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Fig. 4. Notochord and Hedgehog signalling are required for normal MRF expression.
(A) Notochord was ablated at stage 13 and embryos analysed by in situ
hybridisation 2 hours later for XMyf5, XMyoD and actin mRNA.
Arrowheads indicate adaxial tissue with high XMyf5 expression that is
absent after notochord ablation. (B) Xptc2 expression in stage 28
embryos is ablated by cyclopamine treatment, both in the first wave slow
muscle-forming region (arrows) and elsewhere (arrowheads). Solanidine has no
effect (inset). (C) Embryos treated with cyclopamine, or ethanol vehicle
control, at stage 9 and fixed at stage 28 or 32. XMyf5 in PSM is
reduced creating a `gap' in tail expression (arrows). However, dorsal and
ventral somite borders retain XMyf5 expression (arrowheads).
XMyoD is reduced in tail tip (arrows), but unaffected in somitic
stripes anteriorly. The dorsal and ventral somite borders fail to upregulate
XMyoD in presence of cyclopamine (white arrows). Note reduced chevron
form and dorsoventral extent of anterior XMyoD signal.
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