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Fig. 3. Wnt1, but not Wnt3a, is an immediate downstream target of BMP signaling in
the dorsal neural tube. (A-F) Expression of Wnt1 mRNA. (A) An embryo
aged 20 somites with decreasing to no signal opposite the segmental plate
mesoderm. Rostral is towards the top. (B) Graft of CHO-noggin cells inhibits
Wnt1 transcription 10 hours later; (C,D) cross-sections of marked
regions in B at grafted and intact levels, respectively. Asterisk
(*) marks grafted cells. (E) Unilateral noggin electroporation (EP,
*electroporated hemi tube) inhibits Wnt1 transcription 10
hours later. (F) A BMP4-coated bead implanted on the neural tube at the
segmental plate level induces ectopic and premature Wnt1 expression
(arrowhead). (G-I) Expression of Wnt3a mRNA. (G,H) Whole-mount in
situ hybridization of 15 and 21 somite stage (SS) embryos, respectively.
Rostral is towards the left. There is a rostrocaudal gradient of expression
along the neural tube in the younger embryo with no signal adjacent to the
segmental plate mesoderm, but uniform rostrocaudal signal at 21 somites and
onwards (not shown). (I) Noggin overexpression (*) has no effect on
Wnt3a mRNA following 10 hours incubation. Scale bar: 40 µm in
C,D,I.