A Noncanonical Hippo Pathway Regulates Spindle Disassembly and Cytokinesis During Meiosis in Saccharomyces cerevisiae

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Abstract

Meiosis in the budding yeast Saccharomyces cerevisiae is used to create haploid yeast spores from a diploid mother cell. During meiosis II, cytokinesis occurs by closure of the prospore membrane, a membrane that initiates at the spindle pole body and grows to surround each of the haploid meiotic products. Timely prospore membrane closure requires SPS1 , which encodes an STE20 family GCKIII kinase. To identify genes that may activate SPS1 , we utilized a histone phosphorylation defect of sps1 mutants to screen for genes with a similar phenotype and found that cdc15 shared this phenotype. CDC15 encodes a Hippo-like kinase that is part of the mitotic exit network. We find that Sps1 complexes with Cdc15, that Sps1 phosphorylation requires Cdc15, and that CDC15 is also required for timely prospore membrane closure. We also find that SPS1 , like CDC15 , is required for meiosis II spindle disassembly and sustained anaphase II release of Cdc14 in meiosis. However, the NDR-kinase complex encoded by DBF2 / DBF20 MOB1 which functions downstream of CDC15 in mitotic cells, does not appear to play a role in spindle disassembly, timely prospore membrane closure, or sustained anaphase II Cdc14 release. Taken together, our results suggest that the mitotic exit network is rewired for exit from meiosis II, such that SPS1 replaces the NDR-kinase complex downstream of CDC15 .

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Identification of domains required for developmentally regulated SNARE function in Saccharomyces cerevisiae.

P Brennwald, Monica Y. Katz, Aaron M. Neiman … (2000)

Saccharomyces cerevisiae cells contain two homologues of the mammalian t-SNARE protein SNAP-25, encoded by the SEC9 and SPO20 genes. Although both gene products participate in post-Golgi vesicle fusion events, they cannot substitute for one another; Sec9p is active primarily in vegetative cells while Spo20p functions only during sporulation. We have investigated the basis for the developmental stage-specific differences in the function of these two proteins. Localization of the other plasma membrane SNARE subunits, Ssop and Sncp, in sporulating cells suggests that these proteins act in conjunction with Spo20p in the formation of the prospore membrane. In vitro binding studies demonstrate that, like Sec9p, Spo20p binds specifically to the t-SNARE Sso1p and, once bound to Sso1p, can complex with the v-SNARE Snc2p. Therefore, Sec9p and Spo20p interact with the same binding partners, but developmental conditions appear to favor the assembly of complexes with Spo20p in sporulating cells. Analysis of chimeric Sec9p/Spo20p molecules indicates that regions in both the SNAP-25 domain and the unique N terminus of Spo20p are required for activity during sporulation. Additionally, the N terminus of Spo20p is inhibitory in vegetative cells. Deletion studies indicate that activation and inhibition are separable functions of the Spo20p N terminus. Our results reveal an additional layer of regulation of the SNARE complex, which is necessary only in sporulating cells.

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Preferential Occurrence of Nonsister Spores in Two-Spored Asci of SACCHAROMYCES CEREVISIAE: Evidence for Regulation of Spore-Wall Formation by the Spindle Pole Body.

B Byers, Amy L Davidow, L Goetsch (1980)

Yeast cells subjected to a reversible thermal arrest of meiosis yielded progressively fewer spores per ascus as the arrest was extended. Dissection of two-spored asci by a newly developed method that prevents selection of false asci revealed that the spores were not a random sample of the haploid meiotic products. Most, if not all, pairs of spores contain nonsister products of the reductional division. Electron microscopic examination of the meiotic cells revealed the cytological basis for this bias. All four spindle pole bodies (SPBs) present at the second meiotic division normally gain a structural modification (the outer plaque) upon which the initiation of the prospore wall occurs. In the formation of a two-spored ascus, only one spindle pole body on each meiosis II spindle was so modified. These observations suggest that the morphogenesis of spores is regulated at meiosis II by limiting the number of SPBs gaining the outer plaque. The enhancement of spore yield upon addition of fresh medium suggests that this morphogenetic regulation responds more directly to nutrient deprivation arising during the thermal arrest, rather than to elevated temperature per se.

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Ady3p links spindle pole body function to spore wall synthesis in Saccharomyces cerevisiae.

Aaron M. Neiman, M E Nickas (2002)

Spore formation in Saccharomyces cerevisiae requires the de novo synthesis of prospore membranes and spore walls. Ady3p has been identified as an interaction partner for Mpc70p/Spo21p, a meiosis-specific component of the outer plaque of the spindle pole body (SPB) that is required for prospore membrane formation, and for Don1p, which forms a ring-like structure at the leading edge of the prospore membrane during meiosis II. ADY3 expression has been shown to be induced in midsporulation. We report here that Ady3p interacts with additional components of the outer and central plaques of the SPB in the two-hybrid assay. Cells that lack ADY3 display a decrease in sporulation efficiency, and most ady3Delta/ady3Delta asci that do form contain fewer than four spores. The sporulation defect in ady3Delta/ady3Delta cells is due to a failure to synthesize spore wall polymers. Ady3p forms ring-like structures around meiosis II spindles that colocalize with those formed by Don1p, and Don1p rings are absent during meiosis II in ady3Delta/ady3Delta cells. In mpc70Delta/mpc70Delta cells, Ady3p remains associated with SPBs during meiosis II. Our results suggest that Ady3p mediates assembly of the Don1p-containing structure at the leading edge of the prospore membrane via interaction with components of the SPB and that this structure is involved in spore wall formation.