Morphological characteristics of the dino (din^tm84) and mercedes (mes^tm305) mutant embryos. Wild-type embryos are indicated with ‘+’. (A,B) Tailbud stage, lateral view: the pillow is marked with an arrowhead, the tailbud with an arrow. (C,D) 8-somite stage, dorsal view: the end of the notochord and the corresponding position in the wild-type embryo are marked by an arrow. (E,F) 3- somite stage, optical cross section at the level of the 2nd somite: the anterior somites of the mutant are smaller and the neural tube is of normal size. (G,H) 8-somite stage, optical cross section at the level of the 6th somite: the notochord is lost and the somites are fused in dino mutants with a strong phenotype. (I,J) 15-somite stage, optical cross section at the level of the 13th somite: the posterior somites are larger and the neural tube is smaller in dino mutants. (K,L,M) 24 hours, lateral view: cells at the ventral side of the yolk extension are marked with an arrow. (N,O) 48 hours, lateral view: note the smaller head in the din mes double mutant. (P-S) 36 hours, posterior view of tail fin; (S) wild-type embryo injected with Xenopus Bmp-4 mRNA. (T-W) 36 hours, ventral view of tail fin: (V) mes^tm305/mes^tm305 embryo from heterozygous mother; (W) mes^tm305/mes^tm305 embryo from homozygous mother. (X-Z) Lateral views of (X) wild-type, 20- somite stage embryo; (Y) mes^tm305, 20-somite stage embryo; (Z) din^tt250, 15-somite stage embryo, showing acridine orange staining. Apoptotic cells (red) can be detected ventral of the forming yolk extension in din and mes mutant embryos.

Altered gene expression in dino (din^tm84) and mercedes (mes^tm305) mutants during gastrulation, detected by whole- mount in situ hybridization. Expression of: (A) eve1, at 40% epiboly, animal view, dorsal right; (B) eve1, at 70% epiboly, lateral view, dorsal right; (C) eve1, at tailbud stage, vegetal view, dorsal right – the more pronounced staining reflects the expression of eve1 in a group of cells posterior to the Kupfer’s vesicle (Joly et al., 1993); (D) gata2, at 70% epiboly, animal view, dorsal right; (E) gata2, at 70% epiboly, lateral view, dorsal right – the margin of the blastoderm is indicated by arrowheads; (F) sna1, at 80% epiboly, dorsal view; (G) shh, at 70% epiboly, dorsal view; (H) gsc and eve1, at 70% epiboly, animal view, dorsal right; (J) fkd3, at shield stage, animal view, dorsal right. (K) fkd3, at 70% epiboly, dorsal view.

Altered gene expression in mesodermal tissues of dino (din^tm84) and mercedes (mes^tm305) mutants detected by in situ hybridization (C-E) and immunostaining (A,B). (A) fkd2, 10-somite stage, dorsal view of the head region. (B) ntl, 10-somite stage, dorsal view. (C) myoD: top, 10-somite stage, dorsal view; bottom, 22 hours, ventral view of the tail. (D) gata1: top, 10-somite stage, dorsal view; bottom, 22 hours ventral view of the tail. (E) pax2, 22-somite stage, dorsal view of a spread embryo, anterior to the left. The pronephric expression domain is indicated by asterisks (in the mutant), the interneurons are indicated by arrows (in the wild type).

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