Figure 7.

Effect of bud6Δ or kar9Δ in spindle orientation and neck interactions in bni1Δ haploids. Single fluorescence images of representative stages of spindle orientation and cytoplasmic microtubule behavior are shown. (A) bni1 haploids (MYC1T): initial orientation of SPBs facing the bud (a and d, long arrowhead and asterisk). In cells containing short spindles, cytoplasmic microtubule interactions into the bud (b and c, long arrowhead) and to the neck (b–e, short arrowheads); persistent neck interactions during anaphase (f–h, arrowheads). (B) bni1 bud6 haploids (MYC101T): early orientation of SPBs facing the bud and cytoplasmic microtubule attachments to the neck were suppressed. The orientation defect was more severe than in single bud6 mutants. It is however difficult to factor out additional cytoskeletal defects that lead to a slow growth phenotype compared with either bni1 or bud6 single mutants. Short spindles away from the bud neck (a and b); mispositioned spindles in the bud reflecting lack of neck retention (c and d, arrows); anaphase spindles (e–h). (C) bni1 kar9 haploids (MYC102T): initial orientation of SPBs facing the bud neck was delayed (a, arrowhead). As a result, the p of both poles interacting with the neck during spindle assembly was reduced compared with bni1 single mutants (c and d, top cell). Cells with short spindles still oriented primarily by interactions with the neck (b, c, e, f, and h, top, arrowheads). Interactions persisted after onset of anaphase as in bni1 cells (f, right cell; g). Bar, 2 μm.