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Tts1, the fission yeast homologue of the TMEM33 family, functions in NE remodeling during mitosis.

Zhang D, Oliferenko S - Mol. Biol. Cell (2014)

Bottom Line: An amphipathic helix located at the C-terminus of Tts1 is important for ER shaping and modulating the mitotic NPC distribution.Of interest, the evolutionarily conserved residues at the luminal interface of the third transmembrane region function specifically in promoting SPB-NE insertion.Our data illuminate cellular requirements for remodeling the NE during "closed" nuclear division and provide insight into the structure and functions of the eukaryotic TMEM33 family.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604 zhangdan@tll.org.sg snezhana.oliferenko@kcl.ac.uk.

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Evolutionarily conserved TMEM33 motifs are required for Tts1 function in SPB-NE interaction and spindle assembly. (A) Quantification of spindle morphologies in cells with the indicated genetic backgrounds at 24°C (n = 500). Spindle morphologies are categorized as in Figure 4D. The red asterisks highlight Tts1 mutants that were unable to rescue spindle defects in cut11-6 tts1Δ cells. Tts1 mutants that were partially compromised in correcting spindle abnormalities in cut11-6 tts1Δ cells are indicted by blue asterisks. (B) Diagram showing structural features of Tts1 important for its functions in structuring the cortical ER and the mitotic NE and in the mitotic SPB-NE insertion. A possible topology of the third transmembrane domain (TM3) with four conserved residues is shown as well.
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Figure 7: Evolutionarily conserved TMEM33 motifs are required for Tts1 function in SPB-NE interaction and spindle assembly. (A) Quantification of spindle morphologies in cells with the indicated genetic backgrounds at 24°C (n = 500). Spindle morphologies are categorized as in Figure 4D. The red asterisks highlight Tts1 mutants that were unable to rescue spindle defects in cut11-6 tts1Δ cells. Tts1 mutants that were partially compromised in correcting spindle abnormalities in cut11-6 tts1Δ cells are indicted by blue asterisks. (B) Diagram showing structural features of Tts1 important for its functions in structuring the cortical ER and the mitotic NE and in the mitotic SPB-NE insertion. A possible topology of the third transmembrane domain (TM3) with four conserved residues is shown as well.

Mentions: To determine domains important for Tts1 function in the context of mitotic SPB-NE interaction and spindle assembly, we performed complementation analyses by introducing the tts1 mutants described earlier (Figure 1) into the cut11-6 tts1Δ genetic background. All mutants that failed to partition to the ER tubules did not rescue spindle defects in cut11-6 tts1Δ cells (Figure 7A), suggesting that the structural traits specifying localization of Tts1 to the curved ER membranes may be pertinent to its function in SPB-NE insertion. However, the mutant Tts1 proteins where the C-terminal amphipathic helix was disrupted fully rescued the spindle defects in cut11-6 tts1Δ cells in spite of their compromised tubular ER-shaping function (Figure 7A). Moreover, point mutations (P119A, Y123/131I, and H127A) in the conserved residues within the third membrane-spanning region of Tts1 that did not lead to obvious ER architecture defects (Figures 1 and 2, Supplemental Figure S2F, and unpublished data) rendered Tts1 nonfunctional with respect to mitotic spindle assembly (Figure 7A). These observations suggested that the role of Tts1 in promoting SPB insertion was distinct from its functions in sustaining the ER morphology.


Tts1, the fission yeast homologue of the TMEM33 family, functions in NE remodeling during mitosis.

Zhang D, Oliferenko S - Mol. Biol. Cell (2014)

Evolutionarily conserved TMEM33 motifs are required for Tts1 function in SPB-NE interaction and spindle assembly. (A) Quantification of spindle morphologies in cells with the indicated genetic backgrounds at 24°C (n = 500). Spindle morphologies are categorized as in Figure 4D. The red asterisks highlight Tts1 mutants that were unable to rescue spindle defects in cut11-6 tts1Δ cells. Tts1 mutants that were partially compromised in correcting spindle abnormalities in cut11-6 tts1Δ cells are indicted by blue asterisks. (B) Diagram showing structural features of Tts1 important for its functions in structuring the cortical ER and the mitotic NE and in the mitotic SPB-NE insertion. A possible topology of the third transmembrane domain (TM3) with four conserved residues is shown as well.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 7: Evolutionarily conserved TMEM33 motifs are required for Tts1 function in SPB-NE interaction and spindle assembly. (A) Quantification of spindle morphologies in cells with the indicated genetic backgrounds at 24°C (n = 500). Spindle morphologies are categorized as in Figure 4D. The red asterisks highlight Tts1 mutants that were unable to rescue spindle defects in cut11-6 tts1Δ cells. Tts1 mutants that were partially compromised in correcting spindle abnormalities in cut11-6 tts1Δ cells are indicted by blue asterisks. (B) Diagram showing structural features of Tts1 important for its functions in structuring the cortical ER and the mitotic NE and in the mitotic SPB-NE insertion. A possible topology of the third transmembrane domain (TM3) with four conserved residues is shown as well.
Mentions: To determine domains important for Tts1 function in the context of mitotic SPB-NE interaction and spindle assembly, we performed complementation analyses by introducing the tts1 mutants described earlier (Figure 1) into the cut11-6 tts1Δ genetic background. All mutants that failed to partition to the ER tubules did not rescue spindle defects in cut11-6 tts1Δ cells (Figure 7A), suggesting that the structural traits specifying localization of Tts1 to the curved ER membranes may be pertinent to its function in SPB-NE insertion. However, the mutant Tts1 proteins where the C-terminal amphipathic helix was disrupted fully rescued the spindle defects in cut11-6 tts1Δ cells in spite of their compromised tubular ER-shaping function (Figure 7A). Moreover, point mutations (P119A, Y123/131I, and H127A) in the conserved residues within the third membrane-spanning region of Tts1 that did not lead to obvious ER architecture defects (Figures 1 and 2, Supplemental Figure S2F, and unpublished data) rendered Tts1 nonfunctional with respect to mitotic spindle assembly (Figure 7A). These observations suggested that the role of Tts1 in promoting SPB insertion was distinct from its functions in sustaining the ER morphology.

Bottom Line: An amphipathic helix located at the C-terminus of Tts1 is important for ER shaping and modulating the mitotic NPC distribution.Of interest, the evolutionarily conserved residues at the luminal interface of the third transmembrane region function specifically in promoting SPB-NE insertion.Our data illuminate cellular requirements for remodeling the NE during "closed" nuclear division and provide insight into the structure and functions of the eukaryotic TMEM33 family.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604 zhangdan@tll.org.sg snezhana.oliferenko@kcl.ac.uk.

Show MeSH
Related in: MedlinePlus