Fig. 3. PAL-1 immunolocalization in wild-type, mex-6(RNAi) and spn-4(RNAi) embryos. Genotypes and embryo stages are indicated (see Fig. 2B for quantitative summary of staining experiments). (A-D) Wild-type embryos express PAL-1 only in posterior blastomeres starting at the four-cell stage. (E-H) mex-6(RNAi) embryos express PAL-1 at equally high levels in all blastomeres starting at the four-cell stage. (F) In the four-cell mex-6(RNAi) embryo shown, the two anterior cells are dividing before the posterior cells, demonstrating that mex-6(RNAi) embryos can maintain asymmetries in cell cycle time through the four-cell stage. For all 22- to 26-cell embryos, some nuclei are out of the plane of focus. (I-L) spn-4(RNAi) embryos express PAL-1 in all blastomeres at the four-cell stage; PAL-1 is often detected at lower levels in anterior blastomeres than posterior blastomeres, as evident in the eight-cell embryo shown (K). Approximately half of (L) spn-4(RNAi) 22- to 26-cell embryos express PAL-1 in all blastomeres as shown, the remainder express PAL-1 only in posterior blastomeres, similar to (D) wild-type embryos (see Fig. 2B for quantitation). spn-4(RNAi) embryos characteristically maintain asymmetries in cell cycle time as evident in the (K) eight-cell embryo shown, where the anterior blastomeres have proceeded to prophase while the posterior blastomeres are still in interphase.