Anatomical effects of the MO injection. Low magnification images and triad details from fibers of WT (A and B) and morphant (C and D) fish. With very few exceptions, the injected fish were not altered either at the level of whole embryo (insets in A and C) or at the overall level of fiber organization (A and C). Bar, 500 nm. However, details of triad structure show that although the frequency of JF is unaltered, PJF are present in WT (B) but missing from the majority of triads in MO-injected fish (D). In B and D, each set of images shows a set of triads above and the same triads below with highlighting of JF (yellow) and PJF (light purple). The four examples in B are characteristic of WT triads. D shows four different examples of morphant triads. In the triad at left one density, indicated by an arrow, is ambiguous. Such ambiguities are rare, and they contribute to the 10% uncertainty in the counts (see Materials and methods). The two triads in the middle represent the large majority of the 420 morphant triads examined, which show no PJF. The triad at right was selected to illustrate one of the rare triads that clearly retained PJF; these were included in the overall counts shown in Table 1. JSR profiles in triads from morphant fish tend to be slightly distorted, possibly because of lower membrane rigidity in the absence of PJF. Other structural variations are not exclusive to morphant fibers. Bar, 50 nm.