Fig. 6. Pathways regulating the reciprocal asymmetry of POP-1 and SYS-1 in C. elegans. Schematic of the two pathways regulating nuclear SYS-1 and POP-1 levels. SYS-1 levels are elevated by the MOM-2/MOM-5/APR-1 pathway, and nuclear POP-1 levels are decreased by the MOM-4/WRM-1/LIT-1 pathway with input from the MOM-2/MOM-5/APR-1 pathway. Each pathway contributes to an increase in the SYS-1-to-POP-1 ratio, which drives the posterior cell fate. The asterisk denotes that POP-1 activity could be regulated via post-translational modification.