Fig. 1. MEX-5 in oocytes and early embryos. (A) Diagram of MEX-5 (green) and PIE-1 (red) localization from the one-cell to eight-cell stages. At the eight-cell stage, the single germline blastomere expresses PIE-1 and the seven somatic blastomeres express MEX-5; somatic degradation is occurring in the four oldest somatic blastomeres (light green; three are visible in this ventral-up orientation). (B) Diagram of one arm of the gonad showing germ cells progressing through mitosis, meiosis, and forming oocytes. The oldest oocyte (-1 position) enters the spermatheca where it is fertilized by sperm and pushed into the uterus. (C-F'') Each row shows a single one-cell embryo stained for DNA, PAR-3 and MEX-5; arrows indicate nascent maternal (long arrow) and paternal (short arrow) pronuclei. In these wide-field images, fluorescence from cortical PAR-3 is visible in the central focal plane, facilitating comparison with cytoplasmic MEX-5. Anterior is left in all images, and embryos are about 50 µm in length. (G) GFP:MEX-5 in the gonad of a live adult. Embryos a-c are at the one-cell stage; a and b are completing meiosis I and II, c is beginning the first mitotic division (posterior up), and d is at the two-cell stage. (H) Quantitative fluorescence of GFP:MEX-5 at the anterior and posterior poles of five single embryos recorded before and after pronuclear meeting (arrow) as indicated. Error bars indicate s.e.m.