Fig. 3. Expression of Pax3 and Frek mRNAs by mesenchymal cells in the myotome. (A) Cells expressing Pax3 mRNA (blue, arrowheads) intermingle but do not overlap with desmin-positive fibers (brown) in the E4 myotome. At this stage, Pax3 is also transcribed in a DM-derived intermediate domain located between myotome and forming dermis (see Fig. 4 and corresponding text for details). (B) Co-expression of PAX7 immunoreactivity (brown) and Frek mRNA (blue) in mesenchymal cells within the myotome. D, dermis; ID, intermediate domain; M, myotome; NT, neural tube. Scale bar: 30 µm in A; 23 µm in B.