Fig. 5

Light and electron micrographs of cross sections through two 22-hpf embryos injected with chondroitinase ABC (Sigma; B, C), and through an uninjected embryo (A). In the injected embryos chondroitin sulfates are expected to be missing even if their absence was not confirmed by immunostaining in order to ensure good ultrastructural preservation. (A) A semithin section through an uninjected embryo stained with toluidine blue. s, spinal cord; n, notochord; asterisks, somite. (B) A semithin section stained with toluidine blue shows no evidence of nonspecific damage in the spinal cord, notochord, and somite (labeled as in A). The box indicates the approximate frame of the electron micrograph shown in (C) that illustrates another embryo. (C) Electron micrograph of the interface of somite and notochord at the level of the horizontal myoseptum. The microenvironment through which the ventral motor nerve extends shows no evidence of structural damage. In particular the basal lamina (between arrowheads) that separates the notochord from the somite (asterisks) appears intact, as does the medial surface of the somite (between arrows). Within the somite muscle cells have differentiated normally as indicated by the presence of actin filament clusters (a). Magnification bar: 25 μm for (A and B), 3 μm for (C).