Fig. 4. mks¹ is epistatic to polo¹ in respect of mitotic progression and cyclin degradation. (A-D) Orcein-stained squashed preparations of polo¹ mks¹ cells that display overcondensed chromosomes (A,C,D), polyploidy (B,C) and circular (A,B) or bar-like figures (D). The mitotic index, proportions of metaphase:anaphase cells and proportion of polyploids are similar to that in the mks¹ mutant alone (Table 1B). (E) Western blots showing levels of cyclins A and B in wild-type, polo¹, mks¹ and polo¹ mks¹ brains. This reflects cyclin levels in the cycling cells of this tissue. Cyclin A is substantially reduced in, but not absent from, polo¹ cells, suggesting that the APC/C is functional. Cyclin B is still present, indicative of checkpoint delay to mitosis. Both mitotic cyclins are present at equivalent levels in the double mutant combination, indicating loss of APC/C function. Actin was used as a protein-loading control.

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