Figure 8. Ectopic muscle islands, which are found in the central tendon of mice that are heterozygous for Abl2, induce tendon cell differentiation.
(A,B) Whole mount diaphragms, stained with antibodies to myosin heavy chain (MHC), revealed 1 to 4 ectopic islands in the central tendon of Abl2+/− mice. (C) Scx RNA expression is enhanced at the ends of muscle fibers in the ectopic islands (black arrows) as well as at the normal MTJ in the diaphragm muscle. (D) Lineage-tracing experiments in Abl2+/− mice reveal that tendon cells, marked by tdTomato (arrowheads), intercalate between MHC-stained muscle fibers within the ectopic islands but do not contribute to myofibers. (E) Whole mount images reveal ectopic muscles in the central tendon of muscle conditional Abl2 heterozygous mice (Abl2f/+; Pax3cre). Scale bar is 250 µm in D.
Figure 8—figure supplement 1. The orientation of ectopic muscle fibers correlates with the orientation of myofibers in the nearby main costal diaphragm muscle.
Representative images of the central tendon area in whole mounts of the diaphragm from Abl2+/− mice. The cartoon shows the method for measuring and quantifying the orientation of myofibes in ectopic muscle islands, compared to myofibers in the nearest costal diaphragm. The scatter plot shows the angle of each ectopic island in relation to the orientation of the myofibers in the nearest costal diaphragm muscle. The mean value and ±s.d. are shown. Scale bar is 500 µm.