The phosphatase inhibitor Sds23 promotes symmetric spindle positioning in fission yeast

Abstract

A hallmark of cell division in eukaryotic cells is the formation and elongation of a microtubule (MT)‐based mitotic spindle. Proper positioning of the spindle is critical to ensure equal segregation of the genetic material to the resulting daughter cells. Both the timing of spindle elongation and constriction of the actomyosin contractile ring must be precisely coordinated to prevent missegregation or damage to the genetic material during cellular division. Here, we show that Sds23, an inhibitor of protein phosphatases, contributes to proper positioning of elongating spindles in fission yeast cells. We found that sds23∆ mutant cells exhibit asymmetric spindles that initially elongate asymmetrically toward one end of the dividing cell. Spindle asymmetry in sds23∆ cells results from a defect that is distinct from previously identified mechanisms, including MT protrusions and enlarged vacuoles. Combined with our previous work, this study demonstrates that Sds23, an inhibitor of PP2A‐family protein phosphatases, promotes proper positioning of both the bipolar spindle and cytokinetic ring during fission yeast cell division. These two steps ensure the overall symmetry and fidelity of the cell division process.

PP2A-B56 regulates Mid1 protein levels for proper cytokinesis in fission yeast

“…We also note that Par1 and Par2 have distinct subcellular localizations (Jiang & Hallberg, 2000; Le Goff et al, 2001). These findings connect with our previous observation that mutants in fission yeast Sds23, a poorly understood regulator of PP2A and PP6 phosphatases, have defects in Mid1 levels and cytokinesis (Schutt & Moseley, 2020). These results follow a general theme that tightly controlled formation and regulation of specific PP2A holoenzymes is required to control cell division events in time and space (Peris et al, 2023).…”

“…While understudied relative to their kinase counterparts, protein phosphatases are increasingly appreciated as key regulators of cytokinesis (Bollen et al, 2009). For instance, the loss of PP2A and its regulators causes cytokinetic defects in both budding and fission yeast (Goyal & Simanis, 2012; Healy et al, 1991; Jiang & Hallberg, 2001; K. Kinoshita et al, 1996; Le Goff et al, 2001; Moyano-Rodríguez et al, 2022; Moyano-Rodriguez & Queralt, 2019; Schutt & Moseley, 2020). Budding yeast cells lacking Rts1, the B56 regulatory subunit of PP2A, are multinucleated and elongated at elevated temperatures, suggesting a failure to complete cytokinesis (Moyano-Rodriguez & Queralt, 2019).…”

“…The length was measured again in the same cell at the final moment of cytokinetic ring constriction. Ring displacement was determined as the difference between these two measurements for a cell (Schutt & Moseley, 2020).…”

Kinesin-6 Klp9 orchestrates spindle elongation by regulating microtubule sliding and growth

“…It is possible that Dis1, which is still phosphorylated in late metaphase, activates a phosphatase, which subsequently dephosphorylates Klp9 at anaphase onset. Recently, similar to Dis1, the inhibitor of PP2A protein phosphatases, Sds23, has been shown to act upstream of Klp9 and regulate Klp9 recruitment to the spindle ( Schutt and Moseley, 2020 ). Dis1 and Sds23 may act in the same pathway.…”