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Fig. 3. Shh over-expression promotes initial epaxial muscle differentiation but inhibits markers of epaxial myotome expansion and hypaxial body wall myoblasts. Shh mRNA was injected into one cell at the 2-cell stage. Embryos are pictured as dorsal views with anterior to the left and the injected side down (A, C, E), transverse sections with the injected side on the right (B, D, F, H, J, L, N, P, R, U), or lateral views with the uninjected side facing right and injected side facing left (all other panels). Dashed lines indicate the approximate positions of the transverse sections. Red staining represents lineage tracing of co-injected beta-galactosidase mRNA. At stage 20, there is an increase of myf-5 (A, B, arrows, A shown from a posterior vantage point) and myoD (C, D, arrows) and a decrease of pax3 (E, F, arrowheads) expression on the injected side of the embryo. At stages 24 and 31, an increase of myoD expression on the injected side is still observed (I–J, O–P, arrows). The expression of myf-5 in the expanding dorsal and ventral region of the myotome is lost on the injected side (G–H, M–N, arrowheads), but expression in posterior somites where initial myogenesis is occurring is normal (S, S′, arrow). pax3 and lbx1 expression are also lost on the injected side (K–L, Q–R, T–U, arrowheads). Transverse sections of pax3 and lbx1 expression are co-labeled with the 12/101 antibody. At stage 20, there is no significant difference in differentiated muscle on the injected side of the embryo (F). At stages 24 and 31, a wider, shorter amount of differentiated muscle is observed on the injected side (L, R, U). |
