Fig. 5. sep-1 RNAi mimics the 1PB APC/C phenotype. (A,B) H2B::GFP micrographs of individual post-meiotic one-cell stage zygotes. The wild-type zygote in A has completed both meiotic divisions (carets point to the two polar bodies, one is out of the focal plane) and is at the pronuclear migration stage of zygotic development. The female pronucleus (left) travels from the far left end of the zygote to meet up with the male pronucleus (right). Pronuclear meeting normally occurs within the right end of the embryo (arrow). The sep-1 RNAi zygote in B has completed only a single meiotic division prior to developing pronuclei (arrowheads point to the single polar body). Like the APC/C 1PB class, SEP-1 depleted zygotes remain in a meiosis I stage and fail to progress to meiosis II. The sep-1 RNAi zygote transitions directly into an abnormal pronuclear stage embryo (cortical contractions and flows are absent). As in the 1PB class, the female pronucleus and the male pronucleus meet centrally within the cell (arrow). The chromosomes in both pronuclei appear more condensed than in wild-type zygotes.