title: Dependence of Chs2 ER export on dephosphorylation by cytoplasmic Cdc14 ensures that septum formation follows mitosis.
abstract: Cytokinesis, which leads to the physical separation of two dividing cells, is normally restrained until after nuclear division. In Saccharomyces cerevisiae, chitin synthase 2 (Chs2), which lays down the primary septum at the mother-daughter neck, also ensures proper actomyosin ring constriction during cytokinesis. During the metaphase-to-anaphase transition, phosphorylation of Chs2 by the mitotic cyclin-dependent kinase (Cdk1) retains Chs2 at the endoplasmic reticulum (ER), thereby preventing its translocation to the neck. Upon Cdk1 inactivation at the end of mitosis, Chs2 is exported from the ER and targeted to the neck. The mechanism for triggering Chs2 ER export thus far is unknown. We show here that Chs2 ER export requires the direct reversal of the inhibitory Cdk1 phosphorylation sites by Cdc14 phosphatase, the ultimate effector of the mitotic exit network (MEN). We further show that only Cdc14 liberated by the MEN after completion of chromosome segregation, and not Cdc14 released in early anaphase by the Cdc fourteen early anaphase release pathway, triggers Chs2 ER exit. Presumably, the reduced Cdk1 activity in late mitosis further favors dephosphorylation of Chs2 by Cdc14. Thus, by requiring declining Cdk1 activity and Cdc14 nuclear release for Chs2 ER export, cells ensure that septum formation is contingent upon chromosome separation and exit from mitosis.
authors.affiliation: Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Cheen Fei
authors.initials: CF
authors.lastname: Chin
authors.forename: Alexis M
authors.initials: AM
authors.lastname: Bennett
authors.forename: Wai Kit
authors.initials: WK
authors.lastname: Ma
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hall
authors.forename: Foong May
authors.initials: FM
authors.lastname: Yeong
mesh_terms: D000205:Actomyosin / Q000378:metabolism; D019943:Amino Acid Substitution; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism; D002687:Chitin Synthase / Q000235:genetics / Q000378:metabolism*; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000378:metabolism; D048749:Cytokinesis; D004721:Endoplasmic Reticulum / Q000201:enzymology* / Q000378:metabolism; D055786:Gene Knockout Techniques; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008938:Mitosis; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D021381:Protein Transport; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D059008:Time-Lapse Imaging
chemical_list: C074860:CDC14 protein, S cerevisiae; D018797:Cell Cycle Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D011993:Recombinant Fusion Proteins; C086926:SIC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D000205:Actomyosin; D002687:Chitin Synthase; C400821:chitin synthase 2; D016203:CDC2 Protein Kinase; D017027:Protein Tyrosine Phosphatases
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