Fins are not required for MMP specification. (A-D) Brightfield images of four-dayold embryos. Brightfield images of wild-type, dnFgfrexpressing, and Δsix1a;4a;Δsix1b;4b mutant embryos. Fins are present (asterisk) in wild-type (A) and Δsix1a;4a;Δsix1b;4b mutant (B) embryos, but absent in dnFgfr-induced (C) and aldh1a2 mutant (D) embryos (aldh1a2 mutant fin phenotype previously shown by Grandel et al., 2002). (E-J) RNA in situ hybridization for (E, F) met and (G, H) lbx1a in 36 hpf embryos. (E-H) Although migratory streams are severely misshapen in aldh1a2 mutants, MMP markers lbx1a (E, F) and met (G, H) are expressed at levels comparable to wild-type embryos. In aldh1a2-/- mutant MMPs, met expression appears darker than in WT (E, F); this may be due to greater cell density in the mutant, which has impaired migration. Embryos in A-C and E-H were PTU-treated to inhibit pigment formation. MMP arrowheads are color coded as described in Figures 1 and S1. Scale bars are 100 μm.