Fig. 5. BrdU incorporation into the epaxial myotome (4 hour post administration). (A,B) A section from a chick embryo that received a ssXV DML from a 30 somite quail embryo transplanted at ssXIV (23 somites) after overnight re-incubation and harvesting 4 hours after BrdU administration. The section is through the plane of the myocyte nuclei, a single layer at the inner extent of the quail nuclei. The slightly oblique plane of section results in the myotome layer being depicted truly as a single cell layer while the dermomyotome appears stratified. (A) Quail derived dermomyotome and myotome labelled with qcpn antibody. (B) Same section as A showing BrdU-labelled nuclei. Broken line outlines the neural tube. (C) Composite image of A,B. BrdU-labelled nuclei (red) and quail nuclei (green). The asterisk marks the medial part of the myotome comprising dual labelled nuclei and the arrow marks the medial boundary of quail myonuclei that have not incorporated BrdU. One or two quail nuclei are present in the dermis overlying the lateral donor-derived dermomyotome. (D) Schematic interpretation of the section in A-C highlighting the medial position of BrdU-labelled quail myocyte nuclei (bracket, B) and the non-BrdU labelled quail myotome nuclei located laterally (bracket, A). The same distribution of BrdU and/or quail nuclei was seen in three out of three embryos. DML, dorsomedial lip; NT; neural tube.