Fig. 3

col mutant embryos display an increase ventral and posterior mesoderm-derived cells including blood and tail bud cells as well as a decrease in dorso-anterior mesoderm-derived cardiac mesoderm. (A–D) gata1 is expressed by hematopoietic precursor cells of 10- (A) and 26- (C) somite-stage wild-type embryos. At the same developmental stages, there are increased numbers of gata1-expressing cells in col mutants (B,D). The arrowhead in D marks the large number of blood cells in the region of the anus in col embryos. (E,F) At 60% epiboly (7 hpf), ntl is expressed in the ventrolateral mesoderm along the blastoderm margin of wild-type embryos (E). ntl expression is expanded in col mutant embryos (F). ntl at the 10-somite stage (G,H) and wnt8 at the 3-somite stage (I,J) are expressed by mesodermal cells of the tail bud. Increased expression of both ntl (H) and wnt8 (J) in the tail bud mesoderm is observed in col mutant embryos. Twenty-six-somite- (K) and 16-somite- (M) stage, wild-type embryos showing apoptotic cells revealed by TUNEL. The increase in the number of tail bud cells in col mutants is accompanied by an increase in the number of apoptotic cells in the tail (L). The arrow marks the TUNEL -positive cells in the tail of col mutants. (M,N) Lateral views of wild-type (M) and col mutant (N) embryos processed for TUNEL with arrow (N) indicating apoptotic cells ventral to the forming yolk extension in mutant embryos. (O,P) Lateral views of cardiac mesoderm nkx2.5 expression in 24 hpf wild-type (O) and col mutant (P) embryos reveal a reduction in the expression domain in col mutant embryos. (Q,R) dHAND expression in the developing heart (arrows) in 48 hpf wild-type (Q) and col mutant embryos (R) reveals decreased expression in col mutant embryos.