(A) Tailbud stage embryos were treated with 100 μM SB-431542 or 0.2% DMSO for 22 hours prior to harvesting at stage 29 or 36. Embryos were stained with anti-p-Smad2 and cleared. (B) Stage 34 embryos stained for p-Smad2 were cleared to reveal specific structures in the head (top) and tail (bottom). Note that some bilateral structures can be seen twice in cleared heads. br:brain, e:eye, ov:otic vesicle, ba:branchial arches, m:mouth, tb:tailbud, f:fin, nt:posterior neural tube, pw:posterior wall of tailbud, cnh:chordoneural hinge.