Fig. 3. Reductions in APC/C activity result in meiotic defects. DAPI (A-K) and tubulin (A'-K') localization of meiotic chromosomes and spindles in wild type (A-D) and mutant mat-1 (E-K) embryos. The dotted white lines represent the approximate position of the plasma membrane. After fertilization, oocytes progress through MI metaphase (A,A'), anaphase A (B,B'), anaphase B (C,C') and telophase (D,D'; only chromosomes within the polar body can be seen in this focal plane). During oocyte meiosis, the metaphase to anaphase transition promotes a 90° rotation of the anastral spindle axis (A,B,A',B'; see cartoon below. The dotted black line represents the long axis of the spindle). Consequently, one pole of the spindle abuts the plasma membrane (B'; see cartoon below). The cartoon series shows the organization of the meiotic chromosomes and spindles during wild-type meiosis. (E-K') mat-1 mutants incubated at restrictive and semi-permissive temperatures have meiotic defects. (E,E') A metaphase plate and spindle from a metaphase arrested mat-1(ax212) embryo. (F') Spindle rotation without chromosome separation (F; gray arrowhead) from a mat-1(ax72) embryo at 16°C. (G,H) Examples of MI anaphase bridges (white arrows) in mat-1(ax227) at 20°C (G) and mat-1(ax72) at 16°C (H). (I,I') In the small percentage of the embryos that hatch at semi-permissive temperatures, normal meiosis I and II figures are seen [i.e., metaphase II (I,I'; the first polar body is outside of the field)]. (J,J') Despite spindle rotation (J'), chromosome separation during meiosis II is not always normal (gray arrowhead). (K,K') An example of an abnormal elongated meiotic spindle and an abnormally small array of meiosis II chromosomes [mat-1(ax161)]. Scale bar: (in D') 2 µm.

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