Fig. 6. The activation of En1 but not of Wnt11 depends on an ectodermal signal. (A) The ectoderm was removed bilaterally (or unilaterally, see text), over the dorsal region, from somite V (SV) to an equivalent length in the presomitic mesoderm (PSM). Dorsal views and corresponding transverse sections of the thoracic region, 24 hours after bilateral (B,C) or unilateral (D,E) ectodermal excision (indicated by the brackets), hybridized with Wnt11 (B,C) or En1 (D,E) probes. Note the complete healing of the ectoderm (ec), as shown in transverse sections (C,E). (B,C) Wnt11 transcripts are detected (arrowhead) in all somites, although in the central region of the excision they are smaller than normal. (D,E) En1 is absent (arrowhead) from the operated side, in contrast to the non-operated side. nc, notochord; nt, neural tube. Scale bars: 50 µm.

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