Figure 5.

MTs and formation of the nuclear extension. (A) In late G2 phase, nuclei are teardrop shaped. Fine extensions are formed that reach towards the bud. This motility does not result in nuclear displacement. Note that these extensions coalign with interphase MTs (red: nRFP; green: GFP-Tub1) and that their formation depends on dynein (Straube et al, 2001). Bars: 3 μm in series and 1 μm in merged image. (B) At the onset of mitosis, the SPB becomes active and nucleates MTs. Note that SPB-independent MTs are also found (see inset, lower MT has no contact with the SPB), indicating that two populations of MTs exist at the G2/M transition: Tub: GFP-Tub1, nRFP: nRFP. Bar: 5 μm. (C) In late G2 phase, the SPB (stained with γ-tubulin-GFP; Straube et al, 2003) is located at the side of the teardrop nucleus (nRFP). At the onset of prophase, the SPB migrates to the tip of the nucleus and pulls a long extension into the bud (bud neck indicated by asterisk). Elapsed time is given in minutes:seconds. Bar: 3 μm. (D) The SPB forms long astral MTs that reach into the daughter cell (indicated by ‘D') and the mother cell (indicated by ‘M'). After the envelope opens, indicated by the release of the nuclear RFP fusion protein, the SPB migrates into the bud and forms the metaphase spindle. Tub: GFP-Tub1; nRFP: nRFP. Bar: 3 μm. (E) At early prophase, MTs reach into the daughter cell (indicated by ‘D'), but are also tightly associated with the nucleus (indicated by ‘N') within the mother cell (indicated by ‘M', see arrows in overview). The plus-ends of astral MTs are in contact with the cortex (Tub, arrowheads), while the SPB (indicated by asterisk in upper image series) moves into the bud. Motility along the cortex coincides with the appearance of dynein at the tip of the MT (Dyn, arrowheads). Elapsed time is given in seconds. Bar: 3 μm. Supplementary movie for panels B and E is given on the EMBO website.