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Kinetochore microtubule stability is dependent on the integral nuclear membrane protein, Samp1
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.ORCID iD: 0000-0001-5835-503X
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We have previously shown that the transmembrane inner nuclear membrane protein, Samp1, localises to the mitotic spindle during metaphase, where it recruits γ-tubulin, which promotes spindle assembly by increasing the β-tubulin density. Samp1 depleted cells displayed signs of spindle destabilisation, such as increased spindle length, prolonged metaphase and chromosome mis-segregation. Here we show that Samp1 partially localise to cold resistant kinetochore fibres of the mitotic spindle. Posttranscriptional silencing of Samp1 decreased the number of kinetochore fibres and resulted in mis-aligned chromosomes, phenotypes that were rescued by Samp1YFP overexpression. We also show that Samp1 interacts with the Aurora B kinase and that Samp1 depletion increased the distribution of Aurora B in the metaphase plate and increased its activity. The effects of Samp1 on Aurora B increases our understanding of the kinetochore fibres and spindle stability.

Keywords [en]
Samp1, nuclear membrane, mitotic spindle, k-fiber, Aurora B, Chromosome mis-segregation
National Category
Cell Biology
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
URN: urn:nbn:se:su:diva-154092OAI: oai:DiVA.org:su-154092DiVA, id: diva2:1190465
Funder
Swedish Research Council, 621-2010-448Swedish Cancer Society, 110590Stiftelsen Olle Engkvist ByggmästareMagnus Bergvall FoundationAvailable from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-03-20Bibliographically approved
In thesis
1. Characterization of the inner nuclear membrane protein Samp1, during interphase and mitosis
Open this publication in new window or tab >>Characterization of the inner nuclear membrane protein Samp1, during interphase and mitosis
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The nucleus, a hallmark in eukaryotic cells, contains the genome separating it from molecules in the cytoplasm. The nucleus is surrounded by a nuclear envelope consisting of two concentric membranes, the outer nuclear membrane and the inner nuclear membrane, the nuclear lamina and nuclear pore complexes. The cytoskeleton is physically connected with the nucleoskeleton by the LINC complexes, spanning the nuclear envelope. In this way, the cell surface is linked directly to chromatin. There are hundreds of unique inner nuclear membrane proteins, but today we only know the functions of a handful. The best characterized inner nuclear membrane proteins are involved in chromatin organization and gene regulation.

This thesis focuses on Samp1, an integral membrane protein that localizes to the inner nuclear membrane during interphase. During mitosis, a fraction localizes to the mitotic spindle, which is responsible for accurate segregation of chromosomes.

It is difficult to investigate inner nuclear membrane protein-protein interactions, because transmembrane proteins are often associated with the “hard-to-solubilize” nuclear lamina. MCLIP was developed as a method to detect interactions between proteins of the nuclear envelope in live cells. MCLIP has been valuable in identifying interaction partners of Samp1. In interphase, Samp1 distributes in distinct micro-domains of the inner nuclear membrane and interacts with the nuclear lamina, emerin and the LINC complex protein SUN1, suggesting that Samp1 might have a functional role associated with both the nucleoskeleton and cytoskeleton.

In mitosis Samp1 distributes in filamentous membrane structures partially overlapping with kinetochore microtubules of the mitotic spindle. Samp1 binds directly to γ-tubulin and recruits γ-tubulin and Haus6 to the mitotic spindle and thus contributes to spindle assembly. Samp1 also interacts with Aurora B, a kinase important for k-fiber error correction at the kinetochores. Depletion of Samp1 caused an increased activation and distribution of Aurora B at the metaphase plate, decreased formation of stable k-fibers, metaphase prolongation and increased chromosome mis-segregation. Samp1 is the first transmembrane protein found to be involved in mitotic spindle assembly and stability, important for correct segregation of chromosomes.

 

 

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2018. p. 64
Keywords
Samp1, LINC complex, nuclear lamina, MCLIP, nuclear envelope, spindle assembly, spindle stability, k-fiber, gamma tubulin, Aurora B, Haus6, Augmin
National Category
Biochemistry and Molecular Biology Cell Biology
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
urn:nbn:se:su:diva-154093 (URN)978-91-7797-199-3 (ISBN)978-91-7797-200-6 (ISBN)
Public defence
2018-05-03, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2018-04-10 Created: 2018-03-14 Last updated: 2018-04-04Bibliographically approved

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