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Fig. 7. Dermomyotome and hypaxial muscles cannot be rescued after premature differentiation of myoblasts. Embryos were injected in one cell at the 2-cell stage with shh mRNA and subsequently added to cyclopamine at stages 10.5 (A, B), 20 (C, D, M, N), 24 (E, F, O, P), 28 (G, H), 33/34 (I, J), never added to cyclopamine (K, L, S), added to cyclopamine but not injected with shh (R), or not treated (Q). Embryos were fixed at stage 42 (A–L), 31 (M–P), and 33/34 (Q–S). Embryos fixed at stage 42 were examined with the 12/101 antibody, while the rest were probed for pax3 expression. When injected embryos are added to cyclopamine at stage 10.5, there is no difference in hypaxial muscle between the injected and uninjected side (B compared to A). When added at stage 20, hypaxial muscles are normal except for in the most anterior, where they are missing (D, arrowhead). When added to cyclopamine at stage 24 and beyond, or not added at all, hypaxial muscles are missing on the injected side (F compared to E, H to G, J to I, L to K). When injected embryos are added to cyclopamine at stage 20 and fixed at stage 31, there is some recovery of pax3 expression on the injected side (N compared to M, arrow), while those added at stage 24 do not exhibit any pax3 recovery (P compared to O, arrowhead). A transverse section through a stage 33/34 embryo that has only been treated with cyclopamine and stained for pax3 expression (R), exhibits a medial expansion of pax3 at the ventral edge of the somite (arrow) and an increase in pax3 expression along the lateral edge of the somite (arrowhead) as compared to a control embryo (Q). A transverse section of a stage 33/34 embryo that has been injected with shh mRNA in one cell at the 2-cell stage shows a complete loss of pax3 expression in the somite on the injected side (S, arrowhead). |
