The Mitotic Exit Network Regulates Spindle Pole Body Selection During Sporulation of Saccharomyces cerevisiae

Abstract

Age-based inheritance of centrosomes in eukaryotic cells is associated with faithful chromosome distribution in asymmetric cell divisions. During ascospore formation, such an inheritance mechanism targets the yeast centrosome equivalents, the spindle pole bodies (SPBs) at meiosis II onset. Decreased nutrient availability causes initiation of spore formation at only the younger SPBs and their associated genomes. This mechanism ensures encapsulation of nonsister genomes, which preserves genetic diversity and provides a fitness advantage at the population level. Here, by usage of an enhanced system for sporulation-induced protein depletion, we demonstrate that the core mitotic exit network (MEN) is involved in age-based SPB selection. Moreover, efficient genome inheritance requires Dbf2/20-Mob1 during a late step in spore maturation. We provide evidence that the meiotic functions of the MEN are more complex than previously thought. In contrast to mitosis, completion of the meiotic divisions does not strictly rely on the MEN whereas its activity is required at different time points during spore development. This is reminiscent of vegetative MEN functions in spindle polarity establishment, mitotic exit, and cytokinesis. In summary, our investigation contributes to the understanding of age-based SPB inheritance during sporulation of and provides general insights on network plasticity in the context of a specialized developmental program. Moreover, the improved system for a developmental-specific tool to induce protein depletion will be useful in other biological contexts.

A non-canonical Hippo pathway regulates spindle disassembly and cytokinesis during meiosis inSaccharomyces cerevisiae

“…However, the NDR kinase complex encoded by DBF2 DBF20 MOB1 does 107 not seem to be involved in these events. Instead, DBF2 DBF20 MOB1 are important for spore 108 number control, as previously demonstrated (Renicke et al 2017). Likewise, we find that All strains used in this study are in the SK1 background (Kane and Roth 1974) and are 114 described in Supplemental Material Tables S1 and S2.…”

“…Spore number control regulates the number of spindle pole bodies that are competent for 385 prospore membrane growth; this process depends on a spindle pole body modification that 386 happens based on the age of the spindle pole body and the nutrients available to sporulating cells 387 (Davidow et al 1980;Nickas et al 2004;Taxis et al 2005). Depletion of the NDR kinase 388 complex results in fewer spores per ascus forming during sporulation, as seen when MOB1 389 DBF2 DBF20 activity was reduced using a protein depletion system (Renicke et al 2017). We 390 see a similar result using our mob1-mn dbf2-mn dbf20 strain, as assayed by counting refractile 391 spores formed ( Figure S3) or by counting the number of prospore membranes formed as a proxy 392 for the number of spores than can form within the ascus ( Figure 6).…”

“…In meiosis II, cells appear to utilize CDC15 and MOB1-DBF2/20 for distinct roles, unlike 472 in mitosis where Cdc15 activates a conserved Mob1-NDR kinase signaling system, as seen in 473 typical Hippo signaling (Hergovich andHemmings, 2012, Weiss, 2012). In meiosis II, it appears 474 that MOB1-DBF2/20 is important for spore number control (Renicke et al, 2017), in which 475 neither CDC15 nor SPS1 play a role, as assayed by the number of prospore membranes formed. 476…”

“…Dbf20 kinase is 96 active in meiosis II, and its kinase activity as well as its interaction with the Mob1 regulatory 97 subunit is dependent on CDC15 in meiosis II, although deletion of DBF20 did not show a delay 98 in meiosis II exit (Attner and Amon 2012). The major phenotype seen for cells lacking the NDR 99 kinases complex in meiosis is a defect in spore number control (Renicke et al 2017); spore 100 number control is a process that involves the selection of nuclei associated with younger spindle 101 pole bodies over older spindle pole bodies for spore packaging when available energy resources 102 are a low (Davidow et al 1980;Nickas et al 2004;Taxis et al 2005). Nud1 is also involved in 103 spore number control (Gordon et al 2006; Renicke et al, 2017).…”

Asymmetric Segregation of Aged Spindle Pole Bodies During Cell Division: Mechanisms and Relevance Beyond Budding Yeast?

“…Dbf2/20 phosphorylate Kar9 promoting its accumulation to only the aster of the old SPB . Interestingly, MEN also promotes the age‐dependent selection of SPBs during sporulation . Thus, SPB inheritance requires that the cell distinguishes old from new SPBs, a process that we term SPB specification, and is regulated by the MEN.…”