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First published online 3 July 2006
doi: 10.1242/dev.02464

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Regulation of ectodermal Wnt6 expression by the neural tube is transduced by dermomyotomal Wnt11: a mechanism of dermomyotomal lip sustainment

Institute of Anatomy and Cell Biology, Department of Molecular Embryology, University of Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany.

View larger version (72K): [in a new window]   Fig. 1. Wnt11 expression in the DML and Wnt6 expression in the ectoderm overlying the somites are mutually exclusive. (A,E) Whole-mount in situ hybridization of HH stage 15 chick embryos hybridized with Wnt6 (A) and Wnt11 (E) probes. (B-D) Transverse sections at different anteroposterior levels of the embryo shown in A. (B) Section at the level of an epithelial somite. Wnt6 expression in the ectoderm overlying the neural tube, the paraxial mesoderm and the lateral plate mesoderm. (C,D) The somite has compartmentalized and the dermomyotome and the sclerotome are visible. Wnt6 expression is restricted to the ectoderm overlying the lateral lip of the dermomyotome and the lateral plate mesoderm. (F-H) Transverse sections of the embryo shown in E at the AP levels indicated. At the level of the presomitic mesoderm (not shown) and the epithelial somite (F), Wnt11 is not expressed. Wnt11 expression starts after compartmentalization of the somite into dermomyotome and sclerotome, with strong expression in the dorsomedial lip of the dermomyotome (G,H).

View larger version (67K): [in a new window]   Fig. 2. Wnt signaling from the neural tube downregulates Wnt6 expression in the ectoderm overlying the somites. (A) Separation of the somite from the axial organs by insertion of an aluminium foil barrier induces an upregulation of Wnt6 expression in the ectoderm covering the somites (between arrowheads), the Wnt6 expression domain now extending medially to the barrier. (B) Removal of the right half of the neural tube induces Wnt6 expression in the somites on the right (between arrowheads). (C) Implantation of Wnt3a-producing cells into the epithelial somites of HH stage 14 embryos leads to the inhibition of Wnt6 expression in the ectoderm overlying the somites (between arrowheads). (D) Transverse section through the operated region in A showing the upregulation of Wnt6 expression due to the absence of signals from the axial organs. Wnt6 expression is extended lateromedially (arrowhead). The location of the somite is indicated by an asterisk. (E) Transverse section of the embryo shown in B. Wnt6 expression is extended lateromedially (arrowhead). The asterisk marks the region where the neural tube has been removed. (F) Transverse section at the region of operation in C showing the loss of Wnt6 expression in the ectoderm overlying the somite (arrowhead), position of cells is indicated by broken lines.

View larger version (109K): [in a new window]   Fig. 3. Signals from the medial dermomyotome downregulate Wnt6 expression. (A) Removal of the whole dermomyotome leads to the upregulation of Wnt6 expression in the ectoderm overlying the somites (arrowhead). (B) Removal of the medial region of the dermomyotome is sufficient to upregulate Wnt6 expression (arrowhead). (C,D) Transverse section across the operated region of embryos shown in A,B, respectively, showing a lateromedial extension of ectodermal Wnt6 expression (medial extent indicated by arrowheads). (E) Grafting of a medial dermomyotomal lip to the segmental plate, and in situ hybridization against Wnt11. Although no endogenous Wnt11 expression is detectable yet, the graft shows solid Wnt11 expression (arrowhead). (F) Transverse section showing the loss of Wnt6 expression in the ectoderm covering the paraxial mesoderm after grafting medial dermomytomal lip from quail to the segmental plate (arrowheads; asterisk marks a region on the control side slightly damaged during sectioning). (G) Presence of the quail-derived graft shown in F marked by QCPN antibody. (H) Implantation of Wnt3a-producing cells into the somites leads to the upregulation of Wnt11 expression (arrowheads). (I) Transverse section at the operated site of the embryo shown in H. Wnt11 expression is upregulated in the medial dermomyotomal lip (arrowhead); the position of the implanted cells is indicated by a broken line.

View larger version (49K): [in a new window]   Fig. 4. Inhibitory effect of Wnt11 on the expression of ectodermal Wnt6. (A) Electroporation of Wnt11 RCAS constructs along with GFP plasmids leads to the upregulation of Wnt11 expression in somites (arrowheads). (B) Fluorescence image of the embryo in A showing the localization of the constructs electroporated. (C) Overexpression of Wnt11 leads to the loss of Wnt6 expression in the ectoderm (arrowheads). (D) Embryo in C viewed under fluorescence light showing the position of the electroporated Wnt11 construct. (E) Transverse section of the operated region of embryo in C, showing the loss of Wnt6 expression in the ectoderm (arrowhead). (F) Overexpression of dnWnt11 results in the upregulation of Wnt6 expression in the ectoderm (arrowhead). (G) Localization of dnWnt11 plasmid shown by fluorescence emitted by the GFP plasmids that were co-electroporated. (H) Transverse section of the embryo in F at the operated site, showing a lateromedial extension of Wnt6 expression (arrowheads).

View larger version (79K): [in a new window]   Fig. 5. Function of Wnt11 in the epithelialization of somites. (A) Overexpression of Wnt11 RCAS by electroporation leads to small, epithelialized somites showing strong expression of Pax3 (arrowheads). (B) Fluorescence image of the embryo in A, showing the localization of the constructs electroporated. (C) Transverse section of the operated region in A, showing the upregulation of Pax3 expression (arrowhead) and the epithelialized morphology of the somite. (D) Overexpression of Wnt11 leads to small, epithelialized somites showing strong expression of Paraxis (arrowheads). (E) Fluorescence image of the embryo in D, showing the localization of the constructs electroporated. (F) Transverse section of the operated region of embryo in D, showing the upregulation of Paraxis expression (arrowhead). (G) Overexpression of Wnt11 leads to the complete loss of Pax1 expression (arrowheads). (H) Localization of the Wnt11 construct in the embryo shown in G. (I) Transverse section at the level of operation of the embryo in (G) showing loss of Pax-1 expression (arrowhead). The epithelial structure of the somite is maintained.

View larger version (18K): [in a new window]   Fig. 6. A model for the regulation of ectodermal Wnt6 expression and dermomyotome epithelialization. Arrows indicate positive inductions, while a line with bars represents inhibitory actions. (A) Epithelial somite: the expression of Wnt6 (red) is observed in the whole ectoderm covering the neural tube, paraxial mesoderm and the LPM. (B) Compartmentalized somite: Wnt6 expression (red) is restricted to the ectoderm covering the VLL and the LPM. BMP induces Wnt3a and Wnt1 expression in the neural tube, which in turn induces Wnt11 (green) expression in the DML. Wnt11 expression takes over the function of maintaining epithelialization in the DML and downregulates Wnt6 in the ectoderm overlying the central and medial region of the dermomyotome. Thus, epithelial morphology is restricted to the DML and VLL by dermomyotomal Wnt11 and ectodermal Wnt6, respectively.