Fig. 5. Hindlimb muscles of ß1D1D ki/ki E14.5 embryos (D,E,F,H) have reduced numbers of primary myotubes compared to wild-type embryos (A,B,C,G). Transverse sections of lower hindlimb: (A,D) upper (B,E) middle and (C,F) lower region, stained with anti-slow MHC, showing that muscle size is always reduced in ß1D1D ki/ki embryos. (G,H) Higher magnification of EDL in (B,E) showing a clear difference in morphology of the primary myotubes. (I) Graphical representation of the differences in primary myotube numbers in TA, EDL, P muscles and their totals in E14.5 wild-type and ß1D1D ki/ki embryos. (J) Primary myotube diameter in EDL, showing a difference in size between wild-type and ß1D1D ki/ki. (K-N) Transverse sections of E14.5 hindlimbs (middle region), stained for phospho-histone-H3 (K,L) and subjected to TUNEL assay (M,N) show no differences in proliferation or apoptosis in muscle regions between wild-type (K,M) and ß1D1D ki/ki (L,N) embryos. (O-R) Adjacent transverse sections of E17.5 lower hindlimbs stained for slow MHC (O,P) and exposed to the TUNEL assay (Q,R) show a reduction in primary myotubes and increased apoptosis (arrows) in ß1D1D ki/ki (P,R) compared with wild type (O,Q). (S-T) Graphical representation of primary, secondary and total myotube numbers in E17.5 EDL (S) and TUNEL-positive nuclei in E17.5 TA, EDL and P per section, in wild type and ß1D1D ki/ki (T). For abbreviations see Fig. 4. Legend. Bars represent means ± s.d. *P0.05, **P0.01. Scale bars: 200 µm (A-F,K-R), 50 µm (G,H).

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