Fig. 7. Upregulation of embryonic myosin heavy chain expression in gxi mouse muscle. Embryonic myosin heavy chain is expressed in response to regeneration, as it is a developmentally expressed isoform of myosin. (A) Embryonic myosin heavy chain (eMyHC) expression is shown in green, with Evans Blue Dye showing in red. DAPI staining alone is shown (in blue) for both wild-type (WT) and integrin 7 mutant (Itg7^–/–) sections as no embryonic myosin heavy chain staining was present. The pattern of embryonic myosin heavy chain expression differs between -sarcoglycan mutant (gsg^–/–) and gxi double-mutant muscle. In gsg^–/– muscle, embryonic myosin is found in discrete regions consistent with the pattern of focal degeneration and regeneration (A, lower left panel). In contrast, gxi muscle shows widespread expression of eMyHC reflecting widespread degeneration and responsive regeneration. (B) TUNEL-positive nuclei are shown in green and are increased near regions of degeneration in gsg^–/– and are seen scattered throughout gxi muscle. This is consistent with the widespread degenerative pattern and relatively small increase in TUNEL-positive nuclei compared to wild-type muscle. TUNEL-positive cells were absent in sections from the wild type and integrin 7 mutants, and only DAPI staining is shown (blue). Bars in A and B, 100 µm.