Fig. 2. Regions of MEX-5 required for one-cell asymmetry. (A,B) Wild-type or mutant MEX-5 proteins were fused to GFP and scored at the one-cell stage for asymmetry (Asym), P granule localization (Pg), and for degradation after the four-cell stage in somatic blastomeres (Som). ++, wild-type asymmetry; +, reduced asymmetry; (+), weak and variable asymmetry; -, no apparent asymmetry. Representative fluorescence images of some embryos are shown in A. Asterisks by plasmid names indicate fusion proteins with prominent nuclear localization in addition to cytoplasmic localization (arrow in image of pJT35). (B) The C-terminal 22 amino acids of MEX-5 indicating substitutions made within full-length MEX-5. (C) Fluorescence micrographs of transgenic embryos expressing mutant forms of GFP:MEX-5 as listed, at the one-cell, two-cell and eight-cell stages. The eight-cell-stage embryos are labeled and are in the same orientation as in Fig. 1A; asterisks indicate the germline blastomere P₃. Arrows point to somatic blastomeres at the eight-cell stage, where MEX-5 normally is degraded. GFP:MEX-5^{KEN to AAA} appeared identical in all respects to GFP:MEX-5 (not shown). The arrowhead points to an example of prominent P granule localization; note abnormally bright P granules in the P₃ cell for S458A. (D) Ratio of anteroposterior fluorescence at pronuclear meeting, n>30 embryos each; error bars show s.d., ^**P<3x10^-4 (two-tailed t-test). The type of GFP:MEX-5 fusion protein is indicated in brackets along with the plasmid name. fzr-1(-)=fzr-1(ok380); par-1(-)=par-1(it51). (E) Ratio of anteroposterior fluorescence in single one-cell embryos expressing GFP fusion proteins and recorded at 1-minute intervals before and after pronuclear meeting (arrow).