I am so sorry for your loss. She will be missed.

Read more about this research in our ‘First person’ interview with Bethany Campbell: journals.biologists.com/jcs/article/...

It is unclear how NE fenestration occurs. We find a potential for branched actin in fenestration. Branched actin promotes NE break down in starfish oocytes. Our findings suggest that branched actin plays a conserved role in mitosis. For more see our preprint. 10/end
www.biorxiv.org/content/10.1...

Interestingly, cells that do enter mitosis despite CK666 treatment, show aberrant SPB interaction with the actin ring leading to spindle and nuclear division defects. This suggests that the SPB has an affinity for actin and in the absence of branched actin binds the actin ring instead. 9/

Branched actin is known to remodel membrane. If it helps fenestration on the NE we should see branched actin elements on the NE and near the SPB. Indeed, she found Fimbrin and Arp2/3 components on the NE and near the SPB. 8/

If CK666 is required for NE fenestration, treating the cells with CK666 should not display mitotic defects. Indeed, in prophase-arrested nda3-KM11 mutants, treatment with ck666 followed by prophase release did not show any mitotic defects. 7/

She asked if this is because the fenestra fails to form in these cells. Indeed, CK666 treated cells retain higher levels of NLS-GFP in the nucleus a hallmark of fenestration defect. 6/

Cut11 recruitment defects typically indicate failure to inset the SPB in the NE. Just before SPB insertion during fenestration, the SUN domain protein Sad1 forms a ring framing the fenestra. Ck666-treated cells fail to form this ring as seen with Structured illumination microscopy. 5/

She found that on CK666 treatment, the SPB often failed to recruit the Polo-like kinase Plo1 and the SPB docking protein Cut11. 4/

We saw similar defects in mutants of arp3 or actin-bundling protein fimbrin. Fission yeasts undergo closed mitosis and the MTOC or spindle pole body (SPB) duplicates in interphase and just before mitotic onset, is inserted into a fenestra on the nuclear envelope and spindle microtubules nucleate. 3/

We noticed that fission yeast cells treated with the Arp2/3 complex inhibitor CK666 often failed mitotic entry. Dhanya confirmed this finding and it was all the clearer in cell-cycle synchronized cells, where CK666 cells often failed to enter mitosis or did so with a significant delay. 2/

Congratulations Katherine and the Aird lab.