Fig. 8. PBL is not required for activation of the HTL/MAPK pathway. Ventrolateral view of stage 8 embryos heterozygous (A) and homozygous (B) for pbl². Activation of the MAPK pathway, visualised using an antibody specific to dpERK, the dual-phosphorylated form of the MAPK (Gabay et al., 1997a; Gabay et al., 1997b), is seen in the cells at the leading front (arrowheads) of the mesoderm during dorsal migration.