Somite morphogenesis, but not somite polarity, is aberrant in emi1 mutant embryos. (A,B) Lateral views of (A) wild-type and (B) emi1-/- embryos at the 16- to 18-somite stage. (C,D) Lateral view of (C) deltaC morpholino-injected emi1-/- embryos and (D) deltaD morpholino-injected emi1-/- embryos at the 14- to 15-somite stage. (E) An aphidicolin/hydroxyurea-treated embryo at 30 hpf. (F) her1 stripe integrity was examined in emi1-/- and sibling embryos injected with morpholinos against either deltaC or deltaD. her1 expression was rated according to four categories representing increasing levels of disorganization: wild type, stripes with some salt and pepper expression, stripes begin to merge, and no stripes. Distributions of gene expression patterns are displayed for three independent trials (x-axis). Within each gene expression category, the fraction of sibling embryos is subtracted from the fraction of mutant embryos. For example, the wild-type category in the first deltaC morpholino trial included 0.28 fraction of the mutant embryos (28%) and 0.03 fraction of the sibling embryos (3%), giving a graphed value of 0.25. In deltaC morpholino trials, the number of mutants and siblings assayed (mutant/sib) are: 39/74, 27/79 and 16/57. For deltaD morpholino trials, the corresponding numbers are: 60/50, 28/74 and 49/90. These embryos were assayed in Fig. 3N, but here they were examined by a second investigator in a blind trial. (G,H) mesogenin expression in the tailbud of (G) wild-type and (H) emi1-/- embryos at the 15-somite stage. The expression domain is reduced in the mutant. (I,J) mespb expression in the anterior PSM of (I) wild-type and (J) emi1-/- embryos at the 12-somite stage. (K,L) ripply1 expression in (K) wild-type and (L) emi1-/- embryos at the 12-somite stage. (M,N) tbx18 expression in (M) wild-type and (N) emi1-/- embryos at the 12-somite stage. Segmental expression of mespb, ripply1 and tbx18 is established in the mutant. In G-N, anterior is up. (O) Ephrin B2 localization in two wild-type and two emi1-/- embryos. Shown is the 2-9 somite region of 12-somite-stage embryos. Anterior is up. In both mutant and wild type, Ephrin B2 staining is stronger in the cells anterior to each somite border than in the row of cells posterior to each border.