Fig. 2. Sister centromere separation occurs in mks¹ neuroblasts. (A,B) Hybridization of a dodecasatellite probe to squashed preparations of wild-type and mks¹ cells, respectively. Two dots of signal can be detected in wild-type cells (mitotic chromosomes in inset), corresponding to the centromeric regions of the maternal and paternal third chromosome. mks¹ cells show four dots of signal, indicating that the sister centromeric regions have separated. DNA is shown in red, hybridization signal in yellow. Scale bar, 50 µm. (C-H) Immunolocalization of Prod (red, C-E) or Bub1 (red, F-H) on condensed chromosomes (blue) associated with mitotic spindles (green) in wild-type (C,F) and mks¹ mutant cells (D,E,G,H). The paired monochromatic images show Prod (C-E) or Bub1 (F-H) staining alone. Prod is present at four punctate sites on chromosomes 2 and 3 in wild-type cells (C) and four pairs of sites, separated centromeres, in mks¹ (D: one pair is out of the focal plane). (E) A polyploid cell. Bub1 is present on separated kinetochores in mks¹ cells (F, 4N; G, 8N; not all kinetochores are in the focal plane). The mks¹ cell in (H) has progressed into anaphase and the Bub1 signal can no longer be detected. Scale bars, 10 µm.

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