Fig. 6. (A,B) Mesp1/Mesp2 double-null cells express Paraxis. Adjacent parasagittal sections of the Mesp1/Mesp2 double-null chimeric embryo were stained for either Paraxis (A) or lacZ (B). Note that the expression domains of the two genes overlap in the medial sclerotomal region (brackets). (C,D) The rostro-caudal pattern in the dermomyotome is formed in a partially segregating wild-type cell population. Adjacent sections of the Mesp1/Mesp2 double-null chimeric embryos were stained for Dll1 (C) or lacZ (D) mRNA. Red outlines demarcate the dorsal dermomyotome-like compartments. Note that suppression of Dll1 expression occurs in a region mostly occupied by wild-type cells (arrows). Scale bar: 100 µm.