Genetic alterations frequently found in sarcomas are detectable in dystrophic skeletal muscle from clinically tumor-free mice.

(A) Heatmap representation of real-time PCR results from quantification of Jun, Met, Cdkn2a, Nf1 (exon 23 and 56, respectively), and chromosome 8 and 15 copy number in DNA samples extracted from tumor-prone skeletal muscles (QF: quadriceps femoris, TA: tibialis anterior, TRIC: triceps brachii, TS: triceps surae, ISCH: ischiocrural muscles, ILP: iliopsoas, GAC: gastrocnemius, SOL: soleus) from n = 20 different aged MD-mice (mean age of mice: Dmd ^−/−: 590 d; Dysf ^−/−: 640 d; Dmd ^−/− Dysf ^−/−: 482 d) without clinically overt tumors (boxes indicate different individuals). qPCR measurements were highly suggestive of occasional copy number aberrations of the Cdkn2a, Nf1, Met and Jun genes, and chromosome 8 and 15 as well. Muscles from dysferlin-deficient mice that were selected for histopathological examination shown in (C) and (D) are indicated. (B) Real-time PCR results (shown as -ΔCt values) for chromosome 8 and 15, and Cdkn2a revealing elevated levels of chromosome 8 and/or 15 in ∼30% and losses at the Cdkn2a locus in some of muscles from MD-mice but never in wild-type (WT) mice. Some of the observed values indicated relatively high fractions of cells harboring the respective alterations (indicated by filled red circles). (C) Histological examination of 3 select muscles from the genetic screen shown in (A) revealed presence of variably sized microscopic tumor masses, suggestive of well-differentiated liposarcoma, residing between muscle groups and within single muscle fascicles. (D) Histological and immunohistochemical examination of a TA-muscle sample from a 594 d-old Dysf ^−/− mouse, revealing the presence of tumor cells characterized by positive staining for Cdk4 and p27.