Figure 7.

Chtf18 ^−/− eggs are aneuploid with weakened centromeric cohesion at metaphase II. Monastrol-treated metaphase II wild-type and Chtf18^−/− eggs were immunostained with CREST autoimmune serum (kinetochores, red) and DAPI (DNA, blue), and pairs of sister chromatids were scored for aneuploidy. Representative images of the four types of Chtf18^−/− (−/−) eggs observed are shown. (A) Euploid Chtf18^−/− egg containing 20 pairs of sister chromatids. (B) Aneuploid Chtf18^−/− egg containing 19 pairs of sister chromatids +1 single sister chromatid (shown in box). (C) Aneuploid Chtf18^−/− egg containing 20 pairs of sister chromatids +1 extra single sister chromatid (shown in box). (D) Aneuploid Chtf18^−/− egg lacking one chromosome pair (contains 19 pairs of sister chromatids). Scale bars, 5 μm. (E and F) Outer distances between kinetochore pairs were measured in images of monastrol-treated, metaphase II wild-type (+/+) and Chtf18^−/− (−/−) eggs, and representative images are shown (eggs were stained as above). White arrowheads indicate kinetochore pairs magnified in the insets. Scale bars, 5 μm. (G) Scatter plot depicting the outer kinetochore distances for sister kinetochore pairs. Values are the mean ± SEM; wild-type, n = 10; Chtf18^−/−, n = 10; and P = 0.0015^** by the unpaired t-test. (H) Bar graph depicting the populations of kinetochore distances in wild-type and Chtf18^−/− eggs. Wild-type, n = 2 mice; Chtf18^−/−, n = 2 mice; 100 kinetochore pairs were assessed in 5 oocytes for each mouse. Distances between sister kinetochores that were not in the same plane were determined with the Pythagorean theorem.