Fig. 6. No lamellipodia or filopodia form in P₁ isolates. Ea and Ep are labeled with asterisks, and arrows indicate presumptive leading edges of MSxx and P₄. (A) Scanning electron micrograph of a P₁ isolate. (B) F-actin localization. (C) Phosphotyrosine localization. An enrichment of phosphotyrosine was seen at the Ep/P₄ boundary, but is unlikely to be functionally significant as it was not polarized in the direction of movement and it was not present at the Ea/MSxx boundary. Additionally, it was recently shown that phosphotyrosine accumulates at the EMS/P₂ boundary due to a signaling pathway that is not implicated in gastrulation (Bei et al., 2002). Scale bars: 10 µm.