Fig. 3. pam-1 embryos lack early signs of AP polarity. Images from a time-lapse DIC series of a single embryo. (A) In wild type, the oocyte and sperm pronuclei appeared at opposite ends of the embryo, with the sperm pronucleus at the posterior pole. The SPCC cued axis polarization and caused changes in the cortex called pseudocleavage. (B) The oocyte pronucleus migrated to meet the sperm pronucleus in the posterior of the embryo. (C,D) The first spindle displaced toward the posterior and the first cleavage was asymmetric, with a larger anterior cell, AB, and a smaller posterior cell, P₁. (E) These cells then differed in their cell cycle timing and spindle orientations during the next division. (F) In pam-1 embryos, polarization of the cortex was absent and the SPCC did not contact the posterior cortex as the pronuclei first appeared close to the center of the embryo. (G) The pronuclei met in the center of the cell. (H,I) In about 60% of pam-1 embryos, the first mitotic spindle remained in the center of the embryo, resulting in an equivalent cleavage. (J) When this occurred, the two daughter cells divided synchronously with parallel spindle orientations. (K) The position of pronuclear meeting was plotted for five wild-type and ten pam-1 embryos. On average, the pronuclei in pam-1 embryos met closer to the center of the embryo than in wild type. o, oocyte pronucleus; s, sperm pronucleus. Scale bar: 10 µm.