Expression of TNF and IFN in vivo causes the selective downregulation of MyHC. Saline used as a control (100 μl) or CHO cells expressing TNF and IFN (1 × 10⁷ cells per 0.1 ml) were injected into gastrocnemius muscles of nude mice (n = 4 per group). At 6 and 12 days after injection, muscles were harvested, divided into equal sections, and homogenized to prepare either total protein or RNA. Core myofibrillar gene products were examined by Western blotting (A) or Northern analyses (B) (MyHC IIb, α-tropomyosin, troponin T3, α-actin).