Fig. 5. Implantation of sonic-hedgehog-soaked beads results in an increase in slow and fast MyHC expression, and a thickening of the myotome. Embryos were implanted with beads soaked in either BSA (A,C) or N-Shh (B,D,E,G) and assayed by whole-mount in situ hybridization with probes specific for either sMyHC3 (A-D) or efast MyHC (E-G). The effect on both myosin isoforms was the same. (A,C) Implantation of a BSA-soaked bead does not cause an alteration to sMyHC3 expression when viewed dorsally (A) or laterally (C). (B,D) Beads soaked in Shh protein result in a marked increase in MyHC expression and thickening of the myotome. (E) When viewed in cross section, it is apparent that Shh-soaked beads cause a thickening of the adjacent myotome, whereas the contralateral myotome is unaffected. (F,G) At higher magnification of the areas shown in E, it is apparent that myotomal fibers adjacent to the Shh-soaked bead are hypertrophied.