Fig. 4. A schematic representation of the previously published (see text) interactions of several factors in the early embryo. PAL-1, which is negatively regulated by MEX-3, can specify a hypodermal or body wall muscle fate, depending on the level of POP-1. In the presence of high POP-1 (solid black letters), PAL-1 activity results in a hypodermal-like fate. POP-1 can be down-regulated (open lettering) via Wnt/MAP kinase signaling through the combined action of the factors WRM-1 and LIT-1 (see text). PAL-1 specifies a body wall muscle fate when POP-1 levels are low or absent.