) are formed in the cytoplasm of the mother cell (ascus) (reviewed by Neiman 2005). At the onset of meiosis II, the spindle pole body (SPB) is modified by the incorporation of several meiosis-specific proteins, which together make up the meiosis II outer plaque (Knop and Strasser 2000;Bajgier et al. 2001;Nickas et al. 2003). This change in composition converts the function of the cytoplasmic face of the SPB from microtubule nucleation to membrane nucleation. The process of spore construction requires the de novo assembly of two cellular structures, the prospore membrane (PSM) that is generated around the daughter nuclei to create prospores and a protective spore wall that surrounds the prospores. Once the meiosis II outer plaque of the SPB has been assembled, it becomes a site for the docking and coalescence of secretory vesicles to form flattened double-membrane sheets termed PSMs (Moens 1971;Neiman 1998). These nascent PSMs expand during meiosis II, and at the time of nuclear division each PSM completely engulfs the nuclear lobe to which it is anchored via the SPB. At the completion of meiosis II, each PSM fuses with itself so that each daughter nucleus (and assoc...

The NDR Kinase DBF-2 Is Involved in Regulation of Mitosis, Conidial Development, and Glycogen Metabolism in Neurospora crassa

“…How DBF-2 may affect the function of N. crassa mating type loci and interacting genes/gene products has yet to be elucidated. The fact that CDC15 (a DBF2-interacting protein in S. cerevisiae) is required for meiosis II exit, as well as for spore morphogenesis (44), suggests that DBF2 may be linked with sexual reproduction in yeasts as well.…”

Slk1 is a meiosis-specific Sid2-related kinase that coordinates meiotic nuclear division with growth of the forespore membrane

“…This is the case of the budding yeast CDC15 (homologous to cdc7 in fission yeast), mutants of which result in defects in the disassembly of anaphase II spindles and of the meiotic outer plaque of SPBs, leading to a sporulation defect similar to that described in SIN mutants; that is, the inability of forespore membranes to properly engulf haploid nuclei (Pablo-Hernando et al, 2007). Interestingly, the function of Cdc15 in sporulation seems to be independent of MEN and Cdc14 functions in meiotic divisions.…”

“…Blast searches failed to reveal the existence of a meiosisspecific homologue. However, a role for Dbf2 and/or Dbf20 in sporulation cannot be ruled out, because some MEN components have been shown to play a role in spore morphogenesis (Gordon et al, 2006;Kamieniecki et al, 2005;Pablo-Hernando et al, 2007). Dbf20 expression peaks later than Dbf2 during meiosis, suggesting that Dbf20 could be a better candidate to perform a role in sporulation than Dbf2 (Chu et al, 1998).…”

A knockout screen for protein kinases required for the proper meiotic segregation of chromosomes in the fission yeast Schizosaccharomyces pombe

“…Interestingly, the phenotype of spo4Δ cells is similar to that of S. cerevisiae cells depleted for Cdc15. The MEN (mitotic exit network pathway) component Cdc15 is a protein kinase required for the formation of mature spores and for proper spindle disassembly after meiosis II 70 . Finally, it has been shown that cells expressing non-degradable cyclin B have prolonged anaphase B 50 .…”