Table 3

Interphase MTs Push on the Nucleus in S. pombe

Cells with clear deformation of nucleus84
Cells with MT pushing force81
Cells with MT pulling force0
Cells with functional nuclear attachment zone in MT overlap region84
  • 127 interphase cells (PT.65) expressing nup107-GFP and GFP-tubulin were imaged at 5-s intervals for 4–8 min in a single optical plane using confocal microscopy. Analysis of these time-lapse sequences revealed that 84 cells exhibited a clear deformation of the nucleus within this time period in this focal plane. Analysis of MTs during the deformation event was used to determine the type of force involved in deformation. MT pushing force was defined as MT contacting the cell tip, elongating, and producing a pushing force on the nuclear envelope away from the contacted cell tip; the opposite MT in the bundle was not contacting the cell tip. MT pulling force was defined as an MT contacting the cell tip and shortening and producing a pulling force on the nuclear envelope towards the contracted cell tip. Ambiguous force was defined in circumstances where MTs contacted both cell tips during deformation. In all cases examined, the MT overlap region was contiguous with the nuclear envelope and moved with the deformed nuclear envelope, suggesting the presence of a functional nuclear attachment site within the central MT overlap region.