Figure 1—figure supplement 3.

(A) Co-expression of ectoderm (gata2), neuroectoderm (six3), mesendoderm (hgg, papc) and endoderm (sox32) marker genes in blue with ntl, a mesodermal maker exhibiting a similar pattern to the posterior axial mesoderm marker flh in blastoderm explants, in red as determined by double whole mount in situ hybridization of bud stage explants (side view). Both ectoderm (gata2: n = 20, N = 3) and neuroectoderm (six3: n = 24, N = 3) marker genes were expressed predominantly within the round portion of the explant (as shown in the figure). In some cases, six3 expression was also detected in two domains located at the base and at the tip of the extension or, even less frequently, in a single domain at the extension tip (not shown). In contrast to the ectoderm progenitors, mesendoderm marker genes were exclusively found within or adjacent to the extension. Anterior axial mesendoderm (hgg: n = 17, N = 3) was found to localize directly adjacent to the extended region (as schematized in Figure 1G) or at variable positions along the extension (as shown in the figure). Paraxial mesoderm (papc: n = 22, N = 3) was consistently found adjacent to the posterior axial mesoderm (ntl), either exhibiting a single or two flanking domains. Finally, sox32 expression was found both in a compact cell cluster plus some sporadic cells (right), exclusively in a compact cluster (middle) or exclusively in sporadic cells distributed throughout the extension (left) (n = 31, N = 3). Scale bars: 200 µm.