Fig. 5. MyoD expression is repressed by a Bmp signal in the presomitic mesoderm. (A) MyoD expression after injection of control cells. All of the embryos showed normal MyoD expression (n=25). (B) MyoD expression after injection of Noggin-expressing cells. Ninety-one percent of the embryos showed ectopic expression of MyoD in the presomitic mesoderm and first somites (n=42/46). (C) Sections at the level of newly formed somite. (D) Sections at the level of presomitic mesoderm. Arrowheads in C and D indicate the ectopic expression of MyoD, on the injected and contralateral sides of the embryo. The broken line indicates the position of nogginexpressing cells. Sections levels are indicated by arrows in B. (A,B) Composite of a bright-field image of whole-mount or transverse section and a fluorescent image showing the DiI-labeled control and noggin-expressing cells. Somite numbers are indicated by roman numerals.