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Fig. 7. Differential temporal requirement of SHH signal transduction for the
establishment of the presumptive digit expression domains of
5'Hoxd genes. T0: non-cultured control forelimb
bud at the stage indicated. Wt: wild-type control forelimb bud cultured for 15
hours. Cyc: wild-type forelimb bud cultured for 15 hours in the presence of 10
µM cyclopamine. E10.25, 31-33 somites; E10.5, 34-36 somites; E10.75, 37-39
somites. All limb buds are oriented with anterior towards the top and
posterior towards the bottom. (A-C) Effects on Hoxd11
expression. (A) Cyclopamine treatment starting at E10.25 interferes with
upregulation and distoanterior expansion of Hoxd11 expression. (B) By
E10.5, the late Hoxd11 expression domain has been established and
inhibition of SHH signal transduction no longer alters the spatial
distribution, while Hoxd11 expression levels are still affected. (C)
Inhibition of SHH signal transduction from E10.75 onwards no longer alters
Hoxd11 expression. (D-F) Effects on Hoxd12
expression. (D) Cyclopamine treatment starting at E10.25 significantly
interferes with upregulation and expansion of Hoxd12 expression. (E)
Similarly, inhibition of SHH signal transduction at E10.5 blocks the ongoing
distoanterior expansion of Hoxd12 expression (compare Cyc with Wt).
(F) From E10.75 onwards, cyclopamine treatment no longer affects
Hoxd12 expression significantly. (G,H) Effects on
Hoxd13 expression. (G) At E10.5, the establishment of the distal
Hoxd13 expression domain has been initiated (compare T0
with Wt). Cyclopamine treatment blocks the onset of anterior expansion of the
Hoxd13 expression domain in the distal mesenchyme and upregulation of
its expression (Cyc panel). (H) Cyclopamine treatment at E10.75 still
efficiently blocks the ongoing anterior expansion of the Hoxd13
expression domain and upregulation of its expression levels.
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