Fig. 7. Model of PLM polarity regulation by LIN-44. (A) Schematic of embryo showing positions of PLM neuron (green), lin-44-expressing tail epidermal cells (red), and egl-20-expressing epidermal and muscle cells (blue). Based on their expression patterns, hypothetical gradients of EGL-20 and LIN-44 are presented for wild type and lin-44 mutants. Axonal structure of PLM is shown. A high level of LIN-44 is needed to induce correct PLM polarity. (B) The PLM/ALN precursor divides along the AP body axis to produce the anterior daughter PLM and posterior daughter ALN (a, anterior; p, posterior). The centrosomes of PLM and ALN (red spots) are on opposite poles after cell division. In response to LIN-44 signaling via LIN-17, the PLM centrosome moves to the posterior pole and PLM adopts the correct AP polarity. In the absence of LIN-44 or LIN-17, no centrosome movement occurs and PLM polarity is reversed. Axonal structures of PLM and ALN are shown.