Fig. 7

Smoothened overexpression rescues slow muscle development in smu mutants. A plasmid encoding rat smoothened cDNA under the control of the CMV promoter was injected into embryos derived from a cross of two animals heterozygous for smu mutations. S58-labeled slow muscle fibers in uninjected and injected embryos were counted blind, and fiber tallies binned in sets of 50 for clarity of presentation. Uninjected siblings of shh injected and dnPKA injected embryos (Fig. 4) and rsmo injected embryos were pooled. Uninjected embryos (white bars, n=1219) displayed the expected Mendelian proportions: approx. 25% had <50 fibers, approx. 75% had >1000 fibers. rsmo overexpression resulted in a dramatic decrease in the percentage of embryos with <50 fibers and a consequent increase in the percentage of embryos with >50 fibers (black bars, n=351). Numbers of dead and malformed embryos (in which we did not count fibers) for injected embryos and their siblings were very similar (rsmo injected: 71 of 422, siblings: 80 of 492). Therefore we conclude that rsmo is not increasing the number of dead or deformed embryos. Among the embryos with <1000 slow muscle fibers, rsmo injected embryos had an average of 210.0±12.7 slow muscle fibers (n=96) and their uninjected siblings had an average of 22.0±1.3 (n=98). This difference is significant (t-test, P≤0.0005). Values are means ± s.e.m. Insets depict representative embryos for uninjected controls with 0-49 (a) fibers and rsmo injections with 200-249 (b) and >1000 (c) fibers.