Fig. 6. MEX-3 intensity and working model. MEX-3 intensity in ABa and EMS from individual (A) wild-type or (B) spn-4(RNAi) embryos. The average ratio between ABa and EMS intensities is given. (C) Comparison of MEX-3 intensity in wild-type and spn-4(RNAi) blastomeres. Units are arbitrary for MEX-3 intensity. (D) Working model for regulation of PAL-1 expression. MEX-3 exists in active and inactive (*) forms. The active form is normally associated with mex-5 and mex-6 and is competent to repress PAL-1. In the absence of mex-5 and mex-6, the inactive form is targeted for degradation by spn-4. In the absence of spn-4, the inactive MEX-3 accumulates and interferes with active MEX-3.