Fig. 2

Fig. 2 Repression and activation, respectively, of the expression of myoD by DEAB and RA. Flat-mounted embryos, anterior is to the left. (A–B) Comparison of myoD expression in wild-type (A) and neckless (nls; B) siblings at the 12-somite stage. At this stage, myoD is expressed in the lateral aspect of somites (arrowhead) and two rows of adaxial cells (arrows) in wild-type embryos (A) and krox20 is expressed in rhombomeres 3 and 5 (asterisks). The shorter distance between rhombomere 5 and trunk mesoderm (myoD) has been used to identify nls embryos (brackets in panels A and B). Expression of myoD is reduced in nls embryos (B). (C) Closer view restricted to the trunk showing expression of myoD in 10-somite stage embryo. (D) In DEAB-treated embryos, myoD expression is reduced in somites, as well as in adaxial cells (white arrowhead). (E) In RA-treated embryos, myoD expression is up-regulated in somites and strongly induced in anterior psm (bracket). (F) Control at the 12-somite stage. (G–H) Incubation in retinal (Ral) produces the same phenotype as incubation in RA. Embryos incubated in DEAB and Ral are undistinguishable from control embryos demonstrating that Ral needs to be converted locally in RA by Raldhs to induce myoD expression. psm, presomitic mesoderm. Scale bars: in panel A, 100 μm for panels A–B; in panel C, 100 μm for panels C–H.