Lateral presomitic cells expressing <i>Meox2</i> are the dermomytome progenitors.

<p>(A) Expression of <i>Meox2</i> mRNA in the most lateral region (rounded brackets) of presomitic mesoderm at stage 14 (dorsal view and transverse section), 16 (dorsal view), 17/18 (dorsal view and transverse section) and 23 (transverse section). Dotted lines indicate the position of the medial and lateral population of myogenic cells. Vertical lines define the limit between anterior and trunk region. Nc, notochord. (B) Lineage tracing experiments: embryos were injected with WGA-rhodamine (red) in the most lateral presomitic mesoderm (a) or co-injected with WGA-fluorescein (green) in the lateral presomitic mesoderm (c) at stage 13. Transverse sections of the embryo at the trunk level and at stages 18 or 23; embryo injected with WGA-rhodamine and submitted to indirect immunofluorescence with 12/101 antibody followed by secondary Alexa fluor 488 anti-mouse antibody (green) (b) or injected with the both tracers (d, e and f). WGA-rhodamine fluorescence (d), WGA-fluorescein fluorescence (e), merge (f). Dotted lines indicate the bilateral symmetry plan. In (a) and (c): Vertical lines define the limit between anterior and trunk region. (a) and (c) dorsal views, anterior side on the left. (C, D and E). Ablation experiments of presomitic mesoderm at stage 14. After microdissection experiments, embryos were fixed at stage 19 or at the tailbud stage to analyze meox2 and pax3 expression respectively. (C) sham-operated embryos, ectoderm was incised at the lateral level (line), ectoderm and mesoderm were separated from each other on the lateral side, but mesoderm was not removed. (D) Same operation on the mediolateral level but superficial mesoderm was removed (hatched zone) (E) Same operation on the lateral level but superficial mesoderm was removed (hatched zone). Brackets show the axis level corresponding to incision. For complete statistical data, see supporting information, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052359#pone.0052359.s002" target="_blank">figure S2</a>.</p>