Mitotic Expression of Spo13 Alters M-Phase Progression and Nucleolar Localization of Cdc14 in Budding Yeast

Abstract

Spo13 is a key meiosis-specific regulator required for centromere cohesion and coorientation, and for progression through two nuclear divisions. We previously reported that it causes a G2/M arrest and may delay the transition from late anaphase to G1, when overexpressed in mitosis. Yet its mechanism of action has remained elusive. Here we show that Spo13, which is phosphorylated and stabilized at G2/M in a Cdk/Clb-dependent manner, acts at two stages during mitotic cell division. Spo13 provokes a G2/M arrest that is reversible and largely independent of the Mad2 spindle checkpoint. Since mRNAs whose induction requires Cdc14 activation are reduced, we propose that its anaphase delay results from inhibition of Cdc14 function. Indeed, the Spo13-induced anaphase delay correlates with Cdc14 phosphatase retention in the nucleolus and with cyclin B accumulation, which both impede anaphase exit. At the onset of arrest, Spo13 is primarily associated with the nucleolus, where Cdc14 accumulates. Significantly, overexpression of separase (Esp1), which promotes G2/M and anaphase progression, suppresses Spo13 effects in mitosis, arguing that Spo13 acts upstream or parallel to Esp1. Given that Spo13 overexpression reduces Pds1 and cyclin B degradation, our findings are consistent with a role for Spo13 in regulating APC, which controls both G2/M and anaphase. Similar effects of Spo13 during meiotic MI may prevent cell cycle exit and initiation of DNA replication prior to MII, thereby ensuring two successive chromosome segregation events without an intervening S phase.

Construction of strains to identify novel factors for regulation of centromeric cohesion protection (CCP) and sister kinetochore mono-orientation (SKM)

“…It means that the effect of Spo13 expression was more lethal as compared to Rec8 expression. Varela et al first reported that mitotic Spo13 expression altered cell cycle progression and was unable to exit anaphase with change in the cell morphology [27]. We also observed same morphological change (elongated cell) in Spo13 expression strain (Fig.…”

Spo13 prevents premature cohesin cleavage during meiosis

“…The exact role of Spo13 in cohesin protection is currently unclear. Interestingly, SPO13 overexpression blocks cohesin cleavage during mitosis ( Lee et al ., 2002 ; Shonn et al ., 2002 ; Varela et al ., 2010 ), suggesting that Spo13 may also influence cohesin cleavage in meiosis, but how it might do so remains unresolved. Although Spo13 was implicated in ensuring the proper pericentromeric localization of Sgo1 ( Kiburz et al ., 2005 ), other studies have found no difference in chromosomally associated Sgo1 ( Galander et al ., 2019 ; Lee et al ., 2004 ).…”

Studying meiosis in mitosis: Activating the meiosis-specific Red1-Hop1-Mek1 complex in mitotic budding yeast cells

“…Here, we report on the establishment of a system enabling controllable expression of a meiosisspecific complex in mitosis. Similar approaches have been used previously to investigate different aspects of meiosis, such as HR repair and chromosome segregation [8][9][10][11][12] . We express components of the trimeric, meiosis-specific Red1, Hop1 and Mek1 complex (i.e., the RHM complex), and show that this complex can self-assemble even when expressed outside of its natural, physiological environment, i.e., in mitotically-dividing cells.…”

“…Meiosis can thus be seen as an adaptation of the mitotic cell cycle. One approach to understand meiosis-specific mechanisms is via reconstitution in non-physiological environments, for example via in vitro biochemical reconstitutions (e.g., [2][3][4][5][6][7] ), or by expressing meiosis-specific factors in non-meiotic cells (e.g., [8][9][10][11][12] ).…”