Fig. 9. Overexpression of mezzo partially rescues heart morphogenesis in bon mutants and increases the number of sox17- and cas-expressing cells. (A-C) Rescue of heart morphogenesis after injection of mezzo mRNA into bon mutant embryos monitored by expression of nkx2.5 at 30 hours. The failure of heart primordia to migrate and fuse in the midline in bon mutants (B) was partially restored by overexpression of mezzo (C). (D-I) Dorsal views of embryos at 80% epiboly, showing expression of endodermal markers in wild-type embryos (D,G), bon mutant embryos (E,H) and bon mutant embryos injected with mezzo mRNA (F,I). Embryos were injected with 20-40 pg of mezzo mRNA a the one- to four-cell stage and examined for expression of sox17 (F) or casanova (I). The number of sox17- or casanova-positive cells is significantly increased in homozygous bon mutants injected with mezzo mRNA (F,I) compared with control uninjected mutant embryos (E,H). bon mutant embryos were genotyped by PCR.

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