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The Inner Nuclear Membrane Protein Src1 Is Required for Stable Post-Mitotic Progression into G1 in Aspergillus nidulans.

Liu HL, Osmani AH, Osmani SA - PLoS ONE (2015)

Bottom Line: How membranes and associated proteins of the nuclear envelope (NE) are assembled specifically and inclusively around segregated genomes during exit from mitosis is incompletely understood.We suggest the term "reboot regulation" to define this mode of cell cycle regulation.The findings are discussed in relationship to recent studies showing the Cdk1 master oscillator can entrain subservient oscillators that when uncoupled cause cell cycle transitions to be repeated.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Ohio State University, Columbus, Ohio 43210, United States of America.

ABSTRACT
How membranes and associated proteins of the nuclear envelope (NE) are assembled specifically and inclusively around segregated genomes during exit from mitosis is incompletely understood. Inner nuclear membrane (INM) proteins play key roles by providing links between DNA and the NE. In this study we have investigated the highly conserved INM protein Src1 in Aspergillus nidulans and have uncovered a novel cell cycle response during post mitotic formation of G1 nuclei. Live cell imaging indicates Src1 could have roles during mitotic exit as it preferentially locates to the NE abscission points during nucleokinesis and to the NE surrounding forming daughter G1 nuclei. Deletion analysis further supported this idea revealing that although Src1 is not required for interphase progression or mitosis it is required for stable post-mitotic G1 nuclear formation. This conclusion is based upon the observation that in the absence of Src1 newly formed G1 nuclei are structurally unstable and immediately undergo architectural modifications typical of mitosis. These changes include NPC modifications that stop nuclear transport as well as disassembly of nucleoli. More intriguingly, the newly generated G1 nuclei then cycle between mitotic- and interphase-like states. The findings indicate that defects in post-mitotic G1 nuclear formation caused by lack of Src1 promote repeated failed attempts to generate stable G1 nuclei. To explain this unexpected phenotype we suggest a type of regulation that promotes repetition of defective cell cycle transitions rather than preventing progression past the defective cell cycle transition. We suggest the term "reboot regulation" to define this mode of cell cycle regulation. The findings are discussed in relationship to recent studies showing the Cdk1 master oscillator can entrain subservient oscillators that when uncoupled cause cell cycle transitions to be repeated.

No MeSH data available.


Related in: MedlinePlus

Deletion of Src1 causes pleotropic nuclear defects.(A-F) Endogenously GFP-tagged or chRFP-tagged nuclear proteins were analyzed in both wildtype and Δsrc1 cells germinated at 23.5°C for 18 hrs to characterize the terminal arrest phenotypes. For each panel representative cells are displayed as indicated. (A and B) The transmembrane Ndc1, core Nup170 and peripheral Nup49 Nups all locate around the nuclear periphery in both Wt and Δsrc1 nuclei indicating normal NPC assembly. (C) Although the core Nup37 protein locates around all four nuclei in the Δsrc1 cell only one nucleus is highly active for nuclear transport of NLS-DsRed. (D) Ima1 locates around the NE in both the Wt and Δsrc1 cells although only one nucleus is transporting NLS-DsRed in the Δsrc1 cell. (E) Nup2 localizes to the nuclear periphery of the transport competent interphase nuclei in the Wt cell. However in the Δsrc1 cell only one nucleus, indicated by a white arrowhead, localizes Nup2 to its nuclear periphery and is transport competent while in the other nuclei (indicated by yellow arrowheads) Nup2 locates to the nuclear interior, potentially at chromatin, and are more mitotic-like. (F) The nucleolar marker Bop1 locates within all Wt nuclei but is not imported to both nuclei of the Δsrc1 cell. In the nucleus that does not contain any Bop1 the Nup49 protein locates within the nucleus potentially at chromatin; a location only seen during mitotic exit in Wt cells.
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pone.0132489.g004: Deletion of Src1 causes pleotropic nuclear defects.(A-F) Endogenously GFP-tagged or chRFP-tagged nuclear proteins were analyzed in both wildtype and Δsrc1 cells germinated at 23.5°C for 18 hrs to characterize the terminal arrest phenotypes. For each panel representative cells are displayed as indicated. (A and B) The transmembrane Ndc1, core Nup170 and peripheral Nup49 Nups all locate around the nuclear periphery in both Wt and Δsrc1 nuclei indicating normal NPC assembly. (C) Although the core Nup37 protein locates around all four nuclei in the Δsrc1 cell only one nucleus is highly active for nuclear transport of NLS-DsRed. (D) Ima1 locates around the NE in both the Wt and Δsrc1 cells although only one nucleus is transporting NLS-DsRed in the Δsrc1 cell. (E) Nup2 localizes to the nuclear periphery of the transport competent interphase nuclei in the Wt cell. However in the Δsrc1 cell only one nucleus, indicated by a white arrowhead, localizes Nup2 to its nuclear periphery and is transport competent while in the other nuclei (indicated by yellow arrowheads) Nup2 locates to the nuclear interior, potentially at chromatin, and are more mitotic-like. (F) The nucleolar marker Bop1 locates within all Wt nuclei but is not imported to both nuclei of the Δsrc1 cell. In the nucleus that does not contain any Bop1 the Nup49 protein locates within the nucleus potentially at chromatin; a location only seen during mitotic exit in Wt cells.

Mentions: We determined the location of Ndc1 (core transmembrane Nup), Nup170 (core Nup), and Nup49 (peripheral Nup) to see if their recruitment to NPCs was defective in the absence of Src1. The distribution of these proteins was analyzed in Δsrc1 spores germinated for 18 hours. As demonstrated in the representative images shown in Fig 4A and 4B, Src1 is not required for the NE recruitment of Ndc1, Nup170 or Nup49 which were all seen to localize around the nuclear periphery in both wildtype and Δsrc1 cells. Notably however, Δsrc1 nuclei often displayed an irregular size and shape when compared to controls (Fig 4A and 4B).


The Inner Nuclear Membrane Protein Src1 Is Required for Stable Post-Mitotic Progression into G1 in Aspergillus nidulans.

Liu HL, Osmani AH, Osmani SA - PLoS ONE (2015)

Deletion of Src1 causes pleotropic nuclear defects.(A-F) Endogenously GFP-tagged or chRFP-tagged nuclear proteins were analyzed in both wildtype and Δsrc1 cells germinated at 23.5°C for 18 hrs to characterize the terminal arrest phenotypes. For each panel representative cells are displayed as indicated. (A and B) The transmembrane Ndc1, core Nup170 and peripheral Nup49 Nups all locate around the nuclear periphery in both Wt and Δsrc1 nuclei indicating normal NPC assembly. (C) Although the core Nup37 protein locates around all four nuclei in the Δsrc1 cell only one nucleus is highly active for nuclear transport of NLS-DsRed. (D) Ima1 locates around the NE in both the Wt and Δsrc1 cells although only one nucleus is transporting NLS-DsRed in the Δsrc1 cell. (E) Nup2 localizes to the nuclear periphery of the transport competent interphase nuclei in the Wt cell. However in the Δsrc1 cell only one nucleus, indicated by a white arrowhead, localizes Nup2 to its nuclear periphery and is transport competent while in the other nuclei (indicated by yellow arrowheads) Nup2 locates to the nuclear interior, potentially at chromatin, and are more mitotic-like. (F) The nucleolar marker Bop1 locates within all Wt nuclei but is not imported to both nuclei of the Δsrc1 cell. In the nucleus that does not contain any Bop1 the Nup49 protein locates within the nucleus potentially at chromatin; a location only seen during mitotic exit in Wt cells.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4492595&req=5

pone.0132489.g004: Deletion of Src1 causes pleotropic nuclear defects.(A-F) Endogenously GFP-tagged or chRFP-tagged nuclear proteins were analyzed in both wildtype and Δsrc1 cells germinated at 23.5°C for 18 hrs to characterize the terminal arrest phenotypes. For each panel representative cells are displayed as indicated. (A and B) The transmembrane Ndc1, core Nup170 and peripheral Nup49 Nups all locate around the nuclear periphery in both Wt and Δsrc1 nuclei indicating normal NPC assembly. (C) Although the core Nup37 protein locates around all four nuclei in the Δsrc1 cell only one nucleus is highly active for nuclear transport of NLS-DsRed. (D) Ima1 locates around the NE in both the Wt and Δsrc1 cells although only one nucleus is transporting NLS-DsRed in the Δsrc1 cell. (E) Nup2 localizes to the nuclear periphery of the transport competent interphase nuclei in the Wt cell. However in the Δsrc1 cell only one nucleus, indicated by a white arrowhead, localizes Nup2 to its nuclear periphery and is transport competent while in the other nuclei (indicated by yellow arrowheads) Nup2 locates to the nuclear interior, potentially at chromatin, and are more mitotic-like. (F) The nucleolar marker Bop1 locates within all Wt nuclei but is not imported to both nuclei of the Δsrc1 cell. In the nucleus that does not contain any Bop1 the Nup49 protein locates within the nucleus potentially at chromatin; a location only seen during mitotic exit in Wt cells.
Mentions: We determined the location of Ndc1 (core transmembrane Nup), Nup170 (core Nup), and Nup49 (peripheral Nup) to see if their recruitment to NPCs was defective in the absence of Src1. The distribution of these proteins was analyzed in Δsrc1 spores germinated for 18 hours. As demonstrated in the representative images shown in Fig 4A and 4B, Src1 is not required for the NE recruitment of Ndc1, Nup170 or Nup49 which were all seen to localize around the nuclear periphery in both wildtype and Δsrc1 cells. Notably however, Δsrc1 nuclei often displayed an irregular size and shape when compared to controls (Fig 4A and 4B).

Bottom Line: How membranes and associated proteins of the nuclear envelope (NE) are assembled specifically and inclusively around segregated genomes during exit from mitosis is incompletely understood.We suggest the term "reboot regulation" to define this mode of cell cycle regulation.The findings are discussed in relationship to recent studies showing the Cdk1 master oscillator can entrain subservient oscillators that when uncoupled cause cell cycle transitions to be repeated.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, Ohio State University, Columbus, Ohio 43210, United States of America.

ABSTRACT
How membranes and associated proteins of the nuclear envelope (NE) are assembled specifically and inclusively around segregated genomes during exit from mitosis is incompletely understood. Inner nuclear membrane (INM) proteins play key roles by providing links between DNA and the NE. In this study we have investigated the highly conserved INM protein Src1 in Aspergillus nidulans and have uncovered a novel cell cycle response during post mitotic formation of G1 nuclei. Live cell imaging indicates Src1 could have roles during mitotic exit as it preferentially locates to the NE abscission points during nucleokinesis and to the NE surrounding forming daughter G1 nuclei. Deletion analysis further supported this idea revealing that although Src1 is not required for interphase progression or mitosis it is required for stable post-mitotic G1 nuclear formation. This conclusion is based upon the observation that in the absence of Src1 newly formed G1 nuclei are structurally unstable and immediately undergo architectural modifications typical of mitosis. These changes include NPC modifications that stop nuclear transport as well as disassembly of nucleoli. More intriguingly, the newly generated G1 nuclei then cycle between mitotic- and interphase-like states. The findings indicate that defects in post-mitotic G1 nuclear formation caused by lack of Src1 promote repeated failed attempts to generate stable G1 nuclei. To explain this unexpected phenotype we suggest a type of regulation that promotes repetition of defective cell cycle transitions rather than preventing progression past the defective cell cycle transition. We suggest the term "reboot regulation" to define this mode of cell cycle regulation. The findings are discussed in relationship to recent studies showing the Cdk1 master oscillator can entrain subservient oscillators that when uncoupled cause cell cycle transitions to be repeated.

No MeSH data available.


Related in: MedlinePlus