Fig. 6. Meiotic exit is compromised in embryos with reduced APC/C activity. Localization of tubulin, DAPI and phospho-histone H3 (p-H3) in wild type (A-L) and mat-1 meiotic hypomorphs (M-R). Wild-type telophase II is characterized by the presence of a single polar body (white arrow in A,C,E,I) and a MII spindle (A; white arrowhead) that lies between two p-H3 staining (E) haploid chromosome sets (C). In early post-meiotic embryos, the compact MII spindle remnant lies at the surface of the plasma membrane (G; white arrowhead). Both the first (I, white arrow) and second (I, gray arrowhead) polar bodies can be seen, but only the second stains with p-H3 (K). At this stage, both the female (I, black arrowhead) and male pronucleus (J) have formed. The female, but not the male, pronucleus stains weakly with p-H3 (K,L). mat-1 hypomorphs (1PB class) display variable meiotic exit defects, with post-meiotic mutant embryos retaining many meiotic characteristics. Typical defects include large, disorganized meiotic spindle remnants (M; white arrowhead) co-existing with the developing sperm aster (N; caret). When the pronuclei form, only a single polar body (O; white arrow) is present and both the female pronucleus (O; black arrowhead) and polar body stain brightly with p-H3 (Q). In some 1PB class embryos, the male pronucleus (P; black arrowhead) was found to abnormally stain for p-H3 (R; black arrowhead).